Study On The Performance Of Temperature-damaged Waste Concrete Making Recycled Materials And Newmade Recycled Concrete

In recent years,with the acceleration of urbanization,high-rise buildings have emerged in China,and building fire accidents have occurred frequently.The number of buildings demolished each year due to fire damage is increasing,resulting in a large amount of waste concrete.Up to now,the way of resource utilization of waste concrete in fire damage construction is the same as that of ordinary waste concrete,and the influence of temperature damage waste concrete on the performance of recycled concrete aggregate(RCA),recycled concrete powder(RCP)and recycled concrete(RC)is not considered in detail.Based on this,this paper studies the influence of different temperature damage waste concrete on the performance of RCA,RCP and RC,and the performance of modified high-quality recycled aggregate(HRA),active recycled powder(ARP)and RC.The main conclusions are summarized as follows:(1)Compared with RCA-20C(no damage at room temperature),the water absorption of RCA damaged at 300-800℃ increased by 39.1-169.5%.When the damage temperature is the same,with the increase of RCA content,the working performance of recycled aggregate concrete gradually decreases;when the RCA content is the same,the performance of recycled aggregate concrete gradually decreases with the increase of damage temperature.When the RCA content is 100%,the compressive strength of C-100RCA-300C,C-100RCA-600C and C-100RCA-800C concrete is 11.4%,20.4%and 41.4%lower than that of C-RCA-20C,respectively.This is because with the increase of damage temperature,the old mortar on the surface of RCA gradually becomes loose and porous,and the performance of RCA gradually deteriorates.(2)Through mineral composition analysis,it was found that the mineral composition of RCP damaged at 20-600℃ was similar.When the damage temperature is 800℃,new active cementitious components C2S and CaO appear in RCP-800C,which is due to the decomposition of hydration products at high temperature.The activity indexes of RCP-20C and RCP-800C were 72.6%and 90.4%,respectively.The activity of RCP-800C was better than that of RCP-20C.With the increase of RCP content,the performance of recycled fine powder concrete gradually decreases.When the content of RCP is 30%,the compressive strength and capillary water absorption coefficient of C-RCP-800C concrete are 20.9%and 24.9%higher than that of C-RCP-20C respectively.(3)The HRA performance of recycled aggregate after modification is significantly improved.Compared with ORA,the old mortar content and water absorption of HRA-600C and HRA-800C decreased by 86.4%and 51.8%,respectively.The compressive strength of CHRA-800C with 25%,50%and 100%of content is 1.9%,5.6%and 11.5%lower than that of the reference group concrete,respectively.At each dosage level,the total porosity of C-HRA800C concrete is also the lowest.When the content is 100%,the capillary water absorption coefficients of C-100HRA-600C and C-100HRA-800C are 10.0%and 17.3%lower than that of C-100ORA,respectively.The chloride diffusion coefficients of C-100HRA-600C and C100HRA-800C were 20.9%and 22.6%lower than that of C-100ORA,respectively.Therefore,after the optimization of recycled aggregate modification,the durability of recycled aggregate concrete can be significantly improved.At the same time,the by-product powder in the modification process can be collected and prepared into active recycled fine powder to improve the comprehensive utilization rate of waste concrete resources.