Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1999-04-14
2000-12-26
Szekely, Peter A.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524 42, 524 43, 524 44, 524 45, 524 46, 524 55, 524 56, 524 57, 524 58, 524377, 106823, 536 88, 536 91, 536 95, 536 96, 536123, C08K 506, C08L 120, C08L 128, C08L 500
Patent
active
061661198
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a a method of improving the pumpability of cementitious compositions and to a cement additive which is intended to improve the workability of cementitious compositions for pump application.
Pump application is a way of conveying cement compositions such as cement paste, mortar, and concrete to a desired place by means of a pump. In the building of modern large-scale concrete structures, efficient conveyance of large quantities of concrete is achieved by employing a high-capacity pump and a large-diameter pipe or branched pipes, the latter permitting concrete to be cast over a large area at one time. While this method is acceptable for conventional concrete, it is not acceptable for the high strength, high-flow concrete used in high-rise concrete buildings in urban areas, and which concrete exhibits special properties such as high strength and self-filling. If it is attempted to pump such concrete by the method hereinabove described, it will lose flowability during its conveyance, the degree of loss depending on mix proportions, environment and on-site conditions. The carrying out of the process and the quality of the final concrete are thereby compromised.
Several means have been proposed to address this problem, involving increasing the amount of powder or fine aggregate in a concrete mix, decreasing the amount of mixing water, or adding a thickening agent. These means, however, have the disadvantage of increasing the concrete viscosity, raising the pumping pressure, and reducing the durability of the cured concrete (because of the presence of a higher proportion of powder). Such disadvantages sometimes hinder site execution and quality control, and hence the abovementioned means are not a satisfactory solution at the present time.
The use of pumpability admixtures has been suggested, one such admixture containing as essential ingredients polyethylene glycol and polycarboxylic acid-based dispersing agent. Unfortunately, this dispersing agent increases the concrete viscosity or cannot prevent the decrease of flowability completely after pumping.
There is therefore a demand for cement additive which permits smooth pump application of concrete, while ensuring good flowability and pumpability, without causing increase in viscosity.
In British Patent 2,297,086 there is disclosed a pumping aid which is a combination of polyethylene glycol and diethylene glycol monobutyl ether (butyl "Carbitol" (trade mark) or a derivative thereof). An optional component in this pumping aid was a polysaccharide.
This pumping aid provided a considerable advance in the art, but it was found that in certain difficult circumstances its performance was not adequate. Such circumstances included the considerable change in fluidity just after a mixing, or the fluctuations caused by such factors as change in the mix proportions of the composition being pumped, fluctuations in aggregate quality, or an increase in pumping pressure in a desire to reduce time.
It has now been found that it is possible substantially to overcome these problems and provide good pumpability and flowability for such concretes while retaining their good properties. The invention therefore provides a cement pumpability-enhancing additive which consists essentially of acid derivatives, polyacrylic amide derivatives, cellulose ethers, alkylphenyl ethers and polyalkylene glycol fatty acid esters; being respectively 5-55%, 10-80%, 1-20% and 1-20%.
The invention additionally provides a method of improving the pumpability of a cementitious composition by the incorporation therein prior to pumping of an additive as hereinabove defined.
Diethylene glycol monobutylether (hereinafter "DGME") is a well-known material and is commercially available, for example, as butyl "Carbitol" (trade mark). The derivative used in the present invention is preferably an adduct of DGME with 1-2 mol of propylene oxide. It is preferred to have present at least some DGME, and the preferred material is a mixture of DGME and the abovementioned adduct.
The polyethyl
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Matsuo Shigemi
Nagamine Hidenori
Ota Akira
MBT Holding AG
Szekely Peter A.
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