Additive for cement composition and cement composition containing the same

An additive for a cement composition comprising:

• (A) a polycarboxylic acid based copolymer in the form of the reaction product of an unsaturated mono- or di-carboxylic acid selected from the group consisting of acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, and citraconic acid with a copolymerizable unsaturated monomer selected from the group consisting of polyalkylene glycol mono(meth)acrylate, styrene, and those compounds which are formed by adding 1 to 100 mol of alkylene oxide to an unsaturated alcohol, or a salt thereof;
• (B) a water-soluble cellulose ether in the form of hydroxypropyl methyl cellulose or hydroxyethyl methyl cellulose which has a solution viscosity of 50 to 27,800 mPa·s for 2.0 wt % aqueous solution at 20° C.;
• and
• (C) a defoaming agent selected from the group consisting of:
• ethylene oxide-propylene oxide block copolymers, alkylene glycols, alkylene glycol adducts of ethylene oxide and/or propylene oxide, alkylene glycols, alkylene glycol higher alcohol ethers, higher fatty acid esters, alkylene glycol fatty acid esters, sorbitan fatty acid esters, polyoxyalkylene sorbitan fatty acid esters, acetylene glycols, acetylene glycol adducts of ethylene oxide and/or propylene oxide, phosphates, and mixtures thereof,
• wherein the weight ratio of the polycarboxylic acid based copolymer (A) to the water-soluble cellulose ether (B) is from 50/50 to 99/1, and the defoaming agent (C) is present in the additive in an amount equal to 0.1 to 50 weight percent of the defoaming agent (C) based on the weight of the water-soluble cellulose ether (B).