Research On Impact Properties Of Reinforced Recycled Coarse Aggregate PVA Fiber Concrete

Replacing or partially replacing natural sand and gravel with recycled coarse aggregate using construction waste as the raw material not only reduces the demand for natural sand and gravel resources in the construction industry,but also reduces urban waste from the source,saves resources and protects the natural environment.The engineering structure may be subjected to impact loads（such as earthquakes,vehicle impacts,floods,etc.）during use.Therefore,it is of great significance to carry out research on the static and dynamic aspects of recycled concrete.This article takes recycled coarse aggregate concrete as the research object.The properties of recycled coarse aggregate concrete were modified by strengthening recycled coarse aggregates（nano-SiO₂ and cement paste）and adding Polyvinyl alcohol（PVA）fibers.The physical properties of recycled coarse aggregates and the static and dynamic mechanical properties of recycled coarse aggregate concrete were studied respectively.The main research contents are as follows:（1）The effects of Nano SiO₂ solution concentration（0%,1%,2%and 3%）and soaking time（0h,24h,48h,and 72h）on the physical properties（apparent density,crushing index and water absorption）of recycled coarse aggregates were studied and analyzed.The results show that the soaking concentration of 2%and the soaking time of 48h have the best effect on the modification of Recycled coarse aggregate;（2）The study analyzed the effect of cement slurry with different water-cement ratio（0.5,0.7 and 0.9）on the physical properties（apparent density,crushing index and water absorption）of recycled coarse aggregate。The results show that the cement slurry with a water-cement ratio of 0.5 has the best modification effect on recycled coarse aggregates;（3）The study analyzes the influence of replacement rate（0%,30%and 100%）and strengthening method（Nano SiO₂ and cement paste）on the compressive strength,axial compression strength and flexural strength of recycled coarse aggregate concrete;On this basis,further analysis of the influence of adding PVA fiber materials on the mechanical properties of the law;（4）Based on the research results of basic mechanical properties,the dynamic mechanical properties of PVA fiber-reinforced recycled coarse aggregate concrete were further studied and analyzed using the SHPB test device.The effects of strain rate,PVA fiber content,replacement rate and strengthening method on dynamic peak stress and strain were mainly analyzed.The research results show that:with the increase of strain rate,the dynamic peak stress and strain of each group of concrete specimens have been significantly improved;As the substitution rate increases,the dynamic peak stress shows a downward trend but the dynamic peak strain is strengthened;Modified recycled coarse aggregate has a certain enhancement effect on dynamic peak stress;The addition of PVA fiber has no significant effect on the dynamic peak stress but the dynamic peak strain is significantly enhanced.