Mixture Design And Properties Study Of Low Shrinkage Concrete By Internal Curing With Porous Particles

It was found that the effectiveness for shrinkage reduction of concrete by using pre-soaked lightweight aggregate(PSLWA)or super absorbent polymer is relatively low for medium and low-strength concrete.Meanwhile,some negative effects were found as well on mechanical properties and resistance to chloride ion penetration of concrete.In this study,calcined zeolite was used as internal curing agent in concrete.Experimental study and theretical modeling on the concrete internally cured with calcined zeolite were carried out systematically.The contents of present work include the selection and pretreatment process of zeolite,mixtures optimization of the concrete internally cured with calcined zeolite,mechanism analyses on the effects of calcined zeolite on mechanical properties,model of the moisture field based on variation of water content in concrete.Based on the selected zeolite,the initial mixtures of the concrete internally cured with the calcined zeolite were designed that was consistent with the existing concrete internally cured with PSLWA.Development of shrinkage and internal humidity of the concrete internally cured with the calcined zeolite and PSLWA were experimentally studied comparatively.The test results showed that shrinkage and humidity control effect of initial mixtures with the calcined zeolite were close to those concretes internally cured with PSLWA.However,the shrinkage reduction on medium and low-strength concretes were limited and needed to be further studied.According to the development charateristics of shrinkage of concretes with different strength grades,the mixtures of high-strength concrete and medium-low-strength concrete were optimally designed respectively.For high-strength concrete,the calcined zeolite was used to replace part of cement and fine aggregate.Different alternatives were designed.For medium and low-strength concrete,different cementitious materials content and water-to-binder ratios were designed first.Then the mixtures with small difference in humidity between sealed and dried specimen according to moisture field tests were selected.The selected mixtures were internally cured with the calcined zeolite.The test results showed that the amount of cement used in concrete can be reduced by replacing some cement with the calcined zeolite.Meanwhile,shrinkage of the concrete can be further reduced.Cracking resistance under shrinkage load can be improved effectively.Test results of mechanical properties of concrete and mercury intrusion of cement paste showed that the potential of long-term strength growing of the concrete internally cured with the calcined zeolite were higher than those of ordinarily cured concrete and internally cured concrete with PSLWA.The internal pores of the calcined zeolite were filled by hydration products,and the adverse effect of porus zeolite was reduced gradually.The calcined zeolite can overcome the negative effect of PSLWA on mechanical properties and the resistance of chloride ion penetration of concrete.Regarding the modeling of moisture field of concrete under both action of cement hydration and moisture diffusion,a moisture field calculation model was developed based on variation of capillary water content in the cement paste.The theoretical calculation of the humidity drop resulted from cement hydration was performed.The hypothesis when empty capillary pores is formed was verified by the model and moisture field tests.The developed model can be used for moisture field calculation of concrete elements under any given curing conditons and given amount of internal curing water introduced by internal curing agent.The model can be adopted as a reference in mixture design of the internal curing concrete.