The Preparation And Action Mechanism Of The Shrinkage-Reducing Polycarboxylate Based Superplasticizer

High performance concrete (HPC) is provided with high strength, high mobilityand excellent durability. Unfortunately, some problems exist in the application ofHPC, especially the cracks caused by the concrete shrinkage. The concrete cracks notonly affect the appearance of the building, but also reduce safety and service life ofthe building. Therefore, how to reduce concrete plastic shrinkage is the key researchfield to the academia and engineers for years.Compared to traditional PCA, shrinkage-reducing polycarboxylate superplasticizer(SRPCA) can decrease the concrete drying shrinkage. In this paper, the concretedrying shrinkage mechanism was firstly analyzed, and then determines the key factorsaffecting the concrete drying shrinkage. Based on the analysis, some ethanolmolecules were designed, and then esterified with acrylic acid, methacrylic acid andmaleic anhydride to get the shrinkage-reducing monomer. After that, using thismonomer and some other copolymerizable monomers such as methyl allyl ether,acrylic acid and maleic acid anhydride synthesize SRPCA. After numerousexperiments, the SRPCA with best property was synthesized through optimizing theshrinkage-reducing monomer and testing different prescription.The molecular structure and molecular weight were detected through infraredspectroscopy (IR), gel permeation chromatogram (GPC) and other advancedequipment. The IR shows that the expected functional group contain in the SPPCA,and the GPC displays that the Mn and Mw was similar and had narrow molecularweight distribution.Syntheticed shrinkage-reducing polycarboxylate based superplasticizer, andtested the application performance experiments of cement and mortar. Seen by thefluidity of cement paste, water-reducing effect of the synthesized shrinkage-reducingpolycarboxylate based superplasticizer is very good, and the liquidity retention of thecement paste is also good; we can known from the drying shrinkage experiment,synthesized shrinkage-reducing polycarboxylate based superplasticizer can effectivelyreduce the drying shrinkage of cement mortar, cement mortar of28days dryingshrinkage rate compared to blank sample reduced by about20%,; autogenousshrinkage of cement mortar experiment shows that the synthesized SRPCA caneffectively reduce the autogenous shrinkage of cement mortar, cement mortar of28days autogenous shrinkage rate compared to blank sample reduced by about15%.Explore the mechanism of the shrinkage-reducing polycarboxylate basedsuperplasticizer, tested the relationship among the cement mortar drying shrinkageand surface tension, water consumption, evaporation rate ect, and got a furtherunderstanding of the mechanism of shrinkage-reducing polycarboxylate superplasticizer reduction.