Study On The Influence Of Metakaolin On The Mechanics And Frost Resistance Of Ceramsite Lightweight Aggregate Concret

Although light aggregate concrete has the advantages of designable strength and low self-weight,its consumption of cement is higher than that of ordinary concrete,and it is easy to appear the floating phenomenon of lightweight aggregate.Metakaolin has high pozzolanic activity and can be used as a substitute for some Portland cement to produce lightweight aggregate concrete.Its use can improve the performance of concrete,reduce the consumption of cement in the production process,and protect the environment.At the same time,the addition of metakaolin can improve the cohesion of concrete and effectively alleviate the floating of lightweight aggregate.In this paper,the mechanics and frost resistance of metakaolin ceramsite concrete were studied.Different amounts of metakaolin（0%,4%,8%,12%,16%）were used to replace cement in ceramsite lightweight aggregate concrete to make test blocks.The compressive and splitting tensile strength tests were carried out on test blocks cured for3 d,7 d,14 d,28 d and 60 d.The microstructure of ceramsite concrete was analyzed by SEM（scanning electron microscope）,and the changes of microstructure of ceramsite lightweight aggregate concrete with different metakaolin content were observed.The freeze-thaw cycle test was carried out on the test block cured for 28 days by quick freezing method.The results show that:（1）Metakaolin can improve the compressive and splitting tensile strength of ceramsite concrete,and the strength is the highest when the content is 12%.Metakaolin has a better gain effect on the early strength of ceramsite concrete,and also has a certain improvement on the late strength.There was a positive correlation between strength and curing age,and the relationship between strength and age was in line with the power function model.（2）Metakaolin has high pozzolanic activity,which promotes the secondary hydration reaction of cement,reduces the accumulation of amorphous Ca（OH）₂ crystals,and generates more hydration cementitious materials to form intertwined network structures.Metakaolin particles can fill pores,make the microstructure denser,and improve the strength of shale ceramsite concrete.（3）Metakaolin can slow the process of freeze-thaw damage of ceramsite concrete,reduce the degree of freeze-thaw damage,and reduce the amount of spalling and aggregate exposure in freeze-thaw damage.When the content is 8%,the loss of mass and relative dynamic elastic modulus is the least,and the frost resistance of concrete is the best.Through function curve fitting and comparative analysis,it is determined that the quadratic polynomial function freeze-thaw damage model is more accurate.According to the life prediction of the model,the service life of 8%metakaolin ceramsite concrete is the longest.