Method for treating unhardened cementitious compositions, admixtures used in such methods and uses of solid granules produced by such methods - Patents.com

Abstract

The present invention relates to a method for treating unhardened cement compositions, particularly returned concrete, and to an admixture suitable for use in such a method. The admixture of the present invention comprises modified starch and sugar. The present invention also relates to solid granules obtained by such a method and to ready-mix concrete or mortar utilizing the solid granules thus obtained.

Description

[Technical field]

[0001] The present invention relates to a method for treating unhardened cement compositions, particularly returned concrete. The unhardened cement composition is set and dried to form solid granules in the method of the present invention, thereby resulting in a granular reusable material. The present invention may be used in particular to treat unhardened residual concrete or mortar that may be left behind after a work order has been completed or that is off-spec. The present invention also relates to the use of the admixtures used in such a method and the solid granules produced by such a method. [Background technology]

[0002] It is estimated that 1% of any concrete produced cannot be used as originally intended. For example, the amount delivered may exceed the amount demanded or the quality of the concrete produced does not meet the specifications. The result is that the concrete produced cannot be used in its intended application. Such concrete is usually returned to the concrete plant, where it can be subjected to further use or reprocessed in various ways. For example, standard elements can be produced or the concrete can be spread and re-ground after hardening and then used again. It is also possible to wash the concrete with water, in the process non-reactive components such as sand are separated from the cement paste. These components can then be reused to produce ready-mix concrete.

[0003] However, the production of standard concrete elements, e.g. the need for such elements, does not always exist: re-grinding of hardened concrete requires a large amount of energy and at the same time generates a considerable amount of dust and noise, which makes the processing of returned concrete rather unattractive.

[0004] It has also been proposed to solidify the returned concrete to form solid granules. To this end, admixtures are added to the returned concrete while it is still wet. These admixtures convert the wet concrete into hard granules that can be reused, for example, as aggregates for ready-mix concrete. Suitable admixtures are added directly to the mixer truck containing the returned concrete. Typical admixtures absorb free water from the returned concrete and expand, thereby forming agglomerates incorporating the cement and finer fractions of the mixture. Upon rotation of the mixer truck drum, these agglomerates cover the coarser aggregates, forming a layer of variable thickness. The result is that the returned concrete solidifies and is transformed into a multitude of granules of various sizes, each formed by aggregates constituting a central core and an outer coating formed by the agglomerates. The freshly solidified material is compact enough to be accumulated and stored to complete the cement hydration and hardening reactions. Upon hardening, the granular material produced from the returned concrete can be reused, for example, as recycled aggregates for producing ready-mix concrete, partially or totally replacing the fresh aggregates of the roadbed material.

[0005] For example, WO 2012 / 084716 describes a method for producing granules from recycled concrete, which involves adding a flash set promoter and a superabsorbent polymer to a wet cement composition. However, this method often suffers from the stickiness of the resulting granules.

[0006] WO 2016 / 071298 describes a method for producing granules from return concrete, which comprises adding a water absorbent and a crystallization deactivator to a wet cement composition and mixing until a granular material is formed. Water absorbents include superabsorbent polymers and phyllosilicates, particularly vermiculite, which may be natural or synthetic. Crystallization deactivators cited include lactic acid, citric acid and malic acid.

[0007] US 2018 / 0162774 A1 relates to a method for producing aggregate from a changeable cementitious mixture. It discloses pelletizing agents selected from the group consisting of cellulose, chitosan, collagen, polyacrylamide and copolymers of polyacrylamide and polyacrylic compounds, polyamines, polyvinyl alcohol, polysaccharides, lactic acid, methacrylic acid, methacrylate, hydroxyethyl, ethylene glycol, ethylene oxide, and acrylic acid, inorganic flocculants, and inorganic coagulants. Unfortunately, US 2018 / 0162774 A1 does not go into detail about optimizing the pelletizing agent.

[0008] US2020 / 0094263 also relates to a method for producing aggregate from returned concrete. It is proposed to add organic or inorganic flocculants to the returned concrete, where the organic flocculants can consist of anionic and cationic polyelectrolytes or high molecular weight polysaccharides such as cellulose and its derivatives and starch and its derivatives. Also, US2020 / 0094263 does not go into detail regarding the optimization of the flocculants.

[0009] Thus, there remains a need for optimal methods of treating unset cementitious compositions, particularly returned concrete, as well as admixtures that can be used in such methods. Summary of the Invention [Problem to be solved by the invention]

[0010] It is a first object of the present invention to provide a method for treating unhardened cement compositions, particularly returned concrete. It is another object of the present invention to provide an admixture suitable for use in the method for treating unhardened cement compositions, particularly returned concrete. In particular, such a method and admixture should be useful for many different types of returned concrete, particularly the many different types of Portland cement used to make such returned concrete. [Means for solving the problem]

[0011] These and other objects have surprisingly been solved in a particularly efficient manner by a mixture comprising modified starch and a sugar and a method using such a mixture, which are the subject matter of the independent claims.

[0012] The advantages of the admixture of the invention are in particular (i) it efficiently dries unhardened cementitious compositions, particularly returned concrete; (ii) it leads to low strength solid granules which can be easily handled with particularly low EHS risks and lower energy consumption; (iii) maintain its performance even when oversupplied; (iv) It does not leave any residue of treated concrete in the mixing vessel. It is.

[0013] Further aspects of the invention are the subject matter of further independent claims. Preferred embodiments of the invention are the subject matter of the dependent claims.

[0014] In a first aspect, the present invention provides a method for treating an unhardened cementitious composition, in particular returned concrete, comprising the steps of: a) providing an unhardened cementitious composition, in particular return concrete; b) providing an admixture comprising modified starch and sugar; c) mixing the unset cement composition and the admixture to form a set material; d) Discharging the solidified material obtained under c) into a storage facility; e) drying the solidified material to form solid granules; f) optionally separating the dried solid granules into different particle size fractions; The present invention relates to a method comprising the steps of:

[0015] The solid granules produced by the process of the invention can be used, for example, as recycled aggregate, since such solid granules are based on previously used materials, which can be recovered by the process of the invention and made available for reuse as aggregate.

[0016] In this context, returned concrete is intended to refer to unhardened cementitious compositions that are not used as intended and therefore must be recycled.

[0017] Unhardened cement compositions, in particular returned concrete, in this context are slurries of cement, aggregates and optionally additives and / or admixtures in water. In particular returned concrete is concrete or mortar that has been mixed with water but has not set or hardened. Returned concrete is therefore in a wet state. The amounts of any of the cement, aggregates, additives, admixtures and water in the returned concrete may vary within the ratios typically encountered in concrete and mortar. There may be mixtures of different cements, for example Portland cement and aluminate cement, and / or aggregates of different chemical nature and / or particle size. Unhardened cement compositions, in particular returned concrete, may in particular be excess or off-spec material. Unhardened cement compositions, in particular returned concrete, may also be material that needs to be transported from the production site to a recycling site, for example because it is off-spec, but is recycled at the site of production.

[0018] The method of the present invention is effective for any type of unhardened cementitious mixture, such as returned concrete or mortar or any type of concrete or mortar that cannot be used for any reason but is still flowable and has not yet fully hardened. Examples of concrete that cannot be hardened and therefore cannot be used in the present invention are excess concrete that was not used on the site, mortar or concrete that has a wrong mix design and therefore is not used, or concrete or mortar that has lost their properties due to poor mix design.

[0019] According to embodiments, the return concrete has a slump class of S1, S2, S3, S4 or S5 or a flow class of F1, F2, F3, F4, F5 or F6 according to tables 3 and 6 of standard EN 206-1:2000.

[0020] It is particularly preferred that the return concrete of the invention comprises Portland cement, aggregate and water in a water to cement weight ratio of 0.2 to 0.9. The Portland cement is of type I to type V as described in standard ASTM 150-00 or of type CEM I according to standard EN 197-1. Of course, Portland cement according to other national standards such as Japanese, Chinese or Indian standards are also encompassed.

[0021] The admixture provided in step b) comprises modified starch and sugar. The admixture may comprise additional materials, in particular water, fillers, biocides, pigments, cement accelerators, cement retarders, plasticizers, flow regulators, rheology modifiers or mixtures thereof. Suitable fillers are preferably calcium carbonate or magnesium carbonate based fillers. Suitable cement accelerators are preferably alkanolamines, aluminum sulfates, aluminum hydroxides, silicates and alkali or alkaline earth metal hydroxides, hydrogen carbonates, sulfates, nitrates, nitrites or thiosulfates. Suitable cement retarders are preferably hydroxycarboxylic acids or borates.

[0022] However, it is preferred that the admixture provided in step b) of the process of the present invention consists essentially of modified starch and sugar.

[0023] According to an embodiment, the admixture provided in step b) of the method of the invention consists essentially of 70-80% by weight of modified starch and 20-30% by weight of sugar.

[0024] In this context, modified starch is a material derived from natural or synthetic starch, preferably natural starch. The natural starch is not particularly limited and can be, for example, potato starch, corn starch, pea starch, rice starch or wheat starch. Modified starch is prepared by treating natural starch physically, enzymatically or chemically to change its properties. Modified starches useful for the present invention include dextrin, alkaline modified starch, bleached starch, oxidized starch, enzyme treated starch, starch phosphate, acetylated starch, starch ethers such as hydroxypropylated starch or hydroxyethyl starch, carboxymethylated starch and copolymers of starch and organic monomers. The term modified starch does not include natural starch and also does not include biopolymers different from modified starch. In particular, the term modified starch does not include cellulose or modified cellulose.

[0025] A highly preferred modification of starch is to graft the starch with organic monomers. Suitable organic monomers are ethylenically unsaturated monomers, such as styrene, butadiene, (meth)acrylic acid, esters of (meth)acrylic acid, (meth)acrylamide, acrylonitrile, vinyl chloride, vinyl acetate or esters of vinyl alcohol, such as vinyl versatate. Preferably, such modified starches are prepared by grafting from native starch and using ethylenically unsaturated monomers. Grafting can be initiated, for example, by the generation of radicals on the starch by irradiation or the effect of a suitable radical initiator (the "grafting from" method). Grafting can also be achieved by ring-opening polymerization (the "grafting from" method), polycondensation (the "grafting from" method) or esterification (the "grafting to" method) and using different monomers or polymers as grafting agents. A suitable process is described in the article "Modification of starch by graft copolymerization" by J. Meimoun et al. (Wiley-VCH, Starch / Staerke, Vol 70, 2018). The modified starch obtained by such a process may contain starch granules covered with a layer of graft copolymer or may contain crosslinked network structures or aggregates. The grafting rate and the degree of crosslinking can be adjusted by careful control of the polymerization reaction.

[0026] According to a highly preferred embodiment of the invention, the modified starch is a copolymer of starch grafted with acrylic acid and acrylamide. In this connection, it is preferred that the modified starch is a crosslinked network of starch grafted with ethylenically unsaturated monomers, in particular acrylic acid and acrylamide.

[0027] The copolymers of starch grafted with acidic functional groups, in particular the copolymers of starch grafted with acrylic acid and acrylamide, can be partially or completely neutralized with alkali metal or alkaline earth metal bases, in particular with sodium hydroxide, potassium hydroxide or calcium hydroxide.

[0028] In this context, sugars are carbohydrates with at least 6 C atoms. Suitable sugars are hexoses, especially of the aldose or ketose type. Suitable sugars are allose, altrose, glucose, mannose, gulose, idose, galactose, talose and fructose. Other suitable sugars are dimers of hexoses, especially dimers of allose, altrose, glucose, mannose, gulose, idose, galactose, talose and fructose. Suitable dimers of hexoses are especially cellobiose, isomaltose, isomaltulose, lactose, lactulose, maltose, maltulose, merobiose and sucrose.

[0029] According to a particularly preferred embodiment of the invention, the sugar is sucrose, however, any of the sugars as listed above would suffice.

[0030] The unhardened cement composition, especially the return concrete, in step a) of the method of the present invention is most typically provided in a concrete mixer truck. However, it can also be provided in any other equipment suitable for mixing concrete. Mixing equipment includes, but is not limited to, the rotating drum of a conventional concrete truck, a paddle mixer, a disk pelletizer, a drum pelletizer, a pin mixer agglomerator, a ribbon blender, a planetary mixer, a Hobart mixer, a portable concrete mixer, a mixing bucket, a jet mixer, a screw mixer, an auger mixer, a horizontal single shaft mixer, a vertical shaft mixer, a ribbon blender and an orbital mixer. Mixing equipment suitable for intensive mixing is preferred.

[0031] The admixture in step b) of the method of the invention can be provided as a one-component admixture or as a multi-component, in particular two-component, admixture. A one-component admixture contains all the ingredients of the admixture in one container. A multi-component admixture contains the ingredients of the admixture in multiple, preferably two, spatially separated containers. It is therefore possible to provide all the ingredients of the admixture simultaneously in step b) of the method of the invention. This means that all the ingredients of the admixture are added to the unhardened cement composition, in particular the returned concrete, at the same time. This is typically preferred. However, it is also possible to first add the modified starch to the unhardened cement composition, in particular the returned concrete, and then add the sugar at a later point in time.

[0032] The admixture of the present invention is preferably used in an amount of 0.5 to 5 kg / m of unhardened cement composition, particularly of returned concrete. 3 , preferably 1 to 3.5 kg / m 3 The admixture may be provided in the range of 0.5 to 100% by weight of water to cement. For example, a more fluid returned concrete would require a larger amount of admixture. The admixture of the present invention has also been found to be effective when the unhardened cement composition, particularly the returned concrete, contains a large amount of water. A large amount of water is water with a water to cement weight ratio of greater than 0.6, and may be as high as 0.8 or 0.9.

[0033] In step c) of the method of the invention, the mixing of the unhardened cement composition, in particular the return concrete and the admixture as described above, can be carried out in any of the mixing devices described above or in any other mixing device suitable for intensive mixing.

[0034] According to a particularly preferred embodiment of the present invention, the mixing in step c) is carried out in the rotating drum of a conventional concrete car. For example, it is possible to add the admixture of the present invention to the concrete at the building site, back into the rotating drum of a conventional concrete car. Then, mixing can be carried out while driving the concrete car back to the plant, and the returned concrete has solidified on arrival at the plant. Similarly, it is possible to add the admixture of the present invention to the concrete at the plant, for example at a concrete weighing facility, back into the rotating drum of a conventional concrete car. The returned concrete can also be discharged from the concrete car at the plant, for example at a concrete weighing facility, into a mixing device, in particular as described above.

[0035] The mixing time required in step c) of the method of the invention depends on the type of unhardened cementitious composition, in particular the return concrete, and on the measured amounts of admixtures.

[0036] Mixing times may range from 20 seconds to 15 minutes, preferably 1 minute to 10 minutes, and most preferably 2 minutes to 5 minutes. Shorter times will not completely set the unhardened cement composition, especially the returned concrete, while longer times are inefficient and cause the mixture to re-agglomerate.

[0037] When mixing return concrete with the admixture of the present invention in the rotating drum of a concrete truck, the drum should be rotated at maximum speed for the duration of the mix.

[0038] During step c) of the method of the present invention, the unhardened cement composition, in particular the returned concrete, forms a solidified material. Step c) can be completed when all the unhardened cement composition, in particular the returned concrete, has solidified.

[0039] The resulting solidified material may then be discharged from the mixer, in particular the rotating drum of a concrete mixer truck, into a storage facility, which may be the ground, where the solidified material is discharged to form a pile or layer of material.

[0040] The solidified material or solid granules can be stored as other common aggregates for concrete.

[0041] The solidified material is then dried in step e) of the method of the invention to form solid granules. The required drying time depends on the conditions. In particular, the duration of the drying step must be adjusted according to the temperature at which the solidified material is being dried. Typical drying times are between 5 hours and 24 hours. The solidified material can be dried at atmospheric pressure and at temperatures between -10°C and +100°C. The solidified material can be air-dried or dried using an oven at any humidity and at temperatures not exceeding 100°C. Atmospheric pressure and temperatures between +5°C and +45°C are highly preferred.

[0042] The solidified material or solid granules can be subjected to precipitation as long as they remain dry thereafter. The solidified material can also be sprayed or sprinkled with water to avoid sudden moisture loss and cracking.

[0043] After the drying step e) of the method of the invention, the solid granules have acquired sufficient mechanical strength to enable them to be transported by construction vehicles to a storage area.

[0044] The solid granules of the present invention can be easily broken down, for example by a front loader or a crusher.

[0045] The process of the invention may optionally comprise a step of separating said dried solid granules into fractions of different particle sizes.

[0046] According to an embodiment, the fractions of different particle sizes are 0.063-4 mm, 4-8 mm and 6-16 mm. Other fractions of different particle sizes are 0.063-4 mm, 4-16 mm and 16-32 mm. Further fractions of different particle sizes are 0-2 mm, 2-8 mm, 8-16 mm or 8-32 mm. Further fractions of different particle sizes are 0-4 mm, 4-8 mm, 8-16 mm and 16-32 mm. Further fractions of different particle sizes are 0.063-0.125 mm, 0.125-0.25 mm and 0.25-0.355 mm. Further fractions of different particle sizes are 0.08-0.16 mm, 0.16-0.50 mm, 0.50-1.0 mm, 1.0-1.60 mm and 1.60-2.0 mm. Further fractions of different particle sizes are 63-300 μm, 100-600 μm, 500-1200 μm, 900-1500 μm.

[0047] According to an embodiment, separation is performed by filtration, sieving, sedimentation, density separation, centrifugation and / or air sieving, for example in a cyclone.

[0048] Separation can be performed by sieving, for example using common industrial vibratory, rotary or cyclone sieves. Such separation can separate the solid granules based on a preselected particle size. The separator can be made of plastic or metal with variable geometry and hole size. The quality of the separated material is further improved if an air flow countercurrent to the flow of the solid granules in the sieve is passed throughout the sieving process. The air action is designed to further dry the surface of the solid granules. The air flow can be provided by a ventilation system that can also heat the air to facilitate drying of the material in winter and in cold climates.

[0049] According to an embodiment, at the outlet of the size separation system, the fractions of different particle sizes produced are sent directly to a storage tank. The surface of the material produced by the method according to the invention, which is typically larger than 5 mm, is dry and can be stored directly together with natural aggregates with the same particle size characteristics. The fine fraction, smaller than 5 mm, is sufficiently cohesive to be sent directly to a sand storage tank, where it is dispersed in the mass of already stored material. To improve handling in the fresh state before storage, the freshly produced fine fraction can optionally be mixed with a sufficient amount of dry sand or previously produced already hardened fine material.

[0050] The method of treating unhardened cementitious compositions, especially returned concrete, according to the invention can be carried out either discontinuously or continuously. Discontinuous processes are particularly suitable for treating small amounts of unhardened cementitious compositions, especially returned concrete. For larger amounts, continuous processes are more advantageous.

[0051] According to an embodiment, the method of the present invention may further comprise the step of crushing and / or comminuteing the solid granules.

[0052] Suitable crushers are, for example, jaw crushers. Examples of suitable mills for comminuting are vertical roller mills, horizontal roller mills, ball mills or stirred mills.

[0053] According to a further embodiment, the crushing and / or pulverization is carried out under an atmosphere of CO2.

[0054] Crushing and / or comminution of solid granules under an atmosphere of CO2 will lead to carbonation of the cementitious material contained therein.

[0055] In particular, "carbonation" as used herein refers to the incorporation of carbon dioxide into a compound or the chemical reaction of carbon dioxide with a parent material. Thus, "carbonation" refers, in particular, to the reaction of a starting material with carbon dioxide. For example, Portland cement, which consists essentially of calcium, silicate, and aluminum hydrates, can react with carbon dioxide to form the corresponding carbonates.

[0056] Progressive carbonation can be measured by a decrease in pH value.

[0057] Carbonation of the solid granular material allows the binding of CO2 from the environment, thus improving the environmental footprint of the solid granules. Furthermore, it has been found that aggregates can be recovered from the solid granular material during grinding in a particularly clean state, thus resembling fresh virgin aggregates, if the grinding is carried out under an atmosphere of CO2. This is because the carbonated material binder is easier to remove from the surface of the aggregate.

[0058] It is possible to carbonate the solid granules before and / or during the grinding step. However, it is preferred that the carbonation takes place during the grinding step. This is because the carbonated material is more easily removed from the aggregate during grinding, thereby freeing fresh, uncarbonated surfaces which in turn are more easily carbonated and removed. Cleaning of the aggregate is therefore achieved very efficiently.

[0059] In another aspect, the present invention also relates to solid granules obtained by the process as described above. In this context, the term solid granules refers to dry granular material, which is optionally crushed and / or comminuted as described above. In other words, in this context, the term solid granules refers to solid granules obtained in step e) or step f), if present, or after additional crushing and comminution of dry solid granules, if present. As explained above, the solid granules obtained by the process of the present invention can be used, for example, as recycled aggregate.

[0060] Any of the embodiments and / or preferred features as described above also relate to this aspect.

[0061] The solid granules obtained by the method of the present invention can be used to prepare ready-mix concrete or mortar. It is possible to replace fresh aggregate, which is aggregate that has never been used before, with the solid granules of the present invention. The solid granules obtained by the method as described above can constitute at least 30% by weight, preferably at least 50% by weight, more preferably at least 75% by weight, even more preferably at least 90% by weight, especially at least 99% by weight of the total weight of aggregate in the concrete or mortar mix.

[0062] The present invention therefore also relates to a concrete or mortar mixture comprising at least one cement and an aggregate, wherein at least 30% by weight, preferably at least 50% by weight, more preferably at least 75% by weight, even more preferably at least 90% by weight, in particular at least 99% by weight, of the total weight of the aggregate is solid granules obtained by the process according to the invention.

[0063] In yet another aspect, the present invention provides an admixture for use in a method for treating an unhardened cementitious composition, particularly returned concrete, comprising: a) modified starch, and b) sugar The present invention also relates to a mixture comprising:

[0064] Any of the embodiments and / or preferred features as described above also relate to this aspect.

[0065] In particular, the admixture of the present invention consists essentially of modified starch and sugar, preferably consisting essentially of 70-80% by weight of modified starch and 20-30% by weight of sugar.

[0066] In this context, modified starch is a material derived from natural or synthetic starch, preferably from natural starch. The natural starch is not particularly limited and can be, for example, potato starch, corn starch, pea starch, rice starch or wheat starch. Modified starch is prepared by treating natural starch physically, enzymatically or chemically to change its properties. Modified starches useful for the present invention include dextrin, alkaline modified starch, bleached starch, oxidized starch, enzyme treated starch, starch phosphate, acetylated starch, starch ethers such as hydroxypropylated starch or hydroxyethyl starch, carboxymethylated starch and copolymers of starch and organic monomers. The term modified starch does not include natural starch and also does not include biopolymers different from modified starch. In particular, the term modified starch does not include cellulose or modified cellulose.

[0067] A highly preferred modification of starch is to graft the starch with organic monomers. Suitable organic monomers are ethylenically unsaturated monomers, such as styrene, butadiene, (meth)acrylic acid, esters of (meth)acrylic acid, (meth)acrylamide, acrylonitrile, vinyl chloride, vinyl acetate or esters of vinyl alcohol, such as vinyl versatate. Preferably, such modified starches are prepared by grafting from native starch and with an ethylenically unsaturated monomer. Grafting can be initiated, for example, by the generation of radicals on the starch by irradiation or the effect of a suitable radical initiator (the "grafting from" method). Grafting can also be achieved by ring-opening polymerization (the "grafting from" method), polycondensation (the "grafting from" method) or esterification (the "grafting to" method) and by using different monomers or polymers as grafting agents. A suitable process is described in the article "Modification of starch by graft copolymerization" by J. Meimoun et al. (Wiley-VCH, Starch / Staerke, Vol 70, 2018). The modified starch obtained by such a process may contain starch granules covered with a layer of graft copolymer or may contain crosslinked network structures or aggregates. The grafting rate and the degree of crosslinking can be adjusted by careful control of the polymerization reaction.

[0068] According to a highly preferred embodiment of the invention, the modified starch is a copolymer of starch grafted with acrylic acid and acrylamide. In this connection, it is preferred that the modified starch is a crosslinked network of starch grafted with ethylenically unsaturated monomers, in particular acrylic acid and acrylamide.

[0069] The copolymers of starch grafted with acidic functional groups, in particular the copolymers of starch grafted with acrylic acid and acrylamide, can be partially or completely neutralized with alkali metal or alkaline earth metal bases, in particular with sodium hydroxide, potassium hydroxide or calcium hydroxide.

[0070] In this context, sugars are carbohydrates with at least 6 C atoms. Suitable sugars are hexoses, especially of the aldose or ketose type. Suitable sugars are allose, altrose, glucose, mannose, gulose, idose, galactose, talose and fructose. Other suitable sugars are dimers of hexoses, especially dimers of allose, altrose, glucose, mannose, gulose, idose, galactose, talose and fructose. Suitable dimers of hexoses are especially cellobiose, isomaltose, isomaltulose, lactose, lactulose, maltose, maltulose, merobiose and sucrose.

[0071] According to a particularly preferred embodiment of the invention, the sugar is sucrose.

[0072] The admixture of the present invention can be provided as a one-component admixture or as a multi-component, especially two-component, admixture. A one-component admixture contains all the ingredients of the admixture in one container. A suitable container can be a water-soluble bag, for example a bag made of polyvinyl alcohol. This has the advantage that no packaging has to be removed. The admixture can be added to the unhardened cement composition, especially the return concrete, while still packaged and together with the packaging. A multi-component admixture contains the ingredients of the admixture in multiple, preferably two, spatially separated containers. A one-component admixture has the advantage that all the ingredients are premixed in the correct amount and that no dosage errors can occur. A multi-component, especially two-component composition has the advantage that the ratio of the individual components can be easily adjusted as a response to specific requirements.

[0073] The admixture of the invention has been found to be particularly effective with cements of various compositions. In particular, the admixture of the invention is effective with Portland cements having a high content of C3A (tricalcium aluminate, 3CaO·Al2O3). In this context, a high content of C3A is a content of 4% by weight or more, preferably 7% by weight or more, in particular 11% by weight or more, relative to the total dry weight of the cement. The upper limit may be 20% by weight. C3A could therefore be contained in the cement in an amount between 4 and 20% by weight, preferably between 7 and 20% by weight, in particular 11 and 20% by weight, relative to the total dry weight of the cement. Admixtures not according to the invention are less effective when such amounts of C3A are present. [Brief description of the drawings]

[0074] [Figure 1] Figure 1 shows solid granules obtained by the method as described for Examples 1-2. This type of granule can be easily crushed as described in Example 1. The results of crushing are shown on the left in Figure 1. The results as shown in Figure 1 are rated with "1" for the "compactness" of the granules and "1" for the "friability" of the granules. [Diagram 2] Solid granules obtained by the method as described for Examples 2-3 are shown. Granules of this type can be crushed as described for Example 1. The results of crushing are shown on the left in Figure 2. The results as shown in Figure 2 are rated with a "2" for the "compactness" of the granules and a "2" for the "friability" of the granules. [Diagram 3] Figure 3 shows solid granules obtained by the method as described for Examples 3 to 7. This type of granules can hardly be crushed as described in Example 1. The results of crushing are shown on the left in Figure 3. The results as shown in Figure 3 are rated with "3" for the "compactness" of the granules and "3" for the "friability" of the granules. [Figure 4]Solid granules obtained by the method as described for Examples 2-4 are shown. This type of granule cannot be crushed as described for Example 1. The results of crushing are shown on the left in Figure 4. The results as shown in Figure 4 are graded with "c" for the "compactness" of the granules and "not determined" for the "friability" of the granules. [Diagram 5] 1 shows a pile of solid granules discharged into a storage facility. The solid granules were prepared as described in Table 7, Example F1 (Capitol). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0075] The following examples provide further embodiments of the present invention to one of ordinary skill in the art and are not intended to limit the scope of the present invention. EXAMPLES

[0076] The following raw materials were used: Mod starch: modified starch; starch grafted with potassium acrylate and acrylamide (CAS 119131-19-0). Starch: Potato starch, unmodified Cellulose: Carboxymethyl cellulose (Mw 50,000g / mol) Sucrose: Sigma Aldrich; 99.5% ultrapure Glucose: D(+)-glucose; Sigma-Aldrich; 99% ultrapure Gluconate: Sodium D-gluconate; Sigma-Aldrich; 99% ultra pure Citric acid: Sigma Aldrich; 99.5% ultrapure Rice Husk: Pillowganic; Horticulture Garden

[0077] The following admixtures F1-F31 were prepared by mixing the ingredients in Table 1 below until a visually homogenous powder was obtained.

[0078] [Table 1]

[0079] [Table 2]

[0080] Portland cement type I (ASTM 150-00) of the following composition was used:

[0081] [Table 3]

[0082] Example 1: A mortar was prepared by mixing 441.6 g of Portland cement type I (type as shown in Table 3), 358.8 g of concrete sand and 1084.8 g of sand #3 in a Hobart mixer for 1 minute. Then, 1.73 mL of polycarboxylate-based superplasticizer (Sikament 686 supplied by Sika Corp) and water were added to give a water to cement weight ratio of 0.5. Mixing in the Hobart mixer was then continued for 3 minutes at speed #1. The mortar was then mixed manually with a spatula for 30 seconds. Then, the respective admixture types and amounts as shown in Table 3 below were added. Mixing was then continued for another 2 minutes at speed #1. The formation of granules was clearly visible.

[0083] The slump was measured on the mortar mix before the addition of the admixtures according to standard ASTM C143 / C143M using a mini-cone. Thus, the mini-cone was placed on a non-absorbent base plate and then buried in two layers of equal volume of mortar. Each layer was leveled 25 times with a steel rod and then the top was cut off. The mini-cone was slowly lifted in 3-4 seconds and the slump was measured. The slump is an indicator for the similar mix quality of the prepared mortar. The compactness and friability of the granules were graded according to a visual grading scheme (see Figures 1-4). The compactness was judged immediately after the formation of solid granules at the end of mixing. For the friability judgment, the formed block of granules was intended to be dried for 24 h at 20-23 °C / 10% rh and then crushed with one blow using a hammer. A rating of 1 is very good, a rating of 2 is good and a rating of 3 is poor. A rating of "c" means that the sample hardened and no granules formed.

[0084] [Table 4]

[0085] [Table 5]

[0086] Low compaction and friability ratings are desirable. Hence, it is clear from Table 3 that admixture A6 performs best.

[0087] Example 2: The concrete was prepared by mixing 22.23 kg of sand, 29.8 kg of gravel and 9.23 kg of water in a concrete steel drum electric mixer for 45 seconds. Then, 10.26 kg of Portland cement type I (type as shown in Table 4) was added and mixing was continued for 1 minute. Then, 40 mL of polycarboxylate-based superplasticizer (Sikament 686 supplied by Sika Corp) and 1.03 kg of water were added to give a water to cement weight ratio of 0.5. Then, mixing was continued for 3 minutes and 15 seconds. Then, the respective admixture types and amounts as shown in Table 4 below were added. Then, mixing was continued for another 2 minutes. The formation of granules was clearly visible.

[0088] Slump, compactness and friability were measured as described in Example 1.

[0089] [Table 6]

[0090] Example 3: The concrete of Example 3 was prepared in the same manner as Example 2. For Example 3, Portland cements from different suppliers were tested. The Portland cements, admixture types and admixture dosages are shown in Tables 5-8 below. The results obtained are also shown in Tables 5-8 below.

[0091] [Table 7]

[0092] [Table 8]

[0093] [Table 9]

[0094] [Table 10]

Claims

1. 1. A method for treating an unhardened cementitious composition, particularly return concrete, comprising: The following steps: (a) providing an unhardened cementitious composition, particularly return concrete; (b) providing an admixture comprising a modified starch and a sugar; (c) mixing the unset cement composition and the admixture to form a set material; (d) discharging the solidified material obtained under (c) into a storage facility; (e) drying the solidified material to form solid granules; and (f) optionally separating the dried solid granules into fractions of different particle sizes; A method comprising:

2. 10. The method of claim 1, wherein the admixture provided in step (b) consists essentially of modified starch and sugar.

3. 3. The method according to claim 1 or 2, characterized in that the admixture consists essentially of 70-80% by weight of modified starch and 20-30% by weight of sugar.

4. 3. The method according to claim 1 or 2, characterized in that the modified starch is a copolymer of starch grafted with acrylic acid and acrylamide.

5. 3. The method according to claim 1 or 2, characterized in that the sugar is sucrose.

6. 3. The method according to claim 1 or 2, further comprising the step of crushing and / or comminuteing the solid granules.

7. The crushing and / or pulverization may be carried out by CO ２ 7. The method according to claim 6, wherein the method is carried out under an atmosphere of

8. 3. A concrete or mortar mixture comprising at least one cement and aggregate, wherein at least 30% by weight, preferably at least 50% by weight, more preferably at least 75% by weight, even more preferably at least 90% by weight, especially at least 99% by weight of the total weight of the aggregate is solid granules obtainable by the method according to claim 1 or 2.

9. 1. An admixture for use in a method for treating an unhardened cementitious composition, particularly returned concrete, comprising: (a) a modified starch, and (b) sugar A mixture comprising:

10. 10. The admixture of claim 9, characterized in that it consists essentially of modified starch and sugar.

11. 11. The admixture according to claim 9 or 10, characterized in that it consists essentially of 70-80% by weight of modified starch and 20-30% by weight of sugar.

12. 11. An admixture according to claim 9 or 10, characterized in that the modified starch is a graft copolymer of starch comprising a copolymer of starch grafted with acrylic acid and acrylamide.

13. 11. The mixture according to claim 9 or 10, characterized in that the sugar is sucrose.

14. 11. Admixture according to claim 9 or 10, characterized in that it is a one-component admixture.

15. 11. The admixture according to claim 9 or 10, characterized in that it is a multi-component, in particular a two-component, admixture.

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