Alkali-activatable binder composition containing tannin-dispersants

Abstract

The application relates to an alkali-activatable binder composition containing (i) a binder selected from the group of blast furnace slag, silica fume, calcined clay and pozzolans and (ii) water-soluble tannin at a dosage of tannin (ii) with reference to the binder (i) of 0.1 to 4 weight %. The binder (i) may contain cement at a ratio of 10 weight % or less. The application further describes an aqueous building material mixture containing the binder composition and a hardened building structure obtained from the aqueous building material mixture. Furthermore, the use of tannin as a dispersant for a binder component in such an activatable binder composition is described.

Description

[0001] ALKALI-ACTIVATABLE BINDER COMPOSITION CONTAINING TANNIN- DISPERSANTS

[0002] The present invention relates to an alkali-activatable binder composition containing a tannin-dispersant, an aqueous building material mixture containing the binder composition, a hardened building structure obtained from the aqueous building material mixture and the use of tannin as a dispersant for a binder component in an alkali-activatable binder compositions containing an alkali-activatable binder.

[0003] Portland cement was first referred to in British Patent BP 5022, since this time it has undergone continual further development. It is nowadays considered one of the most widespread inorganic binders. Portland cement hardens hydraulically by virtue of its high CaO content.

[0004] Certain slags from metallurgical processes can be used in the form of latent hydraulic binders as supplementary cementitious material in Portland cement. Also possible is an activation with strong alkalis, for example alkali metal hydroxides or waterglasses. Inorganic binder systems based on reactive, water-insoluble compounds on the basis of SiO2 in conjunction with AI2O3, which cure in an aqueous-alkali medium, are likewise common knowledge. Cured binder systems of this kind are also called "geopolymers" and are described for example in US 4,349,386, WO 85 / 03699 and US 4,472,199.

[0005] Reactive oxide mixtures employed in this context include metakaolin, microsilica, slags, fly ashes, activated clay, pozzolans or mixtures thereof. The alkali medium for activating the binders consists typically of aqueous solutions of alkali metal carbonates, alkali metal fluorides, alkali metal hydroxides, alkali metal aluminates and / or alkali metal silicates, such as soluble waterglass. In comparison to Portland cement, geopolymers may be more cost-effective and more stable, and may have a more favourable CO2 emission balance.

[0006] Aqueous cement suspensions are often admixed with dispersants in order to improve their processing properties, such as kneadability, fluidity, sprayability, spreadability or pumpability. These admixtures are capable of disrupting agglomerates, by adsorption to the surface of the particles, and they can disperse the particles formed. Especially in the case of highly concentrated suspensions, this results in a marked improvement in processing properties.

[0007] Examples of the cement dispersants or plasticizers used primarily to date are salts of naphthalenesulphonic acid / formaldehyde condensates (cf. EP 214412 A1 ; identified hereinafter as naphthalenesulphonates), salts of melaminesulphonic acid / formaldehyde condensates (cf. DE 1671017 A; identified below as melaminesulphonates), and also salts of polycarboxylic acids (cf. US 5,707,445 B1 , EP 1110981 A2, EP 1142847 A2; identified below as polycarboxylates). Such polycarboxylates are prepared mostly by radical copolymerization of ethylenically unsaturated carboxylic acids (such as acrylic acid, methacrylic acid or maleic acid and / or salts thereof) and poly(alkylene oxides) having a polymerizable end group (such as methacrylates, allyl ethers or vinyl ethers). This mode of polymer preparation leads to polymers having a comb-like structure.

[0008] The effect as dispersant of the molecules used, is based on two different effects. Firstly, the negatively charged acid groups of the plasticizers adsorb on the cement grain surface, which is positively charged by calcium ions. The electrostatic double layer formed in this way results in electrostatic repulsion between the particles, which is however relatively weak. In the case of the abovementioned comb polymers, this electrostatic repulsion is reinforced additionally by the steric bulk of the non-adsorbing poly (alkylene oxide) chains. This steric repulsion is very much stronger than the electrostatic repulsion, and so it is easy to explain why the plasticizing effect of the polycarboxylates is very much greater than that of the naphthalene- or melaminesulphonates; in other words, in order to obtain comparable plasticization, the polycarboxylate can be added at a significantly lower dosage.

[0009] WO 2006 / 042709 A1 describes a polycondensation product consisting of A) an aromatic or heteroaromatic compound having 5 to 10 C atoms and / or heteroatoms, this compound possessing on average 1 to 300 oxyethylene and / or oxypropylene groups per molecule, which are linked via an O or N atom to the aromatic or heteroaromatic compound; and also, optionally, B) an aromatic compound selected from the group of phenols, phenol ethers, naphthols, naphthol ethers, anilines, furfuryl alcohols and / or an amino resin former selected from the group of melamine (derivatives), urea (derivatives) and carboxamides; and C) an aldehyde selected from the group of formaldehyde, glyoxylic acid and benzaldehyde or mixtures thereof, it being possible for the benzaldehyde to contain, additionally, acid groups in the form of -COOMa, -SOsMa and -POsMa, and for M to be H, alkali metal or alkaline earth metal, ammonium or organic amine radicals, and also for a to be , 1 or 2. It was found that this polycondensation product produces very good plasticization in hydraulic binders, such as cement. As compared with naphthalenesulphonates or melaminesulphonates, it results in substantially better plasticization of the construction material in conjunction with a lower rate of addition, and the fluidity can be maintained over a longer period of time.

[0010] CN 101 549 977 A describes cementitious compositions comprising a binder component including at least 20 weight % Portland cement, 10-55 weight % fly ash and further up to 65 weight % of an active pozzolanic material. Disclosed is also an alkaline activator at a dosage from 0.5 to 15 weight % and a water-reducing agent, which may be also be tannin. The content of cement in these binder systems is relatively high compared to geopolymer binder systems, no examples with tannin are given.

[0011] US 2019 / 382308 A1 discloses in the experimental part Portland cement compositions in which a minor proportion of the cement is replaced by pozzolanic or latent hydraulic binders like slag or fly ash. In some of the examples tannin is used.

[0012] Xie, Y. ET AL: “Study of a complex water-reducing accelerator for portland pozzolana cement”, CHEMICAL ABSTRACTS, vol. 112, no. 14, 2 April 1990, page 337, XP000152012, ISSN: 0009-2258 describes pozzolanic portland cement blends further comprising a water-reducing agent accelerator mix, which comprises inter alia tannin.

[0013] The before mentioned geopolymer based binder systems show distinct different chemical reactivity compared to the cementitious systems. These differences make it difficult or impossible to use the before mentioned dispersants in geopolymer based binder systems. For obtaining acceptable hardening times, the reactive oxide components in the geopolymer binder systems require strong alkaline activation. This higher level of alkalinity imposes particular requirements on the dispersants, which cannot be fulfilled by many commercial concrete plasticizers. Furthermore, the geopolymer based binder systems generally do not have any positively charged grain surfaces due to the low content of calcium. Instead, the surfaces are siliceous (SiO2 surfaces). Moreover, the high level of alkalinity that is required for the activation also brings about a high salt load, which may annihilate a dispersion effect that is possible at lower pH levels (comparably to cement).

[0014] The before mentioned dispersants, when used in geopolymer binder systems, have the disadvantage that the water reduction is usually not satisfactory, particularly the slump-retention over time is not sufficient for many construction projects, where a transportation of the concrete over longer distances is necessary. Also, the early strength development of the geopolymer based concrete is not satisfactory and needs improvement.

[0015] The current discussion on reducing CO2-emissions puts a strong pressure on cement producers to reduce the content of Portland cement in concrete and to replace it, for example, by latent hydraulic and pozzolanic waste products like slags and fly ashes. The use of such supplementary cementitious materials is limited by two hurdles: Firstly, these products show a rather low hydraulic reactivity compared to Portland cement, which results in a slow binding process and low early strengths. Secondly, no suitable plasticizers for these systems are currently available, which would allow for a reduction of the water content without reducing the fluidity and processability of the binder systems.

[0016] Thus, the problem addressed by the inventors was that of substantially avoiding or at least attenuating the disadvantages of the prior art discussed above, particularly the problem of providing a sufficient workability of cementitious systems comprising high percentages of geopolymer binders.

[0017] The solution to the problem is an alkali-activatable binder composition containing (i) a binder selected from the group of blast furnace slag, silica fume, calcined clay and pozzolans, wherein the binder (i) may optionally further contain one or more hydraulic binders selected from Portland cements, aluminate cements, sulfoaluminate cements, and mixtures thereof, with the proviso that the content of the optional hydraulic binders in the binder (i) is 10 weight % or less of the binder (i) and (ii) water-soluble tannin at a dosage of tannin (ii) with reference to the binder (i) of 0.1 to 4 weight %. More preferred exemplified dosages of tannin may be 0.1 to 3 weight %, 0.2 to 3 weight %, 0.5 to 2 weight %, and, more particularly, 0.2 to 1 weight %.

[0018] The binder (i) is a binder selected from the group of blast furnace slag, silica fume, calcined clay and pozzolans. The binder (i) may optionally further contain one or more hydraulic binders selected from Portland cements, aluminate cements, sulfoaluminate cements, and mixtures thereof, with the proviso that the content of the optional Portland cements, aluminate cements and / or sulfoaluminate cements, and mixtures thereof is 10 weight % or less, preferably 5 weight % or less. In order to avoid any misunderstandings, the binder (i) is meant to be the binder selected from the group of blast furnace slag, silica fume, calcined clay and pozzolans and the hydraulic binders (if present) are part of the binder (i).

[0019] More particularly, the inorganic materials used as binder material (i) are selected from one or more of the following exemplified materials: Blast furnace slag, silica fume, calcined clay and pozzolans may be components of exemplified geopolymer binder compositions. In line with this application, those inorganic materials may be used alone or in mixture with each other or in mixture with other binders in the form of latent hydraulic binders as supplementary cementitious material. In the context of the present invention, a latent hydraulic binder is preferably to be understood as meaning a binder in which the molar (CaO + MgO) : SiO2 ratio is between 0.8 and 2.5 and particularly preferably between 1 .0 and 2.0.

[0020] In the formulation of the invention blast furnace slag as latent hydraulic binder can be selected from granulated blast furnace slag, ground granulated blast furnace slag, electrothermal phosphorus slag, steel slag and mixtures thereof. Blast furnace slag is a waste product of the blast furnace process. It may be granulated ("granulated blast furnace slag") or finely pulverized ("ground granulated blast furnace slag"). The ground granulated blast furnace slag varies in its fineness of grinding and particle size distribution according to the origin and preparation form, wherein the fineness of grinding has an influence on the reactivity. The so-called Blaine value, which is typically of the order of a magnitude of 200 to 1000, often between 300 and 500 m2kg’1, is used as a characteristic for the fineness of milling. Blast furnace slag may have a composition comprising 30 to 45 weight % of CaO, about 4 to 17 weight % of MgO, about 30 to 45 weight % of SiO2 and about 5 to 15 weight % of AI2O3, typically about 40 weight % of CaO, about 10 weight % of MgO, about 35 weight % of SiO2 and about 12 weight % of AI2O3.

[0021] Electrothermal phosphorus slag is a waste product of electrothermal phosphorus production. It is less reactive than blast furnace slag and may, for example, contain about 45 to 50% by weight of CaO, about 0.5 to 3 weight % of MgO, about 38 to 43 weight % of SiO2, about 2 to 5 weight % of AI2O3 and about 0.2 to 3 weight % of Fe2Os as well as fluoride and phosphate.

[0022] Steel slag is a waste product of various steel production processes with strongly varying compositions (cf. Caijun Shi, Pavel V. Krivenko, Della Roy, Alkali-Activated Cements and Concretes, Taylor & Francis, London & New York, 2006, pages 42-51 ).

[0023] Microsilica, also referred to as silica fume, is a by-product of silicon or ferrosilicon production and likewise comprises for the most part amorphous SiO2 powder. The particles have diameters of the order of magnitude of 0.1 pm. The specific surface area is of the order of magnitude of 20 to 25 m2g-1. Glass powder, for the purpose of the present invention, reacts similar to amorphous SiO2 powder. In contrast, commercially available quartz sand is crystalline, has comparatively large particles and a comparatively small specific surface area. Therefore, if quartz sand is contained, it generally does not serve as a binder material in line with the concept of the invention described herein, but merely as an inert aggregate.

[0024] The binder composition may comprise at least one calcined clay material as a binder component. Preferably, the calcined clay material has a Dv90 of less than 200 pm, preferably less than 150 pm, more preferably less than 70 pm, or less than 50 pm.

[0025] The Dv90 (by volume) corresponds to the 90thpercentile of the particle size distribution, meaning that 90% of the particles have a size of the Dv90 or smaller and 10% have a size larger than the Dv90. Generally, the Dv90 and other values of the same type, which are characteristic of the granulometric profile (volume distribution) of a collection of particles or grains can be determined by laser granulometry for particle sizes less than 200 pm, or by sieving for particle sizes greater than 200 pm. Nevertheless, when individual particles have a tendency to aggregate, it is necessary to determine their size by electron microscopy.

[0026] Calcined clay materials may be obtained by heat treatment of clays, which contain phyllosilicates, i.e. sheet silicates. Phyllosilicates include 1 :1 and / or 2:1 layered (natural) clays or mixtures thereof, comprising di- and / or trioctahedral sheets or mixtures thereof and a layer charge of 0, e.g., kaolinite, up to a negative layer charge of 1 , e.g. mica or mixtures thereof. Heat treatment of the clay converts the clay minerals by dehydroxylation with release of water. For example, kaolinite may be heat treated to obtain metakaolin (Al2Si2O?). The obtained calcined clay material is a naturally derived material with pozzolanic reactivity. Clays derived from natural deposits to prepare calcined clays can vary in composition and crystalline structure in a broad range. For the purpose of the present invention, a calcined clay is any material prepared by heat treatment of clay, that provides a pozzolanic reactivity. As the composition, crystalline structure, fineness and the processing conditions like temperature and time of heat applied can vary significantly, the reactivity of calcined clays consequently can differ significantly as well.

[0027] For the purpose of the invention, the calcined clay material is a material obtained by calcination of a clay material including at least one non-kaolinitic clay material. While pure metakaolin is a preferred supplementary cementitious material, deposits of pure kaolinite are rarely found, and pure metakaolin is hence expensive. Crude kaolin is of widely varying ore quality and comprises, besides kaolinite, other clay minerals or claylike minerals. In construction compositions, a calcined clay material obtained from a clay material including at least one non-kaolinitic clay material may be employed. It is understood that the calcined clay material suitable for being used in binder composition of the invention may be obtained from clay materials comprising non-kaolinitic clay material as well as kaolinitic clay material, or from clay materials comprising non- kaolinitic clay materials only. This opens the possibility of using clays which are much more widely available than kaolinite. Kaolinitic clay materials include members of the kaolin group, such as kaolinite, dickite, nacrite or halloysite.

[0028] The most relevant non-kaolinitic clay materials which can be used as such or in association with kaolinitic clay materials in order to produce calcined clay materials belong to the

[0029] - smectite group, such as dioctahedral smectites like montmorillonite, nontronite, or trioctahedral smectites like saponite;

[0030] - mica group such as illite, paragonite, ephesite, margarite, or clintonite;

[0031] - chlorite group such as clinochlore or chamosite;

[0032] - pyrophyllite-talc group such as talc or pyrophyllite and vermiculite.

[0033] In an embodiment, the non-kaolinitic clay material comprises at least one clay belonging to the smecticte group and / or illite clay.

[0034] Preferably, the calcined clay material comprises at least 10 weight %, preferably at least 30 weight % of calcined clay obtained from a non-kaolinitic clay.

[0035] An example of a natural clay composition comprises, in percentages by weight, 40 to 45 % of illite clay, 25 to 30 % of kaolinite clay and 25 of 30 % smectite group clay. There are other natural clays that do not comprise kaolinite, for instance compositions comprising 85 to 90 % of smectite group clay and 10 to 15 % of illite clay.

[0036] Calcination changes the clay structure from crystalline to amorphous. The degree to which clay undergoes changes in its crystalline form may depend on the amount of heat to which it is subjected. It is preferable to heat-treat the clay at a temperature sufficient to dehydroxylate the clay to a crystallographically amorphous material while preventing the formation of crystalline high temperature aluminosilicate phases such as mullite. Amorphous phases (or ill defined crystalline phases) are highly reactive phases which are readily activated. Relatively high amounts of amorphous calcium aluminate phases have a positive impact on late strength development of mortars and concretes, e.g., after 28 days. In a preferred embodiment, the calcined clay has an amorphous content in the range from 10 to 100 weight %, preferably 20 to 70 weight %, as determined by quantitative XRD analysis (Rietveld). The pozzolanic reactivity of a supplementary cementitious material, including calcined clays, can be measured by calorimetric analysis on blended cements; see Development of a New Rapid, Relevant and Reliable (R3) Testing Method to Evaluate the Pozzolanic Reactivity of Calcined Clays, Rilem Bookseries 2015, DOI: 10.1007 / 978-94-017-9939-3_67. A cement model paste is prepared by mixing 11.11 g of the supplementary cementitious material (SCM), 33.33 g of portlandite, 60 g of deionized water, 0.24 g of potassium hydroxide, 1 .20 g of potassium sulfate and 5.56 g of calcite. The heat release is recorded over the course of 7 days. The cumulative heat (“Heat”) is calculated from 1.2 hours after the beginning of the calorimetry test onwards. The total heat release (“Hrescaied") is reported in J / (g SCM) as follows:

[0037] J . _ Heat rescaled (mpx0.0997) ’ wherein Heat is the cumulative heat in Joule and mPis the mass of the cement model paste in gram.

[0038] Useful calcined clay materials exhibit a total heat release in the pozzolanic reactivity test of 100 to 600 J / g, in particular 150 to 400 J / g.

[0039] In one embodiment, the calcined clay material is a material obtained by heat treating a clay at a temperature of 400 to 1 ,000 °C, preferably 500 to 900 °C, more preferably 600 to 850 °C.

[0040] In one embodiment, the calcined clay material has a BET value, as measured in accordance with DIN ISO 9277, in the range from 0.1 to 60 m2 / g, preferably 1 to 50 m2 / g, and in particular 1 to 40 m2 / g.

[0041] The calcined clay is generally comprised in an amount of 5 to 80 weight %, preferably 5 to 50 weight %, relative to the amount of the binder component (i).

[0042] In the formulation of the invention the pozzolanic binder can be selected from precipitated silica, pyrogenic silica, glass powder, fly-ash (e.g. brown coal fly ash or mineral coal fly ash), rice husk ash, metakaolin, volcanic ash, tuff, trass, pozzolana and zeolites and mixtures thereof. The test for pozzolanic activity can be effected according to DIN EN 196 part 5. An overview of pozzolans suitable according to the invention is to be found in Caijun Shi, Pavel V. Krivenko, Della Roy, Alkali-Activated Cements and Concretes, Taylor & Francis, London & New York, 2006, pages 51 -60, and pages 61 - 63.

[0043] Exemplified silica suitable for the application according to the invention as a rule has a content of at least 80% by weight, preferably at least 90% by weight, of SiO2. Precipitated silica is obtained industrially via precipitation processes starting from waterglass. Precipitated silica is also referred to as silica gel, depending on the production process. Pyrogenic silica is produced by reacting chlorosilanes, such as, for example, silicon tetrachloride, in an oxyhydrogen flame. Pyrogenic silica is an amorphous SiO2 powder having a particle diameter of 5 to 50 nm and a specific surface area of 50 to 600 m2g_1.

[0044] Metakaolin forms in the dehydration of kaolin. While kaolin releases physically bound water at 100 to 200°C, a dehydroxylation takes place at 500 to 800°C or above with a collapse of the lattice structure and formation of metakaolin (Al2Si2O?). Pure metakaolin accordingly contains about 54 weight % of SiO2 and about 46 weight % of AI2O3.

[0045] Fly ashes are formed, inter alia, in the combustion of coal in power stations. Exemplified fly ashes to be used in the present application are fly ashes of class C containing about 10 weight % of CaO or fly ashes of class F containing less than 8 weight %, preferably less than 4 weight % and typically about 2 weight % of CaO.

[0046] As latent hydraulic binders, certain slags from metallurgical processes can be activated with strong alkalis, such as, for example, waterglasses or alkali hydroxides, and can be used as admixtures to Portland cement. By mixing with aggregates (quartz sand or aggregate having a corresponding grain size) and additives, they can be used as mortars or concretes. Activated latent hydraulic binders generally harden hydraulically, i.e. through crystallization. In general, “alkali-activatable" in the context of the present application means that the binders used in the binder composition may be activated by alkaline activators, in particular, by strong alkalis such as, for example, waterglasses or alkali hydroxides, carbonates, and silicates. As alkaline activator, one strong alkali or a mixture of two or more alkalis may be used. Strong alkalis may be hydroxides of alkaline or earth alkaline metals such as NaOH, KOH, Ca(0H)2, among others. Waterglass, also called sodium silicate or soluble glass, is a compound containing sodium oxide (Na20) and silica (silicon dioxide, SiO2) that forms a glassy solid with the very useful property of being soluble in water. Waterglass is sold as solid lumps or powders or as a clear, syrupy liquid and can be used as alkaline activator for the binder compositions as described herein.

[0047] Further exemplified binder compositions may contain blast furnace slag in a percentage of 90 weight % or less or calcined clay in a percentage of 80 weight % or less or fly ash in a percentage of 50 weight % or less or silica fume in a percentage of 10 weight % or less or any mixture of two or more of the components blast furnace slag, calcined clay and silica fume. More preferred percentage ranges for blast furnace slag are from 10 to 90 weight %, for fly ash from 10 to 50 weight %, and for silica fume from 0 to 10 weight %. In some examples, mixtures of blast furnace slag, calcined clay, and silica fume may be preferred.

[0048] The before mentioned geopolymer based binder systems show distinct different chemical reactivity compared to cementitious systems and, thus, need specific dispersants for obtaining acceptable hardening times. The higher level of alkalinity during the hardening processes imposes increased requirements on the dispersants. During an extensive search for new types of dispersants which may withstand the alkaline environment and are effective, admixtures based on lignin and especially tannins have been found to be effective. A benchmarking of performances in model geopolymeric binders has been carried out using different grades of commercially available tannins. Based on these intensive studies, the binder composition described herein comprises the latent-hydraulic binder component as defined hereinbefore and a water-soluble tannin. The solubility of the tannin in water at 20 degrees Celsius, normal pressure and a pH of 10 is preferably higher than 1 g / l, more preferably higher than 5 g / l. Throughout this specification the term “water-soluble tannin” can be abbreviated as tannin or tannin component. It has been investigated that the tannin component may preferably be contained in a dosage of tannin with reference to the binder of 0.1 to 4 weight %, preferably, between about 0.1 and 3 weight %, and more particularly, about between about 0.5 and 2 weight %. Even though the dosage is rather low, the binder composition of the present invention provides a satisfactory water reduction during its use in aqueous building material mixtures such as mortars or concretes. Compared to other classical superplasticiziers for geopolymeric binders, the tannins provide an improved water solubility, in particular in high pH environments as present in the alkali-activatable binder compositions used in the composition of the present invention. Hence, the tannins as dispersants for latent hydraulic binder components are satisfactory for plasticizing hydroxide-activated geopolymeric binder compositions at the conditions needed during the usage of the binder compositions. It has also been noticed that the tannins as described herein can be used as plasticizers at low dosages as defined in the claims. In some embodiments, the dosage of tannin with reference to the binder is in the range of 0.1 to 4 weight %, preferably, between 0.2 to 3 weight %, more preferably between 0.2 to 1.0 weight %. For the classical superplasticizers which could be used in the geopolymeric compositions, generally much higher dosages must be used in order to notice an advantageous plasticizing effect, if they are usable at all in geopolymer-based binder compositions.

[0049] In the light of the above, the new binder composition using water-soluble tannins in low dosages are satisfactory from the perspective of low costs. Moreover, they are also based on natural products, that means the tannins used are bio-based admixtures. Therefore, they provide a low CO2 equivalent because of the use of the geopolymeric binders as well as of the bio-based dispersants in the binder composition as defined herein. Moreover, the bio-based tannins suitable for the use as dispersants for the binder compositions described herein, are renewable resources which are preferred for future requirements of industrial standards.

[0050] More particularly, the binder composition according to the present invention provides a satisfactory slump-retention over time which is sufficient for many construction projects, even though a transportation of the concrete over longer distances is necessary. Also, the early strength development of the geopolymer based concrete is satisfactory even if an alkali-activated binder system requiring a high level of alkalinity for the activation and bringing about a higher salt load as compared to cementitious systems is used.

[0051] Tannins are like lignin a natural source of phenolic compounds, in particular polyphenolic compounds, and are known as an ample raw material for the synthesis of several biobased materials. As natural raw material, tannins generally are water- soluble phenolic compounds and are subdivided into four classes, hydrolysable, condensed, complex, and phlorotannins. Vascular plants have different concentrations of hydrolysable, condensed, and complex tannins. Non-vascular plants are a source of phlorotannins.

[0052] In line with the present application, exemplified tannins which may be used as dispersants for the binder composition as described herein may be extracted from natural sources, particularly from vascular plants. Hydrolysable tannins are preferred examples of tannins for the geopolymeric binder materials. The tannins for the use as dispersants are compounds of a natural source in the form of natural extracts. Alternatively, synthetically prepared polyphenolic compounds which are identical, similar, or modified polyphenolic compounds as the natural tannins fall within the definition of tannins as used herein.

[0053] In some cementitious systems such as drilling mud compositions, the use of sulfonated tannins is known as additives responsible or functioning as mud thinning agents, for example. However, in the binder composition as described herein, the tannin is used as dispersant. The studies showed that if tannins are used in form of a modified tannin as dispersant, it is preferred that the tannin comprises a sulfur content of less than 1 weight %. It is assumed that higher sulfur contents may decrease the workability of the binder compositions in high-alkaline environments which are present if higher amounts of geopolymeric binder admixtures are used.

[0054] In some examples of the binder composition described herein, tannins with molecular weights in the range of 500 and 3.000 g / mol can be used as the dispersants.

[0055] In a further embodiment, the binder composition may contain organic additives, but in a limited amount which differentiates them from other cementitious compositions used in different technical fields. Cementitious compositions comprising a non-aqueous fluid and an alkali-activated material are, for example, typically used in oilfield applications. In such applications, oil-based drilling muds are present in the system and are adapted to be held in suspension while the cementitious compositions are solidified by specific binder compositions. Such oil-based drilling muds generally are composed of oil as the continuous phase and water as the dispersed phase in conjunction with emulsifiers, wetting agents and gellants. The oil base can be diesel, kerosene, fuel oil, selected crude oil or mineral oil which all fall within organic additives as mentioned herein. According to this application, however, if organic additives are contained in the binder composition, the organic additives are contained in a weight percentage of less than 10 %. Oil-based organic additives as defined before are preferably not contained at all. If, however, such organic additives are present, they are preferably contained in a percentage of less than 5 weight %.

[0056] The binder composition may contain non-calcined clays such as natural kaolin. The use of non-calcined clay as a pozzolanic material may suitably be used for the production of mud-cements in drilling applications, or for geopolymers, and soil stabilization. Therefore, the potential use of non-calcined clays as supplementary cementitious material is known. However, due to the relatively lower reactivity compared with calcined clays, non-calcined clays generally are not preferred as binders as suitably being used in the binder composition as described herein. Hence, the binder composition described herein may contain non-calcined clays in a weight percentage of non-calcined clays with reference to the binder of less than 5 %, preferably, less than 2 %, in particular, less than 1 %.

[0057] The formulation of the invention may further contain one or more hydraulic binders. Exemplified hydraulic binders can be selected from Portland cements, aluminate cements, sulfoaluminate cements, and mixtures thereof, and the content of Portland cements, aluminate cements and / or sulfoaluminate cements in the binder (i) is 10 weight % or less, more preferably 5 weight % or less. If the amount of the one or more hydraulic binders is too high, the formation of a desired hybrid matrix may no longer be possible. The term "% by weight’ or “weight percentage" as used throughout this specification (if not indicated differently) is based on the total amount of binders, activators and polycondensation products as defined hereinabove, each calculated as dry substance. With other words, percentages are based on the water-free formulation.

[0058] According to another embodiment of the present application, an aqueous building material mixture is described herein. The aqueous building material mixture may contain an alkali-activatable binder composition as defined herein and water, wherein the weight ratio of water to binder is 0.25 to 2.0, more preferably 0.25 to 0.8. Generally, the weight ratio of water to binder is less than 1 .0. In some applications of those binder compositions, for example in backfill applications or the like, the weight ratio of water to binder may be higher, for example up to 2.0.

[0059] The alkali-activatable binder composition comprises geopolymeric binders, optionally cementitious binders, at a proportion of not more than 10 weight % of the binder (i), and the tannin-based dispersant as defined before. In some examples, the aqueous building material mixture may further comprise at least one of an aggregate and additive.

[0060] Exemplified aggregates are, among others, mineral admixtures or mineral additions such as stones. Many types of stones are available such as basalt, marble, limestone, sandstone, quartzite, travertine, slate, gneiss, laterite, and granite which can be used as aggregates in construction materials. The stones used for building construction should be hard, durable, tough, and should be free from weathered soft patches of material, cracks, and other defects that are responsible for the reduction of strength and durability. Stones for construction purposes are obtained by quarrying from solid massive rocks. Each type of stone lend itself to various construction applications based on its properties.

[0061] Exemplified additives for concrete may be chemical additives or mineral additives. Chemical additives are used to reduce the costs, guarantee the quality during mixing and all through the curing process, or to improve the properties of the hardened concrete. Mineral additives generally are used to increase concrete strength, reduce the permeability levels, or to affect the nature of the hardened concrete. More particularly, additives may, for example, be used as set retarding agents, air entrainment additives, accelerating additives, shrinkage reducing agents, water reducing agents, superplasticizers, or corrosion inhibiting agents, or for imparting other properties to hardened concrete.

[0062] The aqueous building material mixture may further contain an alkaline activator for activating the binder composition during the hardening process. The alkaline activator may be selected from the group of alkali-, or earth alkali hydroxides, carbonates and silicates. Specific examples are strong alkalis such as, for example, waterglasses or alkali hydroxides, carbonates, and silicates. As alkaline activator, one strong alkali or a mixture of two or more alkalis may be used. Strong alkalis may be hydroxides of alkaline or earth alkaline metals such as NaOH, KOH, Ca(0H)2, among others. The alkalinity of the alkaline activators is high enough to activate the geopolymeric binders used in line with the invention.

[0063] When using the heretofore described binder composition comprising at least one geopolymeric binder and a tannin-based dispersant, a hardened building structure may be obtained. Therefore, the application further relates to a hardened building structure obtained or being obtainable from the aqueous building material mixture described herein. The use of tannins, more particularly, the use of tannins extracted from a natural source as powdered additives for alkali-activated concrete or mortar mixtures allows an easy route to manufacture hardened building structures with satisfactory properties. Especially, tannins as dispersant for geopolymer binders as described herein can be applied in powdered form or in liquid admixture because they are well soluble at an alkaline pH. The tannin dispersant imparts to the binder composition satisfactory slump retention properties which are constant over at least 1 hour, in some examples over 2 hours or even longer. Hence, the use of the tannins as plasticizers for geopolymeric concrete or mortar mixtures provide improved results during the processing of concrete mixtures. In these geopolymeric systems, the use may satisfactorily reduce the water / binder ratio (W / B) and may maintain the workability over time. In the production of cementitious construction material mixtures such as concrete, this effect can be utilized in order to achieve particularly advantageous effects, since otherwise, in order to achieve a readily processible consistency, substantially more water would be needed than would be necessary for the subsequent hydration process. As a result of this excess water, which gradually evaporates after hardening has taken place, cavities remain, which significantly impair the mechanical strength and robustness of the hardened construction material. Said tannin-based dispersants are used in order to reduce the water fraction which is excessive with respect to the water needed for hydration, and / or to optimize workability for a given water / cement ratio.

[0064] In some examples, a one-pot product with the activator and the binder composition has been provided by using tannins as dispersants for geopolymer binders.

[0065] A further embodiment of the invention is the use of water-soluble tannin as a dispersant for a binder component in an alkali-activatable binder composition, wherein the binder is an alkali-activatable binder (i) selected from the group of blast furnace slag, silica fume, calcined clay and pozzolans, wherein the binder composition may optionally further contain one or more hydraulic binders selected from Portland cements, aluminate cements, sulfoaluminate cements, and mixtures thereof, with the proviso that the content of the optional hydraulic binders in the binder (i) is 10 weight % or less, preferably 5 weight % or less, of the binder (i) and the dosage of water-soluble tannin with reference to the binder (i) is 0.1 to 4 weight %.

[0066] In these applications, exemplified dosages of tannin with reference to the binder is 0.1 to 4 weight %, preferably 0.2 to 3 weight %, more preferably 0.2 to 1 weight %.

[0067] As described before, tannins might be used for modifying the slump retention of an alkali-activatable binder composition containing an alkali-activatable binder selected from the group of blast furnace slag, silica fume, calcined clay and pozzolans at a dosage of tannin with reference to the binder of 0.1 to 4 weight %, preferably 0.2 to 3 weight %, more preferably 0.2 to 1 weight %. The tannin in powdered or liquid form may act as a slump-retainer over a time period of up to at least 60 minutes, more particularly, up to 90 minutes or longer. Examples

[0068] Some examples of binder compositions have been prepared and tested regarding their slump retention in geopolymer systems. For testing the slump retention of different mortar mixes over up to 60 minutes, a Haegermann cone with 15 shocks on a table was used as parameter measured according to standard procedures (DIN EN 1015- 3). The obtained slump retentions (in centimeters) for the examples according to the invention and the reference examples are shown in the Figure 1 (binder systems without cement) and Figure 2 (binder systems with partial binder replacement by cement).

[0069] In the examples and the comparative examples, different mortar mixes (according to EN 196-1 ) were prepared based on 650 g binder composition, 1350 g sand (Norm sand), and 260 g water. The sand was mixed with water, then the activator and the binder composition (admixed in water) were added. In all examples, 4 weight % sodium hydroxide as alkaline activator was used.

[0070] As reference binder compositions, binders based on Burnt Oil Shale (BOS), slag (Karlstadt 4000 from Schwenk (S)), fly-ash (POWERMENT® from Kraftwerk HKV Volklingen (FA)), silica fume (940LI from Elkem (SF)) and calcined clay (10-12G from the LC3 Technical Research Center in India (CC)) were prepared and tested as described above. The following six exemplified binder compositions were prepared and tested:

[0071] Composition 1 : binder BOS mixed with 1 weight % TanninA Composition 2: binder BOS mixed with 1 weight % TanninB Composition 3: binder CC mixed with 1 weight % TanninA Composition 4: binder CC mixed with 1 weight % TanninB Composition 5: binder S / FA / SF with 1 weight % TanninA Composition 6: binder S / FA / SF with 1 weight % TanninB

[0072] TanninA is a hydrolysable tannin obtained as natural extract mainly from Castanea sativa (“Fintan C” supplied by Silvateam S.p.A., Italy). TanninB is a condensed tannin obtained as natural extract mainly from quebracho Schinopsis lorentzii (“Fintan Q” supplied by Silvateam S.p.A., Italy).

[0073] The first and second exemplified binder compositions were based on BOS, the third and fourth were based on CC, the fifth and sixth based on a binder mixture of S, FA and SF. In all six binder compositions comprising tannin dispersants TanninA and TanninB, respectively, the slump retention of the mortar mixes prepared was higher compared to the mortar mixes with the corresponding reference binders. The measurements shown in the Figure 1 qualitatively confirm the improved characteristics of the prepared mortars by using different binder systems and different tannins as described hereinbefore. Therefore, the improved workability could be confirmed by these examples.

[0074] Another set of data (Fig. 2) was produced to demonstrate the limit of cement that could be incorporated in a geopolymer binder without deteriorating the performance of tannin as a slump retainer. The same testing conditions applied, using the binder S / FA / SF and 5, 10 or 20% of cement as part of the binder composition, the total of 100 % comprises all binders including the cement. As cement Mergelstetten 52.5 R from Schwenk was used and Tannin B was the slump retainer. The following six exemplified binder compositions were prepared and tested, showing that slump retention can be achieved with 5 and 10% cement, but at a ratio of about 20 weight % cement replacement the slump retention deteriorates.

[0075] Composition 7: binder S / FA / SF with 5% cement and no admixture

[0076] Composition 8: binder S / FA / SF with 5% cement and with 1 weight % TanninB Composition 9: binder S / FA / SF with 10% cement and no admixture

[0077] Composition 10: binder S / FA / SF with 10% cement and with 1 weight % TanninB Composition 11 : binder S / FA / SF with 20% cement and no admixture

[0078] Composition 12: binder S / FA / SF with 20% cement and with 1 weight % TanninB

Claims

Claims1 . An alkali-activatable binder composition containing (i) a binder selected from the group of blast furnace slag, silica fume, calcined clay and pozzolans, wherein the binder (i) may optionally further contain one or more hydraulic binders selected from Portland cements, aluminate cements, sulfoaluminate cements, and mixtures thereof, with the proviso that the content of the optional hydraulic binders in the binder (i) is 10 weight % or less of the binder (i) and (ii) water-soluble tannin at a dosage of tannin (ii) with reference to the binder (i) of 0.1 to 4 weight %.

2. The binder composition according to claim 1 , containing blast furnace slag in a percentage of 90 weight % or less or calcined clay in a percentage of 80 weight % or less or silica fume in a percentage of 10 weight % or less or any mixture of two or more of the components blast furnace slag, calcined clay and silica fume.

3. The binder composition according to claim 1 or claim 2, in which the tannin is a hydrolysable tannin.

4. The binder composition according to any of claims 1 to 3, in which the tannin comprises a sulfur content of less than 1 weight %.

5. The binder composition according to any of claims 1 to 4, in which the tannin has a molecular weight in the range of 500 to 3.000 g / mol.

6. The binder composition according to any of claims 1 to 5, in which organic additives are contained in a weight percentage of less than 10 %.

7. The binder composition according to any of claims 1 to 6, containing noncalcined clays in a weight percentage of non-calcined clays with reference to the binder (i) of less than 5 %.

8. Aqueous building material mixture containing the alkali-activatable binder composition of any of claims 1 to 7 and water, wherein the weight ratio of water to binder is 0.25 to 2.0.

9. The aqueous building material mixture of claim 8, further comprising at least one of an aggregate and additive.

10. The aqueous building material mixture of claim 8 or 9, containing an alkaline activator selected from the group of alkali or earth alkali hydroxides, carbonates, silicates, and any mixture thereof.

11. Hardened building structure obtained from the aqueous building material mixture of any of claims 8 to 10.

12. Use of water-soluble tannin as a dispersant for a binder component in an alkali- activatable binder composition, wherein the binder is an alkali-activatable binder (i) selected from the group of blast furnace slag, silica fume, calcined clay and pozzolans, wherein the binder composition may optionally further contain one or more hydraulic binders selected from Portland cements, aluminate cements, sulfoaluminate cements, and mixtures thereof, with the proviso that the content of the optional hydraulic binders in the binder (i) is 10 weight % or less of the binder (i) and the dosage of water-soluble tannin with reference to the binder (i) is 0.1 to 4 weight %.

13. The use of tannin according to claim 12 for increasing the workability of an alkali- activatable binder composition.

14. The use of tannin according to claim 13 for increasing the slump retention of an alkali-activatable binder composition.

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