Fresh concrete or mortar composition for 3d-printing

Abstract

A fresh concrete or mortar composition for 3D-printing comprising one or more cementitious materials, including a hydraulic cement, in an amount of 260-750 kg / m3, aggregates, water, at least one viscosity modifying admixture and at least one plasticizer, wherein the composition is obtained by adding the at least one viscosity modifying admixture to a mixture of, or while mixing, the one or more cementitious materials, the aggregates, said water and the at least one plasticizer, and wherein the composition has a first initial yield stress of 0.2-1.5 kPa measured 2 minutes after the addition of the at least one viscosity modifying admixture, which increases to ≥ 5 kPa, preferably > 10 kPa, during a subsequent resting period of 60 minutes at a temperature of 5-30°C, and the composition has a second initial yield stress of 0.2-3 kPa measured after the composition has rested for 30 minutes after the addition of the at least one viscosity modifying admixture and thereafter has been re-mixed for 30 seconds, which increases to ≥ 5 kPa, preferably > 10 kPa, during a subsequent resting period of 60 minutes at a temperature of 5-30°C.

Description

[0001] Fresh concrete or mortar composition for 3D-printing

[0002] The invention refers to a fresh concrete or mortar composition for 3D-printing comprising one or more cementitious materials , including a hydraulic cement , aggregates , water, at least one viscosity modi fying admixture and at least one plastici zer , and optionally at least one mineral addition .

[0003] Further, the invention refers to the use of such a fresh concrete or mortar composition and to a method of building structural and architectural components layer-by-layer, such as by means of 3D concrete printing .

[0004] 3D printing is a building technique that is commonly called "additive manufacturing" and consists of j oining material to produce obj ects , layer upon layer, from 3D model data or other electronic data source . In particular, successive layers of material are formed under computer control by means of an industrial robot . It has already been proposed to develop 3D printers capable of producing structural buildings from a construction material that can be a mortar or a concrete . According to these proposals , the construction material is extruded through a noz zle to build structural components layer-by-layer without the use of formwork or any subsequent vibration . The possibility to build structures without formwork is a maj or advantage in terms of production rate , architectural freedom and cost reduction .

[0005] Usually, 3D printing of construction materials is a continuous process that comprises conveying fresh concrete , mortar or micro-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 , the mortar or the micro-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 .

[0006] However, the construction material must not only be suf ficiently fluid for conveying and extrusion purposes , but also suf ficiently 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 or deforming .

[0007] Therefore , a flowable construction material adapted for 3D printing typically contains a considerable amount of a hydraulic binder that has a short initial setting time , such as an aluminate cement . However, a binder having a short initial setting time will increase the risk that material builds up in the mixing devices , pumps , and in the printing head .

[0008] Another aspect to be considered is the printing speed . A high printing speed is needed for reducing construction time and to ensure an adequate interlayer adhesion . This is in some cases achieved by using a hydraulic binder that has a short initial setting time , as the deposed material will harden quickly and be able to support the layers that are subsequently deposited . 3d printed elements also require a strong bonding strength between the deposited layers , to ensure an adequate overall strength of the 3d printed structure . For this purpose , it is beneficial to place a layer while the preceding layer is still fresh . However, with a hydraulic binder having a short initial setting time the operational flexibility is very limited .

[0009] From the point of view of operational flexibility, it would be desirable to have a flowable construction material that has good slump retention and thus a long initial setting time , i . e . a constant consistency that does not increase too much with time , because this would allow to have more time for adj ustments of the printing process , such as for changing printing parameters during the construction .

[0010] To accommodate some of the above requirements , it has been proposed to add various admixtures to the flowable construction material in the deposition head immediately before the material is placed through an outlet of the deposition head . This allows to separately optimi ze the material characteristics for the process of pumping the material to the deposition head and for the process of placing the material layer by layer . In particular, the construction material can be designed to have a low plastic viscosity and a low yield stress for a good pumpability, and is adj usted to obtain the material properties that are desired for the placing process by adding a suitable admixture in the deposition head . For example , WO 2017 / 221058 Al discloses adding a viscosity modi fying agent to the flowable construction material in the deposition head so as to increase the yield stress .

[0011] However, adding an admixture to the material in the deposition head involves several disadvantages , such as related to the need to control the admixing process including accurately controlling the dosage of the admixture , and related to the complex additional equipment needed on the deposition head, which increases the weight and thus the maneuverability as well as the costs of the deposition head .

[0012] Slump retention is also crucial for ready-mix concrete , as it plays a signi ficant role in maintaining the quality of the concrete from the batching plant to its final placement at the construction site . In ready-mix concrete , the mixture is premixed and then transported, often over considerable distances and timeframes . During this period, the concrete must maintain its workability, ensuring that it remains fluid and malleable for easy pumping and shaping upon arrival .

[0013] It would be desirable to provide a fresh 3D-printable concrete or mortar that , on the one hand, can be provided as a ready-mix concrete to the 3D-printing site and that , on the other hand, has a suf ficient yield stress development once extruded through the noz zle of a 3D print head . The fresh 3D- printable concrete or mortar shall also provide flexibility as to the timing of the addition of the viscosity modi fying admixture .

[0014] In order to solve this obj ect , the invention according to a first aspect thereof provides a fresh concrete or mortar composition for 3D-printing comprising one or more cementitious materials , including a hydraulic cement , in an amount of 260-750 kg / m3, aggregates , water, at least one viscosity modi fying admixture and at least one plastici zer , and optionally at least one mineral addition, wherein the composition is obtained by adding the at least one viscosity modi fying admixture to a mixture of , or while mixing, the one or more cementitious materials , the aggregates , said water and the at least one plastici zer , and optionally the mineral addition, and wherein the composition has a first initial yield stress of 0 . 2- 1 . 5 kPa measured 2 minutes after the addition of the at least one viscosity modi fying admixture , which increases to 1 5 kPa, preferably > 10 kPa, during a subsequent resting period of 60 minutes at a temperature of 5-30 ° C, and the composition has a second initial yield stress of 0 . 2 -3 kPa measured after the composition has rested for 30 minutes after the addition of the at least one viscosity modi fying admixture and thereafter has been re-mixed for 30 seconds , which increases to 1 5 kPa, preferably > 10 kPa, during a subsequent resting period of 60 minutes at a temperature of 5-30 ° C .

[0015] The fresh mortar or concrete of the invention of fers enhanced flexibility through its re-mixing feature , which is particularly relevant for ready-mix concrete used in 3D- printing applications . The composition can maintain its initial yield stress even after a resting period of 30 minutes followed by a re-mixing process for 30 seconds . This ability is crucial in scenarios where ready-mix concrete is required to be transported over distances and may face delays . The re-mixing capability ensures that the concrete retains its optimal properties for 3D-printing, even under unpredictable on-site conditions . Further, the yield stress development according to the invention is particularly beneficial for 3D-printing . Initially, the composition exhibits a yield stress of 0 . 2 - 1 . 5 kPa shortly after mixing, which then increases signi ficantly after a short resting period . Post re-mixing, this yield stress still rises to more than 5 kPa, preferably over 10 kPa, within 60 minutes . Such controlled yet adaptable yield stress development is beneficial for ensuring the structural integrity of 3D-printed obj ects , as it allows the freshly printed layers to support subsequent layers without risk of deformation or collapse .

[0016] Preferably, said re-mixing is carried out in a concrete mixer or any type of mixing equipment suitable for mixing concrete . Examples of mixers suitable for mixing concrete include but are not limited to planetary-type , conical-type , hori zontaltype or drum-type mixers . Suitable speed to operate the mixer to carry out the re-mixing is from 5 to 2000 rpm .

[0017] Preferably, said re-mixing is carried out at a mixing speed from 20 to 400 rpm .

[0018] For construction proj ects utili zing ready-mix concrete for 3D-printing, the invention of fers the advantage of sustained workability and consistency . Despite the intervals between mixing, resting, and re-mixing, the concrete maintains its fluidity and malleability . This consistent quality from mixing to final placement is essential for large-scale and time-sensitive construction proj ects , ensuring uni formity and reliability in the final 3D-printed structures . Further, the invention offers flexibility regarding the timing of adding the viscosity modifying admixture. The viscosity modifying admixture may be added when mixing the one or more cementitious materials, the aggregates, water and the at least one plasticizer, and optionally the mineral addition, i.e. together with the water addition to a dry premix, or delayed, i.e. some time after the water addition. In particular, the viscosity modifying admixture may be added to the fresh concrete or mortar mixture one hour or more after the water addition. For example, the delayed addition of the viscosity modifying admixture may be carried out on the job-site, either in the ready-mix truck or in a separate mixing unit.

[0019] The viscosity modifying admixture increases the viscosity and thus ensures the thixotropy and / or yield strength development before setting begins, i.e. from just after mixing with water up to the initial setting time. Due to its increased viscosity the fresh concrete or mortar is sufficiently firm in order to provide the required mechanical stability of the 3D printed structure before the hydraulic cement sets. The addition of the viscosity modifying admixture results in that the increased yield stress property of the mortar or concrete is attained in its fresh state, that is to say before the setting has occurred. Therefore, the increase in yield stress that is achieved by the viscosity modifying admixture is independent from the setting process of the hydraulic cement of the mortar or concrete.

[0020] According to the invention the fresh mortar or concrete has an initial yield stress of 0.2-1.5 kPa measured 2 minutes after the addition of the at least one viscosity modifying admixture, which increases to 1 5 kPa, preferably > 10 kPa, during a subsequent resting period of 60 minutes at a temperature of 5-30 ° C . Herein, said increase in yield stress is ef fected by the viscosity modi fying admixture , which implies that the increase in yield stress is attained within the initial setting time of the mortar or concrete .

[0021] The same applies to the increase in yield stress after remixing has occurred . According to the invention, after remixing the yield stress increases from a second initial yield stress of 0 . 2-3 kPa to 1 5 kPa, preferably > 10 kPa, during a subsequent resting period of 60 minutes at a temperature of 5-30 ° C . Herein, said increase in yield stress is ef fected by the viscosity modi fying admixture , which implies that the increase in yield stress is attained within the initial setting time of the mortar or concrete .

[0022] Generally, the initial setting time is defined as the time elapsed between the moment water is added to the cement to the time at which the paste starts losing its plasticity . In particular, the initial setting time is the time period between the time water is added to the cement and the time at which a 1 mm square section needle fails to penetrate the cement paste , placed in the Vicat ' s mould 5 mm to 7 mm from the bottom of the mould .

[0023] The yield stress is measured with a scissometer . A scissometer consists of a pale vane that has a diameter of 33 mm and a height of 50 mm . This pale is plunged into the material to be tested and to which an increasing torque is applied . When a failure occurs in the material , the vane starts to rotate , generally as the torque reaches its maximum value , which is considered as the characteristic value that is representative of the yield stress of the material . Preferably, the fresh concrete or mortar composition does not contain a setting accelerator.

[0024] According to the invention, the fresh concrete or mortar composition comprises one or more cementitious materials, including a hydraulic cement, in an amount of 260-750 kg / m3. A hydraulic cement is understood to be a hydraulic binder comprising at least 50 wt.-% of CaO and SiCy that sets due to a chemical hydration reaction between the dry ingredients and water. The hydraulic cement may contain other components in addition to CaO and SiO2- A hydraulic cement is as defined in EN 197-1 and EN 197-5 and comprises several types of hydraulic cements, including ordinary Portland cement, Portland composite cements, and various types of blended cements containing supplementary cementitious materials like fly ash, slag, or pozzolanic materials. Various supplementary cementitious materials, such as, e.g., silica fume, granulated blast-furnace slag (gbfs) , fly ash, natural pozzolans, calcined clays or ground limestone, may be added to Portland cement, in order to obtain Portland composite cements. The supplementary cementitious materials, typically between 10 and 50 wt.-% of the total weight of the hydraulic cement, are in most applications ground granulated blast furnace slag, fly ash, pozzolans, ground limestone or mixtures thereof.

[0025] Preferably, Portland cement is mixed with any mineral addition described in the cement standard EN 197-1 of April 2012.

[0026] The hydraulic cement may also be a fine or an ultrafine cement, i.e. a hydraulic cement that is ground to a higher fineness than standard hydraulic cements. The fineness can for example be higher that 5000 cm2 / g and reach values up to 13000 cm2 / g or even 15000 cm2 / g (expressed as cement Blaine fineness) .

[0027] Preferably, the cementitious material present in the fresh mortar or concrete consists of Portland cement, i.e. the fresh mortar or concrete does not contain any cementitious material other than Portland cement. Portland cement is a cement of the type CEM I as described according to the European EN 197-1 Standard of April 2012.

[0028] Other suitable cementitious materials that may be used in the invention comprise the cements of the types CEM II, CEM III, CEM IV or CEM V described according to the European EN 197-1 Standard of April 2012.

[0029] Preferably, the fresh concrete composition is designed such that, before adding the at least one viscosity modifying admixture, it has a slump of 100-210mm, measured in a slump flow test as defined in EN 12350-2:2019-09.

[0030] Preferably, the fresh mortar composition is designed such that, before adding at least one viscosity modifying admixture, it has a slump of 160-200mm, measured in a slump flow test as defined ASTM C230 / C230M : 2020-06.

[0031] According to the invention, the fresh concrete or mortar composition comprises at least one viscosity modifying admixture. The at least one viscosity modifying admixture is preferably chosen from the group consisting of starch, modified starch, hydroxyethyl cellulose, cellulose, HASE polymers (hydrophobically modi fied alkali-swellable emulsions ) and ASE polymers ( alkali-swellable emulsion) .

[0032] The fresh concrete or mortar composition preferably does not contain clay or colloidal silica as the at least one viscosity modi fying admixture . Although these types of viscosity modi fying admixture provide a suf ficient yield stress develops , the reversibility is not existing : the yield stress does not decrease upon remixing the mortar or concrete .

[0033] Preferably, the fresh concrete or mortar composition does not contain any fine material having a d50 of 5 pm or less .

[0034] According to the invention, the fresh mortar or concrete composition comprises at least one plastici zer . Preferably, the at least one plastici zer is chosen from the group consisting of phosphonate-based superplastici zers , polycarboxylate superplastici zers ( PCE ) , and hydrolysable polymers . Suitable hydrolysable polymers have an anionic charge quantity that increases during the open time of mortars / concrete , when in contact with mortar or concrete . Examples of suitable monomers include acrylic esters and amides .

[0035] Particularly good results have been achieved in a preferred embodiment , wherein the at least one plastici zer comprises a polycarboxylate and a hydrolysable polymer . An example for a plastici zer of this type is the product Sika® ViscoCrete® Tempo- 533 .

[0036] Generally speaking, any type of aggregates may be used in the fresh mortar or concrete composition of the invention . In order to enable a good extrudability and printability of the fresh mortar or concrete composition, the aggregates may preferably have a maximum particle si ze of 10 mm .

[0037] According to a second aspect of the invention, the invention provides for the use of a fresh concrete or mortar composition according to the first aspect of the invention for building structural and architectural components layer- by-layer, such as for 3D concrete or mortar printing, comprising placing the fresh concrete or mortar composition through an outlet of a deposition head while moving the deposition head, in order to form a layer of fresh concrete or mortar, wherein successive layers of fresh concrete are place on top of each other .

[0038] According to a third aspect of the invention, a method of building structural and architectural components layer-by- layer, such as by means of 3D concrete printing, is provided comprising the steps of : providing a fresh concrete or mortar composition according to the first aspect of the invention by adding the at least one viscosity modi fying admixture to a mixture of , or while mixing, the one or more cementitious materials , the aggregates , said water and the at least one plastici zer, and optionally the mineral addition, wherein the composition has a first initial yield stress of 0 . 2- 1 . 5 kPa measured 2 minutes after the addition of the at least one viscosity modi fying admixture , storing or transporting the fresh concrete or mortar composition without stirring, while the yield stress increases , re-mixing the fresh concrete or mortar composition for a time period of preferably 15- 60 seconds , such as 30 seconds , thereby reducing the yield stress to a second initial yield stress of 0 . 2 -3 kPa, placing the fresh concrete or mortar composition through an outlet of a deposition head while moving the deposition head, in order to form a layer of fresh concrete or mortar, wherein successive layers of fresh concrete or mortar are placed on top of each other, allowing the layer of fresh concrete or mortar to rest during a subsequent resting period of 60 minutes or longer at a temperature of 5-30 ° C, in which the yield stress of the fresh concrete or mortar increases to 1 5 kPa, preferably > 10 kPa, measured after a resting period of 60 minutes .

[0039] A preferred mode of operation consists in that , after the placement of a first layer of the fresh mortar or concrete composition, at least one subsequent layer of the fresh mortar or concrete composition is placed onto the first layer, wherein the amount of viscosity modi fying admixture is selected so as to achieve a yield stress that is suf ficient so that the first layer does not collapse and / or does not deform under the load of said at least one subsequent layer .

[0040] In this connection, "not collapsing" means that the height of the layer is not reduced by more than 10% , preferably more than 5% , under the load of the at least one subsequent layer .

[0041] "Not deforming" means that the layers maintain their shape as extruded until setting occurs .

[0042] The invention will now be described in more detail by reference to the following examples . Examples

[0043] In the examples, a fresh mortar base formulation according to

[0044] Table 1 was used:

[0045] Table 1

[0046] Yield stress development tests were conducted with different types and dosages of viscosity modifying admixtures and plasticizers .

[0047] The following viscosity modifying admixtures were tested:

[0048] Stabilizer 120: supplied by Sika, based on modified starch ARIC 5335: supplied by Agrana, based on modified starch

[0049] Acrysol TT-615: supplied by Dow Chemical, hydrophobically modified alkali-swellable (HASE) copolymers of methacrylic acid and ethyl acrylate ester + hydrophobic acrylic ester monomers

[0050] The following plasticizers were tested:

[0051] Plasticizer 1 : superplasticiser based on polycarboxylates and hydrolysable polymers, Viscocrete Tempo 533 supplied by Sika,

[0052] Plasticizer 2: superplasticiser based on diphosphonate, Optima 100 supplied by Chryso

[0053] Plasticizer 3: superplasticiser based on modified polycarboxylates, Premia 180 supplied by Chryso

[0054] Plasticizer 4: superplasticiser based on chains of modified polycarboxylic ether, Glenium 27 supplied by BASF,

[0055] Plasticizer 5: superplasticiser based on modified polycarboxylates, Plast Omega 132 supplied by Chryso

[0056] The following mixing scheme was applied with an addition of the viscosity modifying admixture at the ready-mix plant (Examples 1-3) : The following mixing scheme was applied with a deferred addition of the viscosity modifying admixture on site (Examples 4-6) :

[0057] In a first test, the initial yield stress was measured 2 minutes after the addition of the viscosity modifying admixture ("first initial yield stress") . Thereafter, the fresh mortar was allowed to rest for a period of 60 minutes at a temperature of 5-30°C. After the resting period the yield stress was measured again ("first yield stress increase") .

[0058] In a second test, the fresh mortar was allowed to rest for 30 minutes from the addition of the viscosity modifying admixture, was then re-mixed for 30 seconds and the initial yield stress was measured ("second initial yield stress") . Thereafter, the fresh mortar was allowed to rest for a period of 60 minutes at a temperature of 5-30°C. After the resting period the yield stress was measured again ("second yield stress increase") . Example 1 :

[0059] Stabilizer 120 was used as a viscosity modifying admixture and was added to the fresh mortar base formulation of Table 1 in a deferred way, namely 1 hour after water addition.

[0060] Two types of plasticizers were tested: Plasticizer 1 was used at a dosage of 4.8 g per liter of mortar and Plasticizer 2 used at a dosage of 7.2 g per liter of mortar.

[0061] Yield stress measurements were conducted on the following mortar compositions:

[0062] At a lower dose rate than Plasticizer 2 (with a lower VMA dose rate) , Plasticizer 1, i.e. a superplasticiser based on polycarboxylates and hydrolysable polymers, provides a higher yield stress build-up rate (10.2 vs 4.4 kPa / h) . 30 minutes after VMA introduction, remixing the mortar breaks yield stress down to low values (as required) before buildability is regained (good rate with Plasticizer 1, insufficient rate with Plasticizer 2) . Therefore, in this example, Plasticizer loffers a more efficient alternative to Plasticizer 2. 30 minutes after VMA introduction, remixing the mortar breaks yield stress down to low values (as required) before buildability is regained.

[0063] Example 2 :

[0064] ARIC 5335 was used as a viscosity modifying admixture and was added to the fresh mortar base formulation of Table 1 in a deferred way, namely 1 hour after water addition.

[0065] Two types of plasticizers were tested: Plasticizer 1 was used at a dosage of 4.8 g per liter of mortar and Plasticizer 2 used at a dosage of 7.2 g per liter of mortar.

[0066] Yield stress measurements were conducted on the following mortar compositions:

[0067] As with Example 1, Plasticizer 1, i.e. a superplasticiser based on polycarboxylates and hydrolysable polymers, at a lower dose rate than Plasticizer 2 (with a lower VMA dose rate) , provides a higher yield stress build-up rate (5 vs 4.7 kPa / h) . 30 minutes after VMA introduction, remixing the mortar breaks yield stress down to low values (as required) before buildability is regained (good rate with Plasticizer 1, insufficient rate with Plasticizer 2) . Therefore, in this example, Plasticizer 1 offers a more efficient alternative to Plasticizer 2. 30 minutes after VMA introduction, remixing the mortar breaks yield stress down to low values (as required) before buildability is regained.

[0068] Example 3:

[0069] Acrysol TT-615 was used as a viscosity modifying admixture and was added to the fresh mortar base formulation of Table 1 in a deferred way, namely 1 hour after water addition.

[0070] Five types of plasticizers were tested: Plasticizer 1 was used at a dosage of 4.8 g per liter of mortar, Plasticizer 2 used at a dosage of 7.1 g per liter of mortar, Plasticizer 3 used at a dosage of 3.3 g per liter of mortar, Plasticizer 4 used at a dosage of 5 g per liter of mortar and Plasticizer 5 used at a dosage of 7.7 g per liter of mortar.

[0071] Yield stress measurements were conducted on the following mortar compositions:

[0072]

[0073] When comparing Plasticizer 1 with Plasticizer 2, Plasticizer 1, i.e. a superplasticiser based on polycarboxylates and hydrolysable polymers, is again a more efficient alternative to Plasticizer 2. With Plasticizer 1, 30 minutes after the VMA introduction, remixing the mortar breaks yield stress down to a lower value than that obtained with Plasticizer 2.

[0074] When comparing Plasticizer 1 with Plasticizer 3, the yield stress build-up rate is excessive with Plasticizer 3 (beyond 15 kPa / h) , due to its insufficient rheology retention capability. And, again, with Plasticizer 1 the initial yield stress value after remixing at 30 minutes is much more acceptable (lower) than with Plasticizer 3. When comparing Plasticizer 1 with Plasticizer 4 and Plasticizer 5, Plasticizer 1, i.e. a superplasticiser based on polycarboxylates and hydrolysable polymers, offers a more performant alternative, due to its better yield stress buildup rate.— 30 minutes after VMA introduction, remixing the mortar breaks yield stress down to low values (as required) before buildability is regained.

[0075] Example 4 :

[0076] Stabilizer 120 was used at different dosages as a viscosity modifying admixture and was added to the fresh mortar base formulation of Table 1 immediately after water addition.

[0077] Three types of plasticizers were tested: Plasticizer 1 was used at a dosage of 4.8 g per liter of mortar, Plasticizer 2 used at a dosage of 7.2 g per liter of mortar and Plasticizer 3 used at a dosage of 3.3 g per liter of mortar.

[0078] Yield stress measurements were conducted on the following mortar compositions:

[0079] In this example, precast Plasticizer 3 is the one that provides the most suitable yield stress build-up rate (6.9- 10.5 kPa / h) , followed by Plasticizer 1 (3.3-8.6 kPa / h) and Plasticizer 2 (1.6-5.2 kPa / h) . Again, Plasticizer 1 offers a more efficient alternative to Plasticizer 2 (lower dose rate and higher yield stress performance) .

[0080] Example 5:

[0081] ARIC 5335 was used at different dosages as a viscosity modifying admixture and was added to the fresh mortar base formulation of Table 1 immediately after water addition.

[0082] Three types of plasticizers were tested: Plasticizer 1 was used at a dosage of 4.8 g per liter of mortar, Plasticizer 2 used at a dosage of 7.1-7.2 g per liter of mortar and Plasticizer 3 used at a dosage of 3.3 g per liter of mortar.

[0083] Yield stress measurements were conducted on the following mortar compositions:

[0084] As with Example 4, precast Plasticizer 3 is the one that provides the most suitable yield stress build-up rate (8.1- 11.2 kPa / h) , followed by Plasticizer 1 (2.9-5.9 kPa / h) and Plasticizer 2 (1.5-2.9 kPa / h) . Again, Plasticizer 1, i.e. a superplasticiser based on polycarboxylates and hydrolysable polymers, offers a more efficient alternative to Plasticizer 2 (lower dose rate and higher yield stress performance) .

[0085] Example 6:

[0086] Acrysol TT-615 was used as a viscosity modifying admixture and was added to the fresh mortar base formulation of Table 1 immediately after water addition.

[0087] Five types of plasticizers were tested: Plasticizer 1 was used at a dosage of 4.8 g per liter of mortar, Plasticizer 2 used at a dosage of 7.1 g per liter of mortar, Plasticizer 3 used at a dosage of 3.3 g per liter of mortar, Plasticizer 4 used at a dosage of 5 g per liter of mortar and Plasticizer

[0088] 5used at a dosage of 7.7 g per liter of mortar.

[0089] Yield stress measurements were conducted on the following mortar compositions:

[0090] When comparing Plasticizer 1 with Plasticizer 2, Plasticizer 1 is, again, a more efficient alternative to Plasticizer 2.

[0091] When comparing Plasticizer 1 with Plasticizer 3, the latter is more efficient (dose rate / yield stress build-up rate) .

[0092] When comparing Plasticizer 1 with Plasticizer 4 and Plasticizer 5, Plasticizer 1 offers a more performant alternative (yield stress build-up rate) .

[0093] Conclusion: The Examples 1-6 show that selected plasticizer / VMA combinations provide appropriate 1stand 2ndinitial yield stress, as well as 1stand 2ndyield stress increase. The plasticizer 1, i.e. a superplasticiser based on polycarboxylates and hydrolysable polymers, offers an interesting alternative to other plasticizer types, in configurations where the VMA addition is done immediately after water introduction or delayed. In combination with the VMA, Plasticizer 1 helps provide appropriate yield stress build-up, by means of lower dose rates.

Claims

Claims :

1. A fresh concrete or mortar composition for 3D-printing comprising one or more cementitious materials, including a hydraulic cement, in an amount of 260-750 kg / m3, aggregates, water, at least one viscosity modifying admixture and at least one plasticizer, and optionally at least one mineral addition, wherein the composition is obtained by adding the at least one viscosity modifying admixture to a mixture of, or while mixing, the one or more cementitious materials, the aggregates, said water and the at least one plasticizer, and optionally the mineral addition, and wherein the composition has a first initial yield stress of 0.2-1.5 kPa measured 2 minutes after the addition of the at least one viscosity modifying admixture, which increases to 1 5 kPa, preferably > 10 kPa, during a subsequent resting period of 60 minutes at a temperature of 5-30°C, and the composition has a second initial yield stress of 0.2-3 kPa measured after the composition has rested for 30 minutes after the addition of the at least one viscosity modifying admixture and thereafter has been re-mixed for 30 seconds, which increases to 1 5 kPa, preferably > 10 kPa, during a subsequent resting period of 60 minutes at a temperature of 5-30°C.

2. Fresh concrete or mortar composition according to claim 1, wherein the fresh concrete or mortar composition, before adding the at least one viscosity modifying admixture, has a slump of 100-210mm, measured in a slump flow test as defined in EN 12350-2:2019-09.

3. Fresh concrete or mortar composition according to claim1 or 2, wherein the at least one plasticizer is present in an amount of 0.1-1.0 wt . % based on the dry weight of cement.

4. Fresh concrete or mortar composition according to claim 1, 2 or 3, wherein said re-mixing is carried out in a planetary-type, conical-type, horizontal-type or drum-type mixer at a speed in the range 20-400 rpm.

5. Fresh concrete or mortar composition according to any one of claims 1 to 4, wherein the at least one viscosity modifying admixture is chosen from the group consisting of starch, modified starch, hydroxyethylcellulose, cellulose, HASE polymers (hydrophobically modified alkali-swellable emulsions) and ASE polymers (alkali-swellable emulsion) .

6. Fresh concrete or mortar composition according to claim 5, wherein the at least one viscosity modifying admixture is present in an amount of 0.4-8 g / 1, based on the fresh concrete or mortar composition.

7. Fresh concrete or mortar composition according to any one of claims 1 to 6, wherein the fresh concrete or mortar composition does not contain clay or colloidal silica as the at least one viscosity modifying admixture.

8. Fresh concrete or mortar composition according to any one of claims 1 to 7, wherein the at least one plasticizer is chosen from the group consisting of phosphonate-based superplasticizers, diphosphonate-based superplasticizers, polycarboxylate superplasticizers (PCE) , and hydrolysable polymers .9 . Fresh concrete or mortar composition according to any one of claims 1 to 8 , wherein the at least one plastici zer comprises a polycarboxylate and a hydrolysable polymer .10 . Fresh concrete or mortar composition according to any one of claims 1 to 9 , wherein the fresh concrete or mortar composition does not contain a setting accelerator .11 . Fresh concrete or mortar composition according to any one of claims 1 to 10 , wherein the aggregates have a maximum particle si ze of 10 mm .12 . Use of a fresh concrete or mortar composition according to any one of claims 1 to 11 for building structural and architectural components layer-by-layer, such as for 3D concrete or mortar printing, comprising placing the fresh concrete or mortar composition through an outlet of a deposition head while moving the deposition head, in order to form a layer of fresh concrete or mortar, wherein successive layers of fresh concrete are place on top of each other .13 . Method of building structural and architectural components layer-by-layer, such as by means of 3D concrete printing, comprising the steps of : providing a fresh concrete or mortar composition according to any one of claims 1 to 11 by adding the at least one viscosity modi fying admixture to a mixture of , or while mixing, the one or more cementitious materials , the aggregates , said water and the at least one plastici zer , and optionally the mineral addition, wherein the composition has a first initial yield stress of 0 . 2- 1 . 5 kPa measured 2 minutes after the addition of the at least one viscosity modi fying admixture ,storing or transporting the fresh concrete or mortar composition without stirring, while the yield stress increases , re-mixing the fresh concrete or mortar composition for a time period of preferably 15- 60 seconds , such as 30 seconds , thereby reducing the yield stress to a second initial yield stress of 0 . 2-3 kPa, placing the fresh concrete or mortar composition through an outlet of a deposition head while moving the deposition head, in order to form a layer of fresh concrete or mortar, wherein successive layers of fresh concrete or mortar are placed on top of each other, allowing the layer of fresh concrete or mortar to rest during a subsequent resting period of 60 minutes or longer at a temperature of 5-30 ° C , in which the yield stress of the fresh concrete or mortar increases to 1 5 kPa, preferably > 10 kPa, measured after a resting period of 60 minutes .

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