CS259280B1 - Cement mix - Google Patents

Abstract

The solution deals with a cement mixture. Its essence is that, in addition to Portland clinker-based cement and optionally water and/or modifying additives and/or; admixtures and/or fillers, it contains, based on the weight of cement, 0.5 to 45% by weight of ground granular silica fume, while the mixture of cement and ground granular silica fume has a specific surface area of 180 m2.kg1, preferably 250 m2.kg_:t. The cement mixture according to the solution can be produced either by grinding granular silica fume together with other cement components during its production, or by separately grinding granular silica fume and adding it to other components of the cement mixture. The use of the cement mixture according to the solution is advantageous especially where increased waterproofness or corrosion resistance against the action of chemically aggressive waters is required.

Description

The invention relates to a cement mixture, particularly for saving Portland clinker.

The most energy-intensive operations in the production of Portland clinker-based cements include its firing. If, in order to save Portland clinker, granulated blast furnace slag is added to its grinding in addition to gypsum, the energy consumption of cement grinding increases, since the more difficult changeability is one of the characteristic properties of slag.

It is known from patent literature, for example Austrian patent No. 312 490, or Japanese patent application Sho 44-70689, published in 1973, that siliceous fly ash, generated in various metallurgical processes, especially in the production of ferrosilicon, can be used to replace part of Portland cement in the production of cement mixtures. If an effective plasticizer is added at the same time, the strength and water resistance of hardened cement mixtures can be increased.

From patent certificates 204 397, 214 137 and 214 626, it is known that if silica fume is added during the production of cement mixtures together with a dispersant and others, due to the effect of using suitable selected additives, a significant increase in their waterproofness and corrosion resistance is achieved.

Silica fume in the captured state has a high content of amorphous silica, up to 74-98%, and consists of small spheres with an average size of the order of 0.1 aggregated into particles with sizes of the order of /un to 10 ,um. They have a high specific surface area, usually 15,000 to 25,000 m. kg ^-1 . Due to their extremely high fineness, they are among the most reactive pozzolans. However, as a result of these properties, they have an extremely low bulk density in the captured state — 160 to 200 kg. m~ ³ . Their transport in this state is uneconomical, because at least 5 m ³ of space is required to transport 1 ton of fume. Handling of fly ash is also difficult due to its high dustiness, and conventional equipment, such as those used in concrete plants for cement dosing, cannot be used for its movement and dosing. The high fineness and low bulk density are also a disadvantage when adding fly ash in a flooded state to the mill when grinding cement.

Granulated fly ash, sometimes also referred to as pelletized fly ash, consists of granules (pellets) with a bulk density of 760 kg. m~ ³ . The dimensions of the granules are in the order of millimeters. The purpose of granulation is to facilitate the removal of fly ash to a landfill and then reduce dustiness at the landfill. However, granulation so deteriorates the hydraulic activity of the fly ash and the resulting properties of the hardened cement mixture that the fly ash treated in this way is unusable for the given purpose.

The above problems are solved by the cement mixture according to the invention. Its essence is that, in addition to the usual components of cements based on Portland clinker, such as Portland clinker, gypsum, and optionally granulated blast furnace slag, and optionally also known components of cement mixtures, such as water and/or filler and/or known modifying additives and/or admixtures, it contains, based on the weight of cement, 0.5 to 45% by weight of pre-compacted granular silica fume, wherein the mixture of cement and pre-compacted granular silica fume has a specific surface area of at least 180 m ² .kg ^-1 , preferably 250 m ² .kg ^-1 .

The cement mixture according to the invention can be produced in two ways:

1. Or it is prepared by grinding together Portland clinker, gypsum and granulated fly ash, and possibly also known modifying additives, for example according to ON 72 2320 "Concrete additives. Common provisions", which is then used in the usual way for the production of various dry plaster mixtures, or in the usual way on construction sites produced mortars, concretes and the like,

2. or the granulated silica fume is ground separately, while known modifying additives can also be added during its grinding, after which one of the components in the production of dry plaster mixtures, or mortars, concretes and the like produced on construction sites is added in the usual way. The granulated silica fume must then be ground to such a fineness that, at the dose used, its mixture with cement has a specific surface area of at least 180 m ² . kg ^-1 .

If necessary, modifying additives can be added separately during the production of dry plaster mix, or during the construction of manufactured mortar or concrete, i.e. outside the grinding of cement containing granulated silica fume, or the grinding of silica fume itself.

The advantages of the invention are documented by the following application examples.

Example 1

Granulated silica fly ash from ferrosilicon production with a bulk density of 740 kg. m ^-3 was used for the tests, which had the following chemical composition:

S1O2 -I- insoluble residue

Al2O3 + Fe2O3

CaO

MgO

Total sulfur as SO3 Loss on annealing

90.22% by weight.

2.02% by weight 2.01% by weight

1.41% by weight.

1.42% by weight 2.02% by weight

As for the comparative cement, the cement used was laboratory-prepared from Portland clinker, containing ^18.7 % C3A (calculated according to Boguaj and 0.86 °/o SO3, and from pure gypsum (approx. 99% CaSOé.žHaO). Cement prepared by mixing 96.44 °/o clinker, ground to a surface area of F = 274 m ² . kg ^-1 , and 3.56% of gypsum, ground to a specific surface of 259280 F - 450 m ² .kg' ¹ was marked A. The specific surface of the mixture F was 280 m ² .kgď.

According to the invention, it was made from % granulated silica fume

91.62% of the above clinker

3.38% of the above gypsum was ground together to form cement marked B, which had a specific surface area of F - 275 m ² . kg ¹ .

In strength tests after 1, 3 and 28 days according to ČSN 72 2117, the following results were achieved, shown in Table 1.

Table 1

Type of cement mixture

Strength* [MPa] after 1 day 3 days days

Bending tension Pressure Bending tension Pressure Bending tension Pressure Mortar from comparative cement A 3.7 14.3 6.0 29.5 9.8 46.5 Cement mortar B according to the invention 4.0 15.3 6.5 31.2 10.4 50.0 Example 2 the cement mentioned. Since moderate surface of milk-

For the tests, Portland cement of class PC 400 with a content of 15.0% C.iA and 1.87% SOs, with a specific surface area F = 271 m ² . kg' ¹ , and granulated fly ash of Example 1, ground to a finer degree than the granulated fly ash was not measurable ^according to Blain, the particle size distribution was determined by the sedimentation method according to Andreasen, using calcium lignosulfonate as a dispersant. The following values were measured, as shown in Table 2.

Table 2

Size of particles smaller than the given size Content of particles smaller than the given size / % wt.

40 91.25 30 90.64 20 80.61 10 53.71 5 22.71 3 10.43 2 6.85

Two mortars were made from the above ingredients and a dispersant based on sulfonated melamine formaldehyde resin:

— .comparative, marked C, only from Portland cement without additives and admixtures, — according to the invention, marked D, with the replacement of 10% of cement with ground granulated drift and with the addition of 1% of the dry matter of the above-mentioned dispersant.

The mortar production procedure was followed according to ČSN 72 2117, with the difference that the constant water ratio v/c = 0.5 required by the standard was not observed. The mixing water dose was chosen so that the fresh mortars had the same workability, measured as plasticity according to ČSN 72 2441, equal to 160 + 5 mm. The achieved results are shown in Tab. 3.

Table 3

Marking and type of mortar

Strength ratio [MPa] after 24 hours 28 days c + creep Tensile Pressure Tensile Pressure in bending in bending

C — comparative D — subject of invention

0.545 1.5

0.495 2.3

5.2 8.0 42.6

8.0 9.1 60.9

The results obtained, shown in Table 3, show that mortar D according to the invention had, compared to comparative mortar C, increased compressive strength after 24 hours by 53.85% and after 28 days by 42.96%.

Example 3

By grinding together the components listed in Example 1 — 88.73% Portland cement, 3.27% gypsum, 7.75% granulated fly ash and additionally 0.25% powdered calcium lignosulfonate to a specific surface area F = 280 m ² . kg ^{1 ,} the cement according to the invention was prepared.

Using the procedure according to ČSN 72 2117, including the standard prescribed amount of mixing water, a mortar according to the invention, marked E, was made from it. The fresh mortar had a plasticity of 160 mm, the same as the comparative mortar, marked A according to example 1. The mortar according to the invention, marked E, had the following strengths, listed in Table 4.

Table 4 Strength [MPa] after days days

Bending tension Pressure

6.7 33.4

Bending tension Pressure

10.8 54.4

The possibilities of replacing part of Portland clinker in the production of cement, or replacing part of cement in the production of mortars and concretes do not describe or limit all the advantages of the cement mixtures according to the invention; they are particularly advantageous where increased waterproofing and increased corrosion resistance of concrete against the action of sulfate, carbon dioxide and other aggressive waters are required. The transport of granulated silica fume and its handling are significantly more advantageous than for fume not treated by granulation, which makes it possible to technically and economically solve its use in the production of cement mixtures.

Claims (1)

253280 The results reported in Table 3 show that the mortar D according to the invention had increased compression strength after 24 hours by 53.85% and after 42 days by 42.96% by comparison with comparative mortar C. Example 3 By co-grinding the components of Examples 1-88.73% of Portland sim, 3.27% of gypsum, 7.75% of granular fly and increasing and] 0.25% of calcium lignosulfonate powder to surface F = 280 m2. According to the method of ČSN 72 2117, including the standard of the prescribed amount of water, a mortar according to the invention was produced therefrom, designated E. The fresh mortar had a plasticity of 160 mm, the same as the reference mortar designated A according to Example 1 The mortar of the invention, designated E, has the following strengths, shown in Table 4. Table 4 Strength [MPa] after 3 days 28 days Flexural pull Pressure 6.7 33.4 Flexural pull Pressure 10.8 54.4 Options replacing part of the portland in the production of cement or replacing cement parts in the production of mortars and concretes do not meet or limit all the advantages of the cementitious compositions according to the invention, particularly where waterproofing and corrosion resistance of the concrete against sulphate are required. , carbonic and other aggressive leadership. The handling of granular silica dust is more substantial than that of the non-drift. granulation, which makes it technically and economically possible to solve its use in the production of cementitious mixtures. fredhet A cementitious composition comprising cement with Portland clinker and optionally water and / or a known modifying additive and / or filler, characterized in that it, based on the weight of the cement, comprises 0.5 to 45% by weight of granulated. with a mixture of cement and drift has a surface area of at least 180 m2.kg_1, at least 250 m2. • kg “1. Severografia, n. P. Plant 7, Most Price 2,40 Kcs