Study On Mechanical Properties And Frost Resistance Of Recycled Concrete

Adding recycled coarse and fine aggregate instead of natural aggregate into concrete can not only alleviate the occupation of land resources and environmental pollution caused by construction waste,but also solve the problem of over exploitation of construction raw materials,and strengthen the comprehensive utilization of renewable resources.In the test,the recycled fine aggregate and recycled coarse aggregate are replaced by natural sand and stone,and air entraining agent is added to improve the frost resistance.Through the test of concrete mechanical properties and frost resistance,the change law of concrete mechanical properties and frost resistance under different recycled fine aggregate content is studied,and the frost resistance life of concrete is predicted by damage model.The achievements are as follows:(1)The performance of recycled coarse and fine aggregate is weaker than that of natural sand and gravel.According to the water absorption of recycled aggregate,the recycled coarse aggregate is pre wetted,and the recycled fine aggregate is added with water to solve the adverse effect of recycled aggregate on slump;Air entraining agent can improve the air content of the mixture.With the increase of recycled fine aggregate content,the air content of the mixture also increases,but the slump has no obvious change.(2)The failure modes of recycled concrete in each group are similar,but there are slight differences;When the content of recycled fine aggregate is between 0% and 20%,the mechanical indexes of concrete change little or even increase;When the content is more than30%,the mechanical properties decrease;When the content is 100%,the mechanical index of the reference group decreases by 26.37%.(3)In the process of freeze-thaw cycle,the mass of recycled concrete increases first and then decreases,so the relative dynamic elastic modulus is more suitable as an index to evaluate recycled concrete;The relative dynamic elastic modulus of concrete with 0%,20% and 40%recycled fine aggregate is 82.9%,78.8% and 72.4% respectively after 200 freeze-thaw cycles,showing good frost resistance.(4)The Weibull damage equation has a high correlation with the results of frost resistance test;The content of recycled fine aggregate is inversely proportional to the frost resistance life of recycled concrete.When the replacement rate of recycled fine aggregate is 100%,the frost resistance life of recycled fine aggregate is 41.86% lower than that of the reference group.