Effect Of Core-shell Carrier On Self-healing And Basic Properties Of Microbial Self-healing Concrete

Concrete is widely used in modern civil engineering,but its brittleness and low tensile strength make it easy to crack in service.Based on the theory of microbially induced carbonate precipitation,the crack self-healing technology has become a research hotspot for its environmental friendliness and wide application prospect.In order to eliminate the disadvantage that microorganisms can not survive for a long time when bacteria powder is added into concrete directly,some scholars proposed a core-shell structure immobilization method with many advantages.However,there is a lack of systematic research on this kind of immobilization method.In this paper,by studying the performance of core-shell carrier and comparing the changes of concrete mixture performance,mechanical properties,self-healing performance and durability before and after the use of core-shell carrier,the influence of the use of core-shell carrier on the performance of microbial self-healing concrete is systematically studied.According to the relevant standards,the properties of the microbial healing agent were studied.The results show that,except that the dry water absorption of the saturated surface is slightly higher than that of the conventional aggregate,the physical properties and harmful substances of the microbial healing agent particles meet the requirements of the standard.The microbial healing agent has good durability,and the shell of the carrier has a significant protective effect on the internal bacterial powder.The influence of core-shell carrier on mixture properties and mechanical properties of concrete was studied.The results show that in the range of 10 kg/m~3～22 kg/m~3,the core-shell carrier increases the slump and expansion of concrete,and slightly reduces the 28 day’s compressive strength.Compared with the direct addition of bacteria powder,the core-shell carrier can slightly improve the slump and expansion of the mixture,slightly reduce the setting time,advance the adiabatic temperature rise,and slightly reduce the compressive strength,flexural strength and peak stress.The C35、C45,and C55 concrete should choose microbial healing agent with strength of at least76N、98N,and 167N respectively.Compared with the ordinary concrete,the core-shell carrier has no obvious weakening effect on mixture properties and mechanical properties of concrete.The influence of the core-shell carrier on the self-healing performance of concrete was studied.The results show that in the range of 10kg/m~3～22kg/m~3,the self-healing performance of concrete increases with the increase of the immobilized microbial healing agent,and the best content is 16kg/m~3.Compared with the direct addition of bacterial powder,The shell-core carrier can increase the heal depth of concrete cracks by 2-3mm,water penetration resistance has been improved,and the morphology and composition of the deposited product are not affected;The effective healing age of concrete cracks has been extended from 7 days to at least 56 days;The water-resistant penetration healing rate of the concrete after the healing of the secondary cracks is increased by 6.8%.The influence of the core-shell carrier on the durability of concrete was studied.The results show that compared with the direct addition of bacterial powder,the core-shell carrier eliminates the air-entrainment and early mineralization of the bacterial powder,slightly reduces the concrete’s impermeability,chloride ion penetration,carbonization and frost resistance,and increases the early shrinkage value,decrease the later shrinkage value.Compared with ordinary concrete,the core-shell carrier has no obvious weakening effect on durability of concrete.