Experimental Study On The Performance Of Recycled Concrete Based On Mixed Bacteria Mineralization To Repair The Defect Of Aggregate

With the rapid advancement of urbanization,a large number of concrete buildings have been demolished,and a large amount of construction waste is generated during the demolition of existing buildings,which has an adverse impact on the environment.The waste concrete is crushed and processed into recycled aggregates,which can effectively solve the construction waste.Stacking and pollution issues have significant social,economic and environmental benefits.However,the surface of recycled concrete aggregate contains some hardened old cement mortar or cracks,resulting in its low density,high water absorption,and poor interfacial adhesion with cement-based materials,resulting in lower mechanical properties and durability of recycled concrete.Ordinary concrete.This paper proposes that the method of microbial mineralization and deposition is used to improve the performance of recycled aggregates,and the recycled aggregates modified by microorganisms are used in the preparation of concrete.In this paper,the mineralization deposition efficiency of aerobic and alkaliphilic mixed bacteria and the performance of mixed bacteria mineralization to enhance recycled aggregates and recycled concrete are experimentally studied,and microscopic analysis methods such as scanning electron microscopy,energy spectrum analysis,phase analysis and thermogravimetric method are used.Reveal its mineralization enhancement mechanism,the main work and conclusions are as follows:（1）First,the new aerobic alkalophilic mixture was screened,and then the mineralization and deposition efficiency of the screened microorganisms was studied.With different substrates as the carbon source,under aerobic conditions,selected synthetic capability of carbonate of microbes,and aerobic basophilic mixed bacteria mineralizing deposition efficiency of study,to study the mineralization time,Ca²⁺concentration,concentration of lactic acid,microbial concentration,calcium source,different mineralized microbes on aerobic basophilic mixed bacteria mineralizing deposition efficiency.The experimental results show that;When the times of enrichment and acclimation were 12 times,the aerobic alkalophilic mixed bacteria screened with lactic acid as carbon source had the strongest ability to synthesize carbonate.When the mineralization deposition time is 7d,the concentration of Ca²⁺is 65g/L,the concentration of lactic acid is 65g/L,and the ambient temperature is 33℃,the mineralization efficiency is the highest.The higher the concentration of bacteria,the better the effect of mineralization deposition,calcium source has little effect on the effect of mineralization.The mineralization and deposition effect of the selected aerobic alkalophilic mixed bacteria is better than that of aerobic pure bacteria.（2）To study the mixed bacteria mineralization restoration of reclaimed aggregate,the influence of different adsorption and mixed bacteria schemes,oxygen supply methods,repair and maintenance time,different types of reclaimed aggregate,and different mineralized microorganisms on the defect restoration of reclaimed aggregate was investigated.The experimental results show that;The water absorption rate and crushing index of reclaimed aggregate decreased by 26%and 18.1%after the secondary vacuum adsorption method.Oxygen had a great influence on the mineralization and deposition process of aerobic alkalophilic mixture.The water absorption rate and crushing index of aerobic alkalophilic mixture decreased by 34.6%and 23.1%with sufficient oxygen.The optimal restoration time of the recycled aggregate was 15d,and the category of the recycled aggregate after the mixed bacterial mineralization restoration was improved by one class.The improvement of physical and mechanical properties of recycled aggregate with different quality after mixed bacteria mineralization repair was similar.The mineralization remediation effect of the selected aerobic alkalophilic mixed bacteria is better than that of aerobic pure bacteria.（3）The specimens of microbial reclaimed concrete were prepared by using the aggregates repaired with defects.Firstly,the effects of different types of aggregates,different aggregate substitution rates,and different mineralized microorganisms on the concrete collapse degree and compressive strength were investigated.Then the influences of the types of recycled aggregate and bacterial fluid,different mineralized microorganisms and carriers on the self-repairing ability of recycled concrete cracks were investigated.The experimental results show that;Under the influence of different aggregate types and substitution rates,the collapse degree and compressive strength of the recycled concrete prepared by the recycled aggregate after defect repair have been significantly improved,and the increase range of the collapse degree and compressive strength of the concrete prepared by the recycled aggregate after the mixed bacteria mineralization repair is higher than that of the aerobic pure bacteria.The crack repair ability of mixed bacteria is better than that of aerobic pure bacteria,and the crack repair effect of regenerated aggregate as carrier is better than that of ceramsite.（4）Analyzing the microstructure of the mineralized products of aerobic alkalophilic mixture and the surface of the regenerated aggregate after mineralization repair.The microstructures of mineralized sediments with different reaction times,different concentrations of bacterial solution,different calcium sources and different types of microorganisms and the surface of reclaimed aggregate were analyzed by scanning electron microscopy.By using energy spectrum analysis,phase analysis and thermogravimetric analysis,the mineral deposits of different nutrients,different calcium sources and different types of microorganisms were analyzed.The analysis results show that;With the increase of the concentration of bacterial solution and reaction time,the crystal size gradually increased,and the crystal morphology was affected by different calcium sources.The crystal morphology of the mineralized products of the mixed bacteria is rhomboid,while the crystal morphology of the mineralized products of Bacillus korii is round.After the two kinds of microbial mineralization repair,the mineralized crystals can completely encapsulate the defects of the regenerated aggregate.The crystal types of the mineralized products of aerobic alkalophilic mixed bacteria and Bacillus korii are calcite crystals.The calcium carbonate content and crystallinity of different mineralized microorganisms are close to each other.