Synthesis Of Organosilane-modified Polycarboxylate Superplasticizer And Their Interaction With Cement-silica Fume Paste With Low Water-binder Ratio

With the development of high performance and ultra-high performance concrete,it is of great significance to design and synthesize high performance polycarboxylate superplasticizer(PCEs)for cement-based materials with low water-binder ratio,which has high viscosity,poor workability and large shrinkage.In addition,we can essentially explore the mechanisms of PCEs and find the influence laws of PCEs structure on the performance of cementitious materials with low water-binder ratio by studying the interaction between PCEs and cement-based materials with low water-binder ratio.And then,we can design the molecular structure of PCEs according to the performance requirements and specific components of cement-based materials.In this paper,we designed,optimized and synthetized a organosilane-modified PCEs by introducing alkoxysilane into the PCEs molecules,which perform well in cement-silica fume(sf)paste with low water-binder ratio.What's more,the interaction between PCEs with different chemical s tructures and cement-silica fume paste with low water-binder ratio system was studied.A novel type organosilane-modified PCEs(S-PCEs)with low molecular weight and high carboxyl density was synthesized by free radical copolymerization as the ammonium persulfate(APS)was initiator,acrylic acid(AA),maleic anhydride(MAH),2-acrylamide-2-methylpropane sulfonic acid(AMPS),vinyltriethoxysilane(VTEO)and allyl alcohol polyoxyethylene ether(APEG)were monomers.S-PCEs has good dispersibility for cement-silica fume paste with low water-binder ratio.The cement-silica fume paste can still meet the mixing and forming requirements when the water-binder ratio is low to 0.14 or the silica fume content is 30%.In addition,with the decrease of water-binder ratio or the increase of silica fume content,the dispersion superiority of S-PCEs is more obvious than that of C-PCEs.Compared with C-PCEs,the yield stress of cement-silica fume paste with low water-cement ratio decreased by 7.95%,the equivalent plastic viscosity decreased by 61.31% and the area of thixotropic ring decreased by 52.98% with the addition of S-PCEs.Based on S-PCEs and the other three types of PCEs with different chemical structures,the interaction between PCEs and cement-silica fume paste with low water-binder ratio was studied.The results show that PCEs with same side chain structures but different types and numbers of anchoring groups have quite different physico-chemical characterizations and adsorption behavior.It's beneficial to decrease surface tension of solution by introducing alkoxysilane into PCEs main chain or reducing its molecular weight.In general,the higher the carboxyl density of PCEs main chain are,the higher the adsorption capacity of PCEs have,and the lower the Zeta potential of the system is.The alkoxysilane of S-PCEs can chemically adsorb on the surface of cementitious materials by carboxyl condensation.S-PCEs molecules can absorb on the surface of cementitious materials by a single chain,forming a more compact arrangement on the surface,which increases the adsorption amount compared with unmodified PCEs.The physico-chemical characterizations and adsorption behavior of four types of PCEs.directly affect the hydration and performances of cement-silica fume paste with low water-binder ratio.When the side chain structure is the same,the higher the amount of PCEs adsorbed in the cement-silica fume system with low water-cement ratio,the better its dispersion.And then the fresh cement-silica fume paste with low water-binder ratio has good workability.At the same time,PCEs with strong dispersing ability can promote the hydration degree of cement,and improve the microstructure of cement-based materials.What's more,it can increase the mechanical strength of cement-based materials for 7d and 28 d.However,high adsorption capacity will prolong the induction period of cement hydration,and delay the formation of cement hydration products,so reduce the mechanical strength at 3d age.In addition,the lower the surface tension of PCEs is,the smaller the plastic viscosity of fresh cement-silica fume paste is,and the smaller the self-shrinkage and dry-shrinkage of hardened paste are.