The Experimental Study On Macro-micro Damage Mechanism Of Recycled Aggregate Concrete Under Freeze-thaw Cycle

With the gradual expansion of the scale of urban development in China,various projects will generate trillions of tons of construction waste.At the same time,in the context of the scientific planning of water conservancy,the demolition of some old and dangerous water conservancy buildings will be put on the agenda.The large amount of waste concrete that came from invading the land also caused great damage to our environment.How to turn waste concrete into waste and give it new use value is an important research topic that is beneficial to environmental protection.Extracting recycled aggregates from abandoned concrete and mixing these aggregates into new concrete can create new concrete materials called recycled aggregate concrete.The nature of recycled aggregates is different from that of natural aggregat es.Whether it will lead to differences between the physical and chemical parameters of recycled concrete aggregates and ordinary concrete,no breakthrough has been made in the study of these problems.In this paper,the frost resistance of recycled concrete is studied.The influence of recycled aggregate and mineral admixture fly ash on the frost resistance of recycled aggregate concrete is analyzed.The freeze-thaw damage evolution of recycled aggregate concrete is clarified.Mechanism,the main research content includes:1.The mechanical properties of recycled aggregate concrete under two gradients of fly ash content and replacement ratio of recycled aggregates were studied.The change of mechanical properties parameters after freeze-thaw cycle test was studied.2.From the macro scale,the effects of fly ash content and replacement ratio of recycled aggregate on the freeze-thaw damage evolution of concrete were analyzed.3.The development and evolution process of the internal pore structure of recycled aggregate concrete under freezing and thawing cycles was analyzed from the microscopic scale.The influence of aggregate-mortar interface and new and old mortar interface on the damage evolution characteristics of the material was studied.It was found that the incorporation of recycled aggregate and fly ash did not significantly improve the initial mechanical properties of concrete;however,the indexes of frost resistance of recycled aggregates and fly ash to recycled aggregate concrete with different substitution rates and the mechanics after freeze-thaw cycling There are significant differences in performance.