Study On Shrinkage Reducing Polycarboxylate Superplasticizer With Different Shrinkage Reducing Monomers

The shrinkage of concrete has always affected the service life of concrete and the durability of concrete structure,it is very important to reduce and control the shrinkage of concrete.In this paper,according to the theory of molecular structure design,different shrinkage reducing monomers with different molecular structures were designed.Combing with the characteristics of the molecular structure of polycarboxylate superplasticizer,the shrinkage reducing monomer is introduced into the molecular structure of polycarboxylate superplasticizer.A shrinkage reducing polycarboxylate superplasticizer with both water reducing and shrinkage reducing functions was prepared.In this paper,butyl acrylate,diethylene glycol monoacrylate and diethylene glycol monobutyl ether acrylate with different structure were designed and prepared by esterification.The results of infrared spectroscopy proved that the preparation was successful and the molecular structure was in accordance with the expected design.It was proved that the shrinkage reducing monomer was successfully grafted onto the molecular structure of shrinkage reducing polycarboxylate superplasticizer.The application properties of shrinkage reducing polycarboxylate superplasticizer with different shrinkage reducing monomer were studied from the aspects of cement paste fluidity,cement mortar strength,drying shrinkage and autogenous shrinkage of cememt moetar.The results showed that shrinkage reducing polycarboxylate superplasticizer with diethylene glycol monobutyl ether acrylate showed the best dispersion and retention performance of cement paste;having little negative effect on the strength of cement mortar;compared with the blank group,the drying shrinkage rate of 56 day’s of cement mortar decreased by 8.5%,and the autogenous shrinkage rate of 28 day’s of cement mortar decreased by 47.6%,indicating that the best performance of diethylene glycol monobutyl ether acrylate.The shrinkage reducing polycarboxylate superplasticizer was prepared by changing the substitution ratio of diethylene glycol monobutyl ether acrylate and its application performance was investigated.The results showed that the shrinkage reducing polycarboxylate superplasticizer with the substitution ratio of less than 40% showed good dispersion and disperision retention for cement paste;it can significantly improve the strength of cement mortar.Compared with the blank group,the drying shrinkage rate of 120 day’s of cement mortar decreased by 14% and the autogenous shrinkage rate of 28 day’s of cement mortar decreased by more than 33.7%.It is concluded that the shrinkage reducing polycarboxylate superplasticizer with a substitution of less than 40% has the best performance in all aspects.In addition,the mechanism of shrinkage reducing polycarboxylate superplasticizer was studied from four aspects: surface tention of solution,heat of hydration of cement,Zeta potential of cement particles and XRD analysis of early cement paste.It is concluded that: Surface tention data prove that the shrinkage reducing monomer diethylene glycol monobutyl ether acrylate has the best performance;The shrinkage reducing polycarboxylate superplasticizer grafted with different shrinkage reducing monomers has delayed the hydration of cement.When the substitution ratio of diethylene glycol monobutyl ether acrylate is less than 20%,the shrinkage reducing polycarboxylate superplasticizer has the best effect on retarding the hydration process of cement.The addition of shrinkage reducing polycarboxylate superplasticizer reduces the Zeta potential of cement particles,it is concluded that the change of Zeta potential will affect the fluidity of cement paste,however,there was no direct corresponding relationship;XRD analysis showed that shrinkage reducing polycarboxylate superplasticizer promoted the formation of calcium hydroxide of hydrated product.In this paper,shrinkage reducing monomers with different molecular structure was designed and prepared,and shrinkage reducing polycarboxylate superplasticizer with different kinds of shrinkage reducing monomer and different substitution ratio of shrinkage reducing monomer was prepared,and its application performance and action mechanism were investigated.It provides a way for design and preparation of subsequent shrinkage reducing superplasticizer and the study of its action mechanism.