Cement additive

A composition for use as a cement additive which comprises a copolymer (A) obtained by polymerizing a monomer mixture (K), wherein;

• said monomer mixture (K) comprises a polyalkylene glycol ester monomer (I) represented by the formula (1):
• wherein R1 represents a hydrogen atom or a methyl group, the R2O groups are the same or different and each represents an oxyalkylene group containing 2 to 18 carbon atoms and the majority thereof are oxyalkylene groups containing not less than 3 carbon atoms, R3 represents an aliphatic hydrocarbon group containing 4 to 30 carbon atoms or an alicyclic hydrocarbon group containing 4 to 30 carbon atoms, and n represents the average number of moles of oxyalkylene groups and is a number of 5 to 300, with the condition that the average number of moles of oxyalkylene groups containing not less than 3 carbon atoms is not less than 5;
• a polyalkylene glycol ester monomer (II) represented by the formula (2):
• wherein R4 represents a hydrogen atom or a methyl group, the R5O groups are the same or different and each represents an oxyalkylene group containing 2 to 18 carbon atoms and the majority thereof are oxyethylene groups, R6 represents a hydrocarbon group containing 1 to 30 carbon atoms, and m represents the average number of moles of oxyalkylene groups and is a number of 2 to 300;
• and
• a carboxylic acid monomer (III) represented by the formula (3):
• wherein R7 represents a hydrogen atom or a methyl group, and M represents a hydrogen atom, a metal atom, an ammonium group or an organic amine group.