FI72962C - Additive mixture for concrete and use, process for its preparation and its use. - Google Patents

Description

1 72962

This invention relates to a concrete-mortar admixture in the form of a slurry containing silica dust, a plasticizing and / or superplasticizing agent and water. The invention also relates to a process for preparing such an admixture mixture and to the use of the admixture mixture as an additive for concrete and mortar.

It is known to use silica dust as a concrete admixture.

CH patent publication 574 88C discloses a cement mixture consisting of cement, silica dust and possibly a plastic sounding agent. However, silica dust and plasticizer are added separately to the cement.

15 GB patent 1,532,178 discloses a process for preparing a cement mixture with a low aluminum content. The mixture consists of silica dust, cement and possibly a plasticizer. The publication further states that cement, silica gel dust and possibly 20 plasticizers can be mixed before they are added to the concrete. However, it is a dry mixture. Thus, a sufficiently homogeneous mixture of silica dust and plasticizer is not obtained.

It has now been found that substantially better results are obtained by adding a mixture of slurry in the form of a slurry containing silica dust, plasticizer and water to the concrete or mortar, while surprisingly being found to have a tendency to gel, allowing long storage time. The mixture further has other advantageous properties, which are described below.

2 72962

The invention thus relates to a mixture of concrete and mortar admixture, characterized in that it is in the form of a slurry containing 10-80% by weight of silica oil, 0.5-40% by weight of plasticizer and / or superplasticizer and the remaining 5 water, and The pH is in the range of 3.0-7.5.

The invention also relates to a process for preparing such an additive mixture. The process is characterized in that one or more plasticizing and / or superplasticizing agents are mixed with water, after which silica-10 dust is added so that the mixture contains 10-80% by weight of silica dust and 0.5-40% by weight of plasticizing and and / or a superplasticizer, and the pH of the mixture is adjusted to 3.0-7.5.

Although events during premixing are not fully understood, it is assumed that premixing has a synergistic effect on the plasticity and workability of the concrete batch. At the same time, higher strength is achieved than in ordinary concrete batches, to which the components are added one by one in the usual way.

The plasticizers and possible accelerators or retarders used in the invention are known, common substances which are currently used in high-strength concrete with a compressive strength of 40-80 MPa.

The invention also relates to the use of an admixture mixture as an additive for concrete and mortar, such that the concrete or mortar contains 2 to 100% by weight of silica dust and 0.1 to 5% by weight of plasticizer and / or superplasticizer, based on the amount of cement.

The mixture can be added to the concrete batch at any stage of the mixing process. Such premixing has a major advantage over the conventional concrete mixing method, in which each component is individually mixed into the concrete. When premixed with water, the plasticizer tends to coat the silica dust particles and disperse them homogeneously in the pulp. As a result, the flocculated substances formed in the material decompose. Such flocculated substances are often formed by mixing the components separately. Flocculated substances 3 72962 can have a very detrimental effect on the uniform strength and durability of cast concrete. If flocculated substances have formed in the concrete deposit, their dispersion requires time-consuming mechanical mixing. This can lead to over-mixing, which can ruin the machinability and castability of the batch.

Since the introduction of aerated concrete in the mid-1930s, more important advances in concrete technology have been the so-called introduction of plasticizers 10.

Plasticizers are chemical compounds that bring concrete into a fluid state for a specified period of time. This means that 1) concrete with a much lower than normal water-cement ratio can be machined in the normal way, or 2) very easy-to-machine "flowable concrete" (indeed self-leveling without undesirable side effects such as mixture release, loss of strength) can be produced. , deterioration of abrasion resistance and water separation) or 3) items 1) and 2) can be combined.

Plasticizers are known additives for concrete. The substances on the market can be divided into six groups: 1. 1. hydroxylated carboxylic acids and their salts, 2. modifications and derivatives of hydroxylated carboxylic acids and their salts, 3. inorganic substances such as zinc salts, borates, phosphates and chlorides, 30 4. carbohydrates, polysaccharides, sugar acids, 5. amines and their derivatives and polymeric compounds such as cellulose ethers and silicones, 6. certain modified lignosulfonic acids.

As used herein, the term plasticizer means one or more ingredients of the above six groups of common substances, either alone or in combination.

4 72962 Conventional superplasticizing agents currently on the market include 1. lignosulfonic acids and their salts and their modifications and derivatives, 5. 2. melamine derivatives, 3. naphthalene derivatives.

By superplasticizer is meant herein one or more of the three groups of substances mentioned above, either alone or in combination.

10 At least twelve superplasticizers are used in normal use. Eight of these belong to the above groups 2) and 3). The preferred substance of group 2) is a sulfonated condensate of melamine and formaldehyde in the usual manner, sold under the designation Melment. The preferred substance of group 15 3) is a sulfonated condensate of naphthalene and formaldehyde.

Concrete containing superplasticizers is often used in casting operations where good casting properties are required, e.g. in densely reinforced sites, pumping-20 in concrete and complex mold casting. The use of superplasticizers in precast concrete elements and precast concrete provides the benefits of a) increased strength at all degrees of curing, b) improved sulfate resistance, c) better bonding to the reinforcing steel, and d) reduced water permeability.

When adding a plasticizer to a concrete deposit, the plasticizing effect lasts for about 30-60 minutes, depending on the conditions at the construction site. When using precast concrete, the material must therefore be added on site.

30 Concrete containing one or more superplasticizers is described in "Super Plasticized Concrete", ACI Journa., May 1977, pp. N6-N11 with written references.

It has been found that by adding to the mortar and concrete 35 a premixed admixture as a slurry containing 10-80% by weight of silica dust, 0.5-40% by weight of plasticizer and / or super- 72962 plasticizer and the rest of water, and having a pH of value of 3.0 to 7.5 can be used to improve the tightness and impermeability of mortar and concrete by many orders of magnitude. It has even been found that unmixed concrete prepared with the admixture mixture of this invention virtually eliminates the ingress of frozen water and aggressive liquids. The freeze-thaw resistance of silica dust-containing concrete is equal to or better than that of air mixed as such with mixed air, 10 and the strength is equal to or better. The compensators for the loss of air and the increased pore distance are the beneficial effects of the addition of silica dust on the basic changes in the pore structure of the concrete 1 adhesive phase. The result is a more even distribution of the adhesive phase and a significantly finer pore structure.

The silica dust used in the present invention is an amorphous silica by-product obtained in the manufacture of ferrous iron and silicon metal. Dust is obtained as fine particles from the flue gases of electric fusion furnaces. Silica dust is of the pozzolan type, i.e. it reacts with lime and moisture at ordinary temperatures and forms compounds with binding capacity. The main component is silica (SiO 2). · Dust usually contains at least 60% Siesta, but the best results are obtained in this invention with a SiO 2 content of at least about 85% by weight.

The following tables show the chemical and physical values obtained with typical samples of the silica used in the invention.

6 72962 TABLE 1

Dust collected from bag filters in Si metal fabrication Component Weight%

SiO 2 91-98 5 SiC 0.2-0.7

Fe 2 O 3 0.05 - 0.15

TiO 2 0.01 to 0.02 A1.0, 0.1 to 0.3 10

MgO 0.2 - 0.8

CaO 0.1 - 0.3

Na 2 O 0.3 - 0.5 15 K 2 O 0.2 - 0.6

Mn 0.003 - 0.01

Cu '0.002 - 0.005

Zn 0.005 - 0.01 20 Ni 0.001 - 0.002 S 0.1 - 0.3 C 0.2-1.0 P 0.03 - 0.06 25 Loss on ignition (1000 ° C) 0.8 - 1.5

Bulk density, from filter, g / l 200 - 300

Bulk density, concentrated, g / l 500 - 700

O

Solids density, g / cm 2.20 - 2.25

Specific surface area, m ^ / cn ^ 18-22

Primary particles less than 1 μm,% 90 7 72962 TABLE 2 Dust collected from bag filters for the production of 75 FeSi

Component Weight%

Si0o 86 - 90 5 ^

SiC 0.1 - 0.4-

Fe 2 O 3 0.3 - 0.9

TiO 2 0.02 - 0.06 Al 2 O 3 0.2 - 0.6

MgO 2.5 - 3.5

CaO 0.2 - 0.5

Na 2 O 0.9 - 1.8 15 K 2 O 2.5 - 3.5

Mn Cu Zn 20 Ni S 0.2 - 0.4 C 0.8 - 2.0 P 0.03 - 0.08

O C

Annealing loss (1000 ° C) 2.4 - 4.0

Bulk density, from filter, g / l 200 - 300

Bulk density, concentrated, g / l 500 - 700

O

Solids density, g / cm 2.20 - 2.25 30 2

Specific surface area, m / g 18-22

Primary particles less than 1 μm,% 90 8 72962

It is best to use dust that is recovered from an electric furnace that produces at least 75% silicon-iron. Dust recovered from an electric furnace producing 50% silicon-containing iron can also be used in the present invention.

By adjusting the reaction conditions, it is also possible to obtain amorphous silica as the main product. This type of amorphous silica can also be prepared synthetically without reduction and reoxidation.

The amorphous silica used in the present invention consists mainly of round particles with a diameter of less than one micron. The circular shape, fineness, and pozzolanic reactivity make this amorphous silica very useful in the present invention.

The SiO 2 content of the amorphous silica can be, for example, at least 60-90% by weight. Its solids density is 2.20-2.25 3 g / cm. The particles are mostly round and at least 90% by weight of the primary particles have a particle size of less than 1 μm. Of course, these values can vary. For example, the SiO 2 content of silica may be lower. The particle size distribution can also be adjusted. For example, it is possible to remove the larger 2 particles. The specific surface area of the dust is 18-22 m / g.

Due to its carbon content, amorphous silica looks dark gray. But carbon can be removed by combustion at a temperature of e.g. 400 ° C.

According to the invention, the mixture is prepared by mixing the main ingredients as an aqueous slurry, thus providing good contact between the ingredients and an even and homogeneous distribution. The additive mixture slurry contains 10 to 80% by weight of silica-30 dust and 0.5 to about 40% by weight (dry weight) of one or more superplasticizers or plasticizers, alone or in combination (preferably 1 to 20% by weight of said superplasticizers or plasticizers alone). or combinations). The rest is made up of water. In one example, 20 kg of silica dust, 1.3 kg of commercial grade naphthalene and formaldehyde sulfonated condensate (super plasticizer) and 1.3 kg of commercial grade cellulose ether (plasticizer) were mixed into 20 liters of homogeneous and homogeneous water, preferably in a Banbury mixer. The pH of the slurry is adjusted with ordinary mineral acid or base to a range of 3.0 to about 7.5, preferably 5.0 to about 6.0, to obtain a slurry of consistency suitable for transport and mixing into the concrete bed. In addition to or instead of adjusting the pH of the slurry, dispersants such as phosphates, citric acid, polyacrylate or glycerol may be used to obtain the desired consistency of the slurry. It is most economical to use water in the preparation of the slurry according to the invention, but it is also possible to use an organic liquid if it is compatible with the concrete or is not harmful in any way.

The relative viscosity of the slurry mixture of this invention was measured with a Haake viscometer using sensor E. 30 and following the equipment manufacturer's instructions. The slurry additive mixture was compared to a "zero mixture" which, when slurried in water, contained the same amount of silica without a plasticizer. Both samples contained 65% by weight silica dust. The results were as follows.

10 72962 Sample Sensor Rotation- Torque- Torque- rmo ...

speed reversal 1 h traverse 7 dec value after day exp. 28 days

N ° llase ° s 32 53 1 50, 50 16 56 1 50 1 50 8 60 1 50 1 50 ^ 64 150 150 2 69 1 50 1 50 1 78 150 150

Treadmill 49 1 50 15Q

Sample A, 2.5 weight,? 32 4 g ^ lignosulfonate 16 ^ ^ ^^ (Borresperse NA) 8 5 ^ 1 y 6 12 18 2 7 U 23 1 9 16 23

Running limit - 2 3.5 15.0 Sample B, 2.5 weight? 32 13 ^ 7 26 sulfonoxystaphthalene 16 20 21 27 ni-formaldehyde condensate 8 25 23 26 densate (Mighty) 4 27 24, 25 2 32 28 27 1 39 34 33

Treadmill 28 28 43 Sample C, 2.5 weights? _ 5 <- 21 57 5 5

sulfonated melamine- J

16 32 6 8 ai formaldehyde condensate (Rescon HP) ^ ^ L 36 74 69 2 42 81 76 1 4-9 91 88

Running track 32 63 72 11 72962

As can be seen from the table, silica dust tends to form a discotropic mixture in water. This often leads to stiffening (gelation) of the slurry.

This is not desirable, as pumping the gelled slurry 5 from the storage tank is very cumbersome in practice. It was quite surprising and unexpected that the superplasticizer in Sample A above effectively reduced the tendency of the slurry to gel, which often occurs when the slurry contains only silica dust.

It is believed that superplasticizers and plasticizers tend to coat silica dust particles during mixing. This reduces the tendency of the sludge to gel. Experience has shown that when the elastic limit of the above table is close to about 25, the slurry is excellently suitable for use in accordance with the present invention. The sludge works satisfactorily up to the running limit of about 75. When the slurry running limit is above 100, pumping becomes cumbersome and the slurry cannot be considered suitable for use in the present invention. A value of 150 represents the upper limit and corresponds to the consistency of a rigid paste.

According to the present invention, the slurry can be stabilized and the tendency to gel can be significantly reduced or eliminated by adding 0.1-10, preferably 2-5% by weight (dry weight) of superplasticizer or plasticizer to the slurry, based on the weight of silica dust in the slurry. In general, the slurry may contain silica dust from 10 weight percent up to about 80 weight percent. One or more superplasticizing or plasticizing agents may be used alone or in combination to stabilize the silica slurry. When a slurry mixture is used as an admixture for concrete or mortar, the superplasticizer or plasticizer may be present in an amount greater than 10% by weight and, as specified herein, may be present in an amount of 0.5 to 40% by weight based on the slurry mixture.

According to the present invention, a sufficient amount of mixture to be added to the fresh concrete or mortar batch is generally such that the fresh concrete or mortar will contain 72962 12 2-100% and preferably 2-25% silica dust by weight of the cement in the concrete batch and 0.1-5% superplastic. a plasticizer, alone or in combination, based on the weight of the cement in the concrete or mortar charge.

Experiments that simulate weather conditions and construction methods at the casting site determine the optimal amounts of the components of the mix and the amount of mix itself that must be added to the concrete by available means. This is consistent with the normal industrial background. Conventional experiments show the effect of the mixture on concrete, with parameters such as concrete air content, consistency, water separation and possible air loss from fresh concrete, cure rate, compressive and bending resistance, resistance to freezing and thawing, loss during drying and permissible chloride content.

The usual way of adding superplasticizing or plasticizing agents often causes disproportionate water separation in the concrete and even discharge of the mixture. The result is a thin, watery cementitious adhesive in which large additive particles are unable to be suspended. It is also known that most superplasticizers and plasticizers plasticize by lowering the surface tension of the aqueous component of the concrete mix. This can cause the separation of larger aggregate particles and reduce the resistance to freezing and thawing, degrade pumping properties, reduce wear resistance, cause surface finishing difficulties and degrade surface quality in mold casting.

The silica dust in the mixture of the present invention is very fine and increases the surface area of the solids per 30 volume units of water. This results in better separation and suspension of large aggregate particles. A change in the behavior of the particles results in improved plasticity and processability. Since the mixture of cement, water and the additive mixture of the present invention contains more solids per unit volume, the cement adhesive becomes less aqueous and the mixture does not so easily disintegrate. Thus, 13 72962 silica dust reduces water separation by retaining water in the cement adhesive. In this way, a homogeneous, very easy to process and easily pumpable mixture is created, in which the tendency to separate the water is reduced.

The compressive strength of concrete containing the admixture mixture of the present invention is generally better than would be expected when adding together the individual strength improvements achieved by adding each component separately.

The reason for this is not entirely clear, but it is believed that super-10 plasticizers or plasticizers improve the distribution of silica dust particles throughout the concrete mass and that there is a certain synergistic effect between the components of the admixture mixture.

The admixture mixture of the present invention is particularly well suited for conventional fresh concrete mixtures and can be mixed into the concrete mass in a conventional manner. For example, a slurry containing 20.5 kg of silica dust, 3.6 kg of dry Lomar D (superplasticizer, sulfonated condensate of naphthalene and formaldehyde) and 20.8 liters of water is added to conventional fresh concrete containing 205 kg Portland cement type I without additives. The workability and consistency of a concrete mix with a water to cement weight ratio of 0.35 are good and no water separates from the fresh mix. The compressive strength of the cured mixture after 28 days 25 is typically high, i.e. on the order of 85 MPa. Freeze-thaw resistance is amazingly good without added air. The concrete mix contains 1C% silica dust (dry) and approx.

1.5% Lomar D (dry) by weight of cement in the concrete mix. The improved tightness of concrete increases the tensile strength of tun-30 against water and aggressive chemicals. The freeze-thaw properties are better than in a concrete or mortar mixture which does not contain said silica dust sludge.

The optimum ratio of ingredients of the additive composition of this invention is determined by standard industrial tests. The ingredients are premixed and thus only one addition step is required at the casting site compared to conventional use, where three or four addition steps are required. All additives can be mixed at once. All ingredients are uniformly and homogeneously dispersed in the additive mixture of the present invention and can be mixed in at 5 times, thus deviating from the conventional practice of adding each ingredient individually to avoid flocculation. The additive mixture of the present invention shortens the loading time and reduces errors because only one charge is required instead of three or four. The need for storage is reduced and quality control is improved because only one manufacturer supplies all the additives included in the additive composition of the present invention. This also eliminates contamination of the storage tank. A further advantage of the slurry mixture of the present invention is that no fine dust is formed at the casting site.

Due to the advantageous effects of silica dust in the concrete mix, the admixture of the present invention improves the sulfate resistance and improves the ability of the concrete containing the admixture to withstand the reaction between base and silica.

Since the additive mixture of the present invention may have to be used under conditions that unduly prolong the curing time, accelerators may be added to the mixture to achieve the best possible curing and early strength. The admixture mixture can also be used in cases where it is desired to slow down the hardening of fresh concrete, e.g. in the casting of a bridge deck, where hardening must take place only after the casting and finishing work have been completed.

The admixture of the present invention has been made "custom-made" as it consists of precisely those ingredients and their amounts which are the best in the concrete used in a given construction work. Any known admixture commonly used in concrete or mortar can be added to the admixture of the present invention.

In addition to the main ingredients, known accelerators such as calcium chloride, calcium nitrate and calcium formate may be added to the additive mixture in amounts commonly used in industry. For a given purpose, the optimum amounts of these substances are determined by standard experiments. One or more accelerators may be n.

5 to about 20% by weight based on the weight of the silica dust in the additive mixture.

The retardants commonly used in concrete or laas-5 drops can also be added to the admixture mixture in the form of glucose or sucrose and in optimum amounts which can be determined by standard experiments. The one or more retardants may be present in an amount of from about 5% to about 20% by weight based on the weight of the silica dust in the additive mixture.

If desired, air-forming agents such as Vinsol resin or Darex, a sulfonated fatty acid derived from fats, may be added to the additive mixture of the present invention for certain uses where a specific concentration is desired. One or more air generating agents may be used in an amount of about 0.5 to about 3% by weight based on the weight of the silica dust.

The admixture mixture of the present invention may contain varying amounts of selected ingredients, but to take full advantage of the present invention, the amount of admixture mixture added to ordinary fresh concrete must be 2-100% siliceous dust by weight of cement and 0.1-5% one or more superplasticizers or plasticizers. singly or in combination, by weight of cement. Water is mixed with the additive mixture in such amounts that a slurry is formed in which the main ingredients are uniformly and homogeneously dispersed. In addition to the main ingredients, accelerating and retarding agents, air generating agents and any other conventional additions are added to the admixture mixture of the present invention in amounts that allow the desired concentration in the fresh concrete batch. In all cases, the optimum amounts of ingredients in the additive composition of this invention are determined by standard testing under simulated climatic conditions that depend on the building materials and construction methods used.

Claims (3)

16 72962 A mixture of concrete and mortar admixture, characterized in that it is in the form of a slurry containing 10 to 80% by weight of silica dust, 0.5 to 40% by weight of plasticizer and / or superplasticizer and the remainder of water and having a pH of the value is in the range of 3.0-7.5. Process for preparing an additive mixture according to Claim 1, characterized in that one or more plasticizing and / or superplasticizing agents are mixed with water, after which silica dust is added so that the mixture contains 10 to 80% by weight of silica dust and 0.5 to 30% by weight. 40% by weight of plasticizer and / or superplasticizer, and the pH of the mixture is adjusted to 3.0-7.5. Use of an admixture mixture according to Claim 1 as an admixture for concrete and mortar, such that the concrete and mortar contain 2 to 100% by weight of silica dust and 0.1 to 5% by weight of plasticizer and / or superplasticizer, based on the amount of cement.