FIELD OF INVENTION

The present invention is in the field of an pre- mixture to be used e.g. in concrete and mortar in order to im ^¬ prove characteristics of a final product, a method to obtain such an pre-mixture, a product, typically being a solid product, such as concrete, glass, and cement, comprising said pre- mixture and use of said pre-mixture.

BACKGROUND OF THE INVENTION

Concrete is a composite construction material composed primarily of aggregate, cement and water, with mortar being similar thereto, however using finer aggregates. There are many formulations that have varied properties. The aggregate is generally a coarse gravel or crushed rocks such as limestone, or granite, along with a fine aggregate such as sand. The cement, commonly Portland cement, and other cementing materials such as fly ash, blast furnace slag cement, ground calcium carbonate, etc. serve as a part of binder for the aggregate. It is noted that these cementing materials typ ^¬ ically do not comprise clay or metakaoline, as at high

temepratures these compounds have been transformed. Typically lime if present is fully burned.

These so-called Supplementary Cementing Materials (SCMs) are recognized by the cement standard EN 197-1 for production of so-called blend or composite cements. Examples hereof are Sil ^¬ ica Fume (6-10%) CEM II D, natural pozzolan (< 35%) CEM' II P and Q, fly ash (< 35%) CEM II V and W, burnt shale (< 35%) CEM II T, limestone (< 35%) CEM II L and LL, blast furnace slag (< 95%) CEM III and combinations (< 55%) CEM IV & V. Origins of these SCM' s are e.g. Silica fume: by product of ferro silicon metal; Pozzolan: natural volcanic earth; Fly ash: powder coal power stations; Burnt shale: lime containing bituminous shale; Blast furnace slag: iron making; and Limestone: natural rock > 75% CaC0 ₃ .

Various chemical admixtures can be added to achieve varied properties. Water is thereafter mixed with this dry or moist composite which enables it to be shaped (typically poured) and then solidified and hardened into rock-hard strength through a mineralogical transformation known as hy- dration and/or pozzolanic reaction. Also particle size and polarity of materials play a role in the performance of con ^¬ crete. Concrete may be reinforced with materials that are strong in tension (often steel) .

Admixtures are ingredients other than water, fine ag ^¬ gregates, (hydraulic) cement, and fibers that are added to the concrete batch immediately before or during mixing, in order to change certain characteristics of the concrete, when set. Such addition is however not always practicable. For instance excess water decreases performance of concrete. Reducing water is a purpose of adding admixtures, thereby maintaining workability with improved performance. A proper use of admixtures may offer certain beneficial effects to concrete, including improved quality, acceleration or retardation of setting time, enhanced frost and sulfate resistance, control of strength development, improved workability, control of shrinkage, and enhanced finishability .

Admixtures may vary widely in chemical composition, and may perform more than one function. Typically admixtures comprise more than one chemical/mineral compound. Two basic types of admixtures are available: chemical and mineral. All admixtures to be used in concrete construction should meet specifications; tests should be made to evaluate how the ad ^¬ mixture will affect the properties of the concrete to be made with the specified job materials, under the anticipated ambient conditions, and by the anticipated construction procedures .

Mineral admixtures (silica fume [SF] ) are usually added to concrete in amounts to improve strength, durability and sustainability of concrete; and to enable a reduction in (Portland) cement content.

Chemical admixtures are added to concrete in very small amounts mainly for the entrainment of air, reduction of water or cement content, plasticization of fresh concrete mixtures, or control of setting time. Sometimes these chemical admixtures are referred to as modifiers.

It is noted that terminology used by the person skilled in the art may vary somewhat. In this respect refer ^¬ ence is made to e.g. Ken W. Day; "Concrete Mix Design, quality control and specification", 2007, 3rd edition, 391 pp. Pub- lisher: Taylor & Francis.

In this respect reference can be made to ASTM C 494, and AASHTO M 194. Air entraining admixtures are specified in ASTM C 260 and AASHTO M 154. Elasticity on mortar prisms of 16x4x4 cm ³ can be tested according to EN 196-1:2005.

Typically admixture dosages are less than 5% by mass of cement, i.e. at a low relative amount, and are added to the concrete at the time of batching/mixing. Some admixtures are mentioned below, as well as exemplary use thereof.

Accelerators speed up hydration (hardening) of the concrete. Retarders slow the hydration of concrete and are used in large or difficult pours where partial setting before the pour is complete is undesirable. Air entrainments add and entrain tiny air bubbles in the concrete, which will reduce damage during freeze-thaw cycles, thereby increasing the concrete's durability. Plasticizers increase the workability of plastic or "fresh" concrete, allowing it to be placed more easily, with less consolidating effort. Superplasticizers (also called high-range water-reducers) are a class of plasticiz- ers that have fewer deleterious effects and can be used to increase workability more than is practical with traditional plasticizers. Pigments can be used to change the color of con ^¬ crete, for aesthetics. Corrosion inhibitors are used to mini ^¬ mize the corrosion of steel and steel bars in concrete. Bond- ing agents are used to create a bond between old and new concrete. Pumping aids improve pumpability, thicken the paste and reduce separation and bleeding.

Some documents recite CaO comprising compositions. NL2002282C recites a pozzolanic binder composition. The composition is however a dry composition, without water added, that inherently does not mix very well.

Pera et al in "Use of thermally converted paper residue as a building material", in Third CANMET/ACI International Symposium on Sustainable Development of Cement and Concrete; San Francisco, California, USA; 2001.09.16-19, 20010101;

20010916 - 20010919 American Concrete Institute, USA; San Francisco, California, USA recites a dry material, without water added. Further the material does not comprise a modifier.

Incidentally applicant on their internet site refers to a commercial product called Top-crete. As with the two previ- ous documents Top-crete is a dry material, without water add ^¬ ed; further no modifier is present.

WO2011/070236 recites a dry matter composition of concrete or mortar, which contains core particles, to the surfac- es of which particles of a hydraulic binder are attached, and separate particles of a hydraulic binder, the core particles consisting of an inert or pozzolanic material and forming, to ^¬ gether with the binder attached thereto, porous granules, which granules in turn are attached to the surface of a dry aggregate. The invention also relates to the concrete or mor ^¬ tar manufactured from said dry matter composition. It is noted that the final composition is dried, i.e. containing no water, whereas the granules when formed are very wet. Such is in line with an objective, namely to form dry granules. The granules are very small (nanoparticles ) . Further only CaOH ₂ is present and no modifier. The powder has a reduced hygroscopicity .

US 5,196,620 A recites municipal solid waste ash which is utilized in the manufacture of an aggregate and is processed to form a cold bonded pellet which, when tested by means of TCLP leaching extraction tests using TCLP No. 2 extraction fluid, does not exceed the 1990 limits for the RCRA priority heavy metals. So in principle it relates to fly ash and the like. It is heat treated in order to form large parti ^¬ cles, immobilizing toxic metals etc., and therefor does not comprise any water. It is considered to be a filling material and not a binding material. It is also expensive, extra steps for processing are involved, which is e.g. complicating and calcining is involved.

WO2010/037903 A recites a grain composition for the man- ufacture of a concrete mass, consisting of granules, each of which contains filler particles, to the surface of which hydraulic binder particles have been attached. The invention al ^¬ so concerns a method as well as equipment for manufacturing the composition as well as a concrete or mortar mass, which contains said composition, and a method for manufacturing this concrete or mortar mass. The same comments as above for the ^λ 620 apply.

Despite availability of various admixtures it is diffi ^¬ cult to use an admixture in practice, for instance due to a relative complex dosing in view of educational skills of a ce- _c

5

ment/concrete worker, in view of required characteristics, etc. Typically a highly educated person needs to be involved, which person typically is not present and can not provide information during mixing. Even further it is difficult to pro- vide a combination of required characteristics to a concrete, such as (relatively) high slump, limited shrinkage, limited carbonation, good chloride resistance, good microstructure and high flexural strength. It is even more difficult to tailor characteristics to a concrete, by adjusting a composition of an admixture.

Therefore there still is a need for relative simple and effective admixtures and method for making the same, which admixtures can be added as such to concrete directly, which increases binder properties of a concrete powder and/or (wet) sand, and which overcomes one or more of the above mentioned disadvantages without jeopardizing beneficial characteristics. SUMMARY OF THE INVENTION

The present invention relates to a method for manufacturing a substantially dry concrete pre-mixture according to claim 7, a substantially dry concrete pre-mixture according to claim 1, a material comprising said pre-mixture and use of said pre-mixture. It is noted that for readability the term "concrete pre-mixture" is used, which in view of the present invention may also relate to "mortar pre-mixture". A mortar typically relates to a workable paste used to e.g. bind construction blocks together and fill gaps between them. It is typically applied by spreading out and is applied as a relatively thin layer.

It is noted that a problem of the present invention is to provide a relatively small amount of water to a relatively large surface (area) , such as 100 gr water to 13600 m ² area. Such is inherently complex. Mixing will take a long time. It has been found that with slightly increasing the tem ^¬ perature the mixing process is speeded up. A temperature of 40-100 °C is preferred, more preferably a temperature of 50-90 °C, such as 60-75 °C. It has been found that at a too high temperature mixing does not take place sufficiently.

It is also noted that the present pre-mixture could be considered as a diluted CaO mixture. The relative concen- tration (either in w/w, v/v or mole/mole) of CaO is not high. _r

6

On a weight basis it is in a range of 5-80% (w/w, relative to a total weight of the pre-mixture) , preferably from 10-40%

(w/w) , more preferably from 20-30% (w/w) , such as from 25-28%

(w/w) .

The present pre-mixture may be considered to be both of chemical and mineral nature. In this respect it is noted that the present pre-mixture is relatively pure, i.e. comprises less than 10% non-intended impurities, typically less than 5% impurities, contrary to e.g. fly-ash. Further the present process of producing the pre-mixture and specifically the present first composition, is well controlled. As a consequence the present pre-mixture and first composition can be maintained and controlled at a relatively constant (chemical and mineral) composition. In this respect it is also noted that the present one or more silica-alumina compounds and one or more calcium compounds have not (or substantially not) reacted with one and another. As a consequence the present pre-mixture can be dosed precisely, e.g. to cement and mortar.

The present concrete or mortar may comprise >15% SCM, such as more than 20%. Further the present concrete or mortar comprises <25% pre-mixture, preferably < 15%, more preferably < 5%, all based on the total weight of the concrete.

In chemistry, a mixture is a material system made up by two or more different substances which are mixed together but are not combined chemically. Mixtures can be either homogeneous or heterogeneous. A homogeneous mixture is a type of mixture in which the composition is uniform. A heterogeneous mixture is a type of mixture in which the components can easily be identified, as there are two or more phases present.

The present pre-mixture provides improved characteristics to e.g. concrete, such as an improved tensile strength, improved strength development, good elasticity, a good slump, limited shrinkage, limited carbonation, good chloride resistance, good microstructure and high compressive strength, such as limited micro-cracking, is easy to handle, does not ^■ interfere with a concrete mixing/forming process, such as by unwanted extra consumption of water e.g. due to an inherent water demand of the pre-mixture or a temperature increase due to an exothermic process, such as formation of Ca(OH) ₂ . The pre-mixture is substantially (or essentially) dry, i.e. it comprises virtually no free water, such as less than 0.1 wt . % . As a consequence the pre-mixture can be handled as a powder or granule, and added as such to a concrete mixture. For addition of the pre-mixture to glass it is essential that the pre- mixture is dry. Typical particle sizes are a D50 of 1 μπι-100 μιη, such as 2-50 μπι, e.g. 5-20 μπι. Typical surface area char ^¬ acteristics (BET) are 5*10 ³ -10 ⁵ m ² /kg material, more preferably 7*10 ³ -5*10 ⁴ m ² /kg material, even more preferably 1*10 ⁴ -3*10 ⁴ m ² /kg material, such as 1, 2*10 ⁴ -2*10 ⁴ m ² /kg material. Experi- ments indicate that a surface area is preferably not too large, as in that case mixing with water becomes cumbersome. On the other hand, too small surface area does not provide im ^¬ proved properties for a final cement or concrete. A typical specific mass is 400-600 kg/m ³ . A typical color is white. The pre-mixture can be given a different color by addition of pigments, colorants, etc.

It is noted that in a case when wet sand is used, e.g. having a water content of less than a few percent (< 5%, preferably <3%) the amount of water in the sand may be taken into account. As a consequence the present pre-mixture may contain less than an equimolar amount of water. Such provides a big advantage as there is no need to (completely) dry the sand .

The present inventors introduce some not EN 197 recog- nized SCM's, such as meta-kaolin calcined kaolin clay, a byproduct of exothermal treated waste paper sludge, containing Meta-kaolin, CaO and CaC0 ₃ , Ground reactive Rice husk silica, Sugar cane minerals and VCAS Vitrified Calcium Alumina Silica waste from fiberglass.

The present pre-mixture can be tailored to required characteristics of a final product. As such, in advance, the present pre-mixture can be made according to specifications.

It is noted that the present pre-mixture can be added as a ready to use mixture, providing required characteristics to a (final) product. It is therefore easy to use, especially compared to providing separate admixtures. The person skilled in the art, also a less skilled person, need not worry on adjusting e.g. quantities. In view of the prior art the present pre-mixture may be considered as a technology jump.

It is noted that additives are often used in a low „

o

concentration. Such complicates mixing of dry powders. With the present method and product water is used to transfer an additive to a solid carrier, i.e. a first composition. The first composition, being satisfied in water demand, is then used as a carrier to add the present pre-mixture to e.g. con ^¬ crete. As a consequence the mixing is improved dramatically. Thereby the effectiveness of expensive additives is increased as well, as can e.g. be seen in view of improved flexural strength .

It is noted that the cement and concrete world are used to working with standard procedures and products. With the present method and pre-mixture optionally also further products, e.g. recycled products, can be incorporated into standard products and procedures, e.g. by tailoring/modifying the present pre-mixture accordingly, such that the fit within standard procedures and products.

The pre-mixture comprises Ca(OH) ₂ . The Ca(0H) ₂ typi ^¬ cally is formed by adding water to CaO. The amount of water is preferably substantially the amount needed to satisfy the water demand of CaO. The water is preferably added slowly, e.g. in order to prevent clogging, and under stirring, e.g. in or ^¬ der to provide a homogeneous mixture. By homogeneous it is indicated that a chemical and physical composition of a present sample taken from the pre-mixture is similar to an average of the pre-mixture, e.g. in terms of particle size distribution, chemical composition, etc. For instance the chemical composi ^¬ tion does not vary more than about 2% from average, preferably less than about 1%. The average of a particle size distribution of a sample also does not vary more than 5% from average, and a variation in size (such as σ) also does not vary more than about 7%.

Preferably a premixer is used wherein water and CaO are mixed, and reacted. The premixer preferably has a double shaft. Therein the CaO can be added using gravity. The mixer preferably has two vertically placed troughs having each a separate shaft. The first through is preferably used to con ^¬ trol and finalize the reaction of the premixer. The second through is used to dry the product obtained, if necessary.

The premixing preferably takes place during an average resident time of 4-8 minutes, at a temperature of 40-60 °C. The temperature may be controlled by the flux of water. Therewith the amount of residual moisture, if any, can be con ^¬ trolled relatively precise. Further, the CaO is reacted substantially complete into Ca(OH) ₂ . Optionally a moisturizer is placed in the mixer to remove dust.

Using the above mixer and premixer also the present first composition and optional modifier may be added and mixed. The optional modifier may be present in the water added, or as a separate component, or both. As such a homogeneous pre-mixture is provided with excellent properties.

In the pre-mixture a first composition is present, the composition comprising a silica-alumina compound and/or a calcium compound. Aluminosilicate minerals (or silica alumina compounds) are minerals composed of aluminum, silicon, and ox ^¬ ygen, plus countercations . They are a major component of kaolin and other clay minerals.

The pre-mixture further comprises a modifier, in order to improve characteristics of e.g. final concrete (i.e. after the concrete has been made and set) .

The present invention provides a solution to one or more of the above mentioned problems and overcomes drawbacks of the prior art.

Advantages of the present description are detailed throughout the description.

DETAILED DESCRIPTION OF THE INVENTION

In a first aspect the present invention relates to a method for manufacturing a substantially dry concrete pre- mixture, comprising the steps of:

a) providing

a first composition that as active component comprises one or more silica-alumina compounds and/or

one or more calcium compounds, and

CaO,

b) forming a homogeneous primary mixture of the first composition and calcium hydroxide with an equimolar amount of water sufficient to substantially satisfy a water demand of the calcium oxide, wherein mixing preferably takes place under stirring and slow addition of water, and

c) optionally providing a further modifier to the primary mixture under further mixing. The further modifier preferably is a chemical modifier.

It is noted that the present pre-mixture can be considered as a pre-hydrolyzed pre-mixture, wherein a water de- mand is satisfied substantially. Such is advantageous as for instance when making a further material such as concrete and using the present pre-mixture no additional water for satisfying a water demand of the pre-mixture needs to be taken into account; the present pre-mixture is ready to use. The pre- mixture further relates to a reactive powder. It is noted that adjusting a water demand of a concrete mixture (e.g. for hydration of an ingredient) is undesirable, e.g. because there is no time available, it is a relatively difficult process, and it is difficult to control, especially for an operator in- volved. The present pre-mixture further provides for a wide range of parameters to be varied, e.g. can be used with high flexibility. Further typical adjuvants of the prior art are quite expensive, contrary to the present mixture. The present dosage is very precise, e.g. in view of desired characteris- tics. As mentioned, prior art adjuvants are typically added as a fluid, e.g. requiring compensation for water content.

Below some details of the first composition are given .

Table 1: Characteristics of a present first composition

CHEMICAL COMPOSITION (wt. % relative to total mass)

1 2 3

CaO 19, 82 20,20 18, 95

Si0 ₂ 18, 01 17, 60 18,76

A1 ₂ 0 ₃ 10, 14 9, 90 10, 56

Mg0 ₂ 0, 58 0,56 0, 64

Fe ₂ 0 ₃ 0, 55 0, 64 0, 52

so ₃ 0, 33 0,45 0,28

Na ₂ 0 0, 25 0,23 0,27

Ti0 ₂ 0, 26 0,28 0,24

K ₂ 0 0,21 0,21 0, 22

P ₂ 0 ₅ 0, 10 0, 11 0, 10

Lol 47, 62 48, 12 47,87

(Los on Ignition)

The first composition preferably comprises 5-80% CaO (w/w, relative to a total weight of the pre-mixture) , prefera- bly from 10-40% (w/w) , more preferably from 20-30% (w/w) , such as from 25-28% (w/w), and/or 5-50% (meta) kaoline (w/w, rela ^¬ tive to a total weight of the pre-mixture) , preferably from 10-40% (w/w) , more preferably from 20-35% (w/w) , such as from 25-30% (w/w) , and/or 5-75% CaC0 ₃ (w/w, relative to a total weight of the pre-mixture) , preferably from 10-60% (w/w) , more preferably from 25-50% (w/w) , such as from 35-45% (w/w) .

A further advantage of the present pre-mixture is that a very smooth and flat, esthetically highly valued, sur- face of a final product is provided. A water to binder ratio can also be improved (typically increased) . The surface also remains flat and smooth over a longer period of time. Further fewer discolorations occur, which is especially appreciated when using a color for e.g. the concrete. The present pre- mixture is also ^" relatively better distributed in a final prod ^¬ uct. Also the components of the present pre-mixture are better distributed, both in the pre-mixture and in the final product. The present pre-mixture is very suited for capturing components from a final product, e.g. calcium (oxide), therewith preventing formation of discolorations, stains, etc. Also a denser final product can be formed.

In an example of the present method the modifier is one or more of a surfactant, an emulsifier, a dispersant, and a co-modifier, preferably one or more of

a linear polymer containing one or more sulphonic acid groups attached to the polymer backbone such as at regular intervals, such as a sulfonated melamine-formaldehyde condensate (SMF) , a sulphonated naphthalene-formaldehyde condensates (SNF) , a mod ^¬ ified lignosulphonates (MLS),

a polycarboxylate derivative, such as a polycarboxylate, an acrylic acid polymer,

a methacrylic acid polymer,

a maleic acid polymer,

an ethylene acrylic acid polymer,

a sulphonic acid polymer,

an acrylamido-methyl-propane sulphonate polymer,

a heteropolyacid polymer,

a copolymer thereof,

a terpolymer thereof, and

mixtures thereof. Such a modifier may also be added to improve distribution of water, and/or as a grinding aid.

It has been found experimentally that one or more of the above compounds can be mixed into the pre-mixture effi ^¬ ciently and homogeneously.

In an example of the present method the first composition comprises meta-kaolin, that may or may not be in the dehydrated form of meta-kaolin. It is preferred to use a kaolin or meta-kaolin compound in view of the supporting properties thereof and availability. The functional features of meta-kaolin are typically better than e.g. those of pozzolan.

In an example of the present method the calcium compounds comprise calcium carbonate and/or calcium oxide, preferably 60-70% of calcium carbonate and 40-30% of calcium oxide. Both the compounds fit very well within a process for making an pre-mixture and concrete and attribute to characteristics of a final product.

In an example of the present method the first composition is obtained by thermal conversion of a material chosen from paper waste and residue from the paper production. It has been found that specifically waste paper sludge and residue can be used well.

In an example of the present method the amount of water added is from 2-30.0% w/w, preferably from 5-25% w/w, more preferably from 8-20% w/w, such as 12-15 % w/w, relative to the total weight of the pre-mixture.

The amount of water is primarily sufficient to substantially satisfy a water demand of CaO. Further oxides or other compounds reacting with water may require additional water.

In an example of the present method steps b) and c) are performed substantially simultaneously, and wherein preferably the modifier is present in the amount of water.

In a second aspect the present invention relates to a substantially dry pre-mixture comprising

a first composition that as the active component comprises one or more silica-alumina compounds and/or one or more calcium compounds,

calcium hydroxide and optionally calcium oxide, and an modifier, such as one or more of a surfactant, an emulsifier, an accelerator, a retarder, an air entrainment, a plasticizer, a pigment, a corrosion inhibitor, a bonding agent, a dispersant, and a co-modifier. The modifier is preferably initially liquid. Further the modifier preferably is a chemical modifier.

As mentioned in the description of the present meth- od, by addition of an equimolar (or stoichiometric) amount of water to CaO the CaO is substantially complete reacted to Ca(OH) ₂ . Some CaO may however still be present, possibly in ^¬ tentional .

Examples of accelerators are CaCl ₂ , Ca(N0 ₃ ) ₂ and NaN0 ₃ . Exam- pies of retarders are polyol retarders, such as sugar, sucrose, sodium gluconate, glucose, citric acid, and tartaric acid. Examples of air entrainments are abietic acid salts (Vinsol Resin), fatty acid salts, alkyl sulphates, olefin sul- phonates, diethanolamines , alcohol ethoxylates and betains . An example of a plasticizer is lignosulphonate . Superplasticizers typically have linear polymers containing sulphonic acid groups attached to a polymer backbone at regular intervals. Examples of superplasticizers are sulphonated naphthalene for ^¬ maldehyde condensate, sulphonated melamine formaldehyde con- densate, acetone formaldehyde condensate, modified lignosul- phonates and polycarboxylate ethers. Examples of pigments are synthetic pigments, such as red, yellow, and orange, (metal) oxides, such as brown and black iron oxides, carbon blacks, cobalt blues, and chromium oxide greens. Examples of corrosion inhibitors are organic (DCS, DAS, DSS) and inorganic compounds, such as calcium nitrate based. Examples of bonding agents are a high solids, water-based emulsion, and acrylic polymer .

In an example of the present pre-mixture the modifier is one or more of

a linear polymer containing one or more sulphonic acid groups attached to the polymer backbone such as at regular intervals, such as a sulphonated melamine-formaldehyde condensate (SMF) , a sulphonated naphthalene-formaldehyde condensates (SNF), a modified lignosulphonates (MLS) ,

a polycarboxylate derivative, such as a polycarboxylate, an acrylic acid polymer,

a methacrylic acid polymer,

a maleic acid polymer,

an ethylene acrylic acid polymer, a sulphonic acid polymer,

an acrylamido-methyl-propane sulphonate polymer,

a heteropolyacid polymer,

a copolymer thereof,

a terpolymer thereof, and

mixtures thereof.

A purpose of using the above modifier is to provide flowing concrete with relatively high slump in a range of 175- 225 mm, or larger. Such a concrete can e.g. be used in heavily reinforced structures, in placements where adequate consolidation by vibration cannot be readily achieved, and in providing high-strength concrete at a water-powder ratio ranging from 0.15 to 0.5, preferably from 0.15-0.3. The powder preferably has particles with a D50 < 125 μπι.

It is noted that in order to increase slump of concrete such depends on factors as the type, dosage, and time of addition of a modifier, water-cement ratio and the nature or amount of cement. A person skilled in the art will be able using standard tests to determine suitable amounts, suitable modifiers, etc., contrary to e.g. a worker actually making the concrete .

When mixing, a further adjuvant may be provided.

It is an objective of the present invention to reduce water requirements, e.g. by 10-30%. A high-strength concrete with e.g. low permeability is provided. Flexural strengths greater than 70 MPa at 28 days have been attained.

A problem associated with using a SCM in concrete may be slump loss, e.g. when particle size engineering is absent or poorly conducted. The present modifier however still provides good or superior slump, e.g. of 245 or more.

Typically in prior art the slump loss problem is overcome by adding the pre-mixture to the concrete just before the concrete is placed. However, there are disadvantages to such a procedure. The dosage control, for example, is not adequate. Further, the addition is complex, e.g. it requires ancillary equipment. An option is to add pre-mixtures at the batch plant. Such may provide dosage control improvement. Further it may reduce wear of mixers. Even more preferred, howev ^¬ er, is to add a present pre-mixture comprising a required dose . _

Examples of polycarboxylates are available from IN- TERPOLYMER such as Rohagit® and Acrytex®, now sold under the trademark SYNTRAN®. Several additional polycarboxylates, including terpolymers, are now available. Similar products can be purchased from BASF. Homopolymers of acrylic acid polymers, such as SYNTRAN ® 8000 series, having a Total Solids of 20-50 wt.%, a pH (25°C) of 2-8.5, a Molecular Weight (GPC) of 2500- 150000, a Brookfield Viscosity [mPa.s] of 20-7000 and optionally a neutralizing agent, such as NaOH, and NH ₄ OH .

Copolymers of acrylic acid and methacrylic acid or maleic acid or ethylene acrylic acid or sulphonic acid or Acrylamido- methyl-propane sulphonate polymers or heteropolyacid, such as SYNTRAN ® 8400 and 8500 series, having a Total Solids of 30-50 wt.%, a pH (25°C) of 2-9, a Molecular Weight (GPC) of 4000- 60000, a Brookfield Viscosity [mPa.s] of 40-3000 and optional ^¬ ly a neutralizing agent, such as NaOH, and NH ₄ OH.

Terpolymers of acrylic acid and two or methacrylic acid, maleic acid, ethylene acrylic acid, sulphonic acid, acrylamido- methyl-propane sulphonate polymer, heteropolyacid, t-bis- dialkylamino acid, such as SYNTRAN ® 8700 and 8800 series, having a Total Solids of 35-45 wt.%, a pH (25°C) of <2-7.5, a Molecular Weight (GPC) of 4000-24000, a Brookfield Viscosity [mPa.s] of 50-8000 and optionally a neutralizing agent, such as NaOH, and NH ₄ OH.

In an example of the present pre-mixture the first composition comprises meta-kaolin, that may or may not be in the dehydrated form of meta-kaolin and/or wherein the calcium compounds comprise calcium carbonate and/or calcium oxide, preferably 60-70% of calcium carbonate and 40-30% of calcium oxide, and/or

wherein the first composition is obtained by thermal conver ^¬ sion of a material chosen from paper waste and residue from the paper production. It is noted that the present invention does not relate to the first composition per se; as identified throughout the description of a given composition first an equimolar amount of water sufficient to substantially satisfy a water demand of the calcium oxide is added.

Kaolinite is a clay mineral, part of the group of industrial minerals, with the chemical composition Al ₂ Si ₂ 0 ₅ (OH) ₄ . From kaolinite endothermic dehydroxylation (or alternatively, dehydration) beginning at 550-600 °C produces disordered metakaolin, Al ₂ Si ₂ 0 ₇ . Metakaolin is not a simple mixture of amorphous silica (Si0 ₂ ) and alumina (AI2O3) , but rather a complex amorphous structure that retains some longer-range order (but not strictly crystalline) due to stacking of its hexagonal layers. The largest use is in the production of paper, including ensuring the gloss on some grades of paper. Commercial grades of kaolin are supplied and transported as dry powder, semi-dry noodle or as liquid slurry.

Thus, kaolin and metakaolin are considered as silica-alumina compounds also forming part of a sorbent obtained from paper- waste or the like.

In a third aspect the present invention relates to a material, such as concrete, mortar, glass, cement, and wet sand, comprising an pre-mixture according to the invention.

In a fourth aspect the present invention relates to a use of an pre-mixture according to the invention in concrete or mortar for improving one or more of hardness, durability, flowability, slump, microstructure, processability, permeabil- ity, shrink behavior, slump retention, bending tensile

strength, water reduction, set-retardation, acceleration, plasticization, air entrainment, neutralization of surface charge, dispersion, agglomeration, viscosity, strength, flex- ural strength, pumpability, and self-healing properties, or in a sorbent, such as a sorbent of a metal, such as mercury. It has been found that the present pre-mixture increases the uptake of metal, e.g. of mercury, and/or makes the uptake more efficient, or in wet sand.

In a fifth aspect the present invention relates to a dry bagged concrete or mortar comprising a pre-mixture according to the invention. By adding water and mixing the concrete or mortar is ready to use. EXPERIMENTS

The present concrete mixture fall in a slump class S5 (EN 206- 1:2000), that is having the highest slump.

The Flexural strength is determined by CENTER point loading (ASTM C 293). The concrete is consolidated by vibration (ASTM C31) and tap sizes to release air pockets. For higher slump, after rodding, molds are tapped to release air pockets and spade along the sides to consolidate. The standard deviation is about 5%.

The invention is elucidated through the examples and figures which are exemplary and explanatory of nature and are not intended to be considered limiting of the invention. To the person skilled in the art it may be clear that many vari ^¬ ants, being obvious or not, and combinations of the examples and embodiments, may be conceivable falling within the scope of protection, defined by the present claims.