| At present,how to deal with construction solid waste has become a thorny issue of social concern in China,and the construction industry is dependent on natural sand and gravel,so there is an urgent need for the resource utilization of construction waste.After crushing,screening and washing,concrete,masonry and tile materials in construction waste can be reused as recycled aggregates.However,the surface layer of recycled aggregates has a large amount of old cement attached to it,resulting in many surface voids,high water absorption and poor thermomechanical properties,which cause the recycled aggregates to have lower working performance,lower pressure resistance and poor durability.Therefore,this paper focuses on the enhancement of recycled aggregates by using the mineralization properties of soil microorganisms,and further investigates the working properties,hardness and water absorption of recycled concrete,and analyzes the mineralization mechanism with the help of scanning electron microscope and thermogravimetric analyzer,the main work and conclusion are as follows:(1)The collected construction waste was crushed and screened,and the aerobic microorganisms required for processing recycled aggregates were screened and cultured,and the mineralized microorganisms completed in the culture were used to enhance different particle sizes and different types of recycled aggregates.The test results showed that: the aerobic alkalophilic mixed cultures used in this paper had better mineralization enhancement effect on recycled aggregates compared with Bacillus cereus;the quality of recycled fine aggregates improved more after mineralization enhancement by aerobic mixed cultures,the water absorption rate of recycled fine aggregates decreased by 29.7% and the crushing index decreased by 19.6%,the water absorption rate of recycled coarse aggregates decreased by 15.7%and the crushing index decreased by 19.6%;the optimal The enhancement time is 15 d,the water absorption rate and crushing index of recycled coarse aggregate decreased by 21.4% and 27.8%,respectively;the performance of recycled masonry aggregate after microbial enhancement is significantly improved,the water absorption rate and crushing index decreased by 29.9% and19.6%,respectively.(2)In this paper,the stability of the bacterial flora in the enhancement maintenance process was maintained by adding trace element solution and mineral solution to the nutrient solution,and different calcium source solutions of calcium nitrate,calcium chloride and calcium lactate were used to modify the recycled aggregates for the study,and the aerobic microbial properties were used to improve the enhancement process by dry and wet cycling and spraying treatment of the recycled aggregates.The test results showed that: the mixed cultures activity and mineralization efficiency were improved after adding mineralized nutrient solution,and the water absorption rate of recycled coarse aggregate was reduced by 19%,and the water absorption rate of recycled fine aggregate was reduced by 29.4%;the best soaking enhancement effect was achieved using calcium chloride and calcium lactate mixed solution group,and the water absorption rate of recycled coarse aggregate was reduced by 26.7% from 7.0% to 5.13%,and the crushing index was reduced by 22.3%;after Dry and wet circulation and spraying method aggregate enhancement effect can reach 60% of the immersion method,dry and wet circulation method treatment coarse aggregate water absorption rate reduction of 9.7%,fine aggregate water absorption rate reduction of 12.5%,spraying method treatment coarse aggregate water absorption rate reduction of 10.4%,fine aggregate 14.3%.(3)The surface of the recycled aggregate after mineralization enhancement by aerobic alkalophilic bacteria was analyzed.The surface microstructure of the recycled aggregates with different microbial species,different types of recycled aggregates,different enhancement maintenance times and different mixed calcium sources were analyzed by scanning electron microscopy;the surface sediment products of the aggregates with different species of microorganisms and with or without the addition of mineralized nutrient solution were analyzed by energy spectrum analysis,physical phase analysis and thermogravimetric analysis.The results showed that: the surface deposits of recycled aggregates treated with mixed cultures were more compact compared with pure bacteria;small-sized pores on the surface of recycled masonry aggregates could be effectively filled by microbial mineralized deposits;the surface deposits of recycled aggregates were the most compact at 15 d of mixed cultures enhanced modification;oval-shaped flakes of calcite deposits appeared on the surface of mixed calcium source group of calcium nitrate and calcium lactate,with crystal flakes of about 10 μm in size and 2-3 μm in thickness.(4)Cement mortar and concrete specimens were prepared using the enhanced recycled aggregates of different particle sizes,and the strength and water absorption of cement mortar,strength,workability and capillary absorption coefficient of concrete were measured under the same replacement rate,after which the effects of different microbial factors on the above test variables were further investigated.The test results showed that the compressive strength,workability and water penetration resistance of the recycled concrete prepared from the restoration-enhanced recycled aggregates were significantly improved under the influence of different aggregate particle sizes and the same substitution rates,and the improvement of the collapse and compressive strength of the recycled concrete from the mixed cultures mineralization restored recycled aggregates was better than that of Bacillus cereus. |
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