| 摘要 |
A cement additive with which the amount of air which comes into a cement composition during the production thereof can be prevented from increasing with kneading time, i.e., the amount of air entrained can be stably kept small. It comprises a compound having a hydrophobic group and a hydrophilic group, such as a carboxyl group bonded through an ester bond or amide bond. For example, the compound is preferably one represented by the following general formula. R1-O(R2O)n-X-R3 In an alkaline brine, the compound is hydrolyzed at the bonding site to become hydrophobic with time and thereby show antifoaming properties. When the cement admixture comprises a combination of the compound with a water-soluble polymer, in particular, a polycarboxylic acid polymer having polyalkylene glycol side chains, then a cement composition can be obtained which has specific values of foaming index and cloud point and specific viscosity characteristics and in which the rate of increase in the amount of air entrained is low.
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