| Concrete is the most widely used building material in the field of civil engineering.Concrete structures are easily cracked during using period,and cracks seriously affect the life and safety of building structures.Therefore,the repair of concrete cracks has become the focus of many researchers.Microbially induced carbonate precipitation(MICP)technology has a broad application prospect in repaire of concrete cracks due to its environmental friendliness.As a result,in this paper crack quantitatively repairing with MICP method for various crack widths was carried out,and based on it,methods aiming at improving MICP repair efficiency under low temperature and alkali environment were proposed.The relevant mechanism was further studied through theoretical calculation.This study is financially supported by National Natural Science Foundation of China(Grant No.51578147,No.51278099),Postgraduate Research & Practice Innovation Program of Jiangsu Province(Grant No.KYCX18?0107),Scientific Research Foundation of Graduate School of Southeast University(Grant No.YBJJ1846).Main results are incorporated as follows:(1)The optimal conditions(initial p H,concentration of urea and calcium)of calcification were obtained.A new medium and an improved technology of adding urea were proposed and their advantages were verified via mineralization tests with MICP,laying a foundation for subsequent repair of wide fractures.Sporosarcina pasteurii was chosen and the influences of various conditions on growth characteristics,urease activity and productive rates for calcium carbonate of it were studied.The suitable temperature,p H,concentration of urea and calcium of the subsequent tests were determined.The new medium was obtained based on the growth characteristics of biofilm to get higher productive rates for calcium carbonate and facilitate the precipitation to aggregate into a group,providing a possibility for wider crack repair.Mineralization tests with MICP were conducted to determine the cementing ability of calcium carbonate produced and the method of adding urea to medium was presented to produce more calcium precipitates and improve the solidifying effect,laying a foundation for the repair of larger scale crack by filling sands.Referring to the MICP mineralization tests with calcium carbonate,mineralization tests with magnesium carbonate were conducted to determin the feasibility of mineralization with magnesium carbonate.The advantage of adding urea was verified again.(2)The pore network growth model was established and its accuracy was verified by the mineralization test results of MICP.The pore network growth model was optimazed based on biofilm growth.Finally,the MICP crack repair model was established.The urea decomposition rate formula obtained.Considering the convective diffusion of solute,transportation of biomass,precipitation of calcium carbonate and chemical reaction during MICP process,the initial calculation model was established.A new growth model of one-dimensional pore network based on the influences of pore body and pore throat was established.After that,considering the biofilm growth,the model of calculating productive rates for calcium carbonate was optimazed again,and its correctness was validated by comparing with the solidifing sands test results of MICP.MICP crack repair theoretical model was established by analogy with curing model to provide theoretical support for the application of MICP in repair concrete cracks.(3)Drop method,injection method,perfusion method and new medium were proposed to repair cracks with different widths,and the repairing effects were studied.The feasibility of the MICP crack repair theoretical model was verified by the results of 0.5?2.0 mm crack repair tests.Through the successful repair of 1.0?2.0 mm cracks,the superiority of new medium to cluster was proved.Sporosarcina pasteurii was chosen and drop method was proposed for the repair of cracks with width between 0.05 mm and 0.15 mm in concrete specimens.The repair of cracks with width between 0.1 mm and 0.5 mm was conducted with injection method.The repair of crack with width between 0.5 mm and 1.0 mm were repaired with perfusion method and the maxium width of crack cured with original LB medium was obtained.Besides,the productive rates for calcium carbonate measured in the tests were compared with the theoretical calculation results to verify the effectiveness and feasibility of the MICP crack repair theoretical model again.The new medium was used to well repaire wide cracks of 1.5 ? 2.0 mm and the superiority of new medium to cluster was proved.The repair effects of different methods were evaluated via different indexes.Different MICP repairing methods corresponding to different crack widths were obtianed.(4)Based on the sands mineralization tests with MICP and indoor crack(1.0?2.0 mm)repair tests,the lateral displacement cracks in the outer wall was successfully repaired and repair effects were evaluated.Sporosarcina pasteurii was chosen and on the basis of sands mineralization tests and indoor crack repair tests with 1.0?2.0 mm,MICP was applied to repair lateral cracks of outer wall at a residential area in Nanjing to verify the feasibility of on-site repair with MICP.Repair effects were studied comparatively through indexes such as seepage speeds of cracks,surface strength,content of calcium carbonate and sonic time values.(5)Aiming at the problem of low urease activity and low productive rates for calcium carbonate at low temperature during the repair of cracks,three improved methods were put forward.Sporosarcina pasteurii,Bacillus megaterium and four strains isolated from the soil were screened out and the suitable strains were selected for practical application at low temperature.The optimal urea and calcium concentrations were obtaind through calcification tests.The three methods,adding nutrients to gelling solution,adding urea to medium during culture and domestication at low temperature,were proposed to improve low productive rates for calcium carbonate at low temperature.Based on the results of previous experiments,Bacillus megaterium was selected and through the MICP solidifying sands tests and crack repaire tests at low temperature,the feasibility and practicability of MICP at low temperature was determined.(6)Aiming at the problem of high p H and low productive rates for calcium carbonate at alkali environment during the repair of crack with MICP,a method of adding alumina to cracks was proposed to improve the repairing efficiency.Sporosarcina pasteurii was chosen and the influence of adding alumina on MICP process was studied by the three indicators: bacterial growth characteristics,urease activity and productive rates for calcium carbonate.The method of adding alumina into cracks was used to repair cracks,and the repaire effects were evaluated through the p H values of leachate,utilization rate of urea,sound time values,productive rates for calcium carbonate and compressive strength.The feasibility and effectiveness of the method,adding alumina to crack,was verified. |
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