METHOD FOR THE PRODUCE OF GRANULES FROM CEMENT COMPOSITIONS

Description

[0001] The present invention relates to a method for producing aggregates and granules from unset cement compositions. In particular, the present invention can be used for processing unset cement residue that may arise after the completion of a work order. More generally, the present invention relates to cement mixtures that have not been used as intended and therefore require recycling. State of the art

[0002] Nowadays, 1% of the concrete produced cannot be used as originally intended. For example, the delivery quantity may exceed requirements due to miscalculations, a certain surplus may have been planned as a reserve, or errors may have occurred during mixing, rendering the produced concrete unsuitable for its intended purpose. Such concrete is usually returned to the concrete plant, where it can be reused or processed in various ways. For example, standard elements can be produced, or the concrete can be spread out, ground again after hardening, and then reused. It is also possible to wash the concrete with water, which separates the non-reactive components such as sand from the cement paste. These components can then be reused to produce new concrete.The resulting slag with the remaining fines can also be added back to the new concrete as mixing water.

[0003] A few years ago, it was also proposed to reuse unused concrete through granulation. This involves adding additives to the concrete, transforming it into granules that can be reused as an additive for fresh concrete after it has fully cured (after about 24 hours).

[0004] However, the existing concrete recycling processes mentioned above have various disadvantages, which will be explained in more detail below. For example, there is not always a need for standard concrete elements during the production of such elements. In many cases, the demand for such elements is significantly smaller than the supply, making such reuse relatively unattractive from an economic perspective. Grinding hardened concrete requires breaking up a poured concrete structure and removing the aggregates by sieving them according to size, making the process relatively complex overall. In addition, breaking up and grinding concrete requires a relatively large amount of energy and simultaneously generates relatively high dust and noise emissions. All of this makes this type of concrete recycling relatively unattractive from an economic perspective.

[0005] When concrete is washed out, as described in DE 39 06 645, for example, sand and gravel components are washed out by adding water and separated from the remaining cement fine sediment. The diluted supernatant cement slurry is collected in a separate sedimentation tank. The separated sand and gravel components can be reused directly. The cement can settle from the diluted cement slurry in the sedimentation tank, and the clear supernatant water can then also be partially reused.

[0006] While the process described in DE 39 06 645 allows for the recycling of gravel and sand components, it has the disadvantage that the generation of waste in the form of cement cannot be completely avoided. Furthermore, relatively large quantities of water are required to wash the residual concrete, resulting in relatively large amounts of contaminated water. Only a small portion of this wash water can be reused for concrete production because it contains large amounts of dissolved salts and suspended solids that impair the hydration of the cement and thus have a negative impact on the mechanical strength of the concrete. Therefore, it is not possible to use the water recovered from this recycling process for the production of high-quality concrete, especially high-strength concrete or air-entrained concrete.Excess water that cannot be used to produce new concrete must be disposed of and neutralized, which incurs additional costs.

[0007] DE 195 18 469 describes a process for the reuse of residual concrete, which a) the addition of a setting retarder for the cement based on a phosphonic acid derivative, precisely matched to the amount of cement, and b) the addition of fresh cement in a mixer vehicle at the end of the desired delay time so that the ratio of cement in the fresh to the old concrete fraction is at least 2:1.

[0008] This method allows the residual concrete to be kept sufficiently fluid in an uncured state in the mixer truck, for example overnight or over the weekend, and then reused in combination with new concrete, thus avoiding the creation of waste. However, this method has the disadvantage of being relatively complicated to implement. For example, it is necessary to know the exact composition of the residual concrete, its quantity, its workability, the temperature and the time after mixing in order to use these parameters to determine the exact amount of setting retarder required to delay setting for the desired period. In addition, the addition of fresh concrete and its ratio to the residual concrete must be precisely balanced and controlled to prevent the resulting new concrete from curing too slowly.For these reasons, the method described in DE 195 18 469 is difficult to implement in practice.

[0009] JP 2004 / 276575 describes a process in which excess concrete is treated with additives that prevent hardening but allow the remaining concrete to coagulate. The coagulated concrete is then dried and solidified, developing weak binding forces so that it can be crushed by equipment. The resulting aggregates can then be separated from the weakly hydrated cement powder and recycled. This system therefore allows the recovery of the aggregate without generating large quantities of waste water. However, the process has the disadvantage that the hardening-inhibiting material must be completely separated from the recovered aggregates to avoid a delay in the hydration of the cement when the recycled aggregate is used to produce new cement.In addition, this process also generates waste because the powder fractions separated from the aggregates cannot be reused and must be disposed of. Finally, the residual cement must be allowed to stand for about a week before it is completely dry. Large areas must be available for the material to dry during this long period. These disadvantages also make this process relatively unattractive from an economic perspective.

[0010] Japanese Utility Model 3147832 describes a material for treating waste concrete that allows the recycling of excess concrete without requiring large areas or long periods for the concrete to cure. The material comprises a superabsorbent polymer in powder or granular form contained in a container formed by a water-soluble paper. When this material is added to a mixer containing the waste concrete, the water-soluble paper coating dissolves, allowing the superabsorbent polymer to come into contact with the concrete. After 5 to 10 minutes of mixing, the superabsorbent polymer absorbs some of the water in the waste concrete; a gel forms, enclosing the cement and other fine particles. The resulting product is a granular material that can be drained from the mixer.The time required for the granular material to harden is significantly shortened compared to JP 2004-276575. Furthermore, this process generates no significant waste because the cement particles and other fine particles are embedded in a gel network that encloses the aggregates. This allows the entire concrete material to be converted into a granular material and recycled, for example, as roadbed fill.

[0011] While the process described in JP 3147832 offers significant advantages over the previously described processes, it also has disadvantages. For example, although the superabsorbent polymer absorbs a significant portion of the free water immediately after addition, some of this water is released from the superabsorbent gel over time, so that the granular material can become wet and sticky again and is prone to re-agglomeration. Furthermore, if the material is not mixed in the mixer for an extended period, no granular material forms, and the concrete mass can form long, rigid blocks, the disposal of which leads to significantly increased costs. These disadvantages are particularly evident in self-compacting concrete because it contains additives made of fine minerals. This means that relatively large quantities of superabsorbent polymer are required to absorb the fine powders contained in the concrete.Another disadvantage is that this process cannot be effectively used with concrete that contains excess water to delay setting, as relatively large amounts of superabsorbent polymers are required. This leads to the formation of a relatively viscous and sticky gel, which can cause agglomeration of the concrete mix.

[0012] JP 2009-126761 describes the use of a flocculant in the form of a superabsorbent as an additive for residual concrete, which, however, has the same disadvantages that have already been explained for JP 3147832.

[0013] Finally, WO 2012 / 084716 A1 describes a process for producing granules from residual concrete, in which a quick-setting agent and a superabsorbent polymer are added to a cement composition, so that granules form as a result of the quick-setting agent's binding. WO 2012 / 084716 proposes, in particular, calcium aluminate hydrates with the general structure (CaO.Al 2 O 3 ) as quick-setting agents.

[0014] However, the process described in WO 2012 / 084716 also has the disadvantage that, after the granules have hardened, the individual granule particles can stick together as a result of setting with the flash setting agent. Therefore, they must be mechanically separated before further use. This is because aluminum salts are used as flash setting agents. Under the setting conditions, these salts can form ettringite, which leads to adhesion between the granules. Due to this partial sticking, dosing the granule aggregates is more difficult than with granules in which the individual granule particles do not stick together.

[0015] Against this background, there is a need for a process for recycling no longer required concrete that yields a granulate as the end product in which the individual granulate particles do not stick together and can thus be dosed relatively easily without requiring prior mechanical separation of the granulate particles. The present invention addresses this problem. Detailed description of the invention

[0016] The present invention accordingly relates to a method according to claim 1, wherein for producing aggregates from unset cement compositions, in particular from unset concrete or residual concrete, the addition a) a water-absorbing agent and b) a crystallization inactivator to an unset cement composition and mixing until a granular material is formed.

[0017] Surprisingly, it was discovered in this context that fresh concrete can be synergistically converted into a granular material by adding a water-absorbing agent and a crystallization inactivator, for example, in a concrete mixer truck or similar mixing device, thus avoiding the disadvantages of the prior art process. In particular, the special combination of the water-absorbing agent and the crystallization inactivator forms a granular material whose individual granule particles do not stick together after complete curing. This means that, for example, in contrast to WO 2012 / 084716, no mechanical separation of granule aggregates is required before further use of the granules.Furthermore, it was found that the addition of the water-absorbing agent and the crystallization inactivator does not significantly impair the mechanical properties of the resulting granular material compared to cement compositions cured without these additives, thus offering significant advantages over known concrete recycling products. The granular materials produced according to the process of the invention are thus characterized by particularly favorable properties and can be used in many applications, for example, in road construction or for the production of furniture, lightweight concrete, or decorative applications.

[0018] The water-absorbing agent according to the process according to the invention is in particular a water-absorbing agent in the form of a superabsorbent polymer or in the form of a layered silicate, with layered silicates in the form of vermiculite being particularly preferred.

[0019] The term "superabsorbent polymers" refers to polymers that can absorb large amounts of water. When superabsorbent polymers come into contact with water, the water molecules diffuse into the voids of the polymer network and hydrate the polymer chains. The polymer can swell and form a polymer gel or slowly dissolve. This step is reversible, so the superabsorbent polymers can be regenerated to their solid state by removing the water. The water absorption property is described by the swelling ratio, which is the ratio of the weight of a swollen superabsorbent polymer to its weight in the dried state.The swelling ratio is influenced by the degree of branching of the superabsorbent polymer, any crosslinking present, the chemical structure of the monomers that form the superabsorbent polymer network, and external factors such as pH, the ionic concentration of the solution, and temperature. Because of their ability to interact with water, superabsorbent polymers are also called hydrogels.

[0020] Examples of superabsorbent polymers usable in the present invention include, among others, natural polymers such as cellulose, chitosan or collagen, synthetic polymers such as poly(hydroxyethyl methacrylate), poly(ethylene glycol) or poly(ethylene oxide) or ionic synthetic polymers such as polyacrylic acid (PAA), polymethacrylic acid (PMAA), polyacrylamides (PAM) or polylactic acid (PLA).

[0021] Superabsorbent polymers made from ionic monomers typically absorb more water than those made from neutral monomers, due to the electrostatic repulsion between the individual polymer chains. The degree of crosslinking corresponds to the number of chemical bonds. The higher the degree of crosslinking and the higher the proportion of crosslinking agents, the shorter the distance between two crosslinking sites, which leads to a reduction in the degree of swelling. However, the degree of swelling also depends on external factors such as pH and temperature. Superabsorbent polymers formed from acidic monomers such as acrylic acid or methacrylic acid can be deprotonated at pH values ​​above 7, generating negative charges in the polymer chains. The associated electrostatic repulsion leads to a higher degree of swelling in alkaline media.Superabsorbent polymers which are particularly suitable in the context of the present invention are ionic superabsorbent polymers, in particular those based on polyacrylamide modified with acrylic acid, which may have either a linear or a cross-linked structure.

[0022] A second class of water-absorbing agents that can be used with particular advantage in the process according to the invention are phyllosilicates, particularly in the form of vermiculite. The term "vermiculite" refers to a phyllosilicate that exists in the monoclinic crystal system with the general chemical composition Mg 0.7 (Mg, Fe, Al) 6 (SiAl) 8 O 20 (OH) 4 · 8 H 2 O. Vermiculite develops leafy, scaly, or massive aggregates that are either colorless or colored gray-white, yellow-brown, gray-green, or green by impurities.

[0023] The amount of water-absorbing agent that leads to particularly favorable results in the process according to the invention depends essentially on the water absorption capacity of the material used. Superabsorbent polymers generally exhibit greater water absorption than layered silicates, so that a small amount of a superabsorbent polymer is sufficient to achieve an effect comparable to a certain amount of layered silicate. The superabsorbent polymer can expediently be added in the process according to the invention in an amount of 0.04 to 2 wt.%, preferably 0.08 to 1 wt.%, and most preferably 0.1 to 0.5 wt.%, based on the total weight of the cement composition. For layered silicates, however, amounts in the range of 2 to 30 wt.%, preferably in the range of 4 to 15 wt.%, and most preferably in the range of 6 to 10 wt.% are appropriate.

[0024] The studies underlying the present invention have shown that the addition of vermiculite powder or a superabsorbent polymer without the addition of a crystallization inactivator leads to unfavorable compactness of the resulting granules after complete curing of the materials. In contrast, significantly more favorable compactness was achieved when a crystallization inactivator was also added to the mixture.

[0025] Carboxylic acids with a molecular weight per acid group of <100 g / mol or α-hydroxycarboxylic acids have proven useful as crystallization inactivators in this context. Particularly suitable and thus particularly preferred α-hydroxycarboxylic acids in the context of the process of the present invention are, for example, lactic acid, citric acid, or malic acid. Particularly suitable carboxylic acids with a molecular weight per acid group of <100 g / mol are, for example, oxalic acid, formic acid, or acetic acid.

[0026] The amount of crystallization inactivator depends largely on the binder content of the cement composition. Amounts of 1 to 15 wt.%, preferably 2 to 10 wt.%, and most preferably approximately 3 to 8 wt.% of crystallization inactivator, based on the binder content in the cement composition, have proven particularly suitable. It has also been observed that hydroxycarboxylic acids require a slightly higher amount of crystallization inactivator, preferably in the range of 2 to 10 and in particular 3 to 8 wt.%. For carboxylic acids, and in particular dicarboxylic acids such as oxalic acid, however, a somewhat lower proportion is sufficient. Amounts in the range of 1 to 10 wt.% and in particular 2 to 7 wt.% have proven particularly suitable.

[0027] For the reasons explained above in connection with WO 2012 / 084716, no calcium aluminate hydrates, and particularly preferably no aluminum salts, are added in the process according to the invention in order to avoid the formation of ettingite.

[0028] When the aforementioned superabsorbent polymers or phyllosilicates are added to uncured cement, especially liquid cement, they remove water from the cement, with a large portion of the water contained in the cement composition being absorbed into the superabsorbent structure or phyllosilicate structure. This reaction leads to the drying of the residual concrete, even in the presence of excess water, and to a significant reduction in workability. The rotation of a concrete mixer truck or other mixing device forms a granular material.

[0029] The mixing time depends on the type of concrete and the dosage of the additives. Typically, about 5 to 10 minutes of mixing time are sufficient to convert fresh concrete into granules, but longer mixing times can also be used. Therefore, within the scope of the inventive method, it is possible to add the water-absorbing agent and the crystallization inactivator to a concrete mixer truck on the construction site and produce a granular material during the return journey to the concrete mixing plant. The granular material produced in the concrete mixer truck can then be emptied without any loss of time upon arrival at the concrete mixing plant, leading to a significant increase in productivity.

[0030] The granular materials according to the present invention can be stored in a relatively small space and fully cure in a short time. For example, granular materials left over at the end of a workday will cure sufficiently after approximately 12 to 24 hours to have sufficient mechanical strength to be transported to a storage area by an excavator.

[0031] It is possible to add the water-absorbing agent and the crystallization inactivator separately or as a mixture to the cement composition. However, within the scope of the present invention, it is preferred if, in a first step, a water-absorbing agent is added to the cement composition in a mixer, which is then mixed with the cement composition until granules are formed, and in a second step, a crystallization inactivator is added to the mixture of cement composition and water-absorbing agent. The crystallization inactivator is then expediently also mixed with the mixture of cement composition and the water-absorbing agent. The water-absorbing agent in the first step initially removes a significant proportion of the water from the concrete, transforming the concrete into sticky, earth-moist granules.To facilitate this process, the mixing drum of a concrete mixer truck can be rotated vigorously for several minutes to ensure a homogeneous distribution of the water-absorbing agent. The crystallization inactivator is then added and thoroughly mixed with the already formed granules of the cement composition and the water-absorbing agent.

[0032] It is possible to add additional components to the cement composition within the scope of the process according to the invention. For example, additives customary for cement compositions can be added, which are selected from the group comprising cement, cement setting accelerators, aluminate hydrate formation activators, retarders, waterproofing and water-repellent agents, weathering inhibitors, slags, natural pozzolans, microsilica, fly ash, quartz sand, calcium carbonate, pigments and colorants, clay, porous hollow glass spheres, plastics, and rubber materials.

[0033] Agents for accelerating the setting of cement include, for example, calcium and sodium nitrate, calcium and sodium chloride, triethanolamine, sodium thiocyanate, and calcium silicate hydrates. However, other known agents for accelerating the hydration of cement can also be used in the process according to the invention. Agents for activating the formation of aluminum hydrates include, for example, inorganic or organic soluble calcium compounds, such as calcium hydroxide, calcium nitrate, calcium acetate, calcium formate, and calcium thiocyanate. Examples of setting retarders are sodium and calcium gluconates, sucrose and other carbohydrates or carbohydrate derivatives, as well as citrates. Waterproofing and water-repellent agents include organosilicone compounds, such as silicones, silanes and siloxanes, colloidal and nano-silica, and calcium stearate; however, other substances with similar effects can also be used.The above-mentioned additives can be formulated with the water-absorbing agent or crystallization inactivator as a single product, or they can be added separately to the cement composition during mixing. Substances with a high amorphous silica content, such as microsilica, and other natural or synthetic pozzolans can be added to improve the durability of the granular material of the present invention.

[0034] To impart new properties to the granules obtained by the process according to the invention for other valuable applications, particularly in road construction and garden furniture construction, pigments or other colorants can be added with the water-absorbing agent and the crystallization inactivator. For example, pigments based on iron, manganese, zinc, or chromium oxides can be used to color the granules black, brown, red, or green. Other colors and effects can be created by adding organic pigments that include fluorescent dyes. These can be used in the form of powders, pastes, solutions, or dispersed forms. The resulting colored granules can be used after complete curing.By appropriately selecting the type and particle size distribution of the granules in the cement mix and white cement, granular materials with exceptional aesthetic value can be produced. These materials can be further polished and used as a substitute for natural stone in, for example, terrazzo flooring.

[0035] A further possibility within the scope of the present invention is the production of lightweight aggregates by adding fine plastic or rubber materials to the fresh cement mix. After the plastic or rubber materials have been incorporated into the concrete or concrete mixes, the addition of the additives according to the present invention results in granular materials that completely enclose the plastic and rubber particles. Such aggregates are characterized by their low density compared to natural aggregates and can be used particularly effectively for the production of lightweight concrete.

[0036] The production of granular materials according to the present invention and the properties of the resulting products as well as their use will be illustrated in more detail below with the aid of some examples. Example 1

[0037] A base mortar consisting of a mixture of 750 g Normo 4 [Siggenthal / Holcim AG], Vigier CEM I 42.5N [Vigier Ciment AG] and CEM I 42.5N [Wildegg / Jura cement] in a weight ratio of 1:1:1 with a Blaine fineness according to EN 197-1 of 3,600 cm 2 < / g, 141 g limestone powder, 738 g sand with a particle size in the range of 0 to 1 mm, 1107 g sand with a particle size in the range of 1 to 4 mm and 1154 g sand with a particle size in the range of 4 to 8 mm was produced in a Hobart mixer A200. For this purpose, the sand, limestone flour, and cement were mixed in a mixer for 1 minute. Then, the mixing water, in which the superplasticizer (0.4 or 0.5 wt.%, based on cement) was dissolved or dispersed, was added, and mixing continued. The total wet mixing time was approximately 3 minutes in each case. The resulting base mortar had a consistent slump of 195-200 mm, measured according to EN 1015-3.

[0038] This base mortar was mixed with a water-absorbing agent and mixed for 3 minutes in a Hobart mixer at mixing speed 2. A crystallization inactivator was then added and mixed for 3 minutes in the mixer at mixing speed 2. The compositions of the individual batches are shown in Table 1 below. Samples 1-12 are according to the present invention; samples V1-V3 are non-inventive comparisons. Table 1 sample mixture Dosage relative to binder Water / binder ratio Water including mixture Drying state trickling cleaning Compactness after 24 hours 1 VC-20HE 0,5 0,42 315 Good Good Good Very good SAP 0,12 Lactic acid (80%) 5,00 2 VC-20HE 0,50 0,42 315 Good Good Good Very good SAP 0,12 oxalic acid 4,00 3 VC-20HE 0,50 0,42 315 Good Good Good Very good Vermiculite powder 8,00 Lactic acid (80%) 5,00 4 VC-20HE 0,5 0,42 315 Good Good Good Very good Vermiculite powder 8,00 oxalic acid 4,00 5 VC-20HE 0,4 0,4 300 Good Good Good Very good Vermiculite powder 8,00 Lactic acid (80%) 5,00 6 VC-20HE 0,4 0,4 300 Good Good Good Very good Vermiculite powder 8,00 oxalic acid 3,00 7 VC-20HE 0,4 0,4 300 Good Good Good Very good Vermiculite powder 8,00 oxalic acid 4,00 8 VC-20HE 0,4 0,4 300 Good Good Good Very good Vermiculite powder 8,00 oxalic acid 5,00 9 VC-20HE 0,5 0,42 315 Good (rough) Good Good Good Vermiculite powder 8,00 citric acid 2,00 10 VC-20HE 0,50 0,42 315 Good (rough) Good Good Good Vermiculite powder 8,00 citric acid 3,00 11 VC-20HE 0,50 0,42 315 Good Good Good Good Vermiculite powder 8,00 citric acid 4,00 12 VC-20HE 0,5 0,42 315 Good Good Good Good Vermiculite powder 8,00 Malic acid 4,00 V1 VC-20HE 0,4 0,4 300 Good Good Good Bad Vermiculite powder 8,00 V2 VC-20HE 0,5 0,4 300 Good Good Good Good SAP 0,12 Al 2 (SO 4 ) 3 × 14H 2 O 1,44 V3 VC-20HE 0,4 0,4 300 Good Good (rough) Good medium Vermiculite powder 8,00 Al 2 (SO 4 ) 3 × 14H 2 O 1,44

[0039] The resulting granules were visually inspected for flow and dryness, and the residues in the mixing vessel were assessed. The mortar granules were then emptied into a pile and allowed to dry for 24 hours. The cured mortar was then assessed for compactness (compactness after 24 hours). The following applies to the evaluation: Dryness: Granules that cannot be compacted and are only slightly damp receive a "good" rating.

[0040] Flowability: No large lumps or sticking together results in a rating of "good".

[0041] Cleaning: The mixing container empties completely without leaving any mortar residue, cement paste, etc.

[0042] Compactness after 24 hours: The mortar pile was assessed for its adhesion among the particles. A compact mass that required force to be applied for subsequent granulation was rated "poor." If the dried mortar pile trickled on its own, the compactness was rated "very good." A "good" rating was given if the mass was still compact but could be made to trickle with minimal force.

[0043] It was found that samples 1 to 8 according to the invention, compared to sample V2 produced according to WO 2012 / 084716, delivered comparable results in terms of dryness, flow, and cleaning. However, compactness was improved in all cases compared to sample V2. Composition V1, which was mixed only with vermiculite, exhibited very poor compactness, which could not be significantly improved even by the addition of aluminum sulfate (sample V3). Samples 9 to 12 also exhibited similar compactness to comparative sample V2, despite not being optimized. Example 2

[0044] To enable reuse of the recovered concrete granulate, it must exhibit certain structural properties, which were investigated below. Sample 1 represents concrete without recycled material, while samples 2, 3, and 4 consisted of approximately 50% granulate material with an addition of 8% vermitculite powder and lactic acid (5%), oxalic acid (4%), and oxalic acid (3%), respectively. These tests showed only a slight change in the curing time of the respective compositions. Furthermore, the concrete granulates resulted in only a slight deterioration in the compressive strength achievable after one day of curing. The results of these tests are presented in Table 2 below. Table 2 sample mixture Dosage relative to binder [%] Water / binder ratio Air content [%] Compressive strength [MPa] 1 day absolutely Δ 1 100% Mix 0,4 0,4 2,8 34,3 2 50% granules with 5% lactic acid 0,4 0,54 3,3 26,7 -22% 3 50% granules with 4% oxalic acid 0,4 0,54 3,8 25,2 -27% 4 50% granules with 3% oxalic acid 0,4 0,4 4,0 26,8 -22%

Claims

1. Method for producing aggregates from fresh cement compositions, particularly in the form of concrete and residual concrete, comprising the addition of a) a water-absorbing agent and b) a crystallization deactivator to a non-set cement composition and mixing until a granular material has formed, characterized in that a carboxylic acid having a molar mass < 100 g / mol per acid group or an α-hydroxycarboxylic acid is used as the crystallization deactivator, with the proviso that no calcium aluminate hydrates are added in the method of the invention.

2. Method according to Claim 1, characterized in that the hydroxycarboxylic acid is present in the form of lactic acid, citric acid or malic acid, and the carboxylic acid having a molar mass < 100 g / mol per acid group is present in the form of oxalic acid, formic acid, or acetic acid.

3. Method according to either of Claims 1 and 2, characterized in that 1 to 15% by weight, preferably 2 to 10% by weight and most preferably 3 to 8% by weight crystallization deactivator relative to the binder content in the cement composition is added.

4. Method according to any of Claims 1 to 3, characterized in that a superabsorbent polymer or a sheet silicate, particularly in the form of vermiculite, is used as the water-absorbing agent.

5. Method according to Claim 4, characterized in that a superabsorbent polymer is added in a quantity from 0.04 to 2% by weight, preferably 0.08 to 1.0% by weight and most preferably 0.1 to 0.5% by weight.

6. Method according to Claim 4, characterized in that a sheet silicate is added in a quantity from 2 to 20% by weight, preferably 4 to 15% by weight and most preferably 6 to 10% by weight.

7. Method according to any of the preceding claims, characterized in that one or more additives selected from the group comprising cement, cement setting accelerators, agents promoting the formation of aluminate hydrates, retarders, water insulating and water repelling agents, weathering inhibitors, slags, natural pozzolans, microsilica, fly ash, quartz sand, calcium carbonate, pigments and colourants, clay, porous hollow glass beads, plastic and rubber materials is / are added to the cement composition.

8. Method according to any of the preceding claims, characterized in that in a first step a water-absorbing agent is added to the cement composition in a mixer and is then mixed together with the cement composition until a granulate has formed, and in a second step a crystallization deactivator is added to the mixture of cement composition and water-absorbing agent.

9. Method according to Claim 8, characterized in that the cement composition is emptied out of the mixer after the water-absorbing agent and the crystallization deactivator have been mixed in, and is dried until the cement has completely set.