Experimental Study On The Effect Of Recycled Coarse Aggregate On Mechanical Property And Durability Of Recycled Concrete

Since the beginning of the opening up policy, the modernization of China’s construction industry has been speeding up. Meanwhile, there exists a large number of waste concrete which will destroy the ecological environment. In order to reduce the pollution of the environment and explore the sustainable development path of harmonious development between man and nature, recycled aggregate emerges as the times require. Compared with ordinary concrete the research of recycled concrete is much more complex. Its performance was affected by many aspects. The performance of recycled coarse aggregate, in particular, has a great influence on the overall performance of recycled concrete. Therefore, this topic aims to study on the effect of recycled coarse aggregate on properties of recycled aggregate concrete.1. In order to have a knowledge of the performance of the original concrete, three kinds of original concrete with different design strength grade were produced, which were all crushed at the age of 60 days to obtain three different kinds of recycled coarse aggregates. And the relationship between recycled aggregates and the original concrete were explored by testing the basic properties of recycled aggregates.2. The groups of recycled concrete were produced using LRA and HRA that replaced natural coarse aggregate by 50%, and using MRA that replaced natural coarse aggregate by 30%, 50% and 100%.3. The mechanical properties tests were carried out after plan-days. The test for resistance of these recycled concrete to rapid freezing and thawing was also started at the same time, and evaluated the frost resistance of recycled concrete. In these experiments, the same water cement ratio of ordinary concrete was a contrast group.4. in order to understand the failure process of recycled concrete under uniaxial compression, investigation was carried out on some specimens of recycled concrete, which were sampled by cutting slices. The high-speed camera obtained the whole process. Moreover, a microscopic investigation was carried out on some specimens of recycled concrete, which were sampled by cutting slices when different freeze-thaw cycles. Through the micro statistics to each slice, the cracking degree of every component in recycled concrete were quantitatively evaluated by two mi crostructural damage parameters: fracture density and cracking ratio. The results reflected the freeze-thaw failure mechanism of recycled concrete, and the influence mechanism on frost resistance of recycled coarse concrete.The experimental results showed that the replacement rate of recycled coarse aggregate which was less than 50% had minimal impact on the mechanical properties of recycled concrete with water cement ratio of 0.45. But the mechanical properties and frost resistance of the total replacement of recycled concrete(100%) were poor. The high strength recycled coarse aggregate had obvious improvement on the mechanical properties and frost resistance of recycled concrete. The influence of middle and low strength of recycled coarse aggregate on the properties of recycled concrete was limited.