Polycarboxylic acid polymer for blending in cement

A cement admixture comprising a polycarboxylic acid polymer, characterized in that

• (1) a molecular weight distribution of the polycarboxylic acid polymer is determined by gel permeation chromatography to provide a molecular-weight distribution curve having an elution time on the horizontal axis,
• (2) a base line is drawn on the molecular-weight distribution curve,
• (3) an elution-starting time, an elution-ending time, and a peak-top time of a peak corresponding to the polymer component are determined respectively as Lh, Ln, and Mp,
• (4) Lm is calculated according to the following Formula (1):
• Lm=(Ln+Mp)/2 (1), and
• (5) P0 and Q0 satisfy the following Formula (2):
• 15≦(P0×100)/(P0+Q0)≦45 (2)
• wherein P0 is defined as a peak area between the elution times Lm and Ln and Q0 is defined as the peak area between the elution times Lh and Mp.

A cement composition comprising

• a cement admixture containing a polycarboxylic acid polymer,
• at least a cement, and
• water, wherein
• (1) a molecular weight distribution of the polycarboxylic acid polymer is determined by gel permeation chromatography to provide a molecular-weight distribution curve having an elution time on the horizontal axis,
• (2) a base line is drawn on the molecular-weight distribution curve,
• (3) an elution-starting time, an elution-ending time, and a peak-top time of a peak corresponding to the polymer component are determined respectively as Lh, Ln, and Mp,
• (4) Lm is calculated according to the following Formula (1):
• Lm=(Ln+Mp)/2 (1), and
• (5) P0 and Q0 satisfy the following Formula (2):
• 15≦(P0×100)/(P0+Q0)≦45 (2)
• wherein P0 is defined as a peak area between the elution times Lm and Ln and Q0 is defined as the peak area between the elution times Lh and Mp.

A method of producing a polycarboxylic acid polymer for a cement admixture, comprising polymerizing a unsaturated monomer component containing a monomer represented by the following Chemical Formula (5):

• [wherein, R1, R2 and R3 each independently represent a hydrogen atom, a methyl group, or —(CH2)zCOOM2[—(CH2)zCOOM2 may form an anhydride with —COOM1 or another —(CH2)zCOOM2];
• Z represents an integer of 0 to 2;
• and M1 and M2 each independently represent a hydrogen atom, an alkali metal atom, an alkali-earth metal atom, an ammonium group or an organic amine group]
• in at least two steps where the amounts of a chain-transfer agent with respect to the unsaturated monomer components are different each other,
• wherein the amounts of the chain-transfer agent used with respect to the unsaturated monomer components are different from each other by 5 times or more between polymerization steps constituting the two steps.