Research On The Performance Of Recycled Aggregate Concrete Modified With Permeable Crystalline Materials

As the economy continues to develop and infrastructure facilities continue to improve,the amount of construction waste generated increases.The waste concrete can be crushed,screened and cleaned to make recycled aggregates.The vigorous development and application of recycled aggregates can greatly reduce the mining of natural sand and gravel,and also effectively solve the problem of waste construction waste piling.However,the high water absorption rate,high crushing index and low apparent density of recycled aggregates themselves affect the application of recycled aggregates in actual engineering.Based on that,this thesis combines the characteristics of recycled aggregates themselves and uses permeable crystalline materials to strengthen recycled aggregates,and analyzes the physical properties of crushing index,apparent density and water absorption rate of recycled aggregates before and after strengthening,and selects the optimal strengthening method.Concrete proportions with 0%,50%and 100%recycled aggregate replacement were designed to study the effects of reinforcing recycled aggregate with permeable crystalline materials on the workability,mechanical properties and durability performance of recycled aggregate concrete.SEM and NMR tests were used to observe and analyze the microscopic pore structure of recycled aggregates and recycled aggregate concrete.The results of macroscopic and microscopic tests were integrated to investigate the mechanism of modified recycled aggregate concrete by permeable crystalline materials.The main contents are as follows:(1)The physical properties of recycled aggregate before and after reinforcement by infiltration crystalline materials were tested.The test results showed that the performance of recycled aggregate was improved with the increase of strengthening time by direct immersion method,but the magnitude of improvement was gradually reduced;the performance index of recycled aggregate was improved more obviously and better by using immersion air-drying method to modify and strengthen recycled aggregate in the same time.(2)The work performance,mechanical properties and durability of the ordinary concrete with recycled aggregate before and after strengthening were tested.The test results showed that the slump of modified recycled aggregate concrete was improved,the compressive strength of concrete was improved by 5.50%～17.96%,and the frost resistance and carbonation resistance of modified recycled aggregate concrete were improved after modified with permeable crystalline materials.(3)The rheological and mechanical properties of the recycled aggregate selfcompacting concrete were tested before and after strengthening.The test results showed that proper reinforcement by immersion of permeable crystalline materials could enhance the rheological properties of recycled aggregate self-compacting concrete;the compressive strength of recycled aggregate concrete after modified by permeable crystalline materials was improved by 0.57%～20.90%compared with that before modification.With the increase of strengthening time,the compressive strength of modified recycled aggregate concrete also increased.(4)The microstructure and pore structure of the recycled aggregate and recycled aggregate concrete before and after strengthening were analyzed with the help of SEM and NMR.The results showed that the pore volume fraction of the modified recycled aggregate concrete decreased and the percentage of harmful pores decreased;more C-SH crystals were observed in the microstructure of the modified recycled aggregate and recycled aggregate concrete to fill the pores and cracks of the recycled aggregate and recycled aggregate concrete,and the structure was more dense.