Research On The Influence Of Aggregate Replacement Ratio On The Performance Of Fiber-Reinforced Recycled Concrete

With the rapid development of global economy,the research and application of recycled concrete have gradually become an important topic in the field of engineering construction.Recycled concrete realizes the sustainable utilization of resources and the reduction of energy consumption by recycling aggregates and cement from waste concrete,while also reducing environmental pollution.However,recycled concrete also has defects such as unstable quality,high technical difficulty,poor frost resistance,and easy cracking,which limits its wide application in the field of engineering construction.Studies have shown that the mechanical properties and toughness of recycled concrete can be effectively improved by adding a certain amount of fibers.Therefore,the research of fiber-mixed recycled concrete has important theoretical significance and practical application value.This paper selects high elastic modulus basalt fibers and low elastic modulus polyacrylonitrile fibers for improving recycled concrete by fiber-mixing.The impact of different fiber-mixing ratios and recycled aggregate substitution rates on the mechanical properties and bending toughness of recycled concrete is mainly studied.The main research work of this paper is as follows:(1)The influence of different fiber-mixing ratios and recycled aggregate substitution rates on the mechanical properties of recycled concrete was explored.It was found that compared with ordinary concrete,the compressive,tensile,and bending strengths of recycled concrete at the same strength level are lower,and the higher the recycled aggregate substitution rate,the greater the reduction in the strength value of recycled concrete.The addition of fibers can partially increase the compressive strength of recycled concrete,but has a greater impact on the bending and tensile strengths.There is an optimal mixing ratio for the fibers,but when the fiber mixing ratio deviates from the optimal ratio,its reinforcement effect on recycled concrete will gradually decrease.The substitution rate of aggregate has almost no effect on the failure mode of concrete specimens;compared with ordinary specimens,the specimens with fibers have significantly improved failure mode.(2)The advantages and disadvantages of commonly used bending toughness evaluation methods at home and abroad were compared,and a bending toughness evaluation method suitable for fiber-mixed recycled concrete was selected to evaluate the bending toughness of recycled concrete beams.The results showed that the addition of recycled aggregate would reduce the bending peak strength,energy absorption value,residual strength and other bending performance indicators of recycled concrete beams,but has no obvious effect on the deflection deformation of specimens;the addition of fibers can enhance the bending peak strength,energy absorption value,residual strength and other bending performance indicators of recycled concrete beams,and the improvement effect of mixing two kinds of fibers is better than that of not mixing or mixing a single kind of fibers.(3)The experimental data were analyzed by SPSS software to clarify the influence of each experimental variable on the experimental results.It was found that in the two variables of fiber addition form and recycled aggregate substitution rate,the recycled aggregate substitution rate had a more significant effect on the compressive and bending performance of fiber-mixed recycled concrete,while the fiber addition form had a greater impact on the tensile performance of fiber-mixed recycled concrete.In addition,the calculation results of SPSS software were basically consistent with the experimental results,so it can be used as a reference for the experimental data.(4)The microscopic morphology characteristics of fiber-mixed recycled concrete were observed and analyzed by scanning electron microscopy,and the enhancement and toughening mechanism of two kinds of fibers on recycled concrete were analyzed from the aspects of fiber bonding and fiber rupture,combined with fiber spacing theory.The ratio of fiber pull-out work to fracture work was calculated from the perspective of fiber energy consumption,and the different effects of mixing two kinds of fibers in recycled concrete were analyzed.