CS223134B1 - Cement cracking with accelerated neraest of strength - Google Patents

Abstract

The cement mixture according to the invention has an accelerated undergrowth of initial strengths. Another modification of its properties is achieved if it contains some of the known additives, in a suitable combination according to the purpose of use. By mixing all the components of the cement mixture with the exception of mixing water, dry prefabricated mixtures can be prepared. The cement mixture according to the invention can be advantageously used wherever an accelerated increase in strength is required, for example when accelerating the hardening of cement mixtures by reheating or during winter concreting.

Description

This invention deals with a cement mixture with an accelerated increase in strength, in which an oemcnt based on Portland cement clinker is used as a binder.

Construction practice urgently needs cement mixtures, for example cement mortars, injection mixtures and concretes with an accelerated increase in strength at normal temperatures, when hardening is accelerated by overheating and during winter concreting. For all these purposes, cement mixtures containing calcium chloride have proven to be the best. However, calcium chloride cannot be used in reinforced concrete because it causes corrosion of steel reinforcement.

From DOS 2 356 637, mixtures of 60-95 parts by weight of portland cement, 2 to 20 parts of calcium sulfate, 5 to 30 parts of alumina cement and 0.2 to 5 parts of the sulfonated product of the condensation of amino-s-triazine with formaldehyde are known, which is essentially a sulfonated melamine-formaldehyde substance, produced as a known plasticizer of cement mixtures under commercial with the designation Melment P 10 or Melment L 10. The cement mixture according to DOS 2 356 637 has a very short setting time after the addition of mixing water, on the order of minutes, and is therefore not suitable for the production of concrete mixes. advance, but a rapid increase in strength is only achieved if the hardening is accelerated by superheating. However, the addition of alumina cement to Portland cement has a negative effect on the increase in strength after longer periods of superheating. Negative effect prí223 134

- 2 dose of aluminate cement to Portland cement is more significant, the higher its dose, and the longer the time of preheating of the concrete. From the literature we know cement mixtures containing the additive aluminum sulfate (L. Bechyně: Technologie betonu, SNTL Praha 1954, volume one - Components of concrete, p.581).

In the fresh state, cement mixtures with the addition of aluminum sulfate have false hardening (A. Joisel: Admixtures for cement. Published by the author, Soisy, France, 1973, p. 127), which practically

makes it impossible to use them to accelerate hardening and increase in strength. On the cause is good solubility? aluminum sulfate in water - 26.6 g of the anhydrous compound dissolves at 20°C in 100 g of aqueous solution (K. Andrlík et al.: Chemical tables, SNTL Bratislava 1967, p. 62), so all aluminum sulfate can react with cement immediately after adding mixing water to the cement mixture. In the technical and patent literature are described cement mixtures containing various combinations of aluminum sulfate and other additives, for example alkaline sofas such as sodium sulfate, plasticizers, sealants, hydrophobizing and other additives. However, the rapid solubility of aluminum sulfate causes false solidification even with the mentioned combinations.

The mentioned disadvantages are eliminated by the cement mixture with an accelerated increase in strength according to the invention. Its essence lies in the fact that, in addition to cement based on portland clinker and water and/or fillers and/or known additives and/or admixtures, it contains, based on the weight of the cement, 0.2 to 10% by weight of incompletely calcined aluminum sulfate with a residual water content of 0.1 to 20% by weight and with a content of at least 50% by weight of particles smaller than 90/ima at least 30 % by weight of particles smaller than 63«*un·

Portland clinker-based cement can be used in the cement mixture according to the invention, for example Portland, Portland slag or pozzolanic Portland cement.

Depending on the need and purpose, silica sand, carbonate wood, river gravel, or lightweight fillers such as expanded clay, expanded perlite or lightweight

223 134 polystyrene.

As known additives, it is possible to use, for example, ground or untreated fly ash, silica fume or lime flour.

E

As we know the additives, it is possible to use - according to the need and the given purpose - plasticizing additives such as the condensation products of fi-naphthalene sulfonic acid with formaldehyde, or salts of lignosulfonic acid, further aerating additives such as abietic acid salts or sulfonated or aulfated fatty alcohols, further retention additives such as water-soluble cellulose derivatives, further polymer dispersions such as monomeric, binary or ternary dispersions, further antifreeze additives such as alcohols with one or more hydroxyl groups or urea, further gasifying additives such as aluminum powder, further solidification regulators such as gypsum, and also inorganic salt additives such as sodium sulfate, potassium nitrate, sodium carbonate, hydrophobicizing additives such as calcium etherate or other insoluble salts of fatty acids and the like.

The water content of aluminum sulfate for the cement mixture according to the invention is adjusted so that crystalline aluminum sulfate, for example octadecahydrate Alg/SO^/^.18 HgO, is heated at a temperature of 180°

339°C until the residual water content is 0.1 to 20% by weight, after which its graining is adjusted so that it contains at least 50% by weight of particles smaller than 9<bnn and at least 30% by weight of particles smaller than 63>ura. The mentioned graining will ensure homogeneity of distribution and reactivity of aluminum sulfate in the cement mixture.

By choosing the temperature and heating time, the original kinetics of dissolution of incompletely calcined aluminum sulfate is achieved. It is not practical to increase the temperature when heating crystalline aluminum sulfate above 339°C. Anhydrous aluminum sulfate is obtained by heating it to a temperature higher than 340°C (J. Gažo et al: General and inorganic chemistry, Alfa, Bratislava, 1974, p. 472), when its complete calcination occurs. Complete calcination reduces the reactivity of aluminum sulfate, which slows down the increase

223 134 strengths of cement mixtures

The advantages of the cement mixture according to the invention and the method of its production are shown by the following implementation examples, i.e

Implementation example 1

250 g of crystalline aluminum sulfate octadecahydrate Alg/SO^/^.ie HgO was crushed to a maximum particle size of 0.3 mm in a drying oven, where the temperature was maintained at 200 + 2°C for 18 hours. Before starting drying, crystalline aluminum sulfate contained approximately 128.4 g of the anhydrous compound and approximately 121.6 g of crystalline water. During the 18-hour heating, crystalline aluminum sulfate lost 100.1 g of crystalline water, so it contained ooa 14.75% by weight of residual water. It was then ground to the following fineness:

overflow through si-to 90 yun 60% by weight overflow through shito 63 jum 45% by weight

The product produced in this way was labeled A®

9.75 g of aluminum sulfate octadecahydrate Alg/SO^/^.ie HgO with a maximum particle size of 0.3 mm was added to 95.25 ml of water 20°C warmer, which corresponds to the use of the solution as mixing water in the production of cement slurry with a water factor of 0.4 at a dose of 2% of anhydrous aluminum sulfate by weight of cement® Crystalline octadecahydrate was dissolved within a few minutes.

5.67 of product A was added to 99.13 ml of water 20°C warmer, which corresponds to a dose of 2% of anhydrous aluminum sulfate based on the weight of cement at a water factor of 0.40. After the first 4 hours, only part of the added product A was dissolved, the rest was completely dissolved only after 18 hours.

They were made from Portland cement class PC 400 with water223 134

- by the 5th factor of 0.35 the following mash:

δ, 1 - comparison without additives No. 2 - according to the invention with 2% of product A by weight of cement, Product A was mixed in mixing water just before adding to the cement, without being dissolved in it} δ, 3 - with 3.92% of crystalline octadecahydrate Alg/SO^/3, .18 HgO, which corresponds to a dose of 2% of anhydrous compound by weight of cement,

From mash No. 1 and 2, test samples were made - cats of 2 cm. From mash No. 3, it was not possible to properly make test samples and compact 1? for false solidification and rapid loss of workability, Test samples from slurries No. 1 and 2 were treated in humid air (20°C, above 90% relative humidity), after which they were tested for compressive strength. The results of the pressure tests of the cubes were as follows:

Table 1

Porridge Strength in MPa 18 hrs, 24 hrs Article 1 - comparative 5.05 7.2 without additives

No. 2 — according to the invention with 2% 13.2 14.8 prod, A

The results shown in tab. 1 show a significantly faster increase in compressive strength for mash no. 2 according to the invention compared to mash δ. 1 - comparative without additives.

223 134

Implementation example 2

The following cases are made from dross Portland cement class SPC 325 and with a water content of 0.35:

No. 4 - comparison without additives

δ. 5 - according to the invention with 2% of product A from the weight of cement Product A was dry homogenized with cement, only then was mixing water added;

No. 6 - e 3.92% of crystalline octadecahydrate by weight of cement, which corresponded to a dose of 2% of anhydrous aluminum sulfate by weight of cement,

8, 4 and 5 were made from the mash using the same procedure as in the example of the realization of 1 test cat with a length of 2 cm. Test samples could not be properly produced from mash No. 6 due to false solidification and sudden loss of workability. The results of the pressure tests of the cubes were as follows:

Table No. 2

Porridge Strength in MPa 6 p.m. 24 hours 8.4- comparatives without additives 4.9 7.0 8. 5 - according to vanález with 2% prod.A 9,θ 11.15

The results shown in Table 2 show an accelerated increase in the strength of slurry No. 5 according to the invention compared to slurry No. 4 - comparative without additives.

Implementation example 3 g of product A according to implementation example 1 was mixed with 223 134 β 12.5 g of anhydrous powdered sodium dinaphthylmethanedisulfonate· The mixture thus prepared was labeled product Β»

SPC 325 pulverized Portland cement mixed slurry with composition according to tab. 3« Each slurry was mixed for 2.4 minutes · Immediately after mixing and further after 5, 10, 15 and 20 minutes after the end of mixing, the consistency of the cement slurry was determined. In order to exclude the effects of random measurements, a new slurry was always mixed for each time period. Consistency was measured as the self-spilling of a truncated cone used to measure the beginning and setting time of cement slurry according to Vicáta or according to ČSN 72 2115. The following results were found when measuring consistency:

_Table 5

Number of porridge Composition of porridge 1 •and •H >O O ra s > 'd H About Φ ί> +» Spill in ©m immediately after 5 minutes· after 10 minutes· half5 minutes after 20 minutes 7 comparatives without additives 0.4 10.6 10.6 10.6 9.9 θ,4 8 comparatives without additives 0.5 19.2 19.2 18.4 18.1 18.1 9 with 3.92% by weight of cement Al _? /S0./-. · 18 H ₂ 0 0.4 8.0 7,θ 7.6 7.6 7.6 10 with 3.92% wt.cem· Al2/S04/3*18 H ₂ 0 0.5 8.2 8.1 8.1 8.0 7.7 11 according to the invention with 2.5% of product B 0.4 23.9 23.7 22.5 21.0 20.3

223 134 " 8 The results shown in Table 3 show a rapid loss of processability of slurries δ. 9 and 10 as a result of false solidification. The best processability was slurry δ. 11 according to the invention.

Implementation example 4

The following slurries were made from PC 400 grade Portland cement with a water component of 0.35.

δ. 12 - comparison without additives

No. 13 - with 0.5% of the weight of sodium dinaphthyl methanedisulionate cement δ· 14 - according to the invention β 2.5% of the weight of the cement of product B according to implementation example No. 3· Product B was dry homogenized with cement, only then was mixing water added·

Test samples made of cement slurries were made - 2 cm wide cats. The molds with the test samples were placed in a reheating chamber in which the temperature of 80 and 1°C and the saturated water vapor pressure were automatically maintained after 1, 2, 3 and 4 hours of reheating.

Table 4

Compressive strengths in MPa after K _and sa hours of reheating 1 2 3 4 δ. 12 - comparison- nesk· cia without additives 0.25 6.2 10.3 No. 13 - only with plasticizer late 0.25 5.8 10.0 δ. 14- according to the invention with 2.5% 2.16 prod. B 6.3 9.5 12.3

223 134

The results shown in table 4 show an accelerated increase in the strength of mash No. 14 according to the invention, while it had substantially better workability in the fresh state compared to mash δ·12 - compared without examples, the same as mash No. 13 - only with plasticizer.

The given examples are only illustrative and do not in any way limit the possibilities of using various known additives or their suitably chosen mutual combinations in the cement mixture according to the invention to modify its properties, for example with the addition of gypsum or sodium sulfate to achieve compensatory shrinkage or to achieve expansion of the hardened cement mixture while simultaneously increasing its strength, or by adding sodium carbonate to achieve smooth solidification of the cement mixture mixture shot by the dry shotcrete method, or with the addition of urea and/or pentaerythritol to achieve a reduction in the freezing temperature of the mixing water while simultaneously slowing down the hardening and increasing the strength of the cement mixture during winter dust.

The cement mixture according to the invention can also be produced in the form of dry prefabricated mixtures to which mixing water is added before use.

The cement mixture according to the invention can be advantageously used wherever an accelerated increase in strength is required, for example when accelerating the hardening of cement mixtures by overheating or during winter concreting.

Claims (1)

Cement mixture with accelerated increase in strength, from existing Portland cement clinker cement, and optionally water and / or filler and / or known additives such as fly ash or ground high slag and / or known additives such as plasticizers, for example dinaptylmethane disulfonate and / or antifreeze agents such as urea and / or solidification regulators such as gypsum or sodium sulfate, and / or accelerating solidification such as sodium carbonate, and / or hydrophobizing salts of fatty acids, characterized in that it contains , based on the cement weight of 0,2 to 10% by weight of incomplete calcined aluminum sulphate, with a residual water content of 0,1 to 20% by weight and a content of at least 50% by weight of particles less than 90 µm and at least 30% by weight of particles less than 63 µm ·