Admixture for fluidifying a cementitious composition with reduced cement content

An admixed cement composition comprising:

• a cement composition comprising:
• from 20 to 64 weight % clinker,
• from 5 to 60 weight % activated clay,
• from 0 to 35 weight % limestone,
• from 0 to 10 weight % calcium sulfate,
• the proportions of clinker, activated clay, limestone and calcium sulfate being relative to the dry weight of the cement composition and
• an admixture comprising a polymer comprising units of following formulas (I) and (II):
• where:
• R1 and R2 are each independently a hydrogen or a methyl,
• R3 is a hydrogen or a group of formula —COO(M)1/m
• R4 is a group of formula —(CH2)p—(OAlk)q—R5 where:
• p is 1 or 2,
• q is an integer of 3 to 300,
• the Alk in each OAlk unit of the group —(OAlk)q— is independently a linear or branched alkylene having 2 to 4 carbon atoms,
• R5 is —OH or a linear or branched alkoxyl having 1 to 4 carbon atoms,
• R11 and R12 are each independently a hydrogen or a methyl,
• R13 is a hydrogen or a group of formula —COO(M)1/m,
• M is H or a cation of valence m,
• when M is H, m is 1 and when M is a cation, m is the valence of the cation M,
• a is a number from 0.05 to 0.25, such that (100×a) represents the molar percentage of units of formula (I) within the polymer, and
• b is a number from 0.75 to 0.95, such that (100×b) represents the molar percentage of units of formula (II) within the polymer,
• the proportion of polymer in the admixture being from 0.001 weight % to 5 weight % relative to the dry weight of the cement composition.