Method of placing a flowable construction material for 3D concrete printing

Abstract

A method of 3D concrete printing, comprises the steps of providing a set- delayed flowable construction material, conveying the construction material to a deposition head, placing the construction material through an outlet of the deposition head in order to form a layer of construction material, before placing the construction material, incorporating into the set-delayed construction material a setting accelerator agent selected from the group of SA-1), which is a setting accelerator comprising a water-soluble silicate source, SA-2), which is a setting accelerator comprising a source of aluminum ions, SA-3), wherein both of setting accelerator agents SA-1) and SA-2) are separately incorporated into the set-delayed construction material, wherein the set control agent comprises (i) a retarder comprising (i-a) an α-hydroxy monocarboxylic acid or a salt thereof, and, optionally, (i-b) a polycarboxylic acid having a carboxylic acid equivalent weight of 333 or less, or a salt thereof; and (ii) an oxyanion source selected from a borate source, a carbonate source, the carbonate source having an aqueous solubility of 15.0 g·L-1 or more at 25 °C, and mixtures thereof; wherein the weight ratio of (ii) to (i) is in the range of from 1.2 : 25, and wherein in the construction material the ratio of the dosage of the set control agent to the dosage of the setting accelerator agent is determined by the following inequation (1): 3 ≤ Dosage set control agent / (1 / 3.5 * Dosage SiO2 + 2.5 / 3.5 * Dosage Al) ≤ 42.0.

Description

[0001] Method of placing a flowable construction material for 3D concrete printing

[0002] The invention refers to a method of placing a flowable construction material comprising a cementitious binder for building structural components layer-by-layer, such as for 3D concrete or mortar printing.

[0003] 3D concrete printing is an emerging technology continuously gaining popularity among architects and construction firms. 3D concrete printing allows the construction of building elements without formwork. There are several benefits of using 3D concrete printing rather than traditional manufacturing methods. A concrete 3D printer not only produces minimal waste, but also significantly reduces the number of active participants needed on site as well as the length of supply chains. Moreover, using a concrete 3D printer, construction can be completed to a significantly higher degree of resilience and geometric complexity.

[0004] Usually, 3D printing of construction materials is a continuous process that comprises conveying fresh concrete or mortar to a deposition head and placing the construction material through an outlet of the deposition head in order to form a layer of concrete. While placing the concrete or the mortar, the deposition head is moved under computer control in order to create a layer of construction material in accordance with the underlying 3D model. In particular, the deposition head places a ribbon of fresh concrete or mortar material. For allowing the fresh concrete or mortar to be moved smoothly through each part of the delivery process to the deposition head, a consistent rheology of the fresh material must be safeguarded.

[0005] However, the construction material must not only be sufficiently fluid for conveying and extrusion purposes, but also sufficiently firm in order to provide the required mechanical stability of the 3D printed structure before the hydraulic binder sets. In particular, the lower layers of the construction material should sustain the load imposed by upper layers without collapsing.

[0006] The development of building materials for 3D printing remains one of the challenges towards a wide-spread application and transformation of the technology in the construction sector. In particular, it is desirous to be able to use locally sourced cementitious binder and cement with a reduced carbon footprint.

[0007] From the technical standpoint, a reliable 3D concrete printing process therefore requires a precise control of the rheology, setting time, and strength development during the different stages of the printing process. While lowering yield stress and viscosity of the mixes is beneficial for the mixing, pumping, and printing stages, rapid yield stress evolution and strength development are required after placing to ensure stability of the printed element and prevent failures, e.g. plastic collapse or elastic buckling. These contradicting rheological properties imply that 3D concrete printing mixes should exhibit controlled yield stress development to go from a stable and pumpable to a printable high yield stress state in an interval matching the characteristic operational time of the product being printed. While rapid yield stress evolution and strength development are desired after placing the construction material to prevent failures such as plastic collapse, fast or immediate loss of workability as is needed in shotcrete applications (flash setting) should be avoided. The yield stress increase or stiffening of the material must be controlled in a way that stiffening or workability loss is delayed to a certain extent so that the material can still be printed and adapt to the shape of nozzle as well as movement of the printing head without causing any clogging or blocking of the print-head during printing operation. Premature hardening also results in a decrease of the bonding strength between successively placed layers.

[0008] A precise control of the rapid transformation in rheological properties from a flowable and pumpable mix to a printable one can be achieved by using the retarder-accelerator combination. That is formulating a retarded concrete / mortar followed by an accelerator addition at the print-head to achieve the required yield stress for placing of “printed” layers. In view of the above, the success in developing a robust material solution for 3D concrete printing lies in using admixtures to modulate the property of locally produced mortar or concrete for a given characteristic operational time.

[0009] WO 2020 / 244981 describes the use of an additive kit in 3D printing of a construction material composition. The additive kit comprises a component A and a component B, wherein component A comprises at least one hardening retarder selected from glyoxylic acid, condensation or addition products of glyoxylic acid or salts thereof; and component B comprises at least one hardening accelerator selected from calcium-silicate-hydrate, calcium carbonate, calcium amidosulfonate, calcium acetate, calcium citrate, calcium formate, calcium nitrate, calcium chloride, calcium hydroxide, lithium carbonate, lithium sulfate, potassium sulfate, sodium sulfate, ground gypsum, aluminium salts, slurries of aluminate cements, and combinations thereof.

[0010] WO 2022 / 184408 describes a composition suitable to be applied to an object via a nozzle comprising, based on the total dry weight of the composition, (a) 15 - 90 % by weight of a cementitious binder; (b) 0,02 - 3 % by weight of an ettringite formation controller comprising a glyoxylic acid condensate and / or a glyoxylic acid adduct and / or glyoxylic acid; (c) 0,15 - 10 % by weight of a magnesium salt accelerator; (d) 0,02 - 2 % by weight of a polyhydroxy compound.

[0011] One-component systems fit for 3D concrete printing are robust in their formulation and relatively easy to use. Mostly, these systems involve the use of high alumina or calcium sulfoaluminate which are expensive raw materials and have a high CO2 footprint. Additionally, one-component systems impose operational limitations to 3D concrete printing processes.

[0012] The present invention seeks to advise a 3D concrete printing method that allows use of locally available cement qualities, including ordinary Portland cements or cements blended with supplementary cementitious materials (SCM) like fly ash or slag and calcined clay, while allowing for a fast construction progress with short time gaps between the placement of successive layers of construction material and that at the same time provides sufficient mechanical strength of the layers capable of sustaining the weight of the subsequently placed layers. WO 2020 / 212607 describes a shotcrete composition comprising a) a cementitious binder; b) an ettringite formation controller comprising (i) a glyoxylic acid condensate and / or a glyoxylic acid adduct; and c) an alkali-free, aluminum-based shotcrete accelerator. The disclosed shotcrete structures are in the form of a shotcrete layer; in other words, WO 2020 / 212607 does not relate to layer-by-layer-wise building of more than one layer. The dosage of the alkali- free, aluminum-based shotcrete accelerator is relatively high, as is usual in shotcrete applications for ensuring extremely fast stiffening and hardening of the shotcrete compositions.

[0013] US 2021 / 0284575 A1 discloses cement compositions for 3D printing comprising from 90 % to 99.5 % by weight of one or more cements selected from a Portland cement, an aluminous cement, a sulphoaluminate cement and a prompt natural cement and from 0.5 % to 10 % by weight of a silicoaluminous filler having a specific surface area of at least 5 m2 / g. In the example part lithium carbonate is used as a hardening accelerator, citric acid as a setting retarder and as a setting trigger is used the aluminum based, alkali free accelerator Chryso Jet 1000 AF.

[0014] Both shotcrete, i.e. sprayed concrete, and construction materials for 3D concrete printing comprise an accelerator, which in both processes is added at or before the deposition head before deposition. The primary function of the accelerator is to expedite the cement hydration and hence bringing about rapid setting time. Despite this mere similarity in terms of use, time, and place of accelerator addition, the material response, i.e. stiffening (sudden increase in yield stress) upon mixing the construction material with accelerator differs in these processes.

[0015] For shotcrete applications, “flash setting”, i.e. fast or immediate loss of workability, is desired to ensure good bonding of the shotcrete layers on a surface including vertical or overhead areas and for the safety of workers from falling material. On the other hand, for the extrusion process, the yield stress increase or stiffening must be controlled in a way that stiffening or workability loss must be retained to a certain extent so that the material can still be extruded and adapt to the shape of deposition head as well as movement of the printing head without causing any clogging and hence damage of the print-head during printing operation. Controlling yield stress increase after the addition of activator facilitates further processing of placed layers, for instance, a post-treatment of the surface of printed layers or surface smoothing is possible by controlling stiffening behaviour.

[0016] The invention relates to a method of placing a flowable construction material comprising a cementitious binder for building structural components layer-by-layer, such as for 3D concrete printing, said method comprising: providing a set-delayed flowable construction material by making a set control agent to exist in the flowable construction material, conveying the set-delayed flowable construction material to a deposition head, placing the construction material through an outlet of the deposition head in order to form a layer of construction material, before placing the construction material, incorporating into the set-delayed construction material a setting accelerator agent selected from the group of

[0017] SA-1), which is a setting accelerator comprising a water-soluble silicate source, SA-2), which is a setting accelerator comprising a source of aluminum ions,

[0018] SA-3), wherein both of setting accelerator agents SA-1) and SA-2) are separately incorporated into the set-delayed construction material, wherein the set control agent comprises (i) a retarder comprising (i-a) an a -hydroxy monocarboxylic acid or a salt thereof, and, optionally, (i-b) a polycarboxylic acid having a carboxylic acid equivalent weight of 333 or less, or a salt thereof; and (ii) an oxyanion source selected from a borate source, a carbonate source, the carbonate source having an aqueous solubility of 15.0 g L'1or more at 25 °C, and mixtures thereof; wherein the weight ratio of (ii) to (i) is in the range of from 1.2 : 25, preferably 2 : 20 and most preferably 5 : 15; and wherein in the set-delayed flowable construction material the ratio of the dosage of the set control agent to the dosage of the setting accelerator agent is determined by the following inequation (1):

[0019] 3 < Dosage set control agent / (1 / 3.5 * Dosage SiC>2 + 2.5 / 3.5 * Dosage Al) < 42

[0020] Dosage set control agent: means the dosage of the set control agent comprising the retarder i) in the set delayed construction material, in weight % of the cementitious binder,

[0021] Dosage SiCh: means the dosage of the setting accelerator SA-1) calculated as SiC>2 incorporated into the set-delayed construction material by the addition of the setting accelerator agent SA-1), in weight % SiC>2 by weight of the cementitious binder,

[0022] Dosage Al: means the dosage of the setting accelerator SA-2) calculated as aluminum ions incorporated into the set-delayed construction material by the addition of the setting accelerator agent SA-2), in weight % aluminum ions by weight of the cementitious binder.

[0023] The dosage SiC>2 can be zero and the dosage Al can be zero, but it is not possible that both dosage SiC>2 and dosage Al are zero.

[0024] Incorporation of the setting accelerator agent into the set-delayed construction material results in that the placed construction material has an increased yield stress when compared to the material during the conveying step.

[0025] Upon hydration of the cementitious system, generally, ettringite is generated in a rapid reaction. This reaction is responsible for the development of early compressive strength of the cementitious composition. However, the newly formed minute ettringite crystals tend to deteriorate the workability or flowability of the cementitious composition. The set control agents used in the method of the invention delays the hydration onset by inhibiting the dissolution of the reactive cement components, in particular aluminates, and / or by masking the calcium ions thereby slowing down the hydration reaction without compromising early compressive strength.

[0026] Set control agent The set control agent comprises (i) a retarder comprising (i-a) an a -hydroxy monocarboxylic acid or a salt thereof, and, optionally, (i-b) a polycarboxylic acid having a carboxylic acid equivalent weight of 333 or less, or a salt thereof; and (ii) an oxyanion source selected from a borate source, a carbonate source and combinations thereof. It is believed that the a -hydroxy monocarboxylic acid or salt thereof in combination with borate ions or carbonate ions from the oxyanion source, retard the formation of ettringite from the aluminate phases originating from the cementitious binder.

[0027] Suitable a -hydroxy monocarboxylic acids and salts thereof include glycolic acid, gluconic acid, and their salts and mixtures thereof. Sodium gluconate is particularly preferred.

[0028] The amount of the a -hydroxy monocarboxylic acid or salt thereof may be in the range of from 0.01 to 0.5 wt.-%, preferably 0.02 to 0.2 wt.-%, relative to the amount of cementitious binder.

[0029] In preferred embodiments, the set control agent further comprises a polycarboxylic acid having a carboxylic acid equivalent weight of 333 or less, or a salt thereof, preferably a polymeric polycarboxylic acid having a carboxylic acid equivalent weight of 333 or less, or a salt thereof.

[0030] By the term polycarboxylic acid, as used herein, is meant a compound comprising more than one carboxylic acid functional group in its molecular structure. This includes low molecular weight compounds having, e.g., two or three carboxylic acid functional groups such as citric acid or tartaric acid. The term “polycarboxylic acid” further includes polymeric compounds constituted of monomeric units incorporating carboxylic acid functionalities, and, optionally, further monomeric units. The polycarboxylic acid can be employed as the free acid or in a partially or completely neutralized form, i.e. , as a salt. The cation is not particularly limited and may be selected from alkali metals, such as sodium or potassium, and ammonium cations.

[0031] For molecules having a low molecular weight, the number of carboxylic acid groups can be counted. The carboxylic acid equivalent weight of the low molecular weight compounds may be determined as the molecular weight divided by the number of carboxylic acid functional groups in its molecular structure. This means, for example, that citric acid having a molecular weight of 192 g / mol and three carboxylic groups has a carboxylic acid equivalent weight of 192 / 3 = 64.

[0032] For polymeric polycarboxylic acid having a higher molecular weight or a molecular weight distribution, the carboxylic acid equivalent weight can be determined by weighing in a sample of the polymeric polycarboxylic acid and titration of the carboxylic acid groups. Alternatively, for a polymeric polycarboxylic acid with known carboxylic group density the carboxylic acid equivalent weight of the polymeric polycarboxylic acid may be determined as the reciprocal of the carboxylic group density, expressed as equivalent per gram of polymer. This means, for example, that a polymeric polycarboxylic acid having a milliequivalent number of 3.0 meq / g has a carboxylic acid equivalent weight of 1 / 0.003 = 333. The molecular weight of the polymeric polycarboxylic acids is preferably 25,000 g / mol or less, more preferably the molecular weight is in the range of 1 ,000 to 25,000 g / mol, most preferably 1 ,000 to 5,000 g / mol.

[0033] The weight-average molecular weight values of the polycarboxylic acids were determined by gel permeation chromatography (GPC). As a stationary phase, a sequence of columns OH- Pak SB-G, OH-Pak SB 804 HQ and OH-Pak SB 802.5 HQ (available from Shodex) was used. As a mobile phase, an eluent of 80 vol.-% of an aqueous solution of HCO2NH4 (0.05 mol / L) and 20 vol.-% of methanol was used. The injection volume was 100 pL at a flow rate of 0.5 mL / min. The molecular weight calibration was performed with polyacrylic acid standards (available from PSS Polymer Standards Service). A Rl-Detector was used for detection.

[0034] Effective polymeric polycarboxylic acids have a carboxylic group density within a certain range. Preferably, the milliequivalent number is 3.0 meq / g or higher, preferably 3.0 to 17.0 meq / g, more preferably 5.0 to 17.0 meq / g, most preferably 5.0 to 14.0 meq / g.

[0035] The polymeric polycarboxylic acid can be employed as the free acid or in a partially or completely neutralized form, i.e., as a salt. The cation is not particularly limited and may be selected from alkali metals, such as sodium or potassium, and ammonium cations.

[0036] Preferably, the polymeric polycarboxylic acid or salt thereof is selected from homopolymers and copolymers of a,p-ethylenically unsaturated carboxylic acids; and copolymers of at least one a,p-ethylenically unsaturated carboxylic acid and at least one sulfo group containing monomer.

[0037] Suitable a,p-ethylenically unsaturated carboxylic acids include acrylic acid, methacrylic acid and maleic acid.

[0038] Suitable sulfo group containing monomers include 2-propene-1 -sulfonic acid (allylsulfonic acid), 2-methyl-2-propene-1 -sulfonic acid (methallylsulfonic acid), vinylsulfonic acid, styrenesulfonic acids, i.e. 2-styrenesulfonic acid, 3-styrenesulfonic acid and 4-styrenesulfonic acid, and 2-acrylamido-2-methylpropane sulfonic acid (AMPS).

[0039] Preferably, the polymeric polycarboxylic acid is a homopolymer of acrylic acid, a homopolymer of methacrylic acid, a copolymer of acrylic acid and maleic acid, or a copolymer of methacrylic acid and maleic acid, most preferably a homopolymer of acrylic acid.

[0040] Examples of suitable polymeric components are commercially available from BASF SE under the trade name SOKALAN®, such as SOKALAN® PA 20, SOKALAN® PA 15, SOKALAN® CP 10S, SOKALAN® PA 25 CL PN, SOKALAN® CP 12S, SOKALAN® PA 40. “CP” generally designates a copolymer whereas “PA” generally designates a polyacrylate. The amount of polymeric polycarboxylic acid or salt thereof, if present, may be in the range of from 0.01 to 2 wt.-%, preferably 0.2-1.2 wt.-%, more preferably 0.2-0.6 wt.-%, relative to the amount of cementitious binder.

[0041] The oxyanion source is at least one of (i) a borate source and (ii) a carbonate source.

[0042] The presence of a borate or carbonate source ensures that the mixing water is initially highly concentrated in borate or carbonate ions. Borate or carbonate ions are believed to adsorb onto mineral phase surfaces along with the a -hydroxy monocarboxylic acid or salt thereof. The latter will also partly remain in the pore solution and initially prevent ettringite to be formed.

[0043] The amount of the oxyanion source may be in the range of from 0.1 to 3 wt.-%, preferably 0.5 to 2.0 wt.-%, more preferably 0.5 to 1.0 wt.-%, relative to the amount of cementitious binder.

[0044] The borate source usually comprises a rapidly soluble, inexpensive, borate compound. Suitable borate sources include borax, boric acid, colemanite, hexahydroborate, and mixtures thereof.

[0045] Only carbonate sources having a sufficient degree of aqueous solubility are suitable for achieving the desired effect. The carbonate source may be an inorganic carbonate having an aqueous solubility of 15 g L'1or more at 25 °C and atmospheric pressure. The aqueous solubility of the inorganic carbonate is suitably determined in water with a starting pH value of 7. It is understood that the pH value at the solubility limit is higher than the starting pH value.

[0046] The inorganic carbonate may be selected from alkaline metal carbonates under the condition that the before mentioned aqueous solubility of 15 g L'1or more at 25 C is fulfilled. Suitable alkaline metal carbonates are sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate and mixtures thereof. It is also possible to use guanidine carbonate as an inorganic carbonate. Sodium carbonate and sodium bicarbonate are especially preferred, in particular sodium carbonate.

[0047] Alternatively, the carbonate source is selected from organic carbonates. “Organic carbonate” denotes an ester of carbonic acid. The organic carbonate is hydrolyzed in the presence of the cementitious system to release carbonate ions. In an embodiment, the organic carbonate is selected from ethylene carbonate, propylene carbonate, glycerol carbonate, dimethyl carbonate, di(hydroxyethyl)carbonate, and mixtures thereof. Preference is given to ethylene carbonate, propylene carbonate, glycerol carbonate, and mixtures thereof, in particular ethylene carbonate and / or propylene carbonate. Mixtures of inorganic carbonates and organic carbonates can as well be used.

[0048] The set control agent is present in the mixing water and / or the dry mix. In a practical embodiment, the set control agent is dissolved in a part of the mixing water, and the dry mix, comprising the cementitious binder, optionally the extraneous aluminate source, and optionally the extraneous sulfate source, is added to the mixture. The remainder of the water is then added to adjust consistency.

[0049] In an alternative practical embodiment, the set control agent is incorporated into the dry mix before the addition of mixing water. Preferably, the set control agent is incorporated in powder form in the dry mix, which contains the cementitious binder, optionally the extraneous aluminate source, and optionally the extraneous sulfate source. Incorporation of the set control agent in powder form may require drying of components of the set control agent which are obtained in form of an aqueous solution during manufacture. For example, it may become necessary to dry the optional (i-b) polycarboxylic acid having a carboxylic acid equivalent weight of 333 or less. In the set control agent, some components can be liquids, like for example various polyols can be present in liquid form. The chemicals may be not available in powder form. Due to their liquid state, they are preferably not part of the set control agent, when the set control agent is to be incorporated into the dry mix. Said liquid components, preferably liquid polyols, are then preferably added to the mixing water or added to the setting accelerator agent, which is explained in the following text. Generally, the liquid components, preferably liquid polyols can also be added, preferably in a continuous way, at the printer head, after or before incorporation of the setting accelerator agent.

[0050] The flowable construction material preferably comprises the set-control agent in an amount of 0.12 to 5.5 weight %, preferably 0.5 to 3 weight % more preferably 0.6 to 2.8 weight % by weight of the cementitious binder. The flowable construction material contains the cementitious binder. Polyols are optional in the set-control agent.

[0051] Setting Accelerator Agent

[0052] According to the invention a setting accelerator agent can be employed selected from the group of

[0053] SA-1), which is a setting accelerator comprising a water-soluble silicate source,

[0054] SA-2), which is a setting accelerator comprising a source of aluminum ions,

[0055] SA-3), wherein both of setting accelerator agents SA-1) and SA-2) are used separately.

[0056] SA-1) setting accelerator comprising a water-soluble silicate source

[0057] According to the invention, a setting accelerator agent SA-1) comprising a water-soluble silicate source can be incorporated into the set-delayed construction material before placing the construction material.

[0058] "Water soluble" for the purpose of the present invention means that the solubility of a silicate source in water at 25°C and atmospheric pressure is 0.1 g L'1or more, preferably 1 g L'1or more, or more preferred 100 g L'1or more. For example, the solubility of the water-soluble silicate source may fall within the range of 100 to 500 g L’1.

[0059] The water-soluble silicate source may be selected from water-soluble alkali metal silicates and quaternary ammonium silicates.

[0060] Alkali metal silicates are commercially available as waterglass. Waterglass can be obtained by the reaction of alkali metal carbonates with quartz sand (silicon dioxide). However, they can also be produced from mixtures of reactive silicas with the appropriate aqueous alkali metal hydroxides.

[0061] As the waterglass, the alkali metal silicates of the following formula may be used: m SiC>2 ■ n M2O, wherein M is an alkali metal, preferably Li, Na or K or a mixture thereof, and the alkali metal silicate has a molar ratio m:n (also termed "modulus") from 0.5 to 5, preferably from 1 to 4, more preferably from 1.7 to 3.3.

[0062] The waterglass is preferably a sodium waterglass, potassium waterglass or lithium waterglass and most preferably a sodium waterglass. However, it is also possible to use a mixture of the waterglasses mentioned.

[0063] Potassium waterglasses are mainly marketed as aqueous solutions because they are very hygroscopic; sodium waterglasses in the advantageous modulus range are also obtainable commercially as solids. The solids contents of commercially available aqueous waterglass solutions are generally from 20 to 60 wt.-%, preferably from 40 to 60 wt.-%.

[0064] Alternatively, or in addition to, the water-soluble silicate source can be a quaternary ammonium silicate, such as tetraalkyl ammonium silicate (including hydroxy- and alkoxycontaining alkyl groups generally of from 1 to 4 carbon atoms in the alkyl or alkoxy group). The most preferable quaternary ammonium silicate is tetramethyl ammonium silicate.

[0065] In view of the ease and efficiency of incorporation, the setting accelerator agent preferably comprises an aqueous solution of the water-soluble silicate source. The silicates form a number of structures in alkaline solution, including orthosilicate (SiC>44) , pyrosilicate (Si2O?6') and longer linear structures, and cyclic and branched structures, all of which are in dynamic equilibrium.

[0066] When cement is mixed with water, the liquid phase of the paste becomes saturated with calcium ions. It is believed that the addition of a water-soluble silicate source to the cement paste leads to the reaction of silicate with calcium ions, with the formation of alkali calcium- silicate-hydrate gel and depletion of the liquid phase of calcium ions. The sudden depletion of calcium ions promotes the dissolution of calcium aluminate phases from the cement. The newly released aluminate ions produce ettringite, a highly hydrated sulfoaluminate crystalline phase containing several water molecules in its structural unit. During its formation, a considerable amount of mixing water is consumed, thus inducing a dramatic increase in the viscosity of the cement mixture, which results in a reduction of the setting time and excellent mechanical strength development.

[0067] In a preferred embodiment the setting accelerator agent SA-1) is incorporated into the set- delayed flowable construction material at a dosage of the water-soluble silicate source calculated as SiC>2 from 0.15 weight % SiC>2 to 4 weight % SiC>2, preferably 0.2 weight % SiC>2 to 3 weight % SiC>2 and more preferably 0.3 weight % SiC>2 to 1 weight % SiC>2 by weight of the cementitious binder.

[0068] The actual dosage of the water-soluble silicate in terms of weight % SiC>2 by weight of the cementitious binder can be easily calculated by the solid content of the water-soluble silicate (if it is not a powder but a liquid) and the before mentioned general formula where the ratio of m:n (modulus) indicates the molar ratio of SiC>2 to M2O (M = alkali metal oxide, the cation alkali metal can be in an analogous way be replaced by quaternary ammonium ions). It is believed that the SiC>2 in the water-soluble silicate is responsible for the accelerating effect.

[0069] In this preferable dosage range and under the condition that the weight ratio of set control agent and setting accelerator agent is suitably chosen (will be explained in the further text), it is possible to print at a reasonable printing speed, because the early strength development is good enough to avoid deformation of the printed structure under its own weight. At the same time, it is possible to avoid problems like clogging of the printer head or to avoid the premature setting of the printed layers, so that no sufficient adhesion between the printed layers can be obtained (so-called cold joint). The printing speed becomes low, when not enough setting accelerator is used, and the clogging and cold joint problems may appear when the setting accelerator dosage is too high.

[0070] SA-2) setting accelerator comprising a source of aluminum ions

[0071] According to the invention, a setting accelerator agent SA-2) comprising a source of aluminum ions can be incorporated into the set-delayed construction material before placing the construction material.

[0072] The reaction of aluminum ion based accelerators, such as aluminium sulfate, with hydrating cement produces ettringite, a highly hydrated sulfoaluminate crystalline phase containing several water molecules in its structural unit. During its formation, a considerable amount of mixing water is consumed, thus inducing a dramatic increase in the viscosity of the cement mixture, which results in a reduction of the setting time and excellent mechanical strength development.

[0073] The source of aluminum ions may include alkali-free accelerators based on aluminum compounds, e.g., aluminum salts such as sulfates, nitrates, fluorides and / or their hydrates. The source of aluminum ions may be selected from aluminum salts and aluminum complexes and mixtures thereof. Preferably, the source of aluminum ions is selected from aluminum salts, especially aluminum sulfates. Preferably the aluminum salts are well soluble in water, preferably the solubility in water at 25 °C and atmospheric pressure is higher than 30 g / l, more preferably higher than 100 g / l and most preferably higher than 300 g / l. It is possible to use also aluminum hydroxide, preferably amorphous aluminum hydroxide, as an aluminum containing starting material if it is transformed into a well soluble form by for example decreasing the pH value of the aqueous system by addition of an acid. Typically, the pH value of the alkali-free accelerators is lower than 4, more preferably lower than 3.

[0074] In a preferred embodiment the setting accelerator agent SA-2) is incorporated into the set- delayed flowable construction material at a dosage of aluminium ions in the range of from 0.027 weight % to 0.351 weight % by weight of the cementitious binder, more preferably 0.03 weight % to 0.3 weight % by weight of the cementitious binder.

[0075] In this preferable dosage range and under the condition that the ratio of set control agent and setting accelerator agent is suitably chosen, it is possible to print at a reasonable printing speed, because the early strength development is good enough to avoid deformation of the printed structure under its own weight. At the same time, it is possible to avoid problems like clogging of the printer head or to avoid the premature setting of the printed layers, so that no sufficient adhesion between the printed layers can be obtained (so-called cold joint). The printing speed becomes low, when not enough setting accelerator is used, and the clogging and cold joint problems may appear when the setting accelerator dosage is too high.

[0076] Preferably, the amount of sulfate in the source of aluminum ions is in the range of from 0.0008 to 0.075 mol, more preferably 0.006 to 0.02 mol, per 100 g of cementitious binder.

[0077] The amount of sulfate ions in the setting accelerator is indicated as a dosage per 100 g of cementitious binder. This means that the said amounts of sulfate ions as indicated in the before standing text, originate from the setting accelerator, which is incorporated into the set-delayed construction material.

[0078] According to European regulations (PREN 934-5 “Admixtures for Sprayed Concrete - Definitions, Requirements, Conformity, Marking and Labelling”), an accelerator is classified as “alkali-free” when the concentration of sodium and potassium, expressed as equivalents of Na2O, is lower than 1 %. Lithium is also an alkali metal, however the scientific literature shows that it does not negatively affect the concrete and therefore it is not considered in the calculation of equivalents of Na2O. “Alkali-free” accelerators may comprise alkaline earth metal compounds, such as calcium salts, magnesium salts, and mixtures thereof.

[0079] Beside the source of aluminum ions, the setting accelerator agent may contain additives to provide shelf stability and other desirable properties to the setting accelerator agent. The setting accelerator agent can be in liquid form or solid form, such as powder form.

[0080] Formulations of setting accelerator agents may be stabilized by various chemicals. Examples of such stabilizers include organic acids such as carboxylic acids, dicarboxylic acids, hydroxycarboxylic acids, aminocarboxylic acids, phosphonic acids, sulfamic acid; inorganic acids such as sulfuric acid, nitrous acid, phosphoric acid, phosphorous acid, hydrofluoric acid, hexafluorosilicic acid, and mixtures thereof; urea; polymeric stabilizers, such as polyacrylamides, polycarboxylates, polysulfonates, and copolymers and mixtures thereof; aluminosilicates such as attapulgite, sepiolite and bentonite; and colloidal silica. Furthermore, setting accelerator agent may additionally comprise calcium and magnesium compounds such as for example sulfates, as well as amines, for example alkanolamines such as diethanolamine, triethanolamine, diisopropanolamine and triisopropanolamine and mixtures thereof.

[0081] Although not an essential component, a water-soluble magnesium salt may be contained in the setting accelerator agent. Any such salt may be used, but the preferred salts are magnesium carbonate, or magnesium sulfate or mixtures of these salts. While the magnesium sulfate used in this invention may be any magnesium sulfate, the preferred magnesium is the hydrate MgSC 7H2O, known as Epsom Salts.

[0082] SA-3) setting accelerator agent employing both SA-1) and SA-2) by separate incorporation into the set delayed construction material

[0083] It is also possible to use both accelerators SA-1) and SA-2), however due to their chemical incompatibility it is necessary to dose them separately, preferably in a continuous way by for example two separate supply lines at the printer head. The chemical incompatibility is due to the fact that the strongly alkaline setting accelerator SA-1) and strongly acid setting accelerator SA-2) would react to non-accelerating chemicals like sodium sulfate and alumosilicates.

[0084] Dosage ratio (weight ratio) of set control agent to setting accelerator agent

[0085] Although the setting times in 3 D concrete printing applications need to be short for allowing a reasonably fast progress of the printing process, a too fast setting as usually needed and practiced in shotcrete applications is not suitable. The very fast setting times in shotcrete applications (underground construction) are needed for ensuring that there is no excessive rebound of the sprayed concrete from the surface to be covered (rock surface or similar substrates). Such short setting times if used in 3D printing applications may result in a not printable material. In other words, there is a danger that the printer head could be damaged by clogging of the material. Another problem is that the extruded printing material may set so quickly that the adhesion between the layers of extruded printing material becomes insufficient. This phenomenon is due to the fact, that the already more or less solidified first layer of printing material is no more able to build up a good adhesion to the next layer of fresh cementitious printing material. This is also sometimes called a “cold joint”.

[0086] In summary, the setting time needs to be balanced between the two requirements" sufficient early strength development for avoiding deformation of the printed material after leaving the printerhead” and “sufficient long setting time for allowing a reasonable adhesion build up between the printed layers and avoiding clogging at the deposition head”.

[0087] It is also to be understood that the suitable range of setting time in 3 D concrete printing applications depends on the machinery of the printing process and the actual requirements of the 3 D concrete printing job site, including the type of binder (cement), the water / binder ratio, the density of the construction material, the temperature and the dimensions of the printed layers, in particular the layer thickness. Moreover, it depends on the circulation period (also called layer time) of the 3 D concrete printing process, because relatively long circulation periods may demand for a longer setting time and vice versa relatively short circulation periods may demand for a shorter setting time. The term circulation period is meant to be the time needed for the printer head to print one layer (one round) of printing material from the starting point until coming back to the starting point. As a matter of course the starting point is not reached exactly again, but typically one layer higher, as the printing usually is done layer by layer.

[0088] It is to be understood that if the circulation period is relatively long, for example depending on the dimensions of the structure to be built and the respective machinery (for example gantry type of machinery), then the setting time can be in the longer range (relatively slow setting), which is achieved by a relatively high dosage of the set control agent and a relatively low dosage of the setting accelerator agent. The cementitious printing material has due to the relatively long circulation period more time to set and develop a sufficient stability until the next layer of material is applied.

[0089] Vice versa, if the circulation period is relatively short, then the setting time is preferably in the shorter range (relatively fast setting), which is achieved by a relatively low dosage of the set control agent and a relatively high dosage of the setting accelerator agent. The cementitious printing material has due to the relatively short circulation period less time to set and to develop early strength until the next layer of material is applied.

[0090] A reasonable balance between the before mentioned multiple requirements can be achieved by controlling the dosage ratio (weight ratio) of the set control agent, which comprises the set retarder (i) to the setting accelerator agent. The calculation of the quotient of the dosage of the set control agent to the dosage of the setting accelerator, results in the weight ratio of the set control agent to the setting accelerator agent (is equivalent), because the set control agent as well as the setting accelerator agent are dosed on the same cementitious binder contained in the set-delayed construction material. The unit of the weight ratio is dimensionless (weight % set control agent by weight of cement divided by weight % setting accelerator agent by weight of cement).

[0091] Generally speaking, a high ratio of the set control agent to the setting accelerator agent results in relatively long setting times and the printing process may only be slow, which is not desired.

[0092] On the other side a low ratio of the set control agent to the setting accelerator agent results in relatively short setting times and the printing process can be relatively fast. However, as before mentioned, too short setting times, respectively too low weight ratios of the set control agent, to the setting accelerator agent, may create problems like clogging at the deposition head or cold joints.

[0093] In this invention different setting accelerator agents SA-1) and SA-2) can be used, also a combination of SA-1) and SA-2) (= SA-3). In each of the three cases the weight ratios of the set control agent to the respective setting accelerator agents are different, because the dosage efficiency of the setting accelerator agents SA-1) and SA-2) is different. It was found that the setting accelerator agent SA-2) (calculated on mass of aluminum ions) is more dosage efficient compared to the setting accelerator agent SA-1) (calculated on mass of SiCh). A lower dosage of aluminum ions in SA-2) is needed compared to the dosage of SiC>2 in SA-1) in order to achieve about the same acceleration effect. Details of the different types of setting accelerator agents are explained in the following chapters. Particularly the weight ratio of set control agent to the setting accelerator agents SA-1) and SA-2) is determined by the inequation (1), as will be explained later on.

[0094] Dosage ratio (weight ratio) of set control agent to the setting accelerator agent SA-1)

[0095] It has been found that the weight ratio of the set control agent to the setting accelerator agent SA-1) calculated on the basis of SiC>2 is to be in the range of 0.86 to 12 when only SA-1) is used. In other word the ratio of the dosage of the set control agent to the dosage of the setting accelerator agent SA-1) calculated on the basis of SiC>2 is to be in the range of 0.86 to 12.

[0096] The weight ratio of the set control agent to the setting accelerator SA-1) is determined by the inequation (1) and the range of 0.86 to 12 is a special case of the inequation (1) (dosage of SA-2) is zero) and can be easily derived from the inequation (1) by simple mathematical transformations as will be shown later.

[0097] Preferable is a method, wherein in the set-delayed flowable construction material the ratio of the dosage of the set control agent to the dosage of the setting accelerator agent SA-1) is determined by the following inequation (1a):

[0098] 0.86 < Dosage set control agent I Dosage SiC>2 12

[0099] Dosage set control agent: means the dosage of the set control agent comprising the retarder i) in the set delayed construction material, in weight % of the cementitious binder.

[0100] Dosage SiCh: means the dosage of the setting accelerator SA-1) calculated as SiC>2 incorporated into the set-delayed construction material by the addition of the setting accelerator agent SA-1), in weight % SiC>2 by weight of the cementitious binder.

[0101] This means particularly that silicate or SiC>2, which are from other sources than the setting accelerator agent SA-1) (for example the cementitious binder or any other components of the set delayed construction material) are not counted here.

[0102] Within the before mentioned range (0.86 to 12) of weight of the set control agent to the setting accelerator agent SA-1), calculated on the basis of SiC>2, it is possible to print at a relatively fast progress speed (allowing also relatively short circulation periods), without that the layerwise deposited construction material may deform under its own weight. The setting times are not too short, so that clogging problems at the deposition head can be avoided, also an insufficient build-up of adhesion between the respective layers of material can be avoided. The setting is not too fast, so that it is possible to avoid a so-called “cold joint” between the layers. In addition, the open times for processing the set-delayed flowable construction material are sufficiently long.

[0103] The person skilled in the art would choose within the proposed dosage (weight) ratio range between 0.86 and 12 the actual ratio suitable for the specific job site, taking into account the specific requirements and conditions of the job site as mentioned before in detail. The weight ratio of set control agent to the accelerator may be finetuned in order to achieve the desired results for the specific job site. It is deemed to be possible to determine the suitable weight ratio by doing a manageable number of experimental trials.

[0104] Dosage ratio (weight ratio) of set control agent to the setting accelerator agent SA-2)

[0105] It has been found that the weight ratio of the set control agent to the setting accelerator agent SA-2), calculated on the basis of aluminum ions, is to be in the range of 2.14 to 30, when only SA-2) is used. In other word the ratio of the dosage of the set control agent to the dosage of the setting accelerator agent SA-2) calculated on the basis of aluminum ions is to be in the range of 2.14 to 30.

[0106] The weight ratio of the set control agent to the setting accelerator SA-2) is determined by the inequation (1) and the range of 2.14 to 30 is a special case of the inequation (1) (dosage of SA-1) is zero) and can be easily derived from the inequation (1) by simple mathematical transformations as will be shown later.

[0107] Preferable is a method, wherein in the set-delayed flowable construction material the ratio of the dosage of the set control agent to the dosage of the setting accelerator agent SA-2) is determined by the following inequation (1b):

[0108] 2.14 < Dosage set control agent / Dosage Al < 30

[0109] Dosage set control agent: means the dosage of the set control agent comprising the retarder i) in the set delayed construction material, in weight % of the cementitious binder.

[0110] Dosage Al: means the dosage of the setting accelerator SA-2) calculated as aluminum ions incorporated into the set-delayed construction material by the addition of the setting accelerator agent SA-2), in weight % aluminum ions by weight of the cementitious binder.

[0111] Particularly this means that aluminum ions, which are from other sources than the setting accelerator agent SA-2) (for example the cementitious binder or any other components of the set delayed construction material) are not counted here.

[0112] Within the before mentioned range (2.14 to 30) of weight of the set control agent to the setting accelerator agent SA-2) calculated as aluminum ions, it is possible to print at a relatively fast progress speed (allowing also relatively short circulation periods), without that the layer-wise deposited construction material may deform under its own weight. The setting times are not too short, so that clogging problems at the deposition head can be avoided, also an insufficient build-up of adhesion between the respective layers of material can be avoided. The setting is not too fast, so that it is possible to avoid a so-called “cold joint” between the layers. In addition, the open times for processing the set-delayed flowable construction material are sufficiently long.

[0113] The person skilled in the art would choose within the proposed dosage (weight) ratio range between 2.14 and 30 the actual weight ratio suitable for the specific job site, taking into account the specific requirements and conditions of the job site as mentioned before in detail. The weight ratio of set control agent to the accelerator may be fine tuned in order to achieve the desired results for the specific job site. It is deemed to be possible to determine the suitable weight ratio by doing a manageable number of experimental trials. Dosage ratio (weight ratio) of set control agent to the setting accelerator agent SA-3 (combination of SA-1) and SA-2))

[0114] The dosage ratio (weight ratio) of the set control agent to the setting accelerators SA-1) and SA-2) is determined by the inequation (1):

[0115] 3 < Dosage set control agent / (1 / 3.5 * Dosage SiC>2 + 2.5 / 3.5 * Dosage Al) < 42

[0116] Dosage set control agent: means the dosage of the set control agent comprising the retarder i) in the set delayed construction material, in weight % of the cementitious binder,

[0117] Dosage SiCh: means the dosage of the setting accelerator SA-1) calculated as SiC>2 incorporated into the set-delayed construction material by the addition of the setting accelerator agent SA-1), in weight % SiC>2 by weight of the cementitious binder.

[0118] Dosage Al: means the dosage of the setting accelerator SA-2) calculated as aluminum ions incorporated into the set-delayed construction material by the addition of the setting accelerator agent SA-2), in weight % aluminum ions by weight of the cementitious binder.

[0119] Preferable ranges of the inequation (1) are as follows:

[0120] 4 < Dosage set control agent / (1 / 3.5 * Dosage SiC>2 + 2.5 / 3.5 * Dosage Al) < 30

[0121] 8 < Dosage set control agent / (1 / 3.5 * Dosage SiC>2 + 2.5 / 3.5 * Dosage Al) < 25

[0122] 9 < Dosage set control agent / (1 / 3.5 * Dosage SiC>2 + 2.5 / 3.5 * Dosage Al) < 20

[0123] Dosage set control agent: means the dosage of the set control agent comprising the retarder i) in the set delayed construction material, in weight % of the cementitious binder,

[0124] Dosage SiCh: means the dosage of the setting accelerator SA-1) calculated as SiC>2 incorporated into the set-delayed construction material by the addition of the setting accelerator agent SA-1), in weight % SiC>2 by weight of the cementitious binder.

[0125] Dosage Al: means the dosage of the setting accelerator SA-2) calculated as aluminum ions incorporated into the set-delayed construction material by the addition of the setting accelerator agent SA-2), in weight % aluminum ions by weight of the cementitious binder.

[0126] In the following the inequation (1) and its technical meaning is explained. As was previously mentioned, the dosage efficiency of the two accelerators SA-1) and SA-2) is different. Therefore, it was necessary to introduce so-called weighting factors, which balance the different dosage efficiencies of the set accelerator agents SA-1) and SA-2). In the inequation (1) the first weighting factor for the accelerator SA-1) is 1 / 3.5 and the second weighting factor for the accelerator SA-2) is 2.5 / 3.5. The dosage efficiency of SA-2) calculated on basis of aluminum ions is higher compared to the dosage efficiency of SA-1) calculated on the basis of SiC>2. Therefore, the weighting factor for SA-2) (2.5 / 3.5) is a higher number compared to the weighting factor for SA-1) (1 / 3.5).

[0127] It is assumed that there is a linear relationship between the weight ratio of the set control agent to the setting accelerator agent SA-1) on the one side and the weight ratio of the set control agent to the setting accelerator agent SA-2) on the other side.

[0128] The ratio of the set control agent to the respective setting accelerator agent SA-1) or SA-2) was as follows at the minimum and the maximum values:

[0129] Minimum weight ratio for SA-1): 0.86 Maximum weight ratio for SA-1): 12

[0130] Minimum weight ratio for SA-2): 2.14 Maximum weight ratio for SA-1): 30

[0131] From the above data, comparing 0.86 and 2.14 for the minima and 12 and 30 for the maxima, it can be concluded that SA-2) is in each case 2.5 times more dosage efficient compared to SA-1). In the case of SA-2), calculated on the basis of aluminum ions, by the factor 2.5 less accelerator is needed in order to achieve the same acceleration effects as compared to SA- 1), calculated on the basis of SiC>2.

[0132] The denominator of the weighting factor becomes then 3.5 (1 part plus 2.5 parts) and the counter becomes 1 for SA-1) and 2.5 for SA-2), resulting in the weighting factors 1 / 3.5 for SA- 1) and 2.5 / 3.5 for SA-2.

[0133] In the inequation (1) the minimum weight ratio of 3 and the maximum weight ratio of 42 are numbers, which were modified by the respective weighting factors. The minimum weight ratio of 3 in inequation (1) can be written alternatively by the weighting factors and the respective minimum values and the maximum weight ratio of 42 in inequation (1) can be written alternatively by the weighting factors and the respective maximum values:

[0134] Minimum: Maximum: 0.86 / (1 / 3.5) = 3 12 / (1 / 3.5) = 42 2.14 / (2.5 / 3.5) = 3 30 / (2.5 / 3.5) = 42

[0135] As previously mentioned, the special cases of SA-1) and SA-2) are derivable from the inequation (1) as will be shown in the following:

[0136] For SA-1):

[0137] 0.86 / (1 / 3.5) < Dosage set control agent / (1 / 3.5 * Dosage SiC>2 + 2.5 / 3.5 * Dosage Al) < 12 / (1 / 3.5)

[0138] Dosage Al is zero, therefore follows:

[0139] 0.86 / (1 / 3.5) < Dosage set control agent / (1 / 3.5 * Dosage SiCh) s 12 / (1 / 3.5) After shortening of the weighting factor 1 / 3.5 follows:

[0140] 0.86 < Dosage set control agent / Dosage SiC>2 12

[0141] For SA-2):

[0142] 2.14 / (2.5 / 3.5) < Dosage set control agent / (1 / 3.5 * Dosage SiC>2 + 2.5 / 3.5 * Dosage Al) < 30 / (2.5 / 3.5)

[0143] Dosage SiC>2 is zero, therefore follows:

[0144] 2.14 / (2.5 / 3.5) < Dosage set control agent / (2.5 / 3.5 * Dosage Al) < 30 / (2.5 / 3.5)

[0145] After shortening of the weighting factor 2.5 / 3.5 follows:

[0146] 2.14 < Dosage set control agent / Dosage Al < 30

[0147] It can be seen from the before standing considerations and explications why the inequation (1) describes the dosage regime of set control agent on the one side and accelerators SA-1) and SA-2) on the other side, including the three cases of only using SA-1) or SA-2) and the case of SA-3), where both of setting accelerators SA-1) and SA-2) are employed separately.

[0148] Polyol

[0149] Preferably the method of the invention utilizes a polyol. The polyol serves primarily the purpose of improving the early strength development (preferably after 2 hours) of the construction material.

[0150] The polyol is preferably made existent in the construction material before placing the construction material through an outlet of the deposition head. The addition of the polyol can be done in various ways and the way of addition is not especially critical.

[0151] The polyol may be included into the set control agent, the setting accelerator agent or both, or the polyol may be added to the set-delayed construction material independently from the set control agent and the setting accelerator before placing the set-delayed construction material. It is convenient and preferable to add the polyol into the flowable construction material by including it into the set control agent or the setting accelerator agent or both, particularly because no separate stream for adding the polyol may be needed. Particularly preferable is the dosage of the polyol by including it into the setting accelerator agent.

[0152] Moreover, it is also possible to dose the polyol separately from the set control agent and the setting accelerator agent before the placing of the construction material, for example, by adding the polyol in a separate stream different to the setting accelerator and the set control agent, preferably at the printer head. It is possible to add the polyol before or also after addition of the setting accelerator agent. Typically, the polyol is dosed into the mixing water for the flowable construction material. As was mentioned before, the polyol can also be introduced into the dry mix, preferably if the polyol is in powder form.

[0153] Preferable is a method, wherein the construction material comprises the polyol in an amount of at least 0.05 weight %, preferably 0.05 to 2.5 weight%, more preferably 0.1 to 1 .0 weight % and most preferably 0,2 to 0,5 weight %. by weight of the cementitious binder.

[0154] It is believed that polyols such as glycerol chelate calcium ions of e.g. calcium sulfate or C3A. As a result, calcium ion dissociation is accelerated. Chelation of calcium ions also stabilizes calcium in solution and accelerates the dissolution of calcium aluminate phases, thereby rendering aluminate from these calcium aluminate phases more accessible.

[0155] “Polyol” is intended to denote a compound having at least two alcoholic hydroxyl groups in its molecule and “polyol” does not comprise saccharides higher than trisaccharides. Preferable are polyols with at least three alcoholic hydroxy groups. Useful polyols have at least 3 alcoholic hydroxyl groups in its molecule, for example 3, 4, 5 or 6 alcoholic hydroxyl groups. Polyols having vicinal hydroxyl groups are preferred. Polyols having at least three hydroxyl groups bound to three carbon atoms in sequence are most preferred.

[0156] The ability of the polyol to chelate calcium ions and thereby stabilize calcium in solution can be assessed by a calcium aluminate precipitation test. In an embodiment, the polyol, in a calcium aluminate precipitation test in which a test solution, obtained by supplementing 400 mL of a 1 wt.-% aqueous solution of the polyol with 20 mL of a 1 mol / L NaOH aqueous solution and 50 mL of a 25 mmol / L NaAICh aqueous solution, is titrated with a 0.5 mol / L CaCh aqueous solution at 20 °C, inhibits precipitation of calcium aluminate up to a calcium concentration of 75 ppm, preferably 90 ppm.

[0157] The test detects the precipitation of calcium aluminate by turbidity. Initially, the test solution is a clear solution. The clear test solution is titrated with a CaCh aqueous solution at a constant dosage rate of, e.g., 2 mL / min, as described above. With ongoing addition of CaCh, precipitation of calcium aluminate results in a change of the optical properties of the test solution by turbidity. The titration endpoint, expressed as the maximum calcium concentration (as Ca2+), before the onset of turbidity can be calculated from the elapsed time to the onset point.

[0158] In a preferred embodiment, the polyol is selected from compounds consisting of carbon, hydrogen, and oxygen only. Preferably the polyol does not contain a carboxyl group (COOH) in its molecule.

[0159] In an embodiment, the polyol is selected from monosaccharides and oligosaccharides with the proviso that the polyol does not comprise saccharides higher than trisaccharides, compounds of general formula (P-l) or dimers or trimers of compounds of general formula (P- I): wherein

[0160] R is -CH2OH, -NH2, n is an integer from 1 to 4, m is an integer from 1 to 8.

[0161] In one embodiment, the polyol is selected from saccharides with the proviso that the polyol does not comprise saccharides higher than trisaccharides. Preferably the polyol does not comprise saccharides higher than disaccharides, most preferably the polyol is a monosaccharide. Useful saccharides include monosaccharides, such as glucose and fructose; disaccharides, such as lactose and sucrose; trisaccharides, such as raffinose. Monosaccharides and disaccharides, in particular sucrose, are especially preferred.

[0162] In another preferred embodiment, the polyol is selected from compounds consisting of carbon, hydrogen, and oxygen only and contains neither a carboxyl group (COOH) nor a carbonyl group (C=O) in its molecule. It is understood that the term “carbonyl group” encompasses the tautomeric form of the C=O group, i.e. a pair of doubly bonded carbon atoms adjacent to a hydroxyl group (-C=C(OH)-).

[0163] Compounds of formula (P-l) wherein X is (P-la) are generally referred to as sugar alcohols. Sugar alcohols are organic compounds, typically derived from sugars, containing one hydroxyl group (-OH) attached to each carbon atom. Useful sugar alcohols are mannitol, sorbitol, xylitol, arabitol, erythritol and glycerol. Among these, glycerol is particularly preferred. It is envisaged that carbonates of polyhydric alcohols such as glycerol carbonate can act as a polyol source.

[0164] Compounds of formula (P-l) wherein X is (P-lb) include pentaerythritol, and tris(hydroxymethyl)aminomethane.

[0165] Compounds of formula (P-l) wherein X is (P-lc) include triethanolamine. Dimers or trimers denote compounds wherein two or three molecules of general formula (P-l) are linked via an ether bridge and which are formally derived from a condensation reaction with elimination of one or two molecules of water. Examples of dimers and trimers of compounds of formula (P-l) include dipentaerythritol and tripentaerythritol.

[0166] Dispersant

[0167] In order to achieve the conveyability or pumpability described above, a water reducer, in particular a plasticizer or a super-plasticizer, preferably a plasticizer based on polyoxy polycarboxylate or phosphonates, is preferably added to the construction material before the conveying step.

[0168] A water reducer makes it possible to reduce the amount of mixing water for a given workability by typically 10-15 %.

[0169] Super-plasticizers belong to a new class of water reducers and are capable of reducing the water contents of mixing water, for a given workability, by approximately 30% by mass.

[0170] It will be appreciated that a number of useful dispersants contain carboxyl groups, salts thereof or hydrolysable groups releasing carboxyl groups upon hydrolysis. Preferably, the milliequivalent number of carboxyl groups contained in these dispersants (or of carboxyl groups releasable upon hydrolysis of hydrolysable groups contained in the dispersant) is lower than 3.0 meq / g, assuming all the carboxyl groups to be in unneutralized form.

[0171] Examples of useful dispersants include

[0172] - comb polymers having a carbon-containing backbone to which are attached pendant cement-anchoring groups and polyether side chains,

[0173] - non-ionic comb polymers having a carbon-containing backbone to which are attached pendant hydrolysable groups and polyether side chains, the hydrolysable groups upon hydrolysis releasing cement-anchoring groups,

[0174] - colloidally disperse preparations of polyvalent metal cations, such as Al3+, Fe3+or Fe2+, and a polymeric dispersant which comprises anionic and / or anionogenic groups and polyether side chains, and the polyvalent metal cation is present in a superstoichiometric quantity, calculated as cation equivalents, based on the sum of the anionic and anionogenic groups of the polymeric dispersant,

[0175] - sulfonated melamine-formaldehyde condensates,

[0176] - lignosulfonates,

[0177] - sulfonated ketone-formaldehyde condensates,

[0178] - sulfonated naphthalene-formaldehyde condensates,

[0179] - phosphonate containing dispersants, preferably the phosphonate containing dispersants comprise at least one polyalkylene glycol unit, and

[0180] - mixtures thereof. Preferably, the dispersant is present in a weight percentage of 0.005 to 1.0, preferably 0.05 to 0.5, more preferably 0.02 to 0.15, relative to the cementitious binder.

[0181] Comb polymers having a carbon-containing backbone to which are attached pendant cementanchoring groups and polyether side chains are particularly preferred. The cement-anchoring groups are anionic and / or anionogenic groups such as carboxylic groups, phosphonic or phosphoric acid groups or their anions. Anionogenic groups are the acid groups present in the polymeric dispersant, which can be transformed to the respective anionic group under alkaline conditions.

[0182] Preferably, the structural unit comprising anionic and / or anionogenic groups is one of the general formulae (la), (lb), (Ic) and / or (Id): wherein

[0183] R1is H, C1-C4 alkyl, preferably H or methyl;

[0184] X is NH-(CniH2ni) or O-(CniH2ni) with n1 = 1 , 2, 3 or 4, or a chemical bond, the nitrogen atom or the oxygen atom being bonded to the CO group;

[0185] R2is OM, PO3M2, or O-PO3M2; with the proviso that X is a chemical bond if R2is OM; wherein

[0186] R3is H or C1-C4 alkyl, preferably H or methyl; n is 0, 1 , 2, 3 or 4;

[0187] R4is PO3M2, or O-PO3M2; wherein

[0188] R5is H or Ci-C4alkyl, preferably H;

[0189] Z is O or NR7;

[0190] R7is H, (CniH2ni)-OH, (CniH2ni)-PO3M2, (CniH2ni)-OPO3M2, (C6H4)-PO3M2, or (C6H4)-OPO3M2, and n1 is 1 , 2, 3 or 4; wherein

[0191] R6is H or C1-C4 alkyl, preferably H;

[0192] Q is NR7or O;

[0193] R7is H, (CniH2ni)-OH, (CniH2ni)-PO3M2, (CniH2ni)-OPO3M2, (C6H4)-PO3M2, or (C6H4)-OPO3M2, n1 is 1 , 2, 3 or 4; and where each M independently is H or a cation equivalent.

[0194] Preferably, the structural unit comprising a polyether side chain is one of the general formulae (Ila), (lib), (He) and / or (lid):

[0195] Ila wherein

[0196] R10, R11and R12independently of one another are H or Ci-C4alkyl, preferably H or methyl;

[0197] Z2is O or S;

[0198] E is C2-Ce alkylene, cyclohexylene, CH2-CeHio, 1 ,2-phenylene, 1 ,3-phenylene or 1 ,4-phenylene;

[0199] G is O, NH or CO-NH; or

[0200] E and G together are a chemical bond; A is C2-C5 alkylene or CH2CH(C6Hs), preferably C2-C3 alkylene; n2 is 0, 1 , 2, 3, 4 or 5; a is an integer from 2 to 350, preferably 10 to 150, more preferably 20 to 100;

[0201] R13is H, an unbranched or branched C1-C4 alkyl group, CO-NH2 or COCH3; lib wherein

[0202] R16, R17and R18independently of one another are H or C1-C4 alkyl, preferably H;

[0203] E2is C2-C6 alkylene, cyclohexylene, CH2-C6H10, 1 ,2-phenylene, 1 ,3-phenylene, or 1 ,4-phenylene, or is a chemical bond;

[0204] A is C2-C5 alkylene or CH2CH(C6Hs), preferably C2-C3 alkylene; n2 is 0, 1 , 2, 3, 4 or 5;

[0205] L is C2-C5 alkylene or CH2CH(C6Hs), preferably C2-C3 alkylene; a is an integer from 2 to 350, preferably 10 to 150, more preferably 20 to 100; d is an integer from 1 to 350, preferably 10 to 150, more preferably 20 to 100;

[0206] R19is H or C1-C4 alkyl; and

[0207] R20is H or C1-C4 alkyl; wherein

[0208] R21, R22and R23independently are H or C1-C4 alkyl, preferably H;

[0209] W is O, NR25, or is N;

[0210] V is 1 if W = O or NR25, and is 2 if W = N;

[0211] A is C2-C5 alkylene or CH2CH(C6Hs), preferably C2-C3 alkylene; a is an integer from 2 to 350, preferably 10 to 150, more preferably 20 to 100;

[0212] R24is H or C1-C4 alkyl;

[0213] R25is H or C1-C4 alkyl;

[0214] wherein

[0215] R6is H or C1-C4 alkyl, preferably H;

[0216] Q is NR10, N or O;

[0217] V is 1 if Q = O or NR10and is 2 if Q = N;

[0218] R10is H or C1-C4 alkyl;

[0219] A is C2-C5 alkylene or CH2CH(C6Hs), preferably C2-C3 alkylene; and a is an integer from 2 to 350, preferably 10 to 150, more preferably 20 to 100; where each M independently is H or a cation equivalent.

[0220] The molar ratio of structural units (I) to structural units (II) varies from 1:3 to about 10:1, preferably 1 :1 to 10:1, more preferably 3:1 to 6:1. The polymeric dispersants comprising structural units (I) and (II) can be prepared by conventional methods, for example by free radical polymerization or controlled radical polymerization. The preparation of the dispersants is, for example, described in EP 0 894 811, EP 1 851 256, EP 2 463 314, and EP 0 753488.

[0221] More preferably, the dispersant is selected from the group of polycarboxylate ethers (PCEs). In PCEs, the anionic groups are carboxylic groups and / or carboxylate groups. The PCE is preferably obtainable by radical copolymerization of a polyether macromonomer and a monomer comprising anionic and / or anionogenic groups. Preferably, at least 45 mol-%, preferably at least 80 mol-% of all structural units constituting the copolymer are structural units of the polyether macromonomer or the monomer comprising anionic and / or anionogenic groups.

[0222] A further class of suitable comb polymers having a carbon-containing backbone to which are attached pendant cement-anchoring groups and polyether side chains comprise structural units (III) and (IV): wherein

[0223] T is phenyl, naphthyl or heteroaryl having 5 to 10 ring atoms, of which 1 or 2 atoms are heteroatoms selected from N, O and S; n3 is 1 or 2; B is N, NH or O, with the proviso that n3 is 2 if B is N and n3 is 1 if B is NH or O;

[0224] A is C2-C5 alkylene or CH2CH(C6Hs), preferably C2-C3 alkylene; a2 is an integer from 1 to 300;

[0225] R26is H, C1-C10 alkyl, Cs-Cs cycloalkyl, aryl, or heteroaryl having 5 to 10 ring atoms, of which 1 or 2 atoms are heteroatoms selected from N, O and S; where the structural unit (IV) is selected from the structural units (IVa) and (IVb):

[0226] Iva wherein

[0227] D is phenyl, naphthyl or heteroaryl having 5 to 10 ring atoms, of which 1 or 2 atoms are heteroatoms selected from N, O and S;

[0228] E3is N, NH or O, with the proviso that m is 2 if E3is N and m is 1 if E3is NH or O;

[0229] A is C2-C5 alkylene or CH2CH(C6H5), preferably C2-C3 alkylene; b is an integer from 0 to 300;

[0230] M independently is H or a cation equivalent;

[0231] IVb wherein

[0232] V2is phenyl or naphthyl and is optionally substituted by 1 or two radicals selected from R8, OH, OR8, (CO)R8, COOM, COOR8, SO3R8and NO2;

[0233] R7Ais COOM, OCH2COOM, SO3M or OPO3M2;

[0234] M is H or a cation equivalent; and

[0235] R8is C1-C4 alkyl, phenyl, naphthyl, phenyl-Ci-C4 alkyl or C1-C4 alkylphenyl.

[0236] Polymers comprising structural units (III) and (IV) are obtainable by polycondensation of an aromatic or heteroaromatic compound having a polyoxyalkylene group attached to the aromatic or heteroaromatic core, an aromatic compound having a carboxylic, sulfonic or phosphate moiety, and an aldehyde compound such as formaldehyde.

[0237] In an embodiment, the dispersant is a non-ionic comb polymer having a carbon-containing backbone to which are attached pendant hydrolysable groups and polyether side chains, the hydrolysable groups upon hydrolysis releasing cement-anchoring groups. Conveniently, the structural unit comprising a polyether side chain is one of the general formulae (Ila), (lib), (lie) and / or (lid) discussed above. The structural unit having pendant hydrolysable groups is preferably derived from acrylic acid ester monomers, more preferably hydroxyalkyl acrylic monoesters and / or hydroxyalkyl diesters, most preferably hydroxypropyl acrylate and / or hydroxyethyl acrylate. The ester functionality will hydrolyze to (deprotonated) acid groups upon exposure to water at preferably alkaline pH, which is provided by mixing the cementitious binder with water, and the resulting acid functional groups will then form complexes with the cement component.

[0238] In one embodiment, the dispersant is selected from colloidally disperse preparations of polyvalent metal cations, such as Al3+, Fe3+or Fe2+, and a polymeric dispersant which comprises anionic and / or anionogenic groups and polyether side chains. The polyvalent metal cation is present in a superstoichiometric quantity, calculated as cation equivalents, based on the sum of the anionic and anionogenic groups of the polymeric dispersant. Such dispersants are described in further detail in WO 2014 / 013077 A1 , which is incorporated by reference herein.

[0239] Suitable sulfonated melamine-formaldehyde condensates are of the kind frequently used as plasticizers for hydraulic binders (also referred to as MFS resins). Sulfonated melamineformaldehyde condensates and their preparation are described in, for example, CA 2 172 004 A1 , DE 44 1 1 797 A1 , US 4,430,469, US 6,555,683 and CH 686 186 and also in Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., vol. A2, page 131 , and Concrete Admixtures Handbook - Properties, Science and Technology, 2. Ed., pages 411 , 412. Preferred sulfonated melamine-formaldehyde condensates encompass (greatly simplified and idealized) units of the formula in which n4 stands generally for 10 to 300. The molar weight is situated preferably in the range from 2500 to 80 000. Additionally, to the sulfonated melamine units it is possible for other monomers to be incorporated by condensation. Particularly suitable is urea. Moreover, further aromatic units as well may be incorporated by condensation, such as gallic acid, aminobenzenesulfonic acid, sulfanilic acid, phenolsulfonic acid, aniline, ammoniobenzoic acid, dialkoxybenzenesulfonic acid, dialkoxybenzoic acid, pyridine, pyridinemonosulfonic acid, pyridinedisulfonic acid, pyridinecarboxylic acid and pyridinedicarboxylic acid. An example of melaminesulfonate-formaldehyde condensates are the Melment® products distributed by Master Builders Solutions Deutschland GmbH.

[0240] Suitable lignosulfonates are products which are obtained as by-products in the paper industry. They are described in Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., vol. A8, pages 586, 587. They include units of the highly simplified and idealizing formula

[0241]

[0242] Lignosulfonates have molar weights of between 2000 and 100 000 g / mol. In general, they are present in the form of their sodium, calcium and / or magnesium salts. Examples of suitable lignosulfonates are the Borresperse products distributed by Borregaard LignoTech, Norway.

[0243] Suitable sulfonated ketone-formaldehyde condensates are products incorporating a monoketone or diketone as ketone component, preferably acetone, butanone, pentanone, hexanone or cyclohexanone. Condensates of this kind are known and are described in WO 2009 / 103579, for example. Sulfonated acetone-formaldehyde condensates are preferred. They generally comprise units of the formula (according to J. Plank et al., J. Appl. Poly. Sci. 2009, 2018-2024): where m2 and n5 are generally each 10 to 250, M2is an alkali metal ion, such as Na+, and the ratio m2:n5 is in general in the range from about 3:1 to about 1 :3, more particularly about 1.2:1 to 1 :1.2. Furthermore, it is also possible for other aromatic units to be incorporated by condensation, such as gallic acid, aminobenzenesulfonic acid, sulfanilic acid, phenolsulfonic acid, aniline, ammoniobenzoic acid, dialkoxybenzenesulfonic acid, dialkoxybenzoic acid, pyridine, pyridinemonosulfonic acid, pyridinedisulfonic acid, pyridinecarboxylic acid and pyridinedicarboxylic acid. Examples of suitable sulfonated acetone-formaldehyde condensates are the Melcret K1 L products distributed by Master Builders Solutions Deutschland GmbH.

[0244] Suitable sulfonated naphthalene-formaldehyde condensates are products obtained by sulfonation of naphthalene and subsequent polycondensation with formaldehyde. They are described in references including Concrete Admixtures Handbook - Properties, Science and Technology, 2. Ed., pages 411 -413 and in Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., vol. A8, pages 587, 588. They comprise units of the formula

[0245] Typically, molar weights (Mw) of between 1000 and 50 000 g / mol are obtained. Furthermore, it is also possible for other aromatic units to be incorporated by condensation, such as gallic acid, aminobenzenesulfonic acid, sulfanilic acid, phenolsulfonic acid, aniline, ammoniobenzoic acid, dialkoxybenzenesulfonic acid, dialkoxybenzoic acid, pyridine, pyridinemonosulfonic acid, pyridinedisulfonic acid, pyridinecarboxylic acid and pyridinedicarboxylic acid. Examples of suitable sulfonated p-naphthalene-formaldehyde condensates are the Melcret 500 L products distributed by Master Builders Solutions Deutschland GmbH.

[0246] Generally, phosphonate containing dispersants incorporate phosphonate groups and polyether side groups.

[0247] Suitable phosphonate containing dispersants are those according to the following formula

[0248] R-(OA2)n6-N-[CH2-PO(OM32)2]2 wherein

[0249] R is H or a hydrocarbon residue, preferably a C1-C15 alkyl radical,

[0250] A2is independently C2-C18 alkylene, preferably ethylene and / or propylene, most preferably ethylene, n6 is an integer from 5 to 500, preferably 10 to 200, most preferably 10 to 100, and

[0251] M3is H, an alkali metal, 1 / 2 alkaline earth metal and / or an amine.

[0252] Cementitious Binder

[0253] The method of the present invention can be used with a variety of cementitious binders, for example Portland cement.

[0254] Generally, the flowable construction material comprises

[0255] - a cementitious binder comprising one or more calcium silicate mineral phases and one or more calcium aluminate mineral phases,

[0256] - optionally, an extraneous aluminate source,

[0257] - optionally, an extraneous sulfate source, wherein the flowable construction material contains 0.02 to 0.20 mol of total available aluminate, calculated as AI(OH)4“, from the calcium aluminate mineral phases plus the optional extraneous aluminate source, per 100 g of cementitious binder.

[0258] After incorporation of the setting accelerator agent, the molar ratio of total available aluminate to sulfate (including aluminate and sulfate intrinsically contained in the cement, optional extraneous aluminate and / or sulfate sources and aluminum and sulfate contained in the setting accelerator agent) is preferably from 0.4 to 3.5.

[0259] In general, the calcium silicate mineral phases and calcium aluminate mineral phases constitute at least 90 wt.-% of the cementitious binder. Further, the calcium silicate mineral phases preferably constitute at least 60 wt.-% of the cementitious binder, more preferably at least 65 wt.-%, most preferably 65 to 75 wt.-%.

[0260] Conveniently, the mineralogical phases are herein indicated by their cement notation. The primary compounds are represented in the cement notation by the oxide varieties: C for CaO, M for MgO, S for SiC>2, A for AI2O3, $ for SO3, F for Fe2Os, and H for H2O.

[0261] Suitably, the calcium silicate mineral phases are selected from C3S (alite) and C2S (belite). The calcium silicate mineral phases provide primarily final strength properties.

[0262] Suitably, the calcium aluminate mineral phases are selected from C3A, C4AF and C12A7, in particular C3A and C4AF.

[0263] In an embodiment, the cementitious binder is Portland cement, in particular ordinary Portland cement (OPC). The term “Portland cement” denotes any cement compound containing Portland clinker, especially CEM I within the meaning of standard EN 197-1 , paragraph 5.2. A preferred cement is ordinary Portland cement (OPC) according to DIN EN 197-1. The phases constituting Portland cement mainly are alite (C3S), belite (C2S), calcium aluminate (C3A), calcium ferroaluminate (C4AF) and other minor phases. Commercially available OPC may either contain calcium sulfate (< 7 wt.-%) or is essentially free of calcium sulfate (< 1 wt.-%).

[0264] Preferably, the flowable construction material contains 0.05 to 0.2 mol of total available aluminate, calculated as AI(OH)4“, from the calcium aluminate mineral phases plus the optional extraneous aluminate source, per 100 g of cementitious binder. More preferably, the flowable construction material contains at least 0.065 mol, in particular at least 0.072 mol, of total available aluminate, per 100 g of cementitious binder.

[0265] It has been found that flowable construction material containing at least 0.05 mol of total available aluminate per 100 g of cementitious binder exhibit optimum performance regarding open time before setting and early strength development. Otherwise, if the cementitious binder contains more than 0.2 mol of total available aluminate per 100 g of cementitious binder, the open time is shorter as early strength development becomes rather fast.

[0266] Commonly, approximate proportions of the main minerals in Portland cement are calculated by the Bogue formula which in turn is based on the elemental composition of the clinker determined, e.g., by means of X-ray fluorescence (XRF). Such methods provide the oxide composition of the elements. This means that the amount of Al is reported as AI2O3. It has been found that cements with apparently the same AI2O3 content exhibit quite different properties regarding early strength and controllability by hydration control. Cement includes very different sources of Al of mineralogical nature and solubility. It has been found that not all Al is available or accessible for the formation of ettringite. Only Al-containing mineral phases with adequate solubility in the aqueous environment of the cement paste participate in the formation of ettringite. Other Al-containing minerals such as crystalline aluminum oxides, e.g. corundum, do not generate aluminate in aqueous environments, due to their limited solubility. Consequently, elemental analysis alone cannot provide reliable values for available aluminate.

[0267] Hence, the invention relies on the available aluminate, calculated as AI(OH)4“. “Available aluminate” is meant to encompass mineral phases and Al-containing compounds that are capable of generating AI(OH)4“ in alkaline aqueous environments. Calcium aluminate phases, such as C3A (CasAhOe), dissolve in an alkaline aqueous environment to yield AI(OH)4“ and Ca2+ions. Herein, the concentration of mineral phases and Al-containing compounds that are capable of generating AI(OH)4“ is expressed as mol of AI(OH)4“ per 100 g of cementitious binder.

[0268] It is believed that the common calcium aluminate mineral phases - in contrast to crystalline aluminum oxides - are sources of available aluminate. Therefore, the amount of available aluminate in a given cementitious binder may be determined by methods capable of discriminating between the mineral phases constituting the cementitious binder. A useful method for this purpose is Rietveld refinement of an X-ray diffraction (XRD) powder pattern. This software technique is used to refine a variety of parameters, including lattice parameters, peak position, intensities and shape. This allows theoretical diffraction patterns to be calculated. As soon as the calculated diffraction pattern is almost identical to the data of an examined sample, precise quantitative information on the contained mineral phases can be determined.

[0269] Generally, calcium aluminate mineral phases capable of generating AI(OH)4“ in alkaline aqueous environments are tricalcium aluminate (C3A), monocalcium aluminate (CA), mayenite (C12A7), grossite (CA2), Q-phase (C20A13M3S3) or tetracalcium aluminoferrite (C4AF). For practical purposes, if the cementitious binder is Portland cement, it generally suffices to assess the following mineral phases only: tricalcium aluminate (C3A), monocalcium aluminate (CA), mayenite (C12A7) and tetracalcium aluminoferrite (C4AF), in particular tricalcium aluminate (C3A) and tetracalcium aluminoferrite (C4AF).

[0270] Alternatively, the amount of available aluminate may be obtained by determining the total amount of Al from the elemental composition of the cementitious binder, e.g., by XRF, and subtracting therefrom the amount of crystalline aluminum compounds not capable of generating available aluminate, as determined by XRD and Rietveld refinement. This method also takes into account amorphous, soluble aluminum compounds capable of generating available aluminate. Such crystalline aluminum compounds not capable of generating available aluminates include compounds of the melilite group, e.g., gehlenite (C2AS), compounds of the spinel group, e.g., spinel (MA), mullite (Al2Ah+2xSi2-2xOio-x), and corundum (AI2O3).

[0271] In one embodiment, the invention makes use of cementitious binders containing 0.05 to 0.2 mol of available aluminate from calcium aluminate mineral phases, as determined by, e.g., XRD analysis.

[0272] Alternatively, if the cementitious binder intrinsically contains an insufficient concentration of available aluminate per 100 g of cementitious binder, an extraneous aluminate source can be added. Hence in some embodiments, the flowable construction material contains an extraneous aluminate source.

[0273] The extraneous aluminate source provides available aluminate as defined above. Generally, the extraneous aluminate source is a sparingly soluble aluminate source, e.g., having an aqueous solubility at 25 °C and atmospheric pressure of 0.05 g L'1or lower, preferably 0.005 g L'1or lower. The limited solubility of the extraneous aluminate source acts to avoid uncontrolled premature setting of flowable construction material. The extraneous aluminate source is contained in the flowable construction material in an undissolved or only partially dissolved form.

[0274] Suitably, the extraneous aluminate source is selected from non-calciferous aluminate sources, such as amorphous aluminum hydroxide; and calciferous aluminate sources such as high alumina cement, sulfoaluminate cement or synthetic calcium aluminate mineral phases.

[0275] Preferably, amorphous aluminum hydroxide is used as an extraneous aluminate source.

[0276] High aluminate cement means a cement containing a high concentration of calcium aluminate phases, e.g., at least 30 wt.-%. More precisely, said mineralogical phase of aluminate type comprises tricalcium aluminate (C3A), monocalcium aluminate (CA), mayenite (C12A7), tetracalcium aluminoferrite (C4AF), or a combination of several of these phases.

[0277] Sulfoaluminate cement has a content of ye’elimite (of chemical formula 4CaO.3AI2O3.SO3 or C4AS$ in cement notation) of typically greater than 15 wt.-%.

[0278] Suitable synthetic calcium aluminate mineral phases include amorphous mayenite (C12A7).

[0279] The flowable construction material may comprise a sulfate source. The sulfate source is a compound capable of providing sulfate ions in an alkaline aqueous environment. Generally, the sulfate source has an aqueous solubility at a temperature of 30 °C to provide a sulfate ion concentration of at least 0.6 mmol g- L'1. The aqueous solubility of the sulfate source is suitably determined in water with a starting pH value of 7. Specifically, the molar ratio of total available aluminate to sulfate (including aluminate and sulfate intrinsically contained in the cement, optional extraneous aluminate and / or sulfate sources and aluminum and sulfate contained in the setting accelerator agent) is in the range of 0.4 to 3.5, preferably 0.57 to 0.8, in particular about 0.67. This means that the mixing ratios in the composition are adjusted so that the highest possible proportion of ettringite is formed from the available aluminate.

[0280] As mentioned earlier, Portland cement in its commercially available form typically contains small amounts of a sulfate source. If the intrinsic amount of sulfate is unknown, it can be determined by methods familiar to the skilled person such as elemental analysis by XRF. As the sulfate source commonly used in the cement production, alkaline earth metal sulfates, alkali metal sulfates, or mixed forms thereof, such as gypsum, hemihydrate, anhydrite, arkanite, thenardite, syngenite, langbeinite, are typically crystalline, the amount thereof can also be determined by XRD. Both the intrinsic amount of sulfate and any added extraneous sulfate source are considered in the calculation of the molar ratio of total available aluminate to sulfate.

[0281] In general, the extraneous sulfate source may be selected from calcium sulfate dihydrate, anhydrite, a - and 3 -hemihydrate, i.e. a -bassanite and 3 -bassanite, or mixtures thereof. Preferably, the calcium sulfate source is a -bassanite and / or 3 -bassanite. The sulfate source is not especially limited, other possible sulfate sources are for example alkali metal sulfates like potassium sulfate or sodium sulfate.

[0282] It is envisaged that an additive can act as a source of both aluminate and sulfate, such as aluminum sulfate hexadecahydrate or aluminum sulfate octadeca hydrate. Preferably, the sulfate source is a calcium sulfate source.

[0283] Preferably, the construction material comprises sulfate, inclusive of the intrinsic SO4 content of the binder and any added extraneous sulfate source, in an amount in the range of from 0.025 to 0.5 mol, per 100 g of cementitious binder.

[0284] In an embodiment, the flowable construction material additionally comprises at least one of a latent hydraulic binder, a pozzolanic binder and a filler material.

[0285] Herein, a “latent hydraulic binder” is preferably a binder in which the molar ratio (CaO + MgO):SiC>2 is from 0.8 to 2.5 and particularly from 1.0 to 2.0. In general terms, the above- mentioned latent hydraulic binders can be selected from industrial and / or synthetic slag, in particular from blast furnace slag, electrothermal phosphorous slag, steel slag and mixtures thereof. The “pozzolanic binders” can generally be selected from amorphous silica, preferably precipitated silica, fumed silica and microsilica, ground glass, metakaolin, aluminosilicates, fly ash, preferably brown-coal fly ash and hard-coal fly ash, natural pozzolans such as tuff, trass and volcanic ash, calcined clays, burnt shale, rice husk ash, natural and synthetic zeolites and mixtures thereof. The slag can be either industrial slag, i.e. waste products from industrial processes, or else synthetic slag. The latter can be advantageous because industrial slag is not always available in consistent quantity and quality.

[0286] Blast furnace slag (BFS) is a waste product of the glass furnace process. Other materials are granulated blast furnace slag (GBFS) and ground granulated blast furnace slag (GGBFS), which is granulated blastfurnace slag that has been finely pulverized. Ground granulated blast furnace slag varies in terms of grinding fineness and grain size distribution, which depend on origin and treatment method, and grinding fineness influences reactivity here. The Blaine value is used as parameter for grinding fineness, and typically has an order of magnitude of from 200 to 1000 m2kg-1, preferably from 300 to 500 m2kg-1. Finer milling gives higher reactivity.

[0287] Herein, the expression “blast furnace slag” is however intended to comprise materials resulting from all of the levels of treatment, milling, and quality mentioned (i.e. BFS, GBFS and GGBFS). Blast furnace slag generally comprises from 30 to 45% by weight of CaO, about 4 to 17% by weight of MgO, about 30 to 45% by weight of SiO2 and about 5 to 15% by weight of AI2O3, typically about 40% by weight of CaO, about 10% by weight of MgO, about 35% by weight of SiO2 and about 12% by weight of AI2O3.

[0288] Electrothermal phosphorous slag is a waste product of electrothermal phosphorous production. It is less reactive than blast furnace slag and comprises about 45 to 50% by weight of CaO, about 0.5 to 3% by weight of MgO, about 38 to 43% by weight of SiO2, about 2 to 5% by weight of AI2O3 and about 0.2 to 3% by weight of Fe2Os, and also fluoride and phosphate. Steel slag is a waste product of various steel production processes with greatly varying composition.

[0289] Amorphous silica is preferably an X ray-amorphous silica, i.e. a silica for which the powder diffraction method reveals no crystallinity. The content of SiO2 in the amorphous silica is advantageously at least 80% by weight, preferably at least 90% by weight. Precipitated silica is obtained on an industrial scale by way of precipitating processes starting from water glass. Precipitated silica from some production processes is also called silica gel.

[0290] Fumed silica is produced via reaction of chlorosilanes, for example silicon tetrachloride, in a hydrogen / oxygen flame. Fumed silica is an amorphous SiO2 powder of particle diameter from 5 to 50 nm with specific surface area of from 50 to 600 m2g-1.

[0291] Microsilica is a by-product of silicon production or ferrosilicon production, and likewise consists mostly of amorphous SiO2 powder. The particles have diameters of the order of magnitude of 0.1 pm. Specific surface area is of the order of magnitude of from 15 to 30 m2g-1.

[0292] Metakaolin is produced when kaolin is dehydrated. Whereas at from 100 to 200 °C kaolin releases physically bound water, at from 500 to 800 °C a dehydroxylation takes place, with collapse of the lattice structure and formation of metakaolin (AhSi2O7). Accordingly, pure metakaolin comprises about 54% by weight of SiO2 and about 46% by weight of AI2O3. Fly ash is produced inter alia during the combustion of coal in power stations. Class C fly ash (brown-coal fly ash) comprises according to WO 08 / 012438 about 10% by weight of CaO, whereas class F fly ash (hard-coal fly ash) comprises less than 8% by weight, preferably less than 4% by weight, and typically about 2% by weight of CaO.

[0293] Preferably, the cementitious binder, before being mixed with water in the presence of the set control agent, comprises less than 5 wt.-%, more preferably less than 3.5 wt.-%, most preferably less than 2 wt.-% of cementitious hydration products, relative to the total weight of the cementitious binder. It generally suffices to assess the following cementitious hydration products: ettringite, portlandite, syngenite. The presence and concentrations of these cementitious hydration products can be determined by Rietveld refinement of an X-ray diffraction (XRD) powder pattern. This means that the cementitious binder has no history of storage in high humidity environments. We believe that otherwise, ettringite among other cementitious hydration products is formed already in the powdery composition. Although these ettringite crystals are broken up at the time of mixing the cementitious binder with water at the time of use, the ettringite formation control provided by the invention is less prominent. Thus, storage of the cementitious binder in high humidity environments should be avoided.

[0294] Printing Process

[0295] For carrying out the inventive process, first a digital 3D model is created using a 3D modelling software. The model is then sliced and translated into G-Code. The G-Code then guides the printhead which deposits material pumped from a cement mixer in layers until the final piece is produced. A typical concrete 3D printer is designed to additively manufacture parts through material extrusion, consisting of a robotic arm, with one end attached to the printhead, and the other either to a gantry or crane-like robotic arm system.

[0296] The conveying step of the inventive method comprises conveying the construction material in a flowable state to the deposition head. In particular, the conveying of the construction material is performed by pumping. Preferably, the material is conveyed in a wet state and is ready to be placed without the need of adding any additional components with the exception of the setting accelerator agent.

[0297] Preferably, the fresh construction material, such as fresh concrete or fresh mortar, is stored in a silo or any other storage container or in a mixer of a ready-mix delivery truck and is conveyed from the storage site directly to the deposition head.

[0298] As for the placing (deposition) method, a distinction can be made between extrusion-based methods and spray-based methods.

[0299] In an embodiment, the step of placing the construction material comprises extruding the construction material through a nozzle of the deposition head. The extrusion process does not use compressed air. Instead of compressed air preferably a screw pump is used, and the construction material is transported by pumps to the deposition head. Generally, after placing a first layer of construction material, at least one subsequent layer of construction material is placed onto the first layer of construction material, wherein the yield stress is selected such that the first layer does not collapse under the load of said at least one subsequent layer of construction material.

[0300] In the spray-based method, the construction material is injected with air and then sprayed onto the substrate or a preceding layer of construction material. Unlike the extrusion method, the construction material injected with air is sprayed from a distance. In this way, reinforcement can be easily incorporated into the concrete structure. For example, the construction material is sprayed over a wire framework. This prefabricated mesh structure acts as both the reinforcement and stay-in-place formwork.

[0301] Preferably, the setting accelerator agent is continuously incorporated to a flow of set-delayed conveyed construction material.

[0302] Conveniently, the setting accelerator agent and the set-delayed construction material are mixed with each other before placing the construction material, wherein a dynamic mixer is preferably used for mixing.

[0303] The method of the invention permits flexible control of yield stress development, allowing for the first layer of construction material to have a sufficient yield stress so that the first layer of construction material does not collapse under the load of the at least one subsequent layer of construction material. This in turn advantageously allows a broad range of printing speeds from fast printing, i.e., time between deposition of subsequent layers down to 4 seconds, to slow printing, i.e., time between deposition of layers up to 90 minutes or even more.

[0304] Fig. 1 depicts sound velocity in mortar vs. time with addition of different accelerators to a mortar system without set control agent.

[0305] Fig. 2 depicts sound velocity in mortar vs. time with addition of different accelerator dosages to a mortar system without set control agent.

[0306] Fig. 3 depicts sound velocity in mortar vs. time with / without addition of accelerator to a mortar system with / without set control agent.

[0307] Fig. 4 depicts sound velocity in mortar vs. time with / without addition of accelerator to a mortar system with / without set control agent.

[0308] Fig. 5 depicts a magnified excerpt of Fig. 3.

[0309] Fig. 6 depicts a magnified excerpt of Fig. 4.

[0310] Fig. 7 depicts Vicat setting times.

[0311] Fig. 8 depicts a correlation between Vicat setting times and dynamic elastic modulus.

[0312] Fig. 9 depicts the evolution of the heat of hydration of cement pastes over time. Fig. 10 depicts sound velocity in mortar (cement-to-slag ratio 50:50) vs. time (up to 70 hours) of mortars containing extraneous sources of aluminum and sulfate, a set control agent, polyol and setting accelerator agent (examples according to the invention) and mortar containing only a setting accelerator agent (comparative example).

[0313] Fig. 11 depicts sound velocity in mortar (cement-to-slag ratio 50:50) vs. time (up to 50 minutes) of mortars containing extraneous sources of aluminum and sulfate, a set control agent, polyol and setting accelerator agent (examples according to the invention) and mortar containing only a setting accelerator agent (comparative example).

[0314] Fig. 12 depicts sound velocity in mortar (cement-to-slag ratio 25:75) vs. time (up to 70 hours) of mortars containing extraneous sources of aluminum and sulfate, a set control agent, polyol and setting accelerator agent (examples according to the invention) and mortar containing only a setting accelerator agent (comparative example).

[0315] Fig. 13 depicts sound velocity in mortar (cement-to-slag ratio 25:75) vs. time (up to 50 minutes) of mortars containing extraneous sources of aluminum and sulfate, a set control agent, polyol and setting accelerator agent (examples according to the invention) and mortar containing only a setting accelerator agent (comparative example).

[0316] Fig. 14 depicts the penetration force of inventive mortars over time.

[0317] Fig. 15 depicts the penetration force of inventive mortars over time.

[0318] The present invention can be further explained and illustrated on the basis of the figures and examples that follow.

[0319] Examples

[0320] Methods

[0321] Initial and final Vicat setting time after the addition of setting accelerator agent.

[0322] Equipment: Hobbart mixer, manual Vicat needle

[0323] Initial and final setting times are measured according to DIN EN 196-3 using a Vicat needle consisting of a cylinder weighing 300 ± 1 g and a needle point with a diameter of 1.13 ± 0.05 mm. The initial setting time is defined as the time at which a paste or mortar deposited in the mold begins to oppose resistance to penetration by the Vicat needle. In practice, the Vicat needle is allowed to fall by gravity. When the needle does not touch the bottom of the mold due to the resistance of the material, the setting has started. Final setting, on the other hand, is defined as having taken place when the Vicat needle, in contact with the upper side of the material, is not breaking its structure but only leaves the print of the pressure of the point of the needle. Setting time (Fig. 7) was determined using a fully automated Vicat-measuring-system from DETTKI equipped with Vicat needle and two different loads (300 g and 1000 g). The measurement was conducted according to DIN EN 196-3.

[0324] The penetration force was measured by a penetrometer device (MecMesin 1000N, Model FL1 K) equipped with a 0 17 mm hemispherical tip. The resistance force excreted by the mortar after adding the accelerator when moving the hemispherical tip towards the bucket containing the mortar was recorded. The time interval between subsequent measurements was 1 minute. It was considered to conduct the measurements always on an intact and new spot on the surface of the mortar with distance of at least 1 cm from the previous measurement’s spot.

[0325] Compressive strength development

[0326] The mortar mixes were each filled into mortar steel prisms molds (16 / 4 / 4 cm), and after 2 h at a temperature of 20 °C and relative humidity of 65%, a hardened mortar prism was obtained. The hardened mortar prism was demolded and compressive strength (= comp, strength). The mortar prism was measured again after 1 , 7 and 28 days.

[0327] Ultrasonic measurement

[0328] Ultrasonic measurements were performed with the “Freshcon system” developed at the University of Stuttgart [H.W. Reinhardt and C.U. Grosse, Continuous Monitoring of setting and hardening of mortar and concrete, Construction and Building Materials 18, (2004) pp.145-154; N. Robeyst, E. Gruyaert, C.U. Grosse and N. De Belie, Monitoring the setting of concrete containing blast-furnace slag by measuring the ultrasonic p-wave velocity, Cement and Concrete Research 38, (2008), pp.1169-1176],

[0329] Sound pulses are generated and received by piezoelectric transducers which travel through the test material. The speed of sound in a homogenous medium is directly related to both elastic modulus and density, thus changes in elasticity will affect pulse transit time through a sample of a given thickness.

[0330] Dynamic elastic modulus

[0331] The dynamic elastic modulus can mathematically be derived from the ultrasound compressional and shear wave velocities.

[0332] Generally, all comparative examples are indicated with * in this specification.

[0333] Example 1 (SA-2) Two mortars were prepared and tested for their performance in 3D-printing, see table 1 : Inventive mortar #1 contains both the set control agent, the setting accelerator agent of the invention and polyol. Comparative mortar #2* did not contain a set control agent.

[0334] Mixing procedure: The set control agent was pre-dissolved in the mixing water with the superplasticizer, and the resulting solution was added to dry mortar and mixed for 60 seconds at 65 rpm, then at 130 rpm for 30 seconds. After a pause for 90 seconds, mixing was continued at 130 rpm for 60 seconds. After allowing to rest for 10 minutes, the setting accelerator agent was added and homogeneously distributed by mixing at 285 rpm for 15 seconds.

[0335] With the inventive mortar 1 , an hourglass-shaped spire comprising overhanging elements was 3D-printed. The results in table 1 demonstrate the positive effects of the inventive retarderaccelerator combination on the initial and final setting time (by manual Vicat needle) as well as on the early and final compressive strength of inventive mortar 1. Comparative mortar 2* on the other side shows a very slow setting and the compressive strength at 2 hours is not measurable.

[0336] Table 1.

[0337] * comparative example

[0338] [1] polyacrylic acid, concentration 45 wt.-%

[0339] [2] Weight ratio of set control agent to the weight of aluminum * 3.572.5 (calculated according to inequation (1))

[0340] Example 2 (SA-2)

[0341] Six mortar mixes comprising the setting accelerator agent as shown in table 2 were prepared as shown in table 3. The setting accelerator agent contains the polyol glycerol. For this purpose, the constituents of the set control agent, i.e. sodium gluconate, Sokalan PA-15 and potassium carbonate, were pre-dissolved together with the mixing water. The resulting solution was added to the commercial dry mix, which is described in the following text. Table 2.

[0342] 1] alkali-free accelerator based on aluminum sulfate; solids content 48.4%

[0343] [2] concentration 98%

[0344] [3] alkali-free accelerator based on aluminum sulfate; solids content 53.5%

[0345] Table 3.

[0346] * comparative example

[0347] [1] % bwoc

[0348] [2] polyacrylic acid, concentration 45 wt.-%

[0349] [3] see table 2

[0350] [2] Weight ratio of set control agent to the weight of aluminum * 3.572.5 (calculated according to inequation (1)

[0351] Mortars 3 to 8 of table 3 comprising a commercial dry mix mortar (containing 48 wt.-% of OPC, 2 wt.-% of High Alumina Cement (HAC) and 50 wt.-% of aggregates) were subjected to ultrasonic measurements. An ultrasonic measurement is a non-destructive testing method which enables in-situ monitoring of microstructure development and viscoelastic properties of mortars. The results are shown in Fig. 1 to 6 and demonstrate the advantages of the flowable construction material used in the inventive method (mortars 7 and 8 against comparative mortars 3* to 6*). Fig. 1 and 2 depict sound velocity curves showing the microstructure development before (comparative mortar 3*) and after (comparative mortars 4*, 5* and 6*) adding the setting accelerator agent to fresh mortar. Fig. 1 illustrates the impact of different types of conventional alkali-free accelerators (accelerator 1 and accelerator 2). Fig. 2 illustrates the impact of using different dosages of the same alkali-free accelerator (accelerator 1).

[0352] Fig. 3 and 4 depict sound velocity curves showing microstructure development before (comparative mortar 3*) and after (comparative mortars 4* and 5*) adding the setting accelerator agent to fresh mortar, as well as microstructure development of mortars produced according to the inventive method (inventive mortars 7 and 8). The arrows indicate the fast microstructure development associated in the mortars produced according to the inventive method. In other words, early age microstructure development is improved in the inventive mortars. The improved early age microstructure is advantageous in the 3D-printing process as it e.g. results in a better extrudability by minimizing the risks of clogging at the nozzle. After placing the construction material, a significant early strength development is achieved rapidly. This advantageously allows for printing at high speeds.

[0353] Furthermore, the significant early strength development profile enhances the stability of the final printed structure and during printing as well. Hence, structural failures related to common extrusion-based 3D-printing processes such as elastic buckling and / or plastic collapse, are reduced with mortars of the inventive method.

[0354] It can be seen from Fig. 3 and 4 that the dosage of the setting accelerator agent and set control agent according to the invention is crucial for altering the evolution of the hydration process (mortars #7 and #8), which is not the case by the sole use of accelerator, compare also Fig. 1 and 2 (comparative mortars 3*, 4*, 5* and 6*).

[0355] Fig. 5 and 6 depict magnified excerpts of Fig. 3 and 4 for the first 100 min. It can be seen that the first minutes after adding the setting accelerator agent are decisive for the printing process. The graphs show that microstructure development in the inventive mortars 7 and 8 is fast in comparison to comparative mortars 4* and 5* (see, e.g. Fig. 5 at 40 min and Fig. 6 at 7 min).

[0356] The graphs further illustrate that the set-on of the microstructure development and hence loosing workability or extrudability is not too fast. Too fast microstructure development could be detrimental for the extruding process. A suitably long-time window of at least 5 min is required for mixing and homogenizing of the components with fresh mortar before the step of placing the layers of construction material.

[0357] Example 3 (SA-2)

[0358] Mortars 5* and 8 according to table 3 were investigated for their Vicat setting time (see Fig. 7) and their dynamic elastic modulus evolution. As shown in Fig. 7, the initial and final Vicat setting times are considerably shorter for mortar 8 compared to comparative mortar 5*, which shows too long setting times.

[0359] A correlation of Vicat setting times and dynamic elastic modulus is shown in Fig. 8. Interestingly, the dynamic elastic modulus values at the obtained Vicat setting times (26 min for mortar 8 of the invention, and 147 min for comparative mortar 5) are almost identical. This reflects the speed of microstructure development and hence the capability of the inventive method for printing at unprecedented high speeds.

[0360] Example 4

[0361] Testing procedure - Monitoring hydration evolution for cement pastes including different types of polyols

[0362] The hydration evolution of the cement pastes was measured using isothermal heat flow calorimetry. TAM Air from TA Instruments was implemented for measuring the development of the heat of hydration over time for a reference sample not containing a set control agent, as well as a sample containing set control agent without polyol and those containing set control agent with one polyol. Different types of polyols were used in this study, such as triethanolamine, erythritol, tris(hydroxymethly)aminoethane, glycerol. Karlstadt CEM I 52,5 R was used for the calorimetry study. Water to cement ratio is 0.45. The dosage of glycerol at 0.25 wt.-% by weight of cement was used to determine the equivalent quantity of OH-groups in mols (0.0040721 mols of OH-groups). For calculating the dosage of other polyols, equal amounts of OH-groups in mols, consistent with the glycerol dosage, were utilized, and the respective weights of the polyols were computed based on the fixed mols of OH-groups (0.0040721 mols of OH-groups). The amount of the set control agent used in this study was fixed. Table 4 shows the weights of each component within the set control agent, expressed as a percentage of 100 g of cement.

[0363] Six cement paste mixes were prepared as shown in table 4. For the samples containing the set control agent with or without a polyol, the constituents of the set control agent, i. e. sodium gluconate, Sokalan PA-15, potassium carbonate and where used, a polyol were pre-dissolved together with the mixing water. The resulting solution was added to the cement.

[0364] In the isothermal heat flow colorimetry tests, it is not possible to use a setting accelerator agent (too fast hydration reaction).

[0365] Table 4.

[0366] 1] % bwoc

[0367] [2] polyacrylic acid, concentration 45 wt.-%

[0368] [3] Examples without polyol for comparison

[0369] As shown in Fig. 9, the influence of adding different polyols to the set control agent is evident by comparing the resulting heat of hydration curves of samples containing set control agent with polyol with the heat of hydration curve of the sample containing the set control agent without polyol. The steep increase of heat of hydration shown in all samples containing a set control agent is being shifted to earlier times for the samples comprising any type of polyol. Additionally, the amplitude of the first heat of hydration plateau for the samples containing a set control agent and polyol is higher compared to the plateau observed for the sample containing only a set control agent (cement paste 2). The plateau is deemed here as an indicator for the controlled formation of ettringite crystals and its amplitude is related to the amount of ettringite crystals formed. The sample #1 without a set control agent is completely lacking the first heat of hydration plateau, indicating the lack of controlled ettringite formation.

[0370] Example 5 (SA-2)

[0371] Four mortar mixes were prepared and tested to validate the positive impact of incorporating glycerol into the setting accelerator agent, see table 6: four different types of setting accelerator agents were used for this purpose, two of them included glycerol in their composition and the other two without glycerol. The composition of the four setting accelerators is shown in table 5. Table 5.

[0372] 1] alkali-free accelerator based on aluminum sulfate; solids content 48.4%

[0373] [2] concentration 98%

[0374] [3] alkali-free accelerator based on aluminum sulfate; solids content 54% Table 6.

[0375] 1] setting accelerator agent without polyol

[0376] [2] polyacrylic acid, concentration 45 wt.-%

[0377] [3] Weight ratio of set control agent to the weight of aluminum * 3.572.5 (calculated according to inequation (1))

[0378] The results presented in table 6 clearly illustrate the positive impact of incorporating glycerol into the setting accelerator agent on the early strength development (2 hours compressive strength). Mortars 10 and 12 are compared to mortars 9 and 11, respectively. Early strength development can help improving structural stability in 3D concrete printing. Moreover, achieving high speeds and vertical build up rates is feasible by ensuring rapid strength development in the printed layers, enabling them to support subsequent layers without inducing deformations.

[0379] Example 6 (SA-2)

[0380] Seven mortars mixes were prepared as shown in table 7. The mortars were subjected to ultrasonic measurements. An ultrasonic measurement is a non-destructive testing method which enables in-situ monitoring of microstructure development and viscoelastic properties of mortars. The results are shown in Fig. 10 to 13 and demonstrate the advantages of the flowable construction material used in the inventive method.

[0381] Table 7

[0382] * comparative examples

[0383] [1] polyacrylic acid, concentration 45 wt.-%

[0384] [2] alkali-free accelerator based on aluminum sulfate; solids content 48.4%

[0385] [3] concentration 98%

[0386] [4] Weight ratio of set control agent to the weight of aluminum * 3.572.5 (calculated according to inequation (1)). The amorphous aluminum hydroxide (Geloxal) used in samples 14 and 17 as an extraneous aluminum source was not considered in the calculation of the weight ratio. The graphs 10 to 13 depict sound velocity curves showing microstructure development of the inventive mortars (mortar 14, 17, 18 and 19) compared to the comparative mortars (mortar 13*, 15* and 16*).

[0387] In mortar 13*, 14 and 18 the amounts of cement and slag used are equal (50:50), whereas for mortars 15*, 16*, 17 and 19 cement was substituted by slag, resulting in a ratio of 25:75 for cement to slag. The quantity of available aluminate in the cement used for this study was assessed using Rietveld refinement of an X-ray diffraction powder pattern. In Karlstadt CEM II C-M (S-LL) 42.5 N cement, the amount of available aluminate in the cement is equal to 0.062 mol per 100g cement. The resulting amounts of available aluminate derived from the cement in the dry mixes with cement-to-slag ratio 50:50 and 25:75 are 0.031 and 0.016 mol in 100 g of cement and slag, respectively.

[0388] Upon using an extraneous source of aluminum (aluminum hydroxide, Geloxal) in the dry mixes (mortar 14 and 17) with cement to slag ratio 50:50 and 25:75, the amount of available aluminate becomes 0.05 (mortar 14) and 0.035 (mortar 17) mol in 100 g of cement and slag, respectively.

[0389] The decreased amount of cement in the mortar mixes 15*, 16*, 17 and 19 renders them rather low in clinker content, resulting in a correspondingly low amount of available aluminate confined in the dry mixes. Low clinker dry mixes are poor in the aluminate constituents, which are favorable for developing early strength (mortar 15*, 16*). Controlled ettringite formation, which is important for 3D concrete printing, can be promoted by using extraneous sources of aluminate and sulfate in the dry mix, as shown in the inventive mortars 14 and 17, even when low clinker binder systems with few available aluminate are used.

[0390] Fig. 10 and 11 depict sound velocity curves showing microstructure development for the comparative mortar 13* (without setting control agent), as well as for the inventive mortars 14 and 18.

[0391] Fig. 10 illustrate the positive impact of using the extraneous aluminate source in combination with set control agent and setting accelerator agent on the microstructural development throughout the entire measurement time of 70 hours.

[0392] Fig. 11 depicts magnified excerpts of Fig. 10 covering the first 50 minutes. It is evident that the microstructural evolution of the comparative mortar 13* (without setting control agent), is progressing slowly compared to the inventive mortars 14 and 18. Furthermore, it is evident that upon using extraneous aluminium and sulfate sources in the inventive mortar 14, the microstructural development evolution is significantly improved, in particular during the first 25 minutes of the measurement.

[0393] Fig. 12 and 13 depict sound velocity curves showing microstructure development for the comparative mortars 15* and 16* as well as for the inventive mortars 17 and 19.

[0394] Fig 13 depicts magnified excerpts of Fig. 12 covering the first 50 minutes. It is evident that the microstructural evolution of the comparative mixes (15* and 16*) is progressing very slow throughout the measurement period, regardless of the amount of accelerator used (0.44% bwoc or 0.87% of Al bwoc; mortar mixes 15* and 16*, respectively). On the other hand, Fig. 13 clearly illustrates the rapid early-age microstructural evolution for the inventive mortar 17. It is worth mentioning that despite using a lower amount of the setting accelerator agent (0.42wt% of Al bwoc) in the inventive mortar 17, compared to double the amount of conventional accelerator (0.87wt.-% of Al bwoc) in the comparative mortar mix 16*, the microstructural evolution of the inventive mortar 17 is much faster than that of the comparative mortar 16*.

[0395] Example 7 (SA-2)

[0396] Twelve mortars were prepared as shown in table 8 and table 9.

[0397] Two cements were used for this study: Karlstadt CEM II C-M (S-LL) 42.5 N and Bernburg CEM I 42.5 N. Three different dosages of the set control agent were used throughout this study: a low dosage of 0.85wt.-% bowc, and a medium dosage of 1.7wt.-% bwoc and a relatively high dosage of 2.77wt.-% bwoc. The dosages of the setting accelerator agent varied according to the intended final application (3D printing or shotcreting as a comparison). The balance between the amounts of the set control agent and the setting accelerator agent is crucial for achieving the required performance of the intended application, whether it be 3D printing (according to the invention) or shotcreting (comparative application). Vicat setting times were recorded for all mortar mixes.

[0398] It is worth mentioning that requirements for 3D-printing and shotcrete applications are fundamentally different from the point of view of setting times as well as stiffening behaviour of the material after the addition of the accelerator. For instance, in the case of 3D printing setting times should be sufficiently long to ensure good bonding between the layers. The layer time (another term is circulation period) in 3D printing might differ depending on the type of 3D printer in use. Generally, there are two commonly used extruder-based printers, namely, the axial robotic arm printer and the gantry printer. The layer time of the robotic arm printer is generally shorter compared to the gantry printer. On the other hand, for shotcrete applications very fast setting times are required to ensure that the sprayed material adhere to the walls or ceiling upon contact with the substrate; therefore, in shotcrete applications the setting times and the stiffening behaviour differ from those for 3D concrete printing applications.

[0399] The required short setting times for shotcreting as shown in table 8 and 9 (comparative mortars 24*, 30*) are met by using high amounts of setting accelerator agent (0.44 wt.-% of Al bwoc) combined with a low dosage of the set control agent, whereas the setting accelerator agent dosages required for 3D printing are significantly lower (0.07 wt.-% of Al. and 0.2 wt.-% of Al bwoc depending on the dosage of the set control agent, medium and high dosages, respectively).

[0400] Fig.14 depicts the curves of the penetration force measurements conducted on the mortars 28 and 29. The curves are considered indicative for the stiffening behaviour of the mortars after the addition of the set control agent. The comparative mortar mix 30* (not shown in the Fig. 14) was not measurable, indicating that the material is stiffening rapidly in a way that renders it not suitable for 3D printing applications due to the risks associated with clogging of the printing head. On the other hand, such a rapid stiffening behaviour is rather beneficial for shotcrete applications. Conversely, in Fig. 14, it is observed that the onset of the stiffness development for the inventive mortars 28 and 29 is slow during the first 5 minutes after the addition of the setting control agent. This slow onset ensures safe and good extrudability and prevents clogging of the printing head while also ensuring good bonding between the layers.

[0401] Table 8

[0402] * comparative examples

[0403] [1] polyacrylic acid, concentration 45 wt.-%

[0404] [2] alkali-free accelerator based on aluminum sulfate; solids content 48.4%

[0405] [3] concentration 98%

[0406] [4] Weight ratio of set control agent to the weight of aluminum * 3.572.5 (calculated according to inequation (1))

[0407] Table 9

[0408] * comparative examples

[0409] [1] polyacrylic acid, concentration 45 wt.-%

[0410] [2] commercially available alkali-free accelerator based on aluminum sulfate; solids content 48.4%

[0411] [3] concentration 98%

[0412] [4] Weight ratio of set control agent to the weight of aluminum * 3.572.5 (calculated according to inequation (1)

[0413] Example 8 (SA-1)

[0414] Two reference mortars and four inventive mortar mixes comprising sodium silicate based setting accelerators of different moduli were prepared as shown in table 10: For this purpose, the constitutes of the set control agent, i.e. sodium gluconate, Sokalan PA-15 and potassium carbonate, were predissolved together with the mixing water. The resulting solution was added to the dry mix as described in table 10.

[0415] Table 10

[0416] 1] polyacrylic acid, concentration 45 wt.-%

[0417] [2] Weight ratio of set control agent to the weight of SiO2 * 3.5 (calculated according to inequation (1)

[0418] The results in table 10 demonstrate the positive effect of the inventive retarder-accelerator combination on the initial and final setting time (by manual Vicat needle) as well as on the early and final compressive strength. The mortars comprising glycerol show enhanced early strength development in comparison to those without glycerol. On the other hand, the samples without glycerol show higher 1 day and 28 days compressive strength compared to the mortars with glycerol. Depending on the intended application and the final properties required for the printed element one can choose whether to incorporate glycerol or not in the set-retarder formulation. Example 9 (SA-1)

[0419] Three mortar mixes using commercially available dry mix mortar (containing 48 wt.-% of OPC, 2 wt.-% of High Alumina Cement (HAC) and 50 wt.-% of aggregates) were 3D-printed using extrusion-based 3D-printing process. Aqueous sodium silicate (modulus 2.5) was injected at the printhead to accelerate the retarded mortar mix.

[0420] Table 11

[0421] 1] Set accelerating agent comprising sodium gluconate, sodium carbonate and glycerol. Sodium carbonate and part of the sodium gluconate were used as powders and premixed with the dry mix mortar. The rest of sodium gluconate, glycerol and the superplasticizer were premixed with the mixing water.

[0422] [2] % bwoc

[0423] [3] SiO2 wt.-% bwoc from the commercially available aqueous sodium silicate; solids content 51 %

[0424] [4] Weight ratio of set control agent to the weight of SiO2 * 3.5 (calculated according to inequation (1)

[0425] Example 10 (SA-1)

[0426] Two reference mortars and two inventive mortar mixes were prepared as shown in table 12. The inventive mortars comprise a set control agent and setting accelerator agent. For this purpose, the constitutes of the set control agent, i.e. sodium gluconate, Sokalan PA-15 and potassium carbonate, were predissolved together with the mixing water. The resulting solution was added to the dry mix.

[0427] Table 12

[0428] * comparative examples

[0429] [1] polyacrylic acid, concentration 45 wt.-%

[0430] [2] concentration 98%

[0431] [3] Weight ratio of set control agent to the weight of SiO2* 3.5 (calculated according to inequation (1))

[0432] The results presented in table 11 demonstrate the advantageous impact of combining the retarder and accelerator in the inventive mortars 40 and 41 on the early strength development (2 hours).

[0433] The inventive mortar 40 exhibits lower 1 day and 28 day compressive strength values compared to the comparative mortar 39*. However, in the field of 3D printing the late strength requirements are usually not so important and strict compared to the important early strength requirements at for example 2 hours.

[0434] Example 10 (SA-1)

[0435] Two mortar mixes using dry mix mortar (containing 34 wt.-% of OPC (CEM I 52,5 R), 5 wt.-% microsilica and 61 wt.-% of aggregates) were prepared as shown in Table 4. The inventive mortar comprises a set control agent and a setting accelerator agent. For this purpose, the constitutes of the set control agent, i.e. sodium gluconate, Sokalan PA-15 and potassium carbonate, were predissolved together with the mixing water. The resulting solution was added to the dry mix. Table 12

[0436] 1] polyacrylic acid, concentration 45 wt.-%

[0437] [2] concentration 98%

[0438] [3] Weight ratio of set control agent to the weight of SiO2 * 3.5 (calculated according to inequation (1))

[0439] The results presented in table 12 show clearly the positive impact of combining the set control agent with the setting accelerator agent on both setting times (determined by manual Vicat needle) as well as on the early strength development.

[0440] Example 11 (SA-1)

[0441] Seventeen mortars were prepared as shown in table 13 and table 14.

[0442] Two cements were used for this study, Karlstadt CEM II C-M (S-LL) 42.5 N and Bernburg CEM I 42.5 N. Three different dosages of the set control agent were used throughout this study, a low dosage of 1.38wt.-% on the weight of cement and a medium dosage of 1.7wt.-% on the weight of cement and a relatively high dosage of 2.77 wt.-% on the weight of cement. The dosages of the sodium silicate based setting accelerator agent varied according to the intended final application (3D printing or shotcrete*). The balance between the amounts of the set control agent and the setting accelerator agent is to be taken into consideration for achieving the required performance of the intended application, whether it be 3D printing or shotcreting. Vicat setting times were recorded for all mortar mixes.

[0443] It is worth mentioning that requirements for 3D-printing and shotcrete applications are fundamentally different from the point view of setting times as well as stiffening behaviour of the material after the addition of the accelerator. For instance, in the case of 3D printing setting times should be sufficiently long to ensure good bonding between the layers. The layer time in 3D printing might differ depending on the type of 3D printer in use. Generally, there are two commonly used extruder-based printers, namely, the axial robotic arm printer and the gantry printer. The layer time of the robotic arm printer is generally shorter compared to the gantry printer. On the other hand, for shotcrete applications very fast setting times are required to ensure that the sprayed material adhere to the walls or celling upon contact with the substrate; therefore, in shotcrete applications the setting times (normally below 2 minutes) and the stiffening behaviour differ from those for 3D concrete printing applications.

[0444] The required short setting times for shotcreting as shown in table 13 and 14 (comparative mortars 52*, 61*) are met by using excessive amounts of accelerator with respect to corresponding amounts of the set control agent (the weight ratio of set control agent to the weight of SiC>2 * 3.5 (calculated according to inequation (1) used in the comparative mortars is 2) , whereas for inventive mortars mixes (47 to 51 and 55 to 60) the ratio of the set control agent to the weight of SiC>2 *3.5 (calculated according to inequation (1) included in the setting accelerator agent is within the range of 5 to 39).

[0445] Fig. 15 depicts the curves of the penetration force measurements conducted on the mortars 55, 56, 58, 59 and 60. The curves are considered indicative for the stiffening behaviour of the mortars after the addition of the set control agent. The comparative mortar mix 61 * (not shown in the Fig. 15) was not measurable, indicating that the material is stiffening rapidly in a way that renders it not suitable for 3D printing applications due to the risks associated with clogging of the printing head. On the other hand, such a rapid stiffening behaviour is rather beneficial for shotcrete applications. The relatively slow onset of stiffening behaviour of the inventive mortars shown in Fig. 15 ensures safe and good extrudability and prevents clogging of the printing head while also ensuring good bonding between the layers.

[0446] Table 13

[0447]

[0448] * comparative examples

[0449] [1] polyacrylic acid, concentration 45 wt.-%

[0450] [2] 36 wt.-% aqueous sodium silicate; modulus 3.3

[0451] [3] concentration 98%

[0452] [4] Weight ratio of set control agent to the weight of SiO2 * 3.5 (calculated according to inequation (1))

[0453] Table 14

[0454] * comparative examples

[0455] [1] polyacrylic acid, concentration 45 wt.-%

[0456] [2] 36 wt.-% aqueous sodium silicate; modulus 3.3

[0457] [3] concentration 98%

[0458] [4] Weight ratio of set control agent to the weight of SiO2 * 3.5 (calculated according to inequation (1)) Example 12 (SA-1 , SA-2 and SA-3)

[0459] Eight mortars were prepared as shown in table 15.

[0460] Karlstadt CEM II C-M (S-LL) 42.5 N was used for this study. Vicat setting times and compressive strength results were collected from three comparative mortar mixes (64*- 66*) and five inventive mortar mixes (67-71). The dosage of the set control agent used in this study was fixed at 1.76% by weight of cement. Two different types of setting accelerator agents were used. The first one is based on aluminium-sulfate and the second one is based on aqueous sodium silicate. The objective of this study is to demonstrate the inventive approach manifested in achieving fast setting times and high early strength development by either adding the set accelerator agents individually (mortar 67 (SA-2) and 71 (SA-1)) to the set delayed mortar or by adding different combinations of the set accelerator agents (mortar 68 (SA-3), 69 (SA-3), and 70 (SA-3)) to the set delayed mortars. In the case of using only one type of set accelerator agent the corresponding dosages (11 g for aluminium sulfate-based accelerator and 7.25 g for the aqueous sodium silicate-based accelerator) were chosen to achieve similar setting times. These dosages are henceforth deemed as 100% for each type of the set accelerator agent. Therefore, the corresponding dosages of the set accelerator agents used in the inventive mortars 68, 69 and 71 are 75%:25% and 50%:50% and 25%:75% respectively, with respect to the original dosages of the set accelerator agents used in mortar mixes 67 and 71. It is worth mentioning that in the cases where combinations of the set accelerator agents were used, the addition to the set delayed mortar was conducted simultaneously, but separately.

[0461] Table 15

[0462] * comparative examples

[0463] [1] polyacrylic acid, concentration 45 wt.-%

[0464] [2] commercially available alkali-free accelerator based on aluminum sulfate; solids content 48.4%

[0465] [3] 36 wt.-% aqueous sodium silicate; modulus 3.3

[0466] [4] Dosage set control agent / (1 / 3.5 * Dosage SiO2 + 2.573.5 * Dosage Al) (calculated according to inequation (1)) The results presented in table 15 show clearly the positive impact of combining the set control agent with the setting accelerator agents (individually or in combination form) on both setting times (determined by manual Vicat needle) as well as on the early strength development.

Claims

1. Claims1. A method of placing a flowable construction material comprising a cementitious binder for building structural components layer-by-layer, such as for 3D concrete printing, said method comprising: providing a set-delayed flowable construction material by making a set control agent to exist in the flowable construction material, conveying the set-delayed flowable construction material to a deposition head, placing the construction material through an outlet of the deposition head in order to form a layer of construction material, before placing the construction material, incorporating into the set-delayed construction material a setting accelerator agent selected from the group of SA-1), which is a setting accelerator comprising a water-soluble silicate source, SA-2), which is a setting accelerator comprising a source of aluminum ions,SA-3), wherein both of setting accelerator agents SA-1) and SA-2) are separately incorporated into the set-delayed construction material, wherein the set control agent comprises (i) a retarder comprising (i-a) an a -hydroxy monocarboxylic acid or a salt thereof, and, optionally, (i-b) a polycarboxylic acid having a carboxylic acid equivalent weight of 333 or less, or a salt thereof; and (ii) an oxyanion source selected from a borate source, a carbonate source, the carbonate source having an aqueous solubility of 15.0 g'L-1or more at 25 ° C, and mixtures thereof; wherein the weight ratio of (ii) to (i) is in the range of from 1.2 : 25, preferably 2 : 20 and most preferably 5 : 15; and wherein in the set-delayed flowable construction material the ratio of the dosage of the set control agent to the dosage of the setting accelerator agent is determined by the following inequation (1):3 < Dosage set control agent / (l / 3.5 * Dosage SiO2+ 2.5 / 3.5 * Dosage Al) < 42.0 Dosage set control agent: means the dosage of the set control agent comprising the retarder i) in the set delayed construction material, in weight % of the cementitious binder,Dosage SiO2: means the dosage of the setting accelerator SA-1) calculated as SiO2incorporated into the set-delayed construction material by the addition of the setting accelerator agent SA-1), in weight % SiO2by weight of the cementitious binder, Dosage Al: means the dosage of the setting accelerator SA-2) calculated as aluminum ions incorporated into the set-delayed construction material by theaddition of the setting accelerator agent SA-2), in weight % aluminum ions by weight of the cementitious binder.

2. Method according to claim 1, wherein the set delayed flowable construction material comprises the set control agent in an amount of 0.12 to 5.5 weight % by weight of the cementitious binder.

3. Method according to any one of the preceding claims, wherein the setting accelerator agent SA-1) is incorporated into the set-delayed flowable construction material at a dosage of the water-soluble silicate source calculated as SiO2from 0.15 weight % SiO2to 4 weight % SiO2by weight of the cementitious binder.

4. Method according to any one of the preceding claims, wherein the setting accelerator agent SA-2) is incorporated into the set-delayed flowable construction material at a dosage of aluminium ions in the range of from 0.027 to 0.351 weight % by weight of the cementitious binder.

5. Method according to any one of the preceding claims, wherein the construction material comprises a polyol in an amount of at least 0.05 wt.-% by weight of the cementitious binder.

6. Method according to any one of the preceding claims, wherein the polycarboxylic acid or salt thereof is a polymeric polycarboxylic acid or a salt thereof, preferably a homopolymer of acrylic acid, a homopolymer of methacrylic acid, a copolymer of acrylic acid and maleic acid, or a copolymer of methacrylic acid and maleic acid.

7. Method according to any one of the preceding claims, wherein the a -hydroxy monocarboxylic acid or salt thereof includes glycolic acid, gluconic acid, their salts, and mixtures thereof.

8. Method according to any one of the preceding claims, wherein the carbonate source is a soluble carbonate source selected from inorganic carbonates, preferably from sodium carbonate, sodium bicarbonate and potassium carbonate, and organic carbonates, preferably from ethylene carbonate, propylene carbonate and glycerol carbonate; and mixtures thereof.

9. Method according to any one of the preceding claims, wherein the water-solublesilicate source is selected from alkali metal silicates and quaternary ammonium silicates.

10. Method according to claim 9, wherein the alkali metal silicate or the quaternary ammonium silicate has a modulus from 0.5 to 5, preferably from 1 to 4, more preferably from 1.7 to 3.3.

11. Method according to any one of claims 1 to 8, wherein the source of aluminum ions includes aluminum salts, aluminum complexes, and mixtures thereof.

12. Method according to any one of claims 5 to 11, wherein at least one of the set control agent and the setting accelerator agent comprises the polyol.

13. Method according to any one of claims 5 to 12, wherein the polyol is selected from monosaccharides and oligosaccharides with the proviso that the polyol does not comprise saccharides higher than trisaccharides, compounds of general formula (P-l) or dimers or trimers of compounds of general formula (P-l):whereinR is -CH2OH, -NH2, n is an integer from 1 to 4, m is an integer from 1 to 8.

14. Method according to any one of the preceding claims, wherein the flowable construction material additionally comprises a dispersant selected from- comb polymers having a carbon-containing backbone to which are attachedpendant cement-anchoring groups and polyether side chains,- non-ionic comb polymers having a carbon-containing backbone to which are attached pendant hydrolysable groups and polyether side chains, the hydrolysable groups upon hydrolysis releasing cement-anchoring groups,- colloidally disperse preparations of polyvalent metal cations, such as Al3+, Fe3+or Fe2+, and a polymeric dispersant which comprises anionic and / or anionogenic groups and polyether side chains, and the polyvalent metal cation is present in a superstoichiometric quantity, calculated as cation equivalents, based on the sum of the anionic and anionogenic groups of the polymeric dispersant,- sulfonated melamine-formaldehyde condensates,- lignosulfonates,- sulfonated ketone-formaldehyde condensates,- sulfonated naphthalene-formaldehyde condensates,- phosphonate containing dispersants, preferably the phosphonate containing dispersants comprise at least one polyalkylene glycol unit, and- mixtures thereof.

15. Method according to any one of the preceding claims, wherein the set delayed flowable construction material comprises- a cementitious binder comprising one or more calcium silicate mineral phases and one or more calcium aluminate mineral phases,- optionally, an extraneous aluminate source,- optionally, an extraneous sulfate source, wherein the flowable construction material contains 0.02 to 0.20 mol of total available aluminate, calculated as AI(OH)4, from the calcium aluminate mineral phases plus the optional extraneous aluminate source, per 100 g of cementitious binder.

16. Method according to any one of the preceding claims, wherein, after incorporation of the setting accelerator agent, the molar ratio of total available aluminate to sulfate in the construction material is 0.4 to 3.5.

17. Method according to any one of the preceding claims, wherein the step of placing the construction material comprises extruding the construction material through a nozzle of the deposition head.

18. Method according to any one of claims 1 to 16, wherein the construction material is injected with air and then sprayed onto a substrate or a preceding layer of construction material.

19. Method according to any one of the preceding claims, wherein the setting accelerator agent is continuously incorporated to a flow of set-delayed conveyed construction material.

20. Method according to any one of the preceding claims, wherein the setting accelerator agent and the set-delayed construction material are mixed with each other before placing the construction material, wherein a dynamic mixer is preferably used for mixing.

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