Effect Of Composite Modification On Mechanical And Fracture Properties Of Fully Recycled Concrete

Recycled aggregates have the advantages of wide sources and low prices,so the research on recycled concrete has received widespread attention from many scholars.However,compared to ordinary concrete,recycled concrete has poor performance,which greatly limits the promotion and application of recycled concrete.To broaden the application range of recycled concrete,it can be modified to make its performance comparable to or even higher than ordinary concrete,thereby achieving efficient utilization of solid waste resources.This article uses sodium silicate modification,emery modification,and sodium silicate-emery composite modification methods to modify fully recycled concrete(the replacement rate of recycled coarse and fine aggregates is 100%).The improvement of mechanical and fracture properties of fully recycled concrete by three modification methods is discussed,and the corresponding modification mechanism is analyzed at the micro level to find the optimal modification plan,this can provide a reference basis for the application of fully recycled concrete in practical engineering.The main research content and conclusions of the thesis are as follows:(1)The strength of ordinary concrete and fully recycled concrete before and after modification was measured through cube compression,axial compression,splitting tensile,and flexural strength tests.Based on this,the improvement of mechanical properties of fully recycled concrete by different modification methods was studied.The research results indicate that sodium silicate modification,emery modification,and sodium silicate-emery composite modification can all improve the mechanical properties of fully recycled concrete,and the strengthening effect of sodium silicateemery composite modification is better than that of sodium silicate and emery single modification.(2)Three-point bending test and digital image correlation method were used to measure the fracture energy,fracture toughness,and other parameters of ordinary concrete and fully recycled concrete before and after modification,to study the improvement of the fracture performance of fully recycled concrete by different modification methods.The research results indicate that sodium silicate modification,emery modification,and sodium silicate-emery composite modification can all improve the fracture resistance of fully recycled concrete,delay the initiation and expansion of cracks,and slow down the failure rate of specimens.Moreover,the improvement effect of sodium silicate-emery composite modification on the fracture performance of fully recycled concrete is better than that of sodium silicate and emery single modification.In addition,digital image correlation methods can track and predict the final direction of crack propagation in the fracture process zone of concrete specimens.(3)Use scanning electron microscopy to observe the interface transition zone and mortar slurry structure in the internal microstructure of fully recycled concrete before and after modification,to study the improvement of the internal microstructure of fully recycled concrete by different modification methods,analyze the corresponding modification mechanism,and explore the relationship between microstructure and macroscopic performance.The research results indicate that sodium silicate modification,emery modification,and sodium silicate-emery composite modification can all improve the internal microstructure of fully recycled concrete.Among them,sodium silicate-emery composite-modified recycled concrete has the best internal microstructure morphology,which explains why the mechanical and fracture properties of sodium silicate-emery composite-modified recycled concrete are better than those of sodium silicate-modified recycled concrete and emery-modified recycled concrete.