Experimental Study On The Performance And Classfication Systems Of Recycled Concrete Coarse Aggregate

With the fast development of construction and transportation, there is a great deal of waste concrete produced every year in the world. The processing of the massive amount of waste concrete will cost a lot of money. Moreover, it will bring about a series of problems including natural resources, energy, environmental protection and sustainable development, etc. There are no classification systems for recycled coarse aggregate in China, so the quantity of utilization waste concrete is very small, and the waste concrete can't be widely used in engineering. Therefore, it is needed to study the processing and application of waste concrete. The classification systems for recycled coarse aggregate was put forward inconsideration of the characteristic of recycled coarse aggregate on basis of the experimental study of the recycled concrete coarse aggregate.First, according to the test methods of natural aggregate, the properties including water absorption, apparent density, crushing index value etc were tested. The mortar content of recycled coarse aggregate was also tested in Dilute Hydrochloric Acid. The cyclic loading experiment was designed, and the index of damage area was put forward. The damage area can be used to evaluate the recycled coarse aggregate.Second, the microstructure and pore structure of different kinds of recycled coarse aggregate were researched by SEM and Auto Poreâ…£9510 Auto Mercury Intrusion Porosimeter. The fractal characteristic of pore structure was studied on basis of the fractal theory. The internal structure compalexity of concrete material was promulgated from the microscopic mechanism based on the fractal theory. The results showed that, the pore structure of recycled coarse aggregate has good fractal characteristic. There was good correlation between fractal dimension and average diameter, pore surface area. There was also good correlation between porosity and permeability. The capillary porosity was put forward to evaluate the recycled coarse aggregate.Third, in the same mix proportion, the recycle concrete was made by use of different kinds of recycled coarse aggregate with replacing 60% of natural aggregate. The influence of different levels of recycled coarse aggregate on physical and mechanical properties and microstructure of recycled concrete was studied.Finally, based on the research results and the experimental data, the classification systems with multiple levels and indexes for recycled coarse aggregate was put forward, which fully consider the characteristics of recycled coarse aggregate and foreign classification method. The classification was also verified by the experiment of mechanical properties and micro structure of concrete. Using this method, different sources of recycled coarse aggregate can be classified distinctly. The method can also be theoretical basis for widely using recycled coarse aggregate in the actual project.