Concrete mixture which yields concrete having high strength at v

Details Concrete mixture which yields concrete having high strength at v Concrete mixture which yields concrete having high strength at v

1999-02-04

2000-02-08

Green, Anthony

Compositions: coating or plastic

Coating or plastic compositions

Inorganic settable ingredient containing

106725, 106809, 106823, C04B 3800, C04B 2416

Patent

active

06022407&

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to an aqueous concrete mixture having an air pore volume between 10 and 85%, preferably between 20 and 85%. In curing, a concrete having uniform density and high strength is obtained. This is achieved by using an aqueous, anionic surface-active compound containing two sulphonic acid groups or a salt thereof. The anionic compound has an air-entraining effect and improves the homogeneity of the concrete mixture.
When making concrete, especially aerated concrete with low density, for instance lower than 1600 kg/m.sup.3, it is difficult to obtain high homogeneity and uniform density and low shrinkage and, thus, high and reproducible strength. Attempts have therefore been made to improve the stability of the mixture as well as air pore formation and strength of the cured concrete mixture by adding, among other things, anionic surfactants, such as xylenesulphonate, alkyl sulphate, alkyl ether sulphate and olefin sulphonate, and polymeric sulphonic-acid-group-containing compounds such as lignosulphonate, naphthalene sulphonate formaldehyde condensate and melamine sulphonateformaldehyde condensate. These compounds have a dispersing and stabilising effect and increase the processability of the concrete mixture. The short-chain surface-active compounds have a particularly good effect on the formation of air pores and thus affect also the frost resistance of the concrete. The polymeric compounds affect first of all the stability, pumpability and flexibility (plasticity) of the concrete mixture and make it possible to reduce the water-cement ratio. Examples of this technique are disclosed in, for instance, WO 94/02428, U.S. Pat. No. 4,045,236, U.S. Pat. No. 4,293,341 and GB-A-2,164,328.
From Japanese Patent Application JP 61-163,155 it is also known to manufacture concrete having a density of about 2400 and an air pore volume of about 2% by adding to the concrete mixture alkyl polyoxypropylene sulphate or alkyl diphenylethersulphonate, preferably together with a salt of a condensate of .beta.-naphthalenesulphonic acid with formaldehyde, a sulphonate of a condensate between melamine with formaldehyde, a salt of a condensate of sulphonated creosote oil with formaldehyde or a lignin sulphonate and co-condensates thereof, for the purpose of improving the appearance of the surfaces of the concrete.
Even if some of the above-mentioned air-entraining additives have a positive effect on the strength of the concrete at low densities, there is a general wish of further increasing the homogeneity of the concrete and, thus, its strength, especially at lower densities.
It has now surprisingly been found that concrete having a density of 250-2200 kg/m.sup.3 and an air pore volume from 15 to 90%, preferably from 20 to 85% and high strength, especially at low densities can be obtained by casting it from a pumpable, aqueous concrete mixture having an air pore volume of 10-85 volume percent, which contains cement, water and an anionic surface-active compound having two sulphonic acid groups of the general formula or 2, the sum of the number of carbon atoms in the group or in the groups R being 6-30, R.sub.1 is an aromatic group containing at least 2 aromatic rings and 10-20 carbon atoms, and M is a preferably monovalent cation or hydrogen. Usually the group R.sub.1 contains only carbon and hydrogen, but oxygen atoms, for example in the form of ketone groups, can also be included. The concrete mixture may also contain aggregate to control the density, or as filler. The anionic compound has both an air-entraining and a stabilising effect and is usually added in an amount of 0.005 to 1.0% based on the weight of cement. When manufacturing concrete having low densities, such as densities below 1600 kg/m.sup.3 but usually above 300 kg/m.sup.3, which generally corresponds to an air pore volume of 25-85 volume percent, the anionic compound is usually added in an amount of 0.1-0.8%, based on the amount of cement. Use can advantageously also be made of the anionic compound when manufacturing concrete having higher d

REFERENCES:
patent: 3468684 (1969-09-01), Proell
patent: 3577248 (1971-05-01), Doan
patent: 4045236 (1977-08-01), Bianchi
patent: 4057608 (1977-11-01), Hashimoto et al.
patent: 4113638 (1978-09-01), Taylor
International Search Report, dated Aug. 22, 1997.
Chemical abstract, No. 107066k, Cement Concrete (58), vol. 106, No. 14, p. 315, Jul. 23, 1986.
Chemical abstract, No. 165873y, vol. 98, No. 20, p. 312, Oct. 7, 1982.

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