Study On The Microscopic Mechanism Of Modified Recycled Concrete By Microbially Mineral Precipitation

At present,a large number of construction building waste has been produced every year in China.The most prominent problem is the construction waste that is not easy to recycle,such as concrete aggregate and mortar.The recycled concrete aggregate is called “the aggregate with cancer”.Compared with natural aggregate,The surface of recycled concrete aggregate adhere to the old mortar,lead to the water absorption of recycled concrete aggregate is too high,and the mechanical property get reduce.The performance of The performance of recycled concrete aggregate is obviously improved have get obviously improved.In paper,the technology of microbially mineral priecipitation deposition was used to modify recycled concrete aggregate.a large number of calcium carbonate been produced in the pores of aggregates and the surface of aggregates by microbially mineral priecipitation,therefore,the water absorption reduced ? the strength improvement and the interface transition zone is optimized.Supported by the National Natural Science Foundation of China(51578342),this paper has carried out the following research works:The mineralization ability of two species of Bacillus pseudofirmus DSM8715 and Bacillus H4 were compared and analyzed.The precipitate produced by mineralization reaction was analyzed.qualitative analysis by X-ray diffraction;quantitative analysis by TGA;The scanning electron microscope(SEM)and the energy spectrum analyzer(EDS)were used to observe the morphology of the precipitate and to determine the composition of the precipitate;Calculate the yield of calcium carbonate based on TG analysis was proposed to characterize the mineralization ability of bacteria.Analytically,The mineralized products of two strains are irregular rhombic calcite type calcium carbonate,The mineralization ratio of Bacillus pseudofirmus DSM8715 and Bacillus H4 is 68.4% and 79.97%.On the basis of macroscopic properties,SEM was used to observe the change of surface morphology of recycled concrete aggregate before and after mineralized treatment,and EDS was used to analyze the composition of material elements on aggregate surface;The pore structure of 6 groups of recycled aggregate with different strains and different treatment methods was analyzed by mercury intrusion porosimetry,The porosity,pore size distribution,critical pore size,pore size were used as the characterization parameters.Analytically,surface morphology of recycled concrete aggregate after mineralized treatment is covered with a layer of irregular,The surface of recycled concrete aggregate with three elements:C:O:Ca=1:3:1,which can be speculated as the material of calcium carbonate.The porosity,pore size distribution,critical pore size,pore size and volume fractal dimension were used as the characterization parameters of the Properties of recycled aggregate.The overall analysis showed that the treatment of Bacillus pseudofirmus DSM8715 by this one was better than the other treatments: The recycled aggregate dipping medium 120 min containing the strains in the mineralization,after taking out with bacteria aggregate,liquid spray on recycled aggregate by incubation,keep the surface wet,spraying time was 20 days,the ambient temperature is room temperature 26 degrees Celsius.To Bacillus H4,the following suggestions for the selection of treatment way to deal with the aggregate effect is the best,the recycled aggregate immersed in the culture medium containing bacteria mineralization,the soaking time is 20 days,the ambient temperature is room temperature of 26 degrees Celsius.On the basis of macroscopic properties,The influence of microbial mineralization deposition technology on interfacial transition zone was studied by SEM and nanoindentation.The morphology and crack width of the interface transition zone were observed and analyzed by SEM,and the elastic modulus and hardness of the interface transition zone and its vicinity were analyzed by nanoindentation.There are a large amount of hydration products around the cracks of the recycled aggregates prepared by microbial mineralization and deposition technology,and the cracks are filled and covered,and the crack width is reduced obviously;The study of the interfacial transition zone of nano indentation and nano mechanical properties,two groups after mineralization treated samples with and without the mineralization of treated samples by the comparative test,the elastic modulus were increased by 90%,about 125%,the hardness was increased by 115%,about 91%.