A composition for modifying a hydratable cementitious composition, comprising: three different carboxylate polymers, identified herein as Polymer I, Polymer II, and Polymer III, each of said polymers being obtained from Components A, B, and C, wherein: Component A is an unsaturated carboxylic acid monomer represented by structural formula 1, Component B is a polyoxyalkylene monomer represented by structural formula 2: Component C is an unsaturated carboxylate ester or amide monomer represented by structural formula 3: wherein R 1, R 2, R 3, R 4, R 5, R 6, R 7, R 8, R 9, and R 10 each individually represent a hydrogen atom, a C 1 to C 4 alkyl group, or -COOM group wherein M represents a hydrogen atom or an alkali metal; Y represents -(CH 2) p - wherein "p" represents an integer of 0 to 6; Z represents -O-, -COO-, -OCO-, -COHN-, or -NHCO-; - n represents linear repeating ethylene oxide groups, propylene oxide groups, butylene oxide groups, or a mixture thereof; "n" represents the average number of repeating - groups and is an integer of from 10 to 250; W represents an oxygen atom or an -NH- group, and R 11 represents a C 1 - C 10 alkyl group or a C 2 - C 10 hydroxyalkyl group; wherein, in Polymer I, the Components A, B, and C are present in a molar ratio (A:B:C) in the range of 2:1:0 to 5:1:0; and further wherein, in Polymer II, the Components A, B, and C are present in a molar ratio (A:B:C) in the range of 0.1:1:0 to 2:1:0; and and further wherein, in Polymer III, the molar ratio of Component A to the sum of Components B and C is in the range (A:B+C) of 0.3:1 to 3:1. Component A is an unsaturated carboxylic acid monomer represented by structural formula 1, Component B is a polyoxyalkylene monomer represented by structural formula 2: Component C is an unsaturated carboxylate ester or amide monomer represented by structural formula 3: wherein R 1, R 2, R 3, R 4, R 5, R 6, R 7, R 8, R 9, and R 10 each individually represent a hydrogen atom, a C 1 to C 4 alkyl group, or -COOM group wherein M represents a hydrogen atom or an alkali metal; Y represents -(CH 2) p - wherein "p" represents an integer of 0 to 6; Z represents -O-, -COO-, -OCO-, -COHN-, or -NHCO-; - n represents linear repeating ethylene oxide groups, propylene oxide groups, butylene oxide groups, or a mixture thereof; "n" represents the average number of repeating - groups and is an integer of from 10 to 250; W represents an oxygen atom or an -NH- group, and R 11 represents a C 1 - C 10 alkyl group or a C 2 - C 10 hydroxyalkyl group; wherein, in Polymer I, the Components A, B, and C are present in a molar ratio (A:B:C) in the range of 2:1:0 to 5:1:0; and further wherein, in Polymer II, the Components A, B, and C are present in a molar ratio (A:B:C) in the range of 0.1:1:0 to 2:1:0; and and further wherein, in Polymer III, the molar ratio of Component A to the sum of Components B and C is in the range (A:B+C) of 0.3:1 to 3:1. R 1, R 2, R 3, R 4, R 5, R 6, R 7, R 8, R 9, and R 10 each individually represent a hydrogen atom, a C 1 to C 4 alkyl group, or -COOM group wherein M represents a hydrogen atom or an alkali metal; Y represents -(CH 2) p - wherein "p" represents an integer of 0 to 6; Z represents -O-, -COO-, -OCO-, -COHN-, or -NHCO-; - n represents linear repeating ethylene oxide groups, propylene oxide groups, butylene oxide groups, or a mixture thereof; "n" represents the average number of repeating - groups and is an integer of from 10 to 250; W represents an oxygen atom or an -NH- group, and R 11 represents a C 1 - C 10 alkyl group or a C 2 - C 10 hydroxyalkyl group; wherein, in Polymer I, the Components A, B, and C are present in a molar ratio (A:B:C) in the range of 2:1:0 to 5:1:0; and further wherein, in Polymer II, the Components A, B, and C are present in a molar ratio (A:B:C) in the range of 0.1:1:0 to 2:1:0; and and further wherein, in Polymer III, the molar ratio of Component A to the sum of Components B and C is in the range (A:B+C) of 0.3:1 to 3:1.