Effect of side-chain length in polycarboxylic superplasticizer on the early-age performance of cement-based materials

Varying the length of side-chain in Polycarboxylic superplasticizer (PCs) have been reported to greatly impact their molecular structure and their compatibility with other concrete raw materials. However, there is less study relating to the influence of side-chain length on early properties of cement-based materials. For this purpose, through a redox initiator system, five types of PCs with different side-chain lengths were synthesized by using 2-methyl allyl polyoxyethylene ether (HPEG) with different molecular weight and acrylic acid (AA) as monomers. The dispersing performance, hydration behavior, microstructure formation and cracking sensitivity in cement-based materials with these different types of PCs were thoroughly examined. The results showed that the initial fluidity of the cement paste increased first and then decreased but the fluidity losses decrease gradually with the increase of side-chain length in PCs. Compared to short side-chain PCs, the long ones can improve hydration heat peak value and shorten dissolution period, thus accelerating the hydration and microstructure formation of cement. The early-age strength increased, while 28-day strength and anti-cracking performance of cement-based materials increased first and then decreased with the increase of side-chain length in PCs. Such information also suggests that there exists a suitable side-chain length in PCs (53 PEO units) which makes cement-based materials have good dispersation, flow maintaining ability and the lowest crack sensitivity.