| In order to further improve the recycling rate of construction waste and expand the use range of recycled aggregate,this paper studies the influence of double-doped recycled coarse and fine aggregate on the durability of recycled concrete on the basis of traditional single-doped aggregate.By adding recycled coarse and fine aggregates to concrete to partially replace natural aggregates,the depletion of mineral resources is delayed to a certain extent,the pollution of construction waste to the environment is reduced,the problem of ’garbage siege’ is further solved,and the resource utilization of construction waste is strengthened.Firstly,the preparation conditions of recycled aggregate were studied.Secondly,the durability of recycled concrete was studied under the condition of constant fine aggregate content and change of coarse aggregate replacement rate.The results are as follows:(1)In the process of recycled aggregate preparation,the aggregate preparation method was first studied.The change of heating temperature,ball-to-material ratio and grinding time will affect the performance of recycled aggregate when preparing recycled aggregate by heating grinding method.In order to improve the quality of aggregate,the orthogonal test scheme of three factors and three levels of heating temperature,ball-to-material ratio and grinding time was selected in this study.By testing and analyzing the slump and cube compressive strength of recycled concrete,the influence of recycled concrete strength was given priority,and the best orthogonal combination was A3B2C2,that is,the optimal parameters for preparing recycled aggregate by heating and grinding method were:heating temperature 300℃,ball-to-material ratio 20,grinding time 1h.(2)Secondly,the influence of coarse aggregate gradation range on the performance of recycled concrete was studied.Through the dry shrinkage test,carbonization test,chloride ion diffusion test and sulfate erosion test of recycled concrete made of different particle size ranges of coarse aggregate,the shrinkage performance,carbonization performance and corrosion resistance of recycled concrete with different particle size ranges of coarse aggregate were tested and analyzed.It is concluded that the maximum particle size of coarse aggregate does not exceed 25mm,that is,the particle size range of coarse aggregate is 4.75mm-25mm,and the prepared recycled concrete is better in performance.(3)Finally,the effect of recycled coarse and fine aggregate on the performance of concrete was studied.Different schemes of fine aggregate replacement rate of 10%and coarse aggregate replacement rate of 0%,10%,15%,20%,25%,30%,40%,50%,60%and 70%were designed.The results show that with the increase of coarse aggregate replacement rate,the shrinkage performance,carbonation performance and corrosion resistance of recycled concrete decrease continuously.When the replacement rate of fine aggregate is 10%and the replacement rate of coarse aggregate is 15%,the durability of recycled concrete is the best,and the shrinkage performance,carbonation performance and corrosion resistance are similar to those of concrete without recycled coarse aggregate.At this time,the shrinkage rates of 14 d,28 d and 60 d are 1.32×10-4,2.52×10-4 and 4.17×10-4,respectively.The carbonization depth of 7d,14d and 28d were 1.8mm,4.8mm and 11.2mm respectively.The chloride diffusion coefficient of 28d was 5.82×10-12m2/s.The compressive strength corrosion resistance coefficient of 90 times of dry-wet cycle is 0.98. |
