Study On Preparation And Properties Of Polycarboxylic Acid Water Reducer With Carboxyl Protection

Polycarboxylate water reducer is an indispensable part of modern concrete,which is widely used in concrete engineering.Polycarboxylate superplasticizer has the characteristics of low dosage,high water reducing and slump retention,and strong molecular structure regulation.However,there are still many disadvantages in the use of polycarboxylate superplasticizer,such as too fast slump loss of concrete mixed with polycarboxylate superplasticizer,and the dispersion effect of superplasticizer decreased when the mud content in fine aggregate is high.In this paper,three different slow-release monomers,acrylamide(AA),hydroxypropyl acrylate(HPA)and hydroxyethyl acrylate(HEA),were used to synthesize carboxyl protected polycarboxylic acid water reducer.The hydrolysis mechanism of slow-release monomers in the carboxyl protected polycarboxylic acid water reducer was verified by infrared spectrum analysis.The compatibility of the slow-release monomers with cement was analyzed by the fluidity test of cement paste.The influence of single mineral and soil on carboxyl protected polycarboxylate water reducer was studied by fluidity experiment and XRD analysis.The results show that the experimental phenomenon of carboxyl group dissociation of AM,HEA and HPA in alkaline environment was found by infrared spectrum analysis.The fluidity of cement paste with different carboxyl protection polycarboxylic acid water reducer systems was tested.With the increase of substitution rate of slow-release monomers for acrylic acid,the fluidity of cement paste increased firstly and then decreased after 2 hours.TPEG2700-AM-AA system with 40% acrylamide substitution rate,TPEG2700-HPA-AA system with 60% hydroxypropyl acrylate substitution rate and hydroxyethyl acrylate substitution system were used respectively When the ratio of HPEG2500-HEA-AA is 80%,the maximum flow rate of HPEG2500-HEA-AA is 2h,which shows that the system has the best slow release effect.When different minerals are mixed with polycarboxylic acid water reducer,it shows different dispersion.Among them,the carboxyl protected polycarboxylic acid water reducer of hydroxyethyl acrylate system showed the best slow-release characteristics for the initial fluidity of albite slurry,the fluidity at 1h and 2h.The carboxyl protected polycarboxylic acid water reducer of hydroxyethyl acrylate system showed the best slow-release characteristicsfor the initial fluidity,the fluidity at 1h and 2h of illite slurry.The polycarboxylic acid superplasticizer of hydroxypropyl acrylate system showed the best slow-release characteristics for the initial fluidity,the fluidity after 1h and 2h.The mixed water reducing agent of carboxyl-protected polycarboxylic acid water reducing agent of different systems and ordinary polycarboxylic acid water reducing agent was tested for the cement cement slurry fluidity,and the acrylamide substitution rate was 40%.HPEG3000-AM-AA system,HPEG3000-HPA-AA system with a 40% substitution rate of hydroxypropyl acrylate,and HPEG3000-HEA-AA system with a 100% substitution rate of hydroxyethyl acrylate showed a maximum flow rate of 2h over time The carboxyl-protected polycarboxylic acid water reducing agent in this system has the best anti-mud effect.