The Preparation And Shrinkage Reducing Mechanism Of Shrinkage Reducing Polycarboxlate Superplasitizer

Chemical admixtures have become an indispensable component in modern concrete,especially polycarboxylate superplasitizers,which are widely used in modern concrete because of their excellent water rducing and dispersibility.However,polycarboxylate superplasticizers are weak in reducing shrinkage and cracking of concrete,and the low water-cement ratio is more likely to shrinkage and cracking in a drying environment.The shrinkage-reducing agent with low surface tension is one of the main measures to suppress shrinkage.However,the shrinkage reducing-agent has high cost,large dosage,and affects the mechanical properties of concretePolycarboxylic superplasticizer(SRPC)with shrinkage reduction function was synthesized by combining the design ability of PCE and the advantages of shrinkage reducing agent.In this paper,SRPC was prepared by free radical polymerization using self-synthesized shrinkage-reducing monomers,and SRPC with shrinkage-reducing properties was obtained.When the content of SRPC is 0.2%,the autogenous shrinkage of SRPC mortar decreases by 54.1% compared with that of blank mortar at 7 days of hydration and 22.8% at 49 days of drying,which indicates that SRPC has a better shrinkage reduction effect.The shrinkage-reducing mechanism of SRPC was investigated by MIP pore structure,surface tension,solution evaporation rate and surface film pressure curve.The results show that SRPC can improve the porosity,change the pore structure and reduce the pore size which affects the shrinkage.SRPC reduces the surface tension of the cement solution,and reduces the capillary pore pressure.SRPC changes the hydrophilic-lipophilic value due to the introduction of a reduced monomer.The interaction between SRPC and cement was analyzed by measuring the change of adsorption capacity,Zeta potential and thickness of adsorption layer on cement particles.The results show that the introduction of shrinkage-reducing monomer in SRPC changes the hydrophilic and hydrophilic value,weakens the effect of water-reducing dispersion,and weakens the amount of adsorption on cement particles.The dispersion and adsorption capacity of SRPC were increased by increasing the carboxyl content of SRPC,but the shrinkage reduction effect was decreased.KH-SRPC was prepared by optimizing SRPC with silane coupling agent gamma-methacryloxypropyl trimethoxysilane(KH-570).KH-SRPC can effectively reduce the shrinkage of mortar while improving the dispersibility.The results show that KH-SRPC is more effective than SRPC in reducing cement hydration heat release and temperature shrinkage.KH-SRPC changes the pore structure and pore size of slurry and reduces the pore pressure of capillary like as SRPC.It provides a certain theoretical basis and direction for the application of SRPC synthesis and engineering in the future.