Study On Carbonation Property Of Waste Fiber Recycled Concrete

With the deepening of China's reform and opening up,the contradiction among resources,environment and population has been escalating.Therefore,in this context,while guaranteeing the sustainable development of China's economy,we must consider the rational allocation of resources and sustainable development.As a new type of green building material that can utilize both waste fiber and waste concrete,waste fiber recycled concrete plays an important role in sustainable green development,and has become a focus of concrete research worldwide.Before large-scale use of waste fiber recycled concrete,it is necessary to study its durability,and carbonation performance,as one of the important indicators to measure durability,is of self-evident importance.With the industrialization process,the carbon dioxide concentration in the environment has increased year by year,and the carbonation of concrete has been paid more and more attention.In modern concrete,a large number of mineral admixtures such as fly ash and slag are added,which will affect the carbonation resistance of concrete to a certain extent.In addition,in engineering practice,the concrete structure is often accompanied by complex stress,which will also affeet the carbonation process of concrete.Therefore,it is necessary to consider the influence of admixtures,loads and other factors on concrete carbonation in the environment.In this paper,the factors(fly ash,slag powder,water reducing agent and steel bar),mechanical factors(bending tension stress load and uniaxial compression stress load)which affect the durability of concrete structures in general atmospheric environment are selected.The carbonation behavior of recycled concrete with waste fibers under single factor is studied through experiments.Finally,a carbonation depth prediction model of waste fiber recycled concrete under general environmental conditions is established.The main research contents are as follows:The effect of various factors(water cement ratio,recycled aggregate content,fiber length,fiber content,pouring surface)on the carbonization law of recycled waste fiber concrete and the effect of two-dimensional diffusion on the carbonization depth in the corner zone of components are studied through the rapid carbonization test of recycled waste fiber concrete.The results show that the greater the water cement ratio,the greater the carbonization depth of recycled waste fiber concrete.The higher the replacement rate of recycled aggregate,the greater the carbonation depth of waste fiber recycled concrete;the longer the length of fiber,the smaller the carbonation depth of waste fiber recycled concrete;with the increase of the proportion of waste fiber,the carbonation depth does not change monotonously,and the optimum content is 0.12%.For waste fiber recycled concrete,the carbonation depth at the top is the largest,followed by on both sides.The bottom surface is the smallest;the carbonation rate of concrete in comer area is higher than that of concrete in two adjacent surfaces.Considering the influence of additives on the carbonization performance of waste fiber recycled concrete,the results show that the higher the fly ash incorporation,the deeper the carbonation.With the increase of slag powder substitution rate,the carbonization resistance first increases and then decreases,and the optimal content is 15%.Using high efficiency water reducer can effectively improve the carbonation resistance of waste fiber recycled concrete.The existence of steel bars inhibits the carbonation of the recycled concrete.Considering the effect of stress state on the carbonation performance of waste fiber recycled concrete,the results show that the carbonation depth of waste fiber recycled concrete under three-point bending tensile stress is always greater than that under no stress,and with the increase of tensile stress level,the carbonation depth increases continuously,while the carbonation depth of concrete under uniaxial compressive stress is always less than that under no stress.The depth of carbonization decreases to a certain extent with the increase of compressive stress.Based on the theory of mass transfer,a prediction model of carbonation depth of waste fiber recycled concrete was established,and a series of correction coefficients are obtained by fitting and revising.The comparison between the calculated values and the experimental results verifies the feasibility of the carbonation depth prediction model,which provides a scientific basis for the life prediction of the waste fiber recycled concrete structure in the general atmospheric environment.