Terpolymers of unsaturated sulfonates, N-vinylamides and ethylenic monomers

A high-flow concrete additive comprising a polymer containing:

• 40-89 wt % of a unit derived from a compound represented by the following general formula (1):
• CH.sub.2 .dbd.CHNR.sup.1 COR.sup.2 ( 1)
• wherein R.sup.1 represents a hydrogen atom and R.sup.2 represents a methyl group,
• 10-50 wt % of a unit derived from a compound represented by the following general formula (2):
• CH.sub.2 .dbd.CR.sup.3 X.sup.1 R.sup.4 SO.sub.3 X.sup.2 ( 2)
• wherein R.sup.3 is a hydrogen atom or methyl group, R.sup.4 is a linear or branched alkylene group of 1 to 4 carbon atoms, X.sup.1 is CONH or COO, and X.sup.2 is hydrogen, an alkali metal, ammonium salt or organic ammonium salt,
• and 1-30 wt % of a unit derived from a compound represented by the following general formula (3):
• CH.sub.2 .dbd.CR.sup.5 X.sup.3 ( 3)
• wherein R.sup.5 a hydrogen atom or methyl group and X.sup.3 is CN, the total of the units derived from the compounds represented by general formulas (1) to (3) being 100 wt %.