Experimental Study On Durability Of Modified Recycled Coarse Aggregate Concrete

In order to improve the performance of recycled coarse aggregate concrete,in order to study the influence of different modification methods on the durability of modified recycled coarse aggregate concrete and its causes,a set of loading test mechanism based on the coupling effect of load and corrosion freeze-thaw environment was established.The recycled coarse aggregate and polyvinyl alcohol solution were soaked in the solution of nano-SiO₂ and fly ash by considering the internal mixing method.Four modification schemes of foamed recycled coarse aggregate,silica fume and fly ash were studied.The main conclusions are as follows:?1?Macroscopic test results show that the durability of recycled coarse aggregate concrete is best when 10%grade I fly ash is added in the internal mixing method,but the durability of recycled coarse aggregate concrete is very poor when 30%grade I fly ash is added in the internal mixing method,even worse than that of recycled concrete without strengthening treatment.?2?Based on the analysis of the durability reasons of the modified recycled coarse aggregate,this paper simulates the interfacial performance between recycled coarse aggregate and new mortar in recycled concrete through meso-experiment,and concludes that the fundamental reason for the durability change is the interfacial performance change of recycled coarse aggregate concrete.?3?In the meso-test,the four modification schemes mentioned above are used to modify the meso-model specimens,and the interfacial bond strength between recycled coarse aggregate and new mortar under each scheme is obtained.The interfacial bond strength of the meso-model specimens modified with 10%grade I fly ash by internal mixing method is the largest,and the interfacial performance of recycled concrete is the greatest.?4?The reason for the modification of recycled coarse aggregate concrete with 10%grade I fly ash is that the use of grade I fly ash instead of a small amount of cement can fill the pore in the mortar matrix,increase the bonding area between aggregate and mortar matrix,and improve the interfacial bonding performance of recycled coarse aggregate concrete.The main oxides in fly ash can react with Ca?OH?₂,which is the initial product of hydration,to produce new materials with higher strength and better compactness,fill micro-voids,and form a tighter interface structure,thus improving the durability of recycled coarse aggregate concrete.