Patent ID: 7026402

Claim:
An admixture for reducing loss of fluidity of cementitious compositions, mortars and concrete, said admixture comprising: (a) at least one cement dispersing agent comprising a Polymer A, and (b) a Polymer B comprising side chains of which at least 10 weight-% can be cleaved in alkaline medium at a pH of from 8–14 at 20° C., said side chains being connected to the backbone of said polymer by ester and optionally amide and/or imide groups, whereby said polymer comprises a mole-% of structural unit A of formula I b mole-% of structural unit B of formula II c mole-% of structural unit C of formula III d mole-% of structural unit D of formula IV and e mole-% of structural unit E of formula V wherein each R1 independently represents a hydrogen atom or a methyl group or mixtures thereof; M represents a hydrogen atom, a metallic cation, an ammonium or organic ammonium cation or mixtures thereof; R2, R20 and R3 independently from each other represent a C 1 –C 12 alkyl- or cycloalkyl group, a C 2 –C 12 hydroxyalkyl group or (R 7 O) z R 8 in which O represents an oxygen atom, R 7 represents a C 2 –C 3 alkylene group or mixtures thereof, R 8 represents a hydrogen atom, a C 1 –C 12 alkyl- or cycloalkyl group, a C 2 –C 12 hydroxyalkyl group, or an unsubstituted or substituted aryl group and z represents a number from 1–250, whereby R2, R3 and R20 optionally are mixtures thereof; R4 and R5 represent independently from each other a hydrogen atom or a substituent as defined for R2, and R4 and R5 optionally form together with the amide nitrogen a ring structure, wherein said ring structure optionally contains at least one additional hetero atom selected from nitrogen, sulfur or oxygen; R6 is a single bond or a methylene group; a, b, c, d and e represent numbers where the sum of a+b+c+d+e=100 and b is a number from 10–90, c is a number from 0–85, d is a number from 0–50 and e is a number from 0–10 and a is 100−(b+c+d+e), whereby a is at least 5, and wherein the sum of e and d is a value between 0.01 and 50, and wherein 5–100 mole % of the residues R 2 are —(R 7 O) z R 8 , with R 7 , z and R 8 as defined above.