Slump retention in cementitious compositions
View Patent ↗The present invention relates to dispersants such as superplasticizers for hydratable cementitious compositions, and more particularly to methods for achieving variable degrees of longer slump life in concrete and mortar without loss of stability. This is achieved by using two admixture systems. The first admixture composition has multi-components for achieving initial-slump-enhancement, later-slump-retention, and limiting initial slump. The second admixture composition has the later-slump-enhancing component. Alternatively, conventional water reducers or superplasticizers can be employed initially, followed by the later-slump-enhancing admixture composition.
1. A method for achieving slump retention in a hydratable cementitious composition over time without significantly changing the initial workability of the composition, comprising adding an additive comprising (a) an initial slump increasing agent (b) a moderating agent that moderates the response of said initial increasing agent when both are added to the cementitious composition, and (c) a long term slump retention agent.
2. The method of claim 1 wherein said initial slump increasing agent comprises a polycarboxylate comb polymer superplasticizer having pendant ionized cement anchoring groups and pendant non-ionizable dispersing groups.
3. The method of claim 1 wherein said moderating agent is selected from the group comprising melamine sulfonate formaldehyde condensate, naphthalene sulfonate formaldehyde condensate, lignosulfonates, and sulfonate, carbonate, phosphate, formate, nitrite, and nitrate salts.
4. The method of claim 1 wherein said long term slump retention agent comprises a polycarboxylate comb polymer superplasticizer having less initially ionized cement anchoring groups than said initial slump increasing agent or initially-non-ionized cement anchoring groups which become ionized over time and pendant non-ionizable dispersing groups.
5. An admixture composition designed to achieve slump retention of a cementitious composition over time without significantly changing its workability,
(iv) a first component operative to increase initial slump of the composition, said first component comprising a polycarboxylate comb polymer superplasticizer having pendant ionized cement anchoring groups and having pendant non-ionizable dispersing groups, wherein the ratio of said ionized cement anchoring groups is 1:1 to 20:1 with respect to said non-ionizable dispersing groups;
(v) a second component operative to moderate the slump-increasing effect of said first component, selected from the group consisting of melamine sulfonate formaldehyde condensate, naphthalene sulfonate formaldehyde condensate, a lignosulfonate, a sulfonate, a carbonate, a gluconate, a phosphate, and a viscosity modifying agent, and mixtures thereof; and
(vi) a long term slump retaining agent comprising a polycarboxylate comb polymer superplasticizer having pendant initially-non-ionized cement anchoring groups, which become ionized over time after being mixed into the wet cementitious mixture, and pendant non-ionizable dispersing groups, wherein the ratio of said initially non-ionized cement anchoring groups is 1:1 to 20:1 with respect to said non-ionizable dispersing groups.
6. A method of extending the slump of a cementitious composition without significantly affecting its setting time comprising adding to said composition a slump extending amount of a comb polycarboxylate superplasticizer that does not affect the initial slump of the composition, yet acts to maintain slump even with increased dosage of said comb polycarboxylate superplasticizer.
7. The method of claim 1 wherein a viscosity modifying agent is used as component (b).
8. The method of claim 7 wherein said viscosity modifying agent is a biopolymer polysaccharide.