Experimental Study On Repairing Surface Defects And Cracks Of Cement-based Materials Based On Microbially Induced Carbonate Precipitation

Microbially induced carbonate precipitation,as a new crack repairing method for cement-based materials,has the advantages of good compatibility,low energy consumption and environmental friendliness.In this thesis,the surface defects and cracks of cementbased materials were repaired by different methods including immobilizing bacteria,adding external additives and adjusting the p H of bacteria suspension,and the influences of different repair methods on the surface coating and crack repair effects were evaluated based on indicators such as the reduction coefficient of surface water absorption and the flexural strength.The main research contents and conclusions are as follows.(1)The growth curve of Sporosarcina pasteurii under different inoculation amount(the volume percentage of bacterial suspension to liquid medium)was measured,and the most suitable culture parameters for Sporosarcina pasteurii was obtained.At the same time,the effect of p H changes on the urease activity of bacteria was studied.It was found that the urease of this strain would lose most of its activity within short time when p H was over 12.(2)The effects of the concentration of cementation solution(equal molar ratio of calcium chloride and urea mixture)and the ratio of bacteria and cementation solution on the precipitation amount of calcium carbonate,the utilization rate of calcium ions and the crystal form of calcium carbonate were studied,and the optimal concentration of cementation solution and ratio of bacteria and cementation solution were obtained.At the same time,the influence of external additive on the peak strength and failure strain of the bio-cemented sand was studied based on the unconfined compressive strength test.The results show that the external additives can effectively improve the unconfined compressive strength and failure strain of the bio-cemented sand,but it cannot play a full role in alkaline environment.(3)The surface defects and cracks of cement-based materials were repaired by different methods(such as immobilizing bacteria,adding additives,adjusting bacteria p H,etc.).The thickness of calcium carbonate and surface water absorption reduction coefficient were measured after the coating of block samples’ surface.The flexural strength and consolidation rate were measured after the repairing of crack.Then the failure mode observation and scanning electron microscopy(SEM)were carried out.The results show that the technology of microorganism mineralization could effectively reduce the surface water absorption of the samples,but there was no significant difference in the surface water absorption of the samples under different methods.The bonding of the interface between the filling medium and cement-based materials determines the flexural strength of the repaired samples.Considering the economy and repair performance comprehensively,the method of adjusting p H of the bacterial suspension is more suitable for the applications practical engineering.