Influence of the structural modification of polycarboxylate copolymer with a low dispersing ability on the set-retarding of Portland cement

摘要

Two structurally modified polycarboxylate (PC) copolymers were synthesized to explore the influence of structural modification with these polymers on the set-retarding of Portland cement. The dispersion ability of these polymers was eliminated by introducing very short graft side chains. The synthesized copolymer structures were verified by FTIR, GPC and H-1 NMR analyses. The initial and final setting times, polymer adsorption capability, strength development, paste fluidity, and XRD of hardened pastes were tested. The test results indicate that the PC copolymers do not increase the cement paste fluidity due to their short graft side chain length, while a significant set-retarding effect is observed when the polymer structure is highly anionic, with the set-retarding effect increasing linearly with polymer dosage up to 1%. The adsorption of copolymer on cement grains rapidly reaches saturation within 5 minutes after mixing for both polymers. Adding these PC copolymers does not noticeably change the early strength development, although the polymers selectively affect the hydration behavior of C3S and C2S at very early ages. Early hydration of groups, such as C3S, C2S, C(3)A and C(4)AF, is not likely to be significantly involved in the mechanism by which carboxylate copolymers with very short graft chains delay cement setting.