Modification Of Recycled Aggregate By Microbially Induced Calcite Precipitation Technology And Its Influence On Concrete Properties

With the rapid development of infrastructure,the demolition and reconstruction of buildings have produced a large amount of construction waste all over the world.At the same time,the demand of concrete materials for aggregate resources is still increasing.Recycled aggregate prepared from construction waste,as a sustainable building material,has a good application prospect.However,the mortar attached to the surface of recycled aggregate limits the wide application of recycled aggregate to a certain extent.Microbially induced calcite precipitation(MICP)technology fills the pores and microcracks of recycled aggregate with biological calcium carbonate produced by mineralization reaction,so as to improve the quality of recycled aggregate.This paper used Bacillus pasteurii induced calcite precipitation technology to modify recycled aggregate,so as to enhance the basic performance of recycled aggregate and improve the performance of recycled concrete prepared from mineralizing recycled aggregate.In this paper,the effects of culture time,culture temperature,initial p H value of culture solution and inoculation amount on urease activity of Bacillus pasteurii were studied.Based on bacterial solution with high urease activity,and the effects of MICP technology on the basic properties of recycled aggregate under different bacterial solution concentrations,urea concentrations and calcium ion concentrations were studied,and the mechanism of microbial mineralization under the environment of recycled aggregate and the reinforcement mechanism of MICP technology on recycled aggregate was discussed.Finally,based on the different concentrations of bacterial solution,urea solution and calcium ion solution,the influence of recycled aggregate modified by MICP technology on the performance of recycled concrete was discussed.Through the above research,the following conclusions are drawn:1.During the growth of Bacillus pasteuri,the p H value of the bacteria solution gradually increased and finally became alkaline.This feature made it possible for it to survive in the alkaline environment of recycled aggregate.When the liquid culture medium with 1%inoculation amount of Bacillus pasteurii was cultured at the environment of 35℃and 9 initial p H of the culture solution for 24 h,the urease activity of bacterial solution was highest.2.Carbonate produced by hydrolysis of urea by Bacillus pasteurii combined with calcium ions in solution and recycled aggregate to produce biological calcium carbonate,which can effectively refine the macropores and capillary pores of recycled aggregate and improve the basic performance of recycled aggregate.When the concentration of bacterial solution was 4.5×10~8cells/m L,urea concentration was0.9 mol/L,and calcium ion concentration was 0.2 mol/L,the performance of recycled aggregate was improved to the highest,water absorption of aggregate decreased by 10.6%,and the porosity of attached mortar decreased by 26.72%.3.The concentrations of bacterial solution,urea and calcium ion will affect the mineralization activity of bacteria.With the increase of the concentrations of bacterial solution or calcium ion,the microbial mineralization activity increased at first and then decreased.This was mainly because the higher concentrations of bacterial solution would make bacteria enter logarithmic phase and decay phase in advance;Higher concentrations of calcium ions would inhibit the microbial mineralization activity.However,when the urea concentrations was high,the decomposition rate of bacteria to urea reached the limit,so the microbial mineralization activity increased first and then tended to be stable with the increase of urea concentrations.When the concentration of bacteria solution was 4.5×10~8cells/m L,the concentration of urea was 0.9 mol/L,and the concentration of calcium ion was 0.3 mol/L,the mineralization activity of bacteria reached the highest.4.The alcium carbonate produced by microbial mineralization improved the pore structure of recycled aggregate,and the microhardness of recycled aggregate concrete made with recycled aggregate strengthened by MICP technology in different interface transition zones were increased,which effectively improved the compressive strength and flexural strength of recycled aggregate concrete.At the same time,the decrease of porosity of recycled aggregate made the water absorption per unit area of recycled aggregate concrete decreased,the water adsorption rate decreased,and the chloride ion permeability resistance improved.