Experimental Study On The Basic Behavious And Microstructure Of Recycled Concrete

It is an important measure to solve harmonious development of concrete aggregate and ecological environment through utilizing abandoned concrete to process the recycled aggregate to make use in the view of sustainable development.Because of the source of the recycled aggregates are different from the natural aggregate and its own specific properties:high porosity, high water absorption rate, low density, low ruggedness and wear resistance, caused the performance of recycled aggregate concrete and natural aggregate concrete are quite different. Therefore, the recycled aggregate concrete properties have been studied in this paper combining the interface microstructure of recycled aggregate concrete from the macroscopic angle, and the main contents are as follows:Firstly, the basic mechanical properties of recycled concrete with different recycled aggregate were tested. The experiment results demonstrate that the cubic compressive strength and prism compressive strength gradually decreased with increasing of recycled aggregate. The recycled aggregate got its optimal additive amount when the ratio of recycled aggregate was less the fifty percente. The modulus of elasticity of recycled concrete was tested with the different recycled aggregate rate, the modulus of elasticity of recycled concrete experiencing a downward trend with the increasing of recycled aggragete.Secondly, some tests have been done to the recycled aggregate concrete interface zone through microscopic hardness, scanning electron microscope and X-ray diffraction, and the resutle showed that there is a zone between new cement stone and old cenment stone, the same between new cement stone and nature aggregate, in addition, the thickness of the interface zone between new cement stone and old cenment stone is about20～40μm, and the thickness of the interface zone between new cement stone and nature aggregate is about50-70μm. X-ray diffraction experiment found that the types of hydration products are similar in the both of interface zone, but there are certain differences in the amount of hydration products and hydration products affects the thickness of interface transition zone and the micro-hardness values to a certain extent. Scanning electron microscopy (SEM) study found that most part of interface transition zone area links closely, but there are still parts of the hole and the structure is loose, the old cement has compact structure, micro cracks were found to exist in the old gravel aggregate. The mechanical properties of recycled aggregate concrete are affected by the thickness of transition zone and the amount of hydration products.Thirdly, the form distribution of aggrrgate for cylinder is tested. The test results showed that the particles of recycled aggregate are20mm and35mm in size and the form distribution of recycled aggregate are not being appeared in obvious stratification for the density and shape are different between recycled aggregate and natural aggregate in specimen.