The Synthesis And Evaluation Of The Shrinkage-Reducing Polycarboxylate Superplasticizer

In this paper,polycarboxylate superplasticizer?PCA?was synthesized by polymerization of TPEG₂₄₀₀,acrylic acid?AA?and ammonium persulfate?APS?as initiator in a certain condition,and then screened five kinds of reducible groups include diethylene glycol,triethylene glycol,tetraethylene glycol,PEG₆₀₀,PEG₁₅₀₀.Esterification reaction was conducted to synthesize a kind of shrinkage-reducing polycarboxylate superplasticizer?SRPC?with the reducible groups grafted to lateral chain of PCA.The polymerization experimental process is designed and optimized by orthogonal test in this experiment.The optimal process is as follows:acid ether n?AA?:n?TPEG?is 1:3,monomer concentration is 30%,initiator's mass percentage is 2.5%,reaction temperature is 75?,and dropping time is 2.5h.The fluidity of cement paste initially reaches 302.5mm and reaches 290mm after1h.In this experiment,single factor optimization test was carried out on the basis of the optimum process of orthogonal test.The results showed that the monomer concentration,acid ether ratio,initiator's mass percentage,dropping time,and reaction temperature were 30%,3,3.5%,2.5h,and 80?respectively for the optimum fluidity of cement paste.Under this condition,the fluidity of cement paste initially reaches317.5mm and reaches 304mm after 1h.The fluidity of cement paste is influenced by the viscosity-average molecular weight and the adsorption capacity of water-reducing agent on the surface of cement particles.This relation is investigated and then applied to analysis the influence of different polymerization conditions on the fluidity of cement paste,which has the guiding meaning for the research and development of water-reducing agent.The structure of shrinkage-reducing polycarboxylate superplasticizer was characterized by Fourier transform infrared spectrometer.The results showed that the polymer was composed of TPEG,acrylic acid and shrinkage reducing group.The water-reducing rate and shrinkage rate were measured by cement mortar water-reducing test and cement mortar dry shrinkage test respectively.The water-reducing rate of three samples was compared.The shrinkage-reducing rate of the self-made RSPC mortar reached to 40.23%at 28d,and the water-reducing rate of cement mortar was 25.56%.By comparison,self-made shrink-reducing polycarboxylate superplasticizer has excellent water-reducing ability and shrinkage-reducing ability.