Influence Of Aggregate On Self-healing Capability Of Concrete

Microcrack is just like larva for crack.If we ignored microcraks,concrete might crack soon.As a typical brittle material,the concrete in the process of using is easy to crack,which cause the service life became short.If cracks was controlled at the initial phase,we can avoid the extension and guarantee the safety and durability of buildings.Now,for the problems of cracks,we mainly pick the method of periodic maintenance and repair.Artificial maintenance is not only expensive,but also can not meet the requires of HPC.The process of cracking will spend a long time,which is from small to big and from surface to inside.If the cracks were controlled at the initial phase by enhancing the self-healing capability of concrete,the service life of concrete can be greatly prolonged.Aggregate is an an integral part of concrete,accounting for more than 80%of the total.There have been a lot of studies on the effect of aggregate on the mechanics and durability of concrete,however,systematic study on the self-healing capability is rarely reported.So it is of great significance for understanding and mastering the law of intrinsic self-healing to study the influence of aggregate on the self-healing capability of concrete based on intrinsic capability.In this paper,the effect of NA,LWA and RFA based on pore structures,internal curing and rehydration were studied and the microstructures of concrete which resulted in intrinsic self-healing effects were characterized,the results are listed as followings:（1）The differences of hydration process influenced by gradation and sand ratio（SR）is affected by moisture-distribution and homogeneity of concrete,which results in various effects of self-healing.From the conclusions of NDT,the smaller D_max,the higher extent of hydration,so the capability of self-healing is enhanced.The most excellent groups of SR are those with a sand ratio of 33%and 43%,but the high self-healing rate of the top 43%SR group is caused by the sinking of coarse aggregate,which is not desirable in practical engineering.Harmful pores are extremely unfavorable to the strength and durability of concrete,but,the conclusions revealed that there is no clear relevance on self-healing.This phenomenon can be attributed to the influence of the hydration products formed by cement hydration products.（2）The study of LWA groups revealed that the capability of internal curing was enhanced with the replacement according to the nature of water absorption.The recovery rate under freeze-thaw cycles and preloading damage is positively correlated with the replacement volume.The increase of the replacement volume will result in poor density and the poor resistance to chloride ion erosion at 28 days.The internal curing of LWA helps concrete to resist freeze-thaw damage,which is the reason that the chloride ion erosion depth of 20%group is larger than of 30%group.According to the microstructure analysis of the LWA groups,the total porosity of concrete shows a trend like decreasing-increasing-decreasing with the increase of the replacement volume.We drew a conclusion that the analysis of SEM and EDS tests was consist with that of recovery rate under freeze-thaw cycles and preloading damage.（3）The study of the RFA groups show that the old mortar on surface can not only bring internal curing,but also in favor of rehydration which is beneficial to the recovery rate of properties under freeze-thaw cycles and preloading damage.In the RFA groups,the strength recovery rate was significantly enhanced,and the maximum was up to 14 times of the control group.Due to the complicated component of RFA,If the volume of RFA increases,the homogeneity is getting weaker and weaker,which is bad for the resistance of concrete to chloride ion erosion.The study on microstructures illustrated that the booming volume of RFA leads to an explosive increase in the number of enrichment peaks and defect types as for pore structures.Confirmed by Vickers hardness,the replacement volume of RFA is helpful to promote rehydration.