Study On Mineral Carbonation Curing Of Solid Waste Lightweight Concrete

The global warming effect has become one of the major environmental issues in today’s society.As an emerging carbon dioxide utilization technology,mineral carbonation（MC）curing is expected to achieve large-scale CO₂ storage and utilization,while improving the performance of ordinary concrete,shortening maintenance time and saving maintenance energy.On the other hand,with the development of building materials,lightweight concrete has gradually become one of the main ways to eliminate industrial solid waste.The existing research lacks the discussion on the performance and mechanism of CO₂ mineralization of solid waste lightweight concrete,especially aerated concrete.In this paper,two common industrial solid wastes,fly ash and blast furnace slag,are selected as the main raw materials for solid waste aerated concrete.The experimental research on MC curing performance of solid waste aerated concrete is carried out.Firstly,aiming at the preparation and pretreatment process of the test piece,the influence mechanism of the dry density,pre-curing time and residual water-cement ratio of the solid waste aerated concrete specimen on the MC curing performance was determined.The solid waste aerated concrete specimen with 3-day pre-curing and dry density of 600kg/m³ has the best MC curing effect.The results also verified that the optimal residual water-cement ratio of solid waste aerated concrete was slightly higher than that of ordinary concrete,and determined the optimal residual water-cement ratio range of 0.25-0.3 for solid waste aerated concrete in this study.At the same time,for the industrial solid waste of fly ash and blast furnace slag,this paper systematically studied the influence mechanism of solid waste type and doping ratio on the CO₂ uptake and material properties of solid waste aerated concrete.The results show that fly ash can promote the loosening of the local structure of the specimen and strengthen the diffusion process of CO₂,but it has an adverse effect on the mechanical properties of the specimen.The blast furnace slag can enhance the mineralization reactivity of the specimen and improve the mechanical properties.However,the dense structure in the early stage is not conducive to the diffusion process of CO₂.In this study,the solid waste content of solid waste aerated concrete with an optimization range of 50%-60%was determined by experiment.Based on 60%solid waste doping ratio,the composite doped fly ash and blast furnace slag were further investigated.The results show that the final carbon fixation rate of the composite solid waste test piece with 30%fly ash+30%blast furnace slag+40%cement is equivalent to the composite test piece of 40%cement+60%blast furnace slag;Compared with the composite specimen of 40%cement+60%fly ash,the compressive strength is increased by 55.37%.Compared with the same formula test piece for natural conservation,the compressive strength of the fly ash-blast furnace slag-cement composite test piece after mineralization was slightly reduced,mainly because the interface structure of fly ash-blast furnace slag inside the test piece was relatively weak.After MC curing,the product is prone to product expansion cracks.In order to solve the problem of low mechanical properties after the above-mentioned solid waste aerated concrete mineralization and conservation,the mineralization conservation strengthening method including internal curing technology and CO₂ pressure swing curing technology was studied.The study found that the strength of the specimen after doping with 0.5%of the curing material can be improved by about 33%;the low pressure CO₂ curing at normal pressure reduces the internal diffusion efficiency of the gas and slightly reduces the carbon fixation rate of the test piece,but it is effective.Reduce the occurrence of expansion cracks in the microstructure.In view of the overall process of MC curing of solid waste aerated concrete,this paper also carried out a comparative analysis of the mineralization maintenance process and the economics of autoclaved curing process.The results show that the investment and operating cost of CO₂ mineralized solid waste aerated concrete process are slightly lower than that of autoclaved curing process,and it has more significant environmental benefits,thus showing good industrial application prospects.