Effects Of Combined Curing And Nano-Materials On Recycled Aggregate Concrete At Low Water/Binder Ratio

Because of the defects of recycled aggregate,the mechanical properties and durability of recycled aggregate concrete are relatively poor.According to the previous results,the combined curing improves the adhesion of matrix and aggregate at the low water/binder ratio of 0.18,which can make up for the limitation of coarse aggregate caused by the low strength.Therefore,this paper uses the following three methods to modify the performance of recycled aggregate concrete based on the low water/binder ratio of 0.18,including,A special combined curing is that after removing the concrete put it in 90 degrees hot water curing for 2 days,250 degrees dry heat curing for 3 days and then set aside to curing age(The curing age of the study was 28 days);Different dosage(replacing the cement quality of 1%,2%,3%)of nano silica and combined curing;Different dosage(replacing the cement quality of I%,2%,3%)of nano alumina and combined curing.The effects of the three methods on the performance of recycled aggregate concrete were compared by means of mechanical properties tests and a durability test of resistance to chloride ion penetration.The comparision of the propeties of recycled aggregate and natural aggregate mainly includes grading analysis,crushing value,apparent density,soundness and water absorption.The research of the properties of recycled aggregate concrete and natural aggregate concrete mainly includes the preparation of nine types of concrete through standard curing,combined curing,addtion of nano-silica under the combined curing regime,combined curing and addtion of nano-alumina under the combined curing regime.Then,the tests of mechanical properties including compressive strength,tensile splitting strength and fracture energy and resistance to chloride ion penetration were carried out.According to the test results,the best method of improving the properties of recycled aggregate concrete is found out;The result of the mechanical properties test shows that compared with standard curing,the combined curing can improve the compressive strength and splitting tensile strength of recycled aggregate concrete by 26.8%and 21.5%.The improvement can be enhanced further with the addition of nano-materials,the higher the dosage of nano-materials,the greater the strength of concrete.The compressive strength and splitting tensile strength of recycled aggregate concrete incorporating 3%nano-alumina under the combined curing are 31.4%and 18.2%higher than that only under the combined curing.Meanwhile,compared with the nano-silica,the nano-alumina has better effect on improving the mechanical properties of recycled aggregate concrete.Moreover,the adhesion of matrix and aggregate can be enhanced based on the low water/binder ratio,which can result in the transfer-aggregate in all types of concrete.The result of chlorine ion test shows that the combined curing or the addition of nano-materials can improve the durability of recycled aggregate concrete effectively.According to the comparison of various modification methods,it can be found that the resistance of chloride ion permeability of recycled aggregate concrete incorporating nano-materials under the combined curing is equal to that of natural aggregate concrete.For example,the electrical conductance of natural aggregate concrete and recycled aggregate concrete incorporating 3%nano-alumina under the combined curing are 289.2 C and 315.8 C,respectively.The penetration level of both of them belongs to a very low-level.The test results of properties of aggregate show that compared with natural aggregate,recycled aggregate has lower crushing value,apparent density and soundness,worse gradation of particle size and higher water absorption.