Cement admixture for improved slump life

Abstract

Described are polymers and cement admixtures which reduce drop in fluidity with time. Said admixture comprises at least one polymer of the present invention and at least one polymer A. The polymer of the present invention comprises side chains of which at least 10 weight-% can be cleaved in alkaline medium. The polymer of the present invention is an acrylic polymer which comprises side chains connected to the backbone by ester linkages. These side chains may be alkyl, hydroxy alkyl, cycloalkyl or polyoxyalkylene groups. Polymer A is a cement dispersing agent. The combination of polymer A with the polymer of the present invention in a weight ratio of 0.1:10-10:1, and preferably 1:10-10:1 reduces the drop in fluidity with time of cementitious compositions.

1 . A polymer 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 structrural 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 from each other 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 (R70) z R8 in which O represents an oxygen atom, R7 represents a C 2 -C 3  alkylene group or mixtures thereof, R8 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 may be mixtures thereof, and whereby preferably at least 0.5 mole-% more preferred 5-100 mole-% and most preferred 50-100 mole-% of the residues R2 are —(R 7 O) z R 8  with R 7 , z and R 8  as defined above  
 R4 and R5 represent independently from each other a hydrogen atom or a substituent as defined for R2, and R4 and R5 may form together a ring structure of which N is part of, this ring structure may further contain other hetero atoms like another nitrogen, sulfur or oxygen atom, or mixtures thereof;  
 R6 is 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 preferably is a value of more than 0, more preferably between 0.01 and 50, and most preferably between 0.01 and 2.  
 
     
     
         2 . The polymer of  claim 1  that contains side chains of formula VI which are connected to the backbone by amide or ester groups, 
       -(A 1 O) x -(B 1 O) y -R9  VI and wherein O represents an oxygen atom and A 1  and B 1  represent independently from each other a C 2 -C 3  alkylene group and A 1 ≠B 1  and    R9 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 x represents a number from 1-250 and y represents a number from 0-250 and the sum of x and y is a number of 1-250 and the order (A 1 O) and (B 1 O) is random, alternating or blockwise, and wherein said side chains of formula VI, are preferably present in an amount of more than 0.5 weight-%, more preferred 5-99 weight-% and most preferred 50-99 weight-% of the polymer.    
     
     
         3 . The polymer of  claim 1  obtainable or produced by a copolymerising reaction of (meth)acrylic monomers.  
     
     
         4 . The polymer of  claim 1  obtainable or produced by polymer analogues reaction of esterification and optionally amidation and/or imidation of a polycarboxylic acid.  
     
     
         5 . The polymer of  claim 1  comprising 5-90 mol %, preferably 20-80 mol % of structural unit A of formula I; and 10-90 mole-%, preferably 15-70 mole-% of structural unit B of formula II; and 0-85 mol % of structural unit C of formula III; and 0-50 mole %, preferably 0-20 mole % of structural unit D of formula IV; and 0-10 mole-% of structural unit E of formula V.  
     
     
         6 . The polymer of  claim 1  wherein at least 15% of the side groups are cleaved at a pH higher than 12.5 at 22° C. within 2 hours.  
     
     
         7 . An admixture for reducing loss of fluidity of cementitious compositions, mortars and concrete, said admixture comprising at least one polymer A and at least one polymer of  claim 1  wherein polymer A is a cement dispersing agent.  
     
     
         8 . The admixture of  claim 7  wherein polymer A is a cement dispersing agent selected from the group consisting of sulfonated melamine condensates, sulfonated naphthalene condensates, lignosulfonates, substituted maleamid-vinyl-copolymers and acrylic or methacrylic copolymers with polyalkyleneoxide side chains, or mixtures thereof.  
     
     
         9 . The admixture of  claim 7  wherein the solid weight ratio of polymers A to the polymers of  claim 1  is from 0.1:10-10:1, preferably from 1:10-10:1.  
     
     
         10 . A mortar, concrete or cementitious binder comprising the polymer of  claim 1 .  
     
     
         11 . A mortar, concrete or cementitious binder comprising the admixture of  claim 7 .  
     
     
         12 . The mortar, concrete or cementitious binder of  claim 11  comprising the admixture in an amount of 0.01 to 10% by weight of the binder, said mortar or concrete having a unit content of binder composition of cement or a mixture of cement and latent hydraulic or inert microscopic powder of 100 to 800 kg/m 3 , preferably of 250 to 650 kg/m 3 .  
     
     
         13 . A method for producing a mortar, concrete or cementitious binder of  claim 11 , wherein the polymer of  claim 1  and polymer A are added separately or premixed as admixture in solid or liquid form.