Formulation Optimization And Industrial Application Of Carbon Dioxide Curing Solid Waste Lightweight Concrete

The greenhouse effect caused by CO₂ has gradually become a common challenge to the global ecosystem.CO₂ emission has become a major problem concerned by governments all over the world.With the industrial capture technology of CO₂ gradually mature,the utilization of CO₂ needs to be solved.As one of the CO₂ utilization technologies,CO₂ mineralized curing concrete technology is expected to store and utilize CO₂ on a large scale.At the same time,it can greatly improve the strength of early concrete,reduce the energy consumption of traditional curing,absorb industrial solid wastes and shorten the curing cycle of concrete,which has good ecological benefits and economic prospects.With the development of energy saving and emission reduction technology in China,the research on low carbon and low energy consumption of aerated concrete in the construction industry has become a new need.In this paper,fly ash and steel slag,two common industrial solid wastes,are selected as the raw materials of aerated concrete,and the formula optimization,maintenance system exploration and industrial application of CO₂ curing aerated concrete are studied.In this paper,the basic formula of fly ash and steel slag as the main raw materials was optimized,respectively from the preparation of aerated concrete optimization process,internal curing material doping and polypropylene fiber doping were explored.The suitable dry density ratio of aerated concrete at grade B06 is obtained.Adding 0.2%superplasticizer can reduce the water-solid ratio of0.4 to 0.31,which can not only ensure the good gas generating conditions of aerated concrete specimens,but also achieve good water reducing effect.The compressive strength of aerated concrete with polypropylene fiber after CO₂ curing is higher than that without polypropylene fiber.The lower the CO₂ curing partial pressure is,the greater the improvement is.When the content of polypropylene fiber is 0.5%,the compressive strength of aerated concrete is the best.At the same time,the effect of polypropylene fiber doping on the pore structure of aerated concrete specimens cured by CO₂ is mainly reflected in the change of the pore size in the range of 10-100nm:with the increase of CO₂curing partial pressure,the corresponding pore volume decreases more.In the optimization study of initial water-solid ratio,it is found that the initial strength of aerated concrete specimen is the highest when the water-solid ratio is 0.38,but considering the fluidity of slurry during preparation,the water-solid ratio of 0.4 is more appropriate.Secondly,this paper explores and studies CO₂ curing aerated concrete from the perspective of CO₂ curing system.The step curing method was proposed,and the optimal CO₂ intervention time was studied.The micro morphology and product changes of the specimens during the optimization and adjustment of CO₂ curing system were characterized by SEM,XRD and mercury injection.The results show that:after natural curing for 4 days,the carbon fixation rate of aerated concrete specimens increases with the increase of curing pressure.Low pressure（1k Pa-0.1MPa）curing and step curing are beneficial to reduce the mechanical strength loss of aerated concrete specimens.The higher the CO₂ concentration/partial pressure in step curing,the higher the apparent carbon fixation rate of aerated concrete specimens;under the same CO₂ curing conditions SEM observation shows that the mineralized reaction products have different morphologies,such as spherical and spindle,XRD analysis further proves that calcium carbonate has three different crystal forms;after CO₂ curing,the pore size in the range of 0.01-0.1μm decreases significantly,and the higher the apparent carbon fixation rate is,the more significant the filling effect of aerated concrete is.When the CO₂ intervention time is less than 24h,the compressive strength of aerated concrete can be greatly improved.When the CO₂ intervention time is 24h and the curing partial pressure is 1MPa,the compressive strength of aerated concrete can reach 2.7MPa.In order to further study the industrial application of CO₂ curing aerated concrete,this study carried out an expanded test to explore the influence of size effect and spatial stacking on CO₂ curing aerated concrete,and designed an industrial scheme of CO₂ curing aerated concrete with annual carbon sequestration of 10000 tons.The results show that volume enlargement will affect the diffusion of CO₂ into aerated concrete,and space stacking will also weaken the diffusion ability of CO₂,so it is necessary to reserve CO₂ channel to ensure the uniformity and integrity of CO₂ curing.A CO₂ curing aerated concrete test scheme with an annual carbon sequestration of 10000 tons is designed,a complete CO₂ curing process is proposed,and the technical and economic analysis is carried out to guide the industrial application of the technology in the future.