NL8304193A - ADDITIVE FOR CONCRETE, CONTAINING A VARIOUS COMPONENT MIXTURE WITH VERY FINE SILICON DIOXIDE, METHOD FOR ITS PREPARATION AND ITS USE. - Google Patents

Description

N.0. 32204 ------ "

Additive for concrete, comprising a multi-component mixture with very fine silica, process for its preparation as well as its use.

The invention relates to a concrete additive comprising a multicomponent mixture containing very fine silica, and at least one water reducing agent or at least one strong water reducing agent. The mixture can advantageously contain one or more water reducing agents in combination with one or more strong water reducing agents together with the very fine silicon dioxide. Accelerators and curing retardants as such or combined may also be used in the mixture as optional ingredients.

For example, the invention is directed to overcoming the drawback experienced in the decomposition of the air-containing concrete void system containing entrained air resulting from the use of water-reducing agents, while at the same time other known advantages such as workability, strength and formability of concrete containing water reducing agents are substantially maintained. According to the present invention, the very fine silicon dioxide and at least one water-reducing agent may or may not be pre-mixed with any further additives and the resulting mixture is added to and mixed with the concrete mass at any desired stage. Premixing is very advantageous compared to the practice of adding each component to the concrete mass in practice, because the action of a water-reducing agent during premixing ensures that the very fine silicon dioxide particles are uniformly coated and homogeneous. dispersed resulting in the breakdown of material flakes. The material flakes, which are formed when the components are added separately according to the usual practice, will be a serious disadvantage for the desired uniform strength and durability of the poured concrete. Once flakes have formed in the concrete mass, a relatively long mixing time is required to disperse the flakes, and over-mixing can be detrimental to the workability and deformability of the material.

Although the pre-mixing mechanism is not fully understood, it is believed to provide a synergistic effect on the plasticity and workability of the concrete. - 2 mass as well as an increased strength compared to conventional concrete masses, to which the components are added separately according to the method customary in practice.

The water reducing agents and any accelerators and retarders of the present invention used are known conventional materials currently used in high strength concrete, which concrete may have a compressive strength of up to about 40-85 MPa ·

One of the major advances in concrete technology over the last decades has been the application of air entrainment to protect concrete from damage caused by freezing of chemicals in the presence of antifreeze and thaw. The use of entrained air in concrete is generally recommended for almost all applications. Tests have shown that concrete containing about 5-7.5% by volume (+ 1%) of air will withstand about 1900 freeze-thaw cycles while concrete containing no entrained air and identical in all other factors, withstands approximately 150 cycles; for example, compare "Mr-Entrained 20 Concrete", Portland Cement Association, Document ISO 45.02T, 1967.

The use of entrained air-containing concrete has many other advantages, such as improved workability, improved anti-freeze resistance such as calcium chloride, improved sulfate resistance and improved water tightness.

A commonly used method of preparing entrained air-containing concrete involves the step of adding an air entraining material during the mixing of the concrete. Experience has shown that the action of mixing is the most important factor in the production of entrained air-containing concrete, and in this respect an even distribution of entrained air-containing voids is essential for the production of chipping-resistant concrete or crumble; an uneven distribution is always a risk if the entrained air is insufficiently dispersed during mixing. Also important are factors such as the size of the quantity of the concrete mass to be mixed, the nature of the mixer and the speed of mixing. Excessive mixing may even result in some of the entrained air being lost, but the techniques and preferred methods used in the mixing phase of entrained air-containing concrete are now fairly well understood and further explanation of the des-1 8304193 3 expert considered superfluous.

A number of air-entraining materials prepared from various materials are currently commercially available, such as thermoplastic resins containing phenol aldehyde and ether groups, and their salts and soaps.

The vinsol resins are undoubtedly the most widely used airborne materials in the United States of America. Vinsol resin is a softwood thermoplastic resin containing phenol aldehyde and ether groups. The sodium soap of vinsol resin is a particularly effective air entraining material and needs to be used in an amount of only about 0.15% by weight, based on the binder, to incorporate entrained air in conventional manner. a concrete material. DAREX AEA, which is a sulfonated hydrocarbon acid derivative of greases and grease sold by Dewey and Almy 15 Chemical Co., is another widely used air entrainer.

The entrained air-containing concrete obtained by the use of known air entrainment products resume a large number of air bubbles which are very small; the average diameter of the air bubbles is usually about 8 x 10 "2 - 2 x 10" * * mm and there may be as many as 400-600 billion bubbles in one cubic meter of entrained air-containing concrete with an air content in the range of 4-6% by volume, and an aggregate with maximum dimensions of about 2.5 cm and about 1.3 cm. The bubbles are not interconnected and are well distributed throughout the binder / water phase. The spacing of the air-containing cavities is an important factor in the freeze-thaw resistance of hardened concrete, and a spacing of less than about 0.02 cm, measured according to ASTM C457, is considered essential to achieve the required resistance against freezing-thawing.

One of the most important developments of concrete since the development of entrained air-containing concrete in the mid 1930s-1940s is the use of so-called water-reducing agents.

Water reducing agents are chemical compounds which, when added to concrete, liquify the concrete for a period of time, so that (1) normal workability can be obtained from concrete, which has a much lower water-binder ratio. than would normally be used or (2) liquid concrete workable under extreme conditions (which is significantly self-leveling without adverse side effects such as segregation, low durability, low wear and bleeding resistance), or (3) a combination of (1) and (2).

Water reducing agents are known additives for concrete.

5 The commonly available materials fall into six different classes: 1. Hydroxylated carboxylic acids and their salts, 2. Modifications and derivatives of hydroxylated carboxylic acids and their salts, 10 3. Inorganic materials such as zinc salts, borates, phosphates and chlorides , 4. carbohydrates, polysaccharides and acids of sugars, 5. amines and their derivatives and polymeric compounds such as cellulose ethers and polysiloxanes, 6. certain modified lignosulfonic acids.

The terms water reducing agent and water reducing agent used in this specification serve to designate one or more of the components of the above classes of conventional materials as such or in combination.

Strong water-reducing agents which are now widely used in the art include: 1. lignosulfonic acids and their salts and modifications and derivatives thereof, 2. melamine derivatives, 3. naphthalene derivatives.

By the terms strong water reducing agent and water reducing agent used herein, one or more of the components of the above three classes of materials are intended as such or in combination.

There are at least twelve widely used strong water reducing agents, all belonging to the above categories (2) and (3). The preferred material in category 35 (2) is a conventional sulfonated condensate of melamine and formaldehyde sold under the trade name Melment, and the preferred material in category (3) is a sulfo naphthalene and formaldehyde condensate.

The strong water reducing agents have a much greater puddle-tifying effect in conventional concrete masses. Best results 332 * 193 * 5 in processability, formability and strength are achieved by using the high water reducing agents of the present invention.

Concrete, which contains strong water reducing agents, is applied on a uLt-5 knitted shell under conditions that require extreme flow properties when pouring, such as in areas of high reinforcement density, during pumping and in structures with a complicated shape. As advantages of the use of strong water-reducing agents in pre-poured concrete and in finished belt mixes can be mentioned: (a) increased strength in any aging state, (b) improved resistance to sulfate attack, ( c) improved adhesion to the reinforcement, (d) improved workability and formability, and (e) reduced water permeability.

When a strong water reducing agent is added to a concrete mix, the plasticizing effect lasts about 30-60 minutes, depending on the conditions of the application. Therefore, it must be added at the application site when it is used in ready-mixed admixture concrete.

Concrete containing one or more strong water reducing agents is described in "Super Plasticized Concrete", ACI Journal, May 1977, biz. N6-N11 and references indicated therein.

Although concrete, which may be referred to as entrained air-containing concrete or water-reducing agent plasticized concrete, has proven to be excellent for many applications requiring only the quality properties attributable to air entrainment or plasticization, difficulties were encountered when an attempt was made to use both an air entrainment mixture and a strong water reducing agent for plasticizing the concrete.

In particular, it is now generally accepted that the system of air-containing cavities of cured entrained air-containing concrete containing a strong water-reducing agent and a neutralized vinsol resin is very defective; that is, the spacing factor of the air-containing voids is greater than about 0.02 cm and there is a possibility that air loss from the fresh concrete may occur. As already mentioned, the parameters of the air-containing cavities, in particular the spacing factor of the system of air-containing cavities, are very important criteria for predicting the presumed behavior of concrete with respect to 8304103 * + 6 resistance against repeated freeze-thaw cycles.

The present invention is based on the problem of producing a concrete having the desired freeze-thaw properties and properties of entrained air-containing concrete together with the excellent workability and improved strengths of water-reducing agent plasticized concrete.

Therefore, it is an object of the invention to provide a water-reducing agent as a plasticizing additive for concrete which will not reduce but improve freeze-thaw resistance.

It has been found that a premixed mixture of very fine silicon dioxide and one or more water reducing agents, preferably a strong water reducing agent, used as such or in combination, when added to mortar and concrete, increases the density and impermeability of the increases mortar or concrete by several orders of magnitude. Indeed, it has been found that no entrained air-containing concrete produced with the very fine silica-containing mixture of the invention is actually impermeable to water (which can freeze) and aggressive liquids. Concrete, which contains the mixture of very fine silicon dioxide, has a freeze-thaw resistance equal to or better than that of entrained air-containing concrete, and it has equal or greater strength. Therefore, degradation of the system with air-containing voids normally encountered with both the normal water-reducing agents and the strong water-reducing agents is of no concern since the loss of air or the increase in bubble spacing is compensated for. due to the beneficial effects of the mixture with very fine silicon dioxide due to fundamental changes in the pore structure of the binder phase of the concrete. More in particular, a more uniform dispersion of the binder phase with a significantly finer pore structure is obtained.

The very fine silicon dioxide of the present invention is an amorphous silicon by-product of the preparation of ferrosilicon and also silicon metal, and is obtained by capturing the finely divided particles from the exhaust gases from electric blast furnaces. Very fine silicon dioxide is a pozzolan, that is to say that in combination with lime and moisture at normal temperature it has a material with cement-like properties. The main component is silicon dioxide (SiO2), and it is usually present in an amount of at least about 60% by weight, but according to the present invention, the best results are achieved when the SiO2 content is at least about 85%. wt% is ·

An amorphous silicon dioxide, which is excellent for use in the present invention, is obtained as a by-product in the production of silicon metal or ferrosilicon in electric reduction furnaces. In these processes, fairly large amounts of silica are formed as a very fine powder, which is recovered by means of filters or other collecting devices. Such silica is available from Elkem a / s, Norway.

The analyzes and physical properties of typical silica samples usable in accordance with the invention are set forth in Tables A and B.

TABLE A

Very fine powder collected during the production of Si metal in a bag filter:

Component Quantity in wt%

SiO 2 94-98

SiC 0.2-0.7

Fe203 0.05 - 0.15 TiO2 0.01 - 0.02 A1203 0.1 - 0.3

MgO 0.2 - 0.8

CaO 0.1 - 0.3

Na20 0.3 - 0.5 25 K20 0.2 - 0.6

Mn 0.003 - 0.01

Cu 0.002 - 0.005

Zn 0.005 - 0.01

Ni 0.001 - 0.002 30 S 0.1 - 0.3 C 0.2 - 1.0 P 0.03 - 0.06 loss on annealing (1000 ° C) 0.8 - 1.5 bulk density, from the bunker, g / 1 200 - 300 35 bulk density, compressed, g / 1 500 - 700 actual density, g / cm ^ 2.20 - 2.25 specific surface area, m ^ / g 18-22 primary particle size, percentage <1 p 90 8304193 * * 8

TABLE B

Fine powder collected in a bag filter for the production of 75% by weight of FeSi:

Component Amount in wt% 5 SiO 2 86 - 90

SiC 0.1-0.4

Fe2 O3 0.3-0.9

TiO2 0.02 - 0.06 A1203 0.2 - 0.6 10 MgO 2.5 - 3.5

CaO 0.2 - 0.5

Na20 0.9-1.8 K20 2.5-3.5

Mn 15 Cu

Zn Ni S 0.2 - 0.4 C 0.8 - 2.0 20 P 0.03 - 0.08 loss on annealing (1000 ° C) 2.4-4.0 bulk density, from the bunker, g / 1 200 - 300 bulk density, compressed, g / 1 500 - 700 actual density, g / cm ^ 2.20 - 2.25 25 specific surface area, m ^ / g 18 - 22 primary particle size, percentage <1 ym 90

Amorphous silicon dioxide of the type described above can be obtained in other processes for the preparation of Si and FeSi, for example in the preparation of silicon, in which silicon dioxide (coarse silicon dioxide, for example quartz) is reduced with carbon. If the alloy is to prepare ferrous silicon, iron is added. Part of the product of this reduction of silicon dioxide can be re-oxidized in the vapor phase (gas phase) (eg in air) to form the fine, particulate silicon dioxide which can be used according to the invention. While the very fine powder collected from an electric oven producing ferrosilicon with at least 75 wt% silicon is preferred, the very fine powder collected from an electric oven used for the production of 50 wt.% ferrosilicon, also used in the present invention.

8304133 9

It is possible to obtain the amorphous silicon dioxide as a by-product, but as the main product, by appropriately adjusting the reaction conditions. Amorphous silicon dioxide of this type can also be produced synthetically without reduction and reoxidation.

The amorphous silicon dioxide used in accordance with the present invention consists essentially of spherical particles less than about 1 micron in size. The spherical shape together with its fineness (pozzolar activity) makes it surprisingly useful according to the present invention.

By way of example, it can be mentioned that the amorphous silicon particles may consist of at least 60-90 wt.% SiO2, will have an actual density of 2.20-2.25 g / cm 2 and a specific surface area of 18 Will have -22 m 2 / g, the particles being substantially spherical, and at least 90 wt% of the primary particles having a particle size of less than 1 micron. Of course, variation of these values is certainly possible. For example, the silicon dioxide may have a lower SiO2 "content. In addition, the particle size distribution can be adjusted, therefore it is possible to remove relatively coarse particles by classification.

Due to a carbon content, the amorphous silicon dioxide can have a dark gray color. However, this carbon can be removed by burning, for example at a temperature above 400 ° C. It is also possible to modify the processes for the preparation of the silicon and ferrosilicon so that the silicon dioxide is obtained in a relatively white form, which, incidentally, is in fact identical to the normally prepared gray silicon dioxide. The modification of the process mainly consists of reducing the amount of carbon or removing the amount of carbon from the material. The other consequence of this change is a change in the ratio of the silicon dioxide produced to the amount of silicon or ferrosilicon; in other words, the ratio of silicon dioxide to silicon or ferrosilicon is higher in the modified process.

The term "very fine silicon dioxide" as used herein refers to the particulate amorphous silicon dioxide obtained by a method of reducing silica and the product obtained in the reduction in the vapor phase (gas phase) in air is oxidized. The term "very fine silica" also includes the same type of amorphous silica, 8304193 * 10, which is produced synthetically without reduction and reoxidation. The very fine silicon dioxide of the present invention is most suitably obtained from the off-gas from silicon metal or ferro-silicon production processes in electric reduction furnaces.

A mixture according to the present invention contains about 30-98% by weight of very fine silica and about 2-50% by weight of one or more water reducing agents, based on the weight of the very fine silicon dioxide in the mixture. One or more large range water reducing agents may also be used as such or in combination with one or more common water reducing agents. These are the main ingredients in the very fine silicon dioxide-containing mixture, in which the chosen strong water-reducing agent and / or the ordinary water-reducing agent is uniformly and homogeneously dispersed in the very fine silicon dioxide.

The ingredients can be mixed in any conventional mixer and, for example, 20 kg of very fine silica and 2 kg of Melment (strong water reducing agent) are mixed with a rotary drum mixer for dry material, the 20 particulate components being are in intimate contact with the mixture, are uniformly and homogeneously dispersed in the mixture according to the present invention. Best results are achieved by mixing the major ingredients in an aqueous suspension to ensure intimate contact between the ingredients and a uniform homogeneous dispersion. The aqueous suspension-like mixture may contain about 10-80 wt.% Very fine silica and preferably about 40-60 wt.% Very fine silica and about 0.5-40 wt.% (Based on the dry weight) of one or more more strong water reducing agents or ordinary water reducing agents as such or in combination and preferably containing about 1.0-20 wt.% thereof as such or in combination therein, the remainder being water.

For example, about 20 kg of very fine silica, about 1.4 kg of sulfated technical grade naphthalene formaldehyde condensate (strong water reducing agent) and about 1.4 kg of technical grade cellulose ether (water reducing agent) become uniform and homogeneous dispersed in about 20 liters of water, preferably using a Banbury mixer. The pH of the aqueous suspension can be adjusted to about 3.0-7.5, preferably about 5.0-6.0 with conventional acid or alkali, to provide a suspension of suitable consistency for transport and mixing with the concrete mass. In addition to or instead of adjusting the pH of the suspension, dispersants such as phosphates, citric acid, polyacrylates or glycerol can be used to achieve the desired consistency of the suspension. Water is the most economical liquid used to form the suspension mixture of the present invention, but an organic liquid may be used if desired provided it is compatible with the concrete and is not otherwise disadvantageous.

The relative viscosity of an aqueous suspension mixture according to the invention was recorded using a Haake viscometer using an E.30 sensor and according to the standard procedure described by the manufacturer and compared to a blank water containing suspension containing the same amount of very fine silica without any water reducing agent. Each sample of the slurry contained 65% by weight of very fine silica for comparison. The results are shown in Table C.

5 - Γ / - j 0 t V \ / v *. · - 'y j 12

Table C

Sample Inverted Measured Measured Measured speed of torsion torsion torsion the sensor- after 1 hour after 7 after 28 _rotation_days_days

Blank 32 53> 150> 150 16 56> 150> 150 8 60> 150> 150 4 64> 150> 150 2 69> 150> 150 1 78> 150> 150 yield strength 49> 150> 150

Sample A

lignosulfate 32 4 8 11 2.5 wt.% 16 4 11 16 (Borresperse NA) 8 5 11 17 4 6 12 18 2 7 14 23 1 9 16 23 yield strength 2 3.5 15.0

Sample B 32 18 17 26 sulfonated condensate 16 20 21 27 naphthalene 8 25 23 26 and formaldehyde, 4 27 24 25 2.5 wt% (Mighty) 2 32 28 27 1 39 34 33 yield point 28 28 43

Sample C 32 21 57 - 55 sulfonated condensate 16 32 63 61 sate of melamine and 8 33 68 64 formaldehyde, 4 36 74 69 2.5 wt.% 2 42 81 76 (Rescon HP) 1 49 91 88 yield point 32 63 72 8 304 193 s 13

As is apparent from the above data, very fine silicon dioxide will tend to form a thixotropic mixture in water, often resulting in the gelling of the aqueous suspension. When the suspension gels this is not advantageous, since in practice it is extremely difficult to pump this material from the storage container. It was surprising and unpredictable that the large range water reducing agent of samples B and C of Table C and the plain water reducing agent of sample A of Table C were found to be effective in reducing the tendency to gel of the aqueous suspension, as is often experienced with very fine silica as such in an aqueous suspension.

It is believed that during mixing, the strong x-ray reducing agents and the common water-reducing agents tend to coat the surface of the very fine silica particles, thereby effectively reducing the gelling tendency of the suspension. Experience has shown that when the yield point in Table C is close to about 25, the aqueous slurry is excellent for the use of the present invention and that the aqueous slurry remains satisfactory up to a yield point of about 75. the yield point of the slurry is above about 100, it becomes difficult to pump and the slurry is no longer considered suitable for use in the present invention.

According to the present invention, an aqueous suspension of very fine silica is stabilized and the gelling tendency can be significantly reduced or eliminated by dispersing about 0.1-10.0 wt%, preferably about 2.0 - 5.0% by weight of a strong water reducing agent or an ordinary water reducing agent in the aqueous suspension, the amounts as a dry matter being based on the weight of the very fine silicon dioxide. Generally, the amount of very fine silica in the aqueous suspension will be at least only 5 wt% and at most about 80 wt%. One or more strong water reducing agents or ordinary water reducing agents may be used as such or in combination to stabilize the very fine silica-containing mixture in aqueous suspension. When the aqueous suspension mixture is to be used as an additive for concrete or mortar, the amount of strong water reducing agent or ordinary water reducing agent may be greater than 10% by weight and, as above already indicated, make up about 0.5 - 40% by weight of the aqueous suspension mixture.

The amount of the mixture according to the invention to be added to a conventional fresh concrete mixture or a conventional fresh mortar will depend on the application purpose. The amount of the mixture to be added is based on the weight of the binder in the concrete or mortar mass.

Generally, a sufficient amount of the mixture according to the invention is added to and mixed with a fresh concrete or mortar mass to contain about 2.0-100 wt.%, Preferably about 2-25 wt.%, Of dry very fine silica. , based on the weight of the binder in the mass, and about 0.1-5% by weight of strong water reducing agent or ordinary water reducing agent as such or in combination, based on the weight of the binder in the concrete or mortar mass.

According to a common industrial practice, the optimum amount of the components in the mixture and the amount of the mixture within the indicated range to be added to the concrete with the other materials 20 is determined by tests, in which the prevailing conditions and the construction regulations, which are important at the place of construction, are simulated. Conventional tests are used to indicate the effect of the mixture on the concrete, as far as the application purpose is concerned with regard to the air content of the concrete, consistency, bleeding of water and possible loss of air from fresh concrete, the hardening speed, compression and bending strength, resistance to freezing and thawing, shrinkage on drying and permissible chloride content.

The known addition of strong water reducing agents and ordinary water reducing agents often cause excessive bleeding and separation in the concrete mass, as indicated by a thin aqueous paste, which cannot keep the coarse aggregate particles in suspension. It is also known that most strong water reducing agents and ordinary water reducing agents cause plasticity by reducing the surface tension of the water component of the concrete mixture. This can result in separation of coarse aggregate particles and result in poor freeze-thaw resistance, poorer pumpability, poor separation resistance, finishing difficulties and poor surface texture in mold making.

83 0 4 1 i .1 15

The addition of very fine silicon dioxide of the mixture according to the invention with its high degree of fineness increases the surface area of the solids per unit volume of water, whereby a better separation and suspension of coarse aggregate particles is achieved and has an improved plasticity and processability by changing the interference of the particles. Since the mixture of binder, water and the composition of the invention contains more solids per unit volume, the paste is less watery and less prone to separation. Bleeding is thereby reduced by the very fine silicon dioxide by retaining the water in the paste. This produces a homogeneous, highly workable, pumpable mixture with reduced bleeding properties.

The compressive strength achieved with concrete containing the mixture of the invention is generally higher than would be expected from the sum of the increases in strength that would be achieved by adding each ingredient separately. The reason for this is not fully understood, but it is believed that the water reducing agent for large ranges or the ordinary water reducing agent provides a better distribution of the very fine silicon dioxide particles in the concrete mass and that certain synergistic effects between the constituents of the mixture according to the invention.

The mixture according to the invention is advantageously used in conventional fresh concrete mixtures and is mixed with the concrete mass using the known techniques currently used for mixing concrete. For example, an aqueous suspension mixture containing about 20 kg of very fine silicon dioxide, about 3.6 kg of dry Lomar D (strong water reducing agent, sulfonated condensate of naphthalene and formaldehyde) and about 20 liters of water can be added without any other additives to and mixed with a conventional fresh concrete material containing about 200 kg of Portland cement type I without any other additive. The resulting concrete mixture, which has a water to binder weight ratio of 0.35, has good workability, consistency and no separation in the fresh state. In the cured state, the compressive strength after 28 days is remarkably high and of the order of about 85 MPa, and the freeze-thaw resistance is surprisingly high even in the absence of entrained air. The concrete mixture contains 10% by weight

40 very fine silicon dioxide (dry) and about 1.5 wt% Lomar D

8% η λ <λ ί

J 'v “f 5 -J J

16 (dry), based on the weight of the binder In the concrete mix. The reduced permeability of the resulting mixture increases the permeability to water and aggressive chemicals, thereby improving the freeze-thaw properties compared to a concrete or mortar mixture containing the aqueous suspension. mixture of very fine silicon dioxide.

The mixture of the present invention is premixed in the optimum amounts, which is determined by tests customary in the art, providing a separate dispensing system as opposed to conventional practice, where three. up to four delivery systems are required at the application site. All additives may be dispensed simultaneously with the mixture of the invention, wherein the ingredients are dispersed evenly and homogeneously as compared to the conventional practice of adding the individual ingredients one after the other to avoid flocculation. With the mixture according to the invention, the loading time of, for example, trucks is reduced and the risk of errors is reduced, because the addition of only one load is required instead of three or four loads. Storage facilities can be reduced and quality control is improved by having one supplier supply all additives in the separate mixture according to the invention, thereby eliminating the problem of storage container soiling. Another advantage of the aqueous suspension form of the mixture according to the invention is that the problem of fine particle dust at the place of application is eliminated. Nevertheless, when used on a relatively small scale, the dry particulate mixture can be packaged, for example in bags of 30 - 50 kg, and delivered to the place of application.

The ability of the mixture of the present invention to provide improved sulfate resistance and improved alkali-silica reaction in concrete containing the mixture is among the beneficial effects of the mixture of very fine silica.

Since the mixture of the present invention can be used under conditions that can unacceptably extend the curing time, accelerating ingredients can be added to the mixture to provide optimum curing properties and fast strength properties. Furthermore, it may be desirable to delay the fresh concrete curing time, such as, for example, with a bridge deck, so that the curing takes place after the installation and finishing have been completed.

The mixture according to the present invention is ready-made with optimum constituents and amounts thereof for the concrete to be used for the construction work to be carried out. Any of the known additives commonly used in the preparation of concrete or mortar can be included in the mixture of the invention.

Accelerators, such as the known calcium chloride, calciuran nitrate and calcium formate, can be incorporated with the main ingredients into the mixture in amounts commonly employed in the art and determined by standard tests for the optimum amount for the particular application. One or more accelerators can comprise about 5-20% by weight, based on the weight of very fine silica in the mixture.

Retardants, such as sugar in the form of glucose or sucrose, which are commonly used in concrete or mortar masses, can also be incorporated into the mixture of the invention at optimal levels, determined by standard tests. One or more retarders may be present in an amount of about 5-20% by weight, based on the weight of the very fine silica in the mixture.

If desired, air entrainment agents such as Vinsol resin or Darex (a sulfonated fatty acid derived from fats and grease) can be incorporated into the mixture of the invention in those special applications where a certain amount of entrained air can provide a desired property deliver. One or more air entrainment agents may be present in an amount of about 0.5-2% by weight based on the weight of the very fine silica.

One or more additives can be incorporated as such or in combination with other additives with the main ingredients in the mixture according to the invention. The compatibility and consistency of the mixture is determined by standard tests as well as the final effect on the respective concrete or mortar mass used in the construction work to be carried out.

The mixture of the invention may contain various amounts of the selected ingredients, but in order to obtain the benefits of the present invention, an amount of the mixture will be 8304193

μ "1 W.

18 * which is mixed with a conventional fresh concrete mass, are sufficient to provide about 2.0-100 wt.% Of very fine silica, based on the weight of the binder, and about 0.1-5 wt.% Of one or more strong water reducing agents or ordinary water reducing agents, as such or in combination, based on the weight of the binder.

Water or an organic liquid compatible with fresh concrete is preferably added to the mixture in an amount sufficient to provide a slurry in which the main ingredients are evenly and homogeneously dispersed. Accelerators, retarders, air entrainment agents and any other conventional additives are mixed with the main components of the mixture of the present invention in an amount sufficient to provide the desired concentration in the fresh concrete mass. In all cases, the optimum amount of the ingredients present in the mixture of the present invention is determined by conventional standard tests under the simulated prevailing conditions for the materials to be used and the construction regulations to be used.

330 * 193

Claims (25)

Cement or mortar additive, characterized in that it comprises a mixture of main constituents, at least one constituent being a water-reducing agent and / or a strong water-reducing agent dispersed in very fine silicon dioxide, the very fine silicon dioxide is present in this mixture in an amount from about 30 wt% to about 98 wt% and one or more water reducing agents are present in an amount from about 2.0 wt% to about 50 wt%, by weight on the weight of the very fine silica. Additive according to claim 1, characterized in that it is suspended in at least one liquid such as water and an organic liquid, the solid content in this suspension being about 20-80% by weight. Additive according to claim 1 or 2, characterized in that it contains one or more water reducing agents and one or more strong water reducing agents. Additive according to claims 1 to 3, characterized in that it contains one or more accelerators, one or more retarders and one or more means for entraining air as such or in combination. Additive according to claims 1 to 4, characterized in that the very fine silicon dioxide is obtained from the waste gas of an electric furnace, which is used for the production of ferrosilicon or silicon metal. Cement or mortar additive, characterized in that it comprises an aqueous suspension containing as main ingredients at least one water reducing agent and / or strong water reducing agent dispersed in the suspension and mixed with the very fine silicon dioxide, wherein the suspension has a solid content of the very fine silicon dioxide and at least one water reducing agent of from about 20 wt% to about 80 wt%, based on dry matter, the very fine silicon dioxide being present in an amount of at least about 10% by weight, based on the solids content of the slurry, and wherein the water reducing agent is present in an amount from about 0.4% by weight to about 40.0% by weight, based on on the solids content therein. Additive according to claim 6, characterized in that it has a pH of about 3.0 to about 7.5. Additive according to claim 6 or 7, characterized in that the very fine silicon dioxide are dispersed uniformly and homogeneously in the suspension with at least one water-reducing agent "6334193 * V". Additive according to claim 6 or 7, characterized in that it contains one or more water-reducing agents and one or more strong water-reducing agents. An additive according to claims 6-9, characterized in that the very fine silicon dioxide is obtained from the waste gas of an electric furnace, which is used for the production of ferrosilicon or silicon metal. 11. Additive according to claims 6-10, characterized in that it contains one or more usual additives in addition to the water-reducing agent in the suspension mixture. 12. Building element of hardened concrete, formed from a conventional concrete mass, characterized in that a mixture is added to the usual concrete mass, the main components of which are at least one water-reducing agent and / or strong water-reducing agent, dispersed in very fine silicon dioxide. , wherein the very fine silicon dioxide is present in the building element in an amount of about 2 - 100% by weight of very fine silicon dioxide, based on the weight of the cement in this building element and wherein the water-reducing agent is present in the building element in an amount of about 0.1-5.0 wt%, based on the weight of the cement in the building element. Building element according to claim 12, characterized in that it contains one or more water-reducing agents and one or more strong water-reducing agents. Building element according to claim 12 or 13, characterized in that the mixture added to the concrete contains one or more conventional additives for concrete. 15. A process for forming a multi-component mixture as an additive for concrete, characterized in that the following steps are carried out: mixing one or more components such as water reducing agents and strong water reducing agents with very fine silicon dioxide, adding silicon dioxide in an amount to provide from about 30 wt% to about 98 wt% of the mixture and adding from about 2.0 wt% to about 50 wt%, based on the weight of silica of at least one ingredient in that mixture and continue mixing until the former ingredient is evenly dispersed in the very fine silica. 16. Method for forming a multi-component 8304193 fc. **. · * '. The existing mixture as an additive for cement, characterized in that the following steps are carried out by mixing one or more components such as water-reducing agents and strong water-reducing agents with water and with very fine silicon dioxide, adding the very fine silicon dioxide to the aqueous suspension in such an amount that about 10 wt.% to about 80 wt.% of very fine silica is provided in the aqueous suspension and adding the former ingredient in such an amount that about 0.5 wt.% to about 40 weight percent (dry matter) of this component in the aqueous suspension is provided. The method according to claim 15, characterized in that it comprises the step of adding the mixture to a conventional concrete mass in an amount sufficient to provide from about 2 wt.% To about 100 wt.% Of the very fine silicon dioxide, based on the weight of the cement in the concrete, and comprises from about 0.10 wt.% to about 5.0 wt.% of the former component, based on the weight of the cement in the concrete mass. 18. Process for preparing an improved fresh concrete mass, characterized in that the following steps are carried out: forming a multicomponent mixture by combining and mixing at least one component such as water reducing agents and strong water reducing agents with water and with very fine silica, adding the aqueous slurry mixture to a conventional fresh concrete concrete mass in an amount sufficient to provide from about 2 wt.% to about 100 wt.% of the very fine silica on the weight of the cement in the concrete, and about 0.10 wt.% to about 5.0 wt.% of the former, based on the weight of the cement, to provide and mix the fresh concrete and the water containing slurry mixture to further dilute the ingredients of the mixture therein. A method according to claim 18, characterized in that it comprises the step of adjusting the pH of the aqueous mixture to about 3.0 to about 7.5 during mixing thereof. A method according to claim 18 or 19, characterized in that it comprises the step of continuing to mix the components of the aqueous suspension mixture until the very fine silicon dioxide and the former component are uniformly and homogeneously in intimate touch are dispersed therein. 21. Process according to claims 18-20, characterized in that it comprises the step of adding and mixing one or more conventional additional additives to the aqueous suspension mixture. 22. Method according to claim 21, characterized in that as usual additive one or more conventional retarders and / or means for entraining air are used. 23. Water-containing suspension, characterized in that it contains very fine silicon dioxide, which is stabilized against gelling with at least one or more water-reducing agents and strong water-reducing agents, this water-reducing agent being present in a suspension in a amount from about 0.1 wt% to about 10 wt% (as dry matter), based on the weight of very fine silica in the slurry. 24. Suspension according to claim 23, characterized in that it contains one or more water-reducing agents and one or more water-reducing agents. A method according to claim 16, characterized in that it comprises the step of adding one or more strong water reducing agents and one or more water reducing agents to the aqueous suspension. H-H-t-H-H-1-l-1-8304193