NL2012081C2 - Cement additive and cements containing said additive; process for preparing concrete and concrete products; use of the cement additive. - Google Patents

Abstract

The present invention relates to a cement additive and to cements containing said additive. In addition, the present invention relates to a process for preparing concrete and concrete products, in which process the cement additive of the invention is used. Further, the present invention is directed to the use of the cement additive for its technical effects.

Description

Title: Cement additive and cements containing said additive; process for preparing concrete and concrete products; use of the cement additive.

The present invention relates to a cement additive or cement additive formulation and to cements containing said additive. Particularly, these cement additives enhance the performance of the used cements (different types of cement compositions and both fresh and used cements) and of the concrete and concrete products produced therewith. The cement additive and its use add value to the cement, concrete and concrete products, wherein it is used. In addition, the present invention relates to a process for preparing concrete and concrete products, in which process the cement additive of the invention is used. Further, the present invention is directed to the use of the cement additive for its technical effects, and particularly to the enhancement of the performance of used cement and produced concrete and concrete products.

In EP-A-2 113 494, a cement additive has been described based on three aluminosilicates, which are referred to as zeohtes (A)-(C) in the present description. This cement additive described is used in combination with cement to immobilize and stabilize waste material used as aggregates. Particularly, the invention described in EP-A-2 113 494 allows to provide a cement containing composition wherein waste materials, especially basic waste material which may be contaminated or polluted soil, industrial residues different types of slurries and sludge, (residual) construction waste materials etc., are stabihzed and immobilized. Especially, the core of EP-A-2 113 494 is formed by an additive mixture to be added to cement, which additive mixture allows the cement to effectively encapsulate waste materials in such a way that the waste material becomes stabilized and the contaminants or pollutants present therein become immobilized; in other words, the waste material is contained in the composition of the invention in such a way that it will not or hardly (that is, below acceptable and allowable hmits) leach out or otherwise escape from the composition.

Particularly, the first aluminosilicate that is required according to the invention described in EP-A-2 113 494 is designated as zeolite (A) and comprises - on a dry basis - 20-30 wt.% Na2Ü; 30-40 wt.% AI2O3; and 30-40 wt.% S1O2, which aluminosilicate is a zeohte that has a tapped density (determined after 1250 taps of at least 400 g/1 (said known method, for instance, being described by Dubrow and Rieradka in Technical Reports Nos. PA-TR-2092; AD-47231 of Picatinny Arsenal, Samuel Feltman Ammunition Labs. Dover N.J. (Nov. 1, 1954; OSTI ID: 4388372)); has an average particle size (determined by sedimentation analysis using a SediGraph 5100 marketed by Micromeritics) of 1.2-2.2 pm; has a calciumbinding capacity of at least 100 mg CaO/g on a 100% basis (anhydrous aluminosilicate) (as described in EP-A-0 384 070); has a pH (in a 5% aqueous suspension at room temperature using a conventional pH meter) above 6; and preferably above 9; has an ignition loss (1 hour; 800 °C) of 15-30 %; and contains <50 ppm water soluble Fe and < 500 ppm total Fe; < 1 ppm water soluble Ni; < 2 ppm water-soluble Cr; and < 7 ppm water-soluble Ti.

The second aluminosilicate that is used is designated as zeolite (B) and is a small particle size aluminosibcate or zeolite that comprises - on a dry basis - 15-35 wt% Na2Ü; 25-40 wt.% AI2O3; and 20-45 wt.% S1O2; has a pH in the range of 7-12 and preferably in the range of 9-12; has an average particle size (determined by sedimentation analysis using a SediGraph 5100 marketed by Micromeritics) of 0.7-2.4, and preferably from 0.9-1.5 pm; has a bulk density of 400-600 g/1; and contains less than 50 ppm iron and less than 5 ppm Ti.

The third aluminosibcate that is used is designated as zeolite (C) and comprises 10-30 wt.% Na2Ü; 20-40 wt.% AI2O3 and 10-50 wt.% S1O2, which aluminosilicate is a zeolite that has a tapped density of 300-600 g/1; has an average particle size (D50) of 1-5 pm; wherein less than 0.1 wt% of the particles have a size of less than 0.1 pm; has a pH above 6, and has an ignition loss of 16-24%.

In EP-A-2 305 620, the combination of these three aluminosilicates (A)-(C) was used in a method for increasing the bending strength and/or the compressive strength and/or the elastic modulus of a concrete material.

The present inventors, who are also the inventors mentioned on EP-A-2 113 494 and EP-A-2 305 620, have studied the systems used in both applications in considerable detail and have carried out much research to try and find the underlying concepts, principles and mechanisms to extend, optimize and/or generalize the teachings in these prior art documents.

From these studies and research efforts, some very interesting and useful insights resulted.

In accordance with the present invention, improvements are realised over the two above-mentioned European patent apphcations in the name of the present inventors.

These improvements allow cement reduction and/or the use of less cement in general, but specifically in various embodiments, such as in concrete without re-enforcement, as is commonly used to prepare, for example, prefab materials and various paving, cobbling or other surfacing materials and floorings.

It is especially considered interesting that by using additives, a cement reduction is observed, when cement quantities are compared to the traditionally or conventionally used weight amounts of cement.

Moreover, the discharge of carbon dioxide coupled to the production of cement to prepare concrete can be reduced as well. It goes without saying that the production of CO2 during the production of cement has, at least nowadays, a significant environmental bearing, and when reductions in cement can be achieved, this is an important advantage of the present invention.

Furthermore, the improvement of the present invention can well be used in especially concrete-based materials having favourable (concrete) engineering properties like high bending strength and/or good compressive strength properties.

However, perhaps the most important aspect of the present invention is that an additive was found that can be based on a more generally defined aluminosilicate mixture, than the additives described in EP-A-2 113 494 andEP-A-2 305 620.

The additive of the present invention allows the development of concrete and concrete products having an enhanced performance and/or allows processes having the potential to influence the technical properties of cement systems in a positive way.

Where especially in EP-A-2 113 494 the focus was on immobihzing waste materials and using such materials as aggregates, the present invention works very well with clean aggregate materials, as well.

Other advantages of the present invention will be described herein-below.

In a first aspect, the present invention relates to an additive mixture comprising a specific aluminosilicate base, characterized in that it further contains calcium chloride, or another suitable chloride source. In a preferred embodiment, calcium carbonate is present to adjust or bring the pH in the cement or concrete mixture to be prepared using the additive of the invention in the range of at least 9.5, preferably between 9.5 and 12, more preferably between 10 and 11.5; moreover it brings a desirable redox potential and may have a complementary role in cationic exchange. In further preferred embodiments, a pozzolanic material and/or fine solids may be present. The fine solids, also called “fines” herein-below, are inert fillers. These fines have a weight-average particle (largest diameter) size of less than 2 pm, preferably less than 1 pm, more preferably less than 0.5 pm, and most preferably less than 0.2 pm. Preferably, microsilica is used as fine solids.

The specific aluminosilicate base is based on hydrated cage structures of interlinked tetrahedrons of alumina (AI2O4) and silica (S1O4) crystal building blocks. It can in essence consist of one aluminosilicate, but in the practice it will consist of a mixture of two or more aluminosilicates, such that the aluminosilicate base meets as a whole the following properties: (a) the aluminosilicate base material has a weight average pore 0 size of between 2.8 and 4.3 A and preferably between 3.0 and 4.0 A; (b) the aluminosilicate base material contains, on a dry basis, i.e. anhydrous (without water of crystallization) 20-40 wt.%, preferably 25-38 wt.% S1O2; 28-36.5 wt.%, preferably 29-35 wt.% AI2O3; and 17-26 wt.%, preferably 19-24 wt.% Na2Ü; and optionally other metal and semi-metal oxides generally present in aluminosilicates; (c) the aluminosihcate base material has a dry solids content in the range of 78 to 88 wt.%, and preferably in the range of 80 to 85 wt.%; (d) the aluminosihcate base material has a loss of ignition (1 hour; 800°C) in the range of 8-22 wt .%; preferably in the range of 10-20 wt.%; (e) the aluminosihcate base material has a tapped bulk density in the range of at least 350 g/1, preferably between 350 and 650 g/1, more preferably between 380-600 g/1; (f) the aluminosihcate base material has a calcium-binding capacity of at least 130 mg CaO, preferably at least 150 mg CaO and more preferably at least 160 mg CaO per g on a 100% basis of aluminosihcate (anhydrous); and (g) the aluminosilicate base material has a hquid carrying capacity (g/100 g aluminosilicate (anhydrous)) of between 40 and 75, preferably between 45 and 70.

Preferably, but not essentially, the aluminosilicate base material has (h) a particle size distribution of at least 90%, preferably at least 95% smaller than 10 pm; less than 10%, and preferably less than 5% smaller than 0.1 pm; the average particle size (D50) being in the range of 1-5 pm, preferably 2-4 pm; and/or (i) a(n average) crystal size in the range of 0.02-1.0 pm.

Suitable methods to determine the properties describing the aluminosilicate base material are well-known to the skilled person working in the area of aluminosilicates and are, for instance, described in the above referred to European patent applications in the name of the present inventors.

In a preferred embodiment, the additive mixture comprises as calcium carbonate source or material, a calcium carbonate material of relatively high purity, such as a calcium carbonate containing, on an anhydrous basis, at least 80 wt.%, preferably at least 90 wt.% and most preferably at least 95 wt.% calcium carbonate. Lime powder is a suitable source.

The aluminosilicate base material, as indicated, contains basically hydrated alumino-silicate minerals made from interlinked tetrahedra of alumina (AIO4) and sihca (S1O4) and these tetrahedra of alumina and sihca are key components in the formulations.

The pozzolanic material, the fine solids, such as microsilica or fly ash, the chloride source and the calcium carbonate material are believed to activate these basic structures for the purpose.

The hquid carrying capacity of the aluminosihcate base material, the water percentage, has a significant influence on the properties of a concrete mixture achieved by using the additive of the invention, and this influences the quality of the final concrete products. That is, water molecules are and can be chemically bound within the (cages of the) aluminosihcate base material, and this significantly improves the water holding capabilities of the finally produced cement or concrete products. Hence, the liquid carrying capacity finally has an influence in quality enhancement of produced concrete. The aluminosihcate base materials which are used, are selected on the basis of being very stable compounds which resist the environmental changing conditions in a stable manner. For instance have these a resistance to high temperature, because of their high melting point. Also they have inherent resistance to burning. The material does not dissolve in water, so that the proposed formulations provide a high degree of flexibility when being used with materials with high water content. Further, the basic quality of produced concrete and concrete products will be maintained with time and the material is equally valuable because of its resistance to oxidation by oxygen (air). Furthermore and importantly, the aluminosihcate base material is not beheved to have any harmful environmental impacts and its use is classified as safe with reasonable precautions.

Without wishing to be bound by any theory, it is beheved that the pozzolanic material and the calcium carbonate material induce the formation of covalent bonds, ionic bonds and/or molecular forces leading to a stabilized cage based matrix and the effects thereof in the hydration process in concrete preparation and in the final concrete material. These ingredients of the additive mixture of the invention are believed to result in a chemical transformation enhancing performance of the concrete or concrete products produced therewith. It is worth mentioning that the used additives help in achieving a desired redox potential, pH and cationic exchange process and other overall chemical dynamics (as said before), which is critical in influencing the final transformation of produced concrete or concrete products. It is beheved that the use of these materials have an activating effect leading to an enhancement of ionic exchange and bond formation in conjunction with on-going cement hydration processes.

Any person working in the technical field, to which the present invention relates, knows the influence of pozzolanic material on cement hydration kinetics. The interesting aspect of the present invention has influence on overall chemical processes which include aluminosihcate and zeolite chemistry and cement hydration processes. A preferred pozzolanic material is a calcium carbonate containing aluminosihcate. Very good results are obtained by using commercially available pozzolanic materials, for instance those sold under the tradename Superpozz, such as Superpozz SV 80 (ex ScotAsh, Scotland), or other suitable pozzolanic materials.

It is expected that insoluble calcium sihcate hydrate and calcium aluminate hydrate compounds are formed possessing cementitious properties.

In accordance with the invention, calcium chloride or another suitable chloride source is present. Such possible chloride sources are barium and magnesium chlorides. As said, the chloride source preferably is calcium chloride. The chloride source induces or activates chemical transformations including those of the cement hydration process and promote covalent bonding.

The chlorides are also taken up in the matrix material formed and as such help concrete to achieve desired properties, as total chlorides added to the concrete mixture do not leach out as water soluble chlorides. A significant amount of chloride is retained in the formed matrix as is proven by chloride analysis from leached out fractions. The chloride ions end up in the cement or concrete matrix in chemically bound form. These are not water soluble and do not seem to be available for any oxidation process.

The fine solids are, as said, essentially inert fillers. These fine solids may comprise microsilica, fumed silica, fly ash, bottom ash and other ashes such as those remaining after waste or refuse incineration. In a preferred embodiment, the fine solids comprise or consist of microsilica. Microsilica has the advantage of providing a large surface-to-volume area as is important as a filler.

These fines fill the intra-crystalline and/or intra-particular and/or intramolecular spaces and by doing so assist in forming a stable matrix, which may participate in enhancing the strength or other performance properties of the final cement or concrete products. In addition, the solid fines may absorb water. Water so absorbed may initiate the stabilisation process with the support cage formation structures and may thus increase the potentials of using aggregates containing a high percentage of water. In conventional concrete the Water/Cement factor (in the total system; so internal and added water) is around 0.5, but using the proposed additive of the invention it is observed that a considerably higher W/C ratio can be achieved. With also aluminosilicates present, this allows flexibility in that the water may re-arrange in matrix formation.

Microsilica or silica fume is an ultrafine silica based material with spherical particles less than 1 pm in diameter, the average generally being around about 0.15 pm. This makes the material approximately 100 times smaller than the average cement particle. The hulk density of silica fume depends on the degree of densification in the silo and varies from 130 (undensified) to 600 kg/m3 (densified). The specific gravity of fines, such as silica fume, is generally in the range of 2.2 to 2.3 g/cc. The specific surface area of silica fume can be measured with the BET method or nitrogen adsorption method. It typically ranges from 15,000 to 30,000 m2/kg.

Moreover, it has advantages when the additive already comprises a part of the cement, and preferably a cement containing up to 80 wt.% Portland cement, most preferably a CEM I 52.5 R cement.

In EP-A-2 113 494, three specific aluminosilicates are described. These materials can be used in accordance with the present invention. But as said, with the present invention the aluminosihcate base material is no longer that critical. EP-A-2 113 494 is incorporated in the present specification for describing said three aluminosilicates and preferred embodiments thereof. Preferably, Zeolite-(A) is a P-type zeohte; Zeolite-(B) is a P-type zeolite; and/or Zeolite-(C) is an A-type zeolite. In this additive mixture, Zeolite-(A), Zeolite-(B) and Zeolite-(C) are combined in a weight ratio of respectively 1 : 0.8-1.2 : 0.8-1.2, and preferably about 1:1:1.

Although all zeolites are aluminosilicates, some contain more alumina, while others contain more silica. In accordance with the present invention, it was found that alumina-rich aluminosilicates are more attracted to polar molecules such as water, while more silica-rich aluminosilicates work better with nonpolar molecules.

The additive of the invention is prepared by mixing the aluminosilicates, the chloride material and optionally, the pozzolanic material, the sohd fines, and the calcium carbonate, optionally together with some cement. Preferred amounts are 1-15 weight parts aluminosilicate, 1-6 weight parts pozzolanic material, 0.5-5 weight parts solid fines, 0.5-10 weight parts calcium carbonate, 1-15 weight parts of the chloride source and preferably calcium chloride, and 0-10 weight parts cement.

Further advantages are obtained when the additive is combined with lime powder, milled sandlime brick and/or lime stone. These materials introduce alkalinity, preferably to a pH of 10-11 and higher in the cement or concrete mixture. Preferably, 50-90 weight parts of this alkaline material is combined with the indicated amounts in weight parts of the additive components.

The alkaline materials described in the previous paragraph to be combined with the additive of the invention have an important advantage in the preparation of concrete materials, when these are first combined with cement, and subsequently the additive mixture of the invention is added.

In a second aspect, the present invention relates to a process to prepare a concrete material. Particularly, the invention relates to a process for preparing a concrete and preferably a construction material, comprising combining with a suitable amount of water, cement and the additive mixture comprised of the aluminosilicate material, the chloride source, and optionally the pozzolanic material, the calcium carbonate, and the fine solids, followed by curing.

In a preferred embodiment, before the additive is added to the cement, first the cement is contacted with the above described alkaline material, such as lime powder, milled sandlime brick and/or lime stone or other calcium carbonates or suitable alkaline providing materials. These materials introduce alkalinity, preferably to a pH of 10-11. Only after this, the additive is added and homogenously mixed.

In a very suitable process, 5-15 weight parts of the additive mixture as defined in claims 1-8 is added, and 95-85 weight parts of the alkaline material, such as lime powder, milled sandlime brick and/or lime stone, to the cement and water.

Preferably, drawn to the weight of the cement, 15-25 weight percent of lime powder, milled sandlime brick and/or lime stone, optionally together with fly ash is used; and 1.5-4.5 weight percent of the additive mixture as defined in claims 1-8.

The cement or concrete mixture including the additive mixture of the invention has a pH in the alkaline range such as a pH of at least 9 or at least 9.5, and preferably has a pH in the range of at least 10, more preferably less than 12 and most preferably less than 11.5.

The concrete obtained by the process of the present invention was found to have an improved compressive strength as compared to a concrete wherein only the aluminosilicates were present. Further, high bending strength properties are found and/or good elasticity modulus properties may be obtained. In general, good overall properties were found. Alternatively, a concrete can be prepared with similar strength properties but considerably less cement.

The cement to be used in the present invention can be selected from all known cements. Preferably, the invention uses Portland cement and/or blast-furnace or high-oven cement; suitable cements are identified by the following types CEM I 32,5 R, CEM I 42,5 R, CEM I 52,5 R, CEM II/B-V

32.5 R, CEM III/A 32,5 N, CEM III/A 42,5 N, CEM III/A 52,5 N, CEM III/B

32.5 N and CEM III/B 42,5 N etc. Preferably, CEM I 52.5 R is used. Also blends of different cements can be used. In the composition of the invention, the cement is used in an amount of 80-500 kg/m3, preferably 90-450 k/m3 and most preferably 100-400 kg/m3 in the final product. It was generally found that the higher the clinker percentage is, the better the advantageous properties of the invention become. Fillers like ashes, including fly ash, may however influence the properties.

The concrete may comprise all kinds of aggregates. Various aggregates typically used in cement compositions may be employed, e.g. coarse aggregates such as gravel, chalk stone, or granite, and fine aggregates such as sand. Also waste materials - such as those described in the above mentioned EP-A-2 113 494, polystyrene particles and wood may be used as aggregates, e.g. soils, including contaminated soil, such as heavy metal contaminated soil, ashes, sieve sand, construction waste, furnace dust, harbor sludge, lead slag, barites sludge, railway ballast, jet grit, iron slag, glass beads, waste incineration slag, grit of different sizes, fly ash, clay, stony mixture, jet dust, crushed asphalt, rubbish, sihcon residue, sand, etc. In a preferred embodiment of the invention, clean aggregates are used.

It goes without saying that dependent on the type of sand and in fact every type of aggregate used, different end results can and will be obtained.

The concrete composition of the invention can further comprise other components and additives known in the art such as water-reducing agents, retarders, colouring agents, accelerators, stabilizers, air entrants and the like. Preferably, rheology controllers (wood absorbs lots of water, which may seriously affect the workability) and additives to control the overall ionic environment are used, for instance to achieve the required workabihty.

In the process of the invention, a suitable amount of water is used to prepare a construction material. Suitable amounts of water can easily be determined by a person skilled in the art. Generally, suitable amounts vary between 4 and 22 vol.%, preferably between 5 and 20 vol.%. Concrete technologists call this the water: cement (W/C) factor which has a relation to water absorption by aggregates, chemical reaction needed for the hydration process and internal water already present in the aggregate material, and finally the required workabihty which provides optimum concrete parameters. In this fight, it is noted that a trained concrete technologist understands that this depends on the water already present in the aggregate material and on the total amount of water needed to be added from outside. This situation bears some complexity, as the skilled person knows by practical experience, in that the (internal) water present in the aggregate is not “free water”; in many conditions it is not available for cement hydration (and hence cement hardening) and for reaction with the cement additives used in this invention. Sometimes when the sand or aggregate is oversaturated with water, there is free water and this free water is available for cement hydration and other chemical processes. Normally, internal water and outside water (which is added from outside), are taken together and this is taken as total water of the system and the amount of water required to be added is determined on the basis of actual water present in the system and the estimation of the total amount of required water. In this way, the amount of outside water can be determined on the basis of these parameters, the inventors report a W/C factor, with reference to the amount of cement used in the mixture.

The invention will be further described on the basis of the following, non-limiting working examples. If percentages are given, these are percentages by weight, unless otherwise indicated.

Example 1

An additive mixture according to the invention is prepared by combining the following ingredients: as aluminosilicate mixture 40 kg of the zeolite mixture described in working example 1 of EP-A-2 113 494; 20 kg calcium chloride; and 10 kg of calcium carbonate.

Example 2

An additive mixture according to the invention is prepared by combining equal weight parts of zeolites (A) and (C) described in working example 1 of EP-A- 2 113 494, and adding that in amount of 40 kg to 20 kg calcium chloride and 10 kg calcium carbonate.

Example 3

An additive mixture according to the invention is prepared by combining 60 weight parts of zeolite (B) and 40 weight parts of zeolite (C) described in working example 1 of EP-A-2 113 494, and adding that in amount of 40 kg to 20 kg calcium chloride and 10 kg calcium carbonate.

Example 4, Example 5, and Reference Example 1

For Example 4, a cement composition is made by thoroughly mixing 80 weight parts cement CEM I 52.5 R (Portland based cement) with 17 weight parts limestone powder. Subsequently, 3 weight parts of the composition according to working example 1 were added and once again the mixture was thoroughly mixed. 200 weight parts of a mixture of clean sand and clean gravel were added and mixed with the cement mixture. A suitable amount of water was added in accordance with conventional practice. The material obtained was added to cylindrical moulds having an internal diameter of 10 cm and a height of 12 cm.

After curing at 20 degrees Centigrade, the moulds were removed and the compressive strength (N/mm2) and bending strength (N/mm2) were determined using the techniques described in EP-A-2 113 494 and EP-2 305 620 after 1 day and after 28 days.

For Example 5, the same procedure was followed, except that now 72 weight parts cement was used (resulting in a cement reduction of 10%).

For Reference Example 1, the same procedure was followed, but now the composition according to example 1 was not introduced.

From the data obtained, the inventors deduced that the addition of the additive mixture according to the invention results in a considerably higher compressive strength after 28 days, but more importantly even after 1 day, when compared to the reference example that does not contain said additive mixture. Similarly, the bending strength increases (also after 1 day and after 28 days).

Additionally, it was shown that the additive mixture of the present invention allows that relative to the reference example a concrete product can be obtained that has similar properties but uses 10 wt.% less cement. In other tests even up to 40 or 50 wt.% less cement can be used.

Claims (12)

An additive mixture comprising an aluminosilicate base material, (a) wherein the aluminosilicate base material has a weight average pore size between 2.8 and 4.3 A and preferably between 3.0 and 4.0 A; (b) wherein the aluminosilicate base material, on a dry basis, i.e. anhydrous (without crystal water), contains 20-40% by weight, preferably 25-38% by weight of SO 2; 28-36.5% by weight, preferably 29-35% by weight of Al 2 O 3; and 17-26% by weight, preferably 19-24% by weight of Na 2 O; and optionally other metal and semi-metal oxides that are commonly present in aluminosilicates; (c) wherein the aluminosilicate base material has a dry solid content in the range of 78 to 88% by weight, and preferably in the range of 80 to 85% by weight; (d) wherein the aluminosilicate base material has a combustion loss (1 hour; 800 ° C) in the range of 8-22% by weight; preferably in the range of 10-20% by weight; (e) wherein the aluminosilicate base material has a whipped bulk density in the range of at least 350 g / l, preferably between 350 and 650 g / l, more preferably between 380-600 g / l; (f) wherein the aluminosilicate base material has a calcium binding capacity of at least 130 mg CaO, preferably at least 150 mg CaO and more preferably at least 160 mg CaO per g on a 100% aluminosilicate (anhydrous) basis; and (g) wherein the aluminosilicate base material has a liquid bearing capacity (g / 100 g of aluminosilicate (anhydrous)) between 40 and 75, preferably between 45 and 70; characterized in that said additive mixture further comprises calcium chloride or another suitable chloride source. The additive mixture according to claim 1, wherein the aluminosilicate base material has a particle size distribution of at least 90%, preferably at least 95% less than 10 μιη; less than 10%, and preferably less than 5% less than 0.1 μιη; wherein the average particle size (D50) is in the range of 1-5 μιη, preferably of 2-4 μιη; and / or an (average) crystal size is in the range of 0.02-1.0 μιη. The additive mixture according to claim 1 or 2, wherein calcium carbonate is present. The additive mixture according to claim 3, comprising as a calcium carbonate source, a calcium carbonate comprising in anhydrous form at least 90% by weight of calcium carbonate. The additive mixture according to any one of the preceding claims, further comprising a pozzolane material and / or fine solids. The additive mixture according to claim 5, wherein the fine solids comprise microsilica and / or fumed silica. The additive mixture according to any of the preceding claims, comprising cement, and preferably Portland cement. The additive mixture according to any of the preceding claims, comprising 1-15 parts by weight of aluminosilicate, 0-6 parts by weight, preferably 1-5 parts by weight of pozzolane material, 0-5 parts by weight, preferably 0.5-4 parts by weight of fine solids, 0- 10 parts by weight, preferably 0.5-9 parts by weight of calcium carbonate, 1-15 parts by weight of the chloride source and preferably calcium chloride, and 0-10 parts by weight of cement. The additive mixture according to any one of the preceding claims, comprising a calcium carbonate source, preferably lime powder, ground sand-lime brick and / or limestone. A method for manufacturing a concrete and preferably a construction material, comprising combining with a suitable amount of water, cement and the additive mixture according to any of claims 1-9, followed by curing. A method according to claim 10, wherein the cement is first combined with a calcium carbonate, and preferably with lime powder, ground lime sandstone and / or limestone, optionally together with an ash, such as a fly ash, and then with the additive mixture as defined in one of claims 1-8. A method according to claim 10 or 11, wherein 5-15 parts by weight of the additive mixture as defined in any of claims 1-8 is added, and 95-85 parts by weight of the calcium carbonate, optionally together with ash, such as fly ash.