Feasibility Study Of Coal Gangue As Aggregate Of Cement Concrete

Coal gangue is a waste, produced in coal industry. The amount of the coal gangue is increasing in our country, causing a serious pollution of environment. At present, a large number of coal gangue is generated every year. If coal gangue can't be made rational use, it will be great losses of social, economic and environmental. Producing cement concrete with coal gangue aggregate, can greatly reduce the dosage of natural aggregate in civil engineering, and has made better economic and social benefits.The coal gangue aggregate is obtained by crushing and sieving coal gangue, and is proposed to produce cement concrete instead of part of natural aggregate in this study. The physical properties of coal gangue aggregate are investigated firstly, and then the microstructure characteristics of different kinds of coal gangue aggregate are analyzed. The mechanical property, pore structure and durability of concrete containing coal gangue aggregate are also measured. The effect of fundamental characteristics and content on mechanical property, pore structure and durability of coal gangue aggregate concrete was studied through a large number of laboratory tests. The results show that:(1) Volatility of properties of coal gangue changes greatly. The performances of coal gangue aggregates are great differences in different locations, even at the same location.(2) The main composition of coal gangue is SiO2.The SEM experiments indicate that, pore-structure of coal gangues aggregate is different from that of natural aggregate, and the microstructure of natural aggregate is more homogenous than that of coal gangues aggregate.(3) The pore structures of coal gangue mortar have typical fractal nature. Fractal dimension can assess the characteristics of pore structure in some condition. The strength of coal gangue mortar has a certain relation to the pore structure. The larger pore diameter of coal gangue mortar is, the bigger porosity of coal gangue mortar is, the smaller fractal dimension of coal gangue mortar is, the lower performance of coal gangue mortar becomes. With the increase of small size pores less than 20 nm and decrease of large size pores beyond 100 nm, compressive strength and flexural strength of coal gangue mortar become larger.(4) Alkali reactivity of all coal gangue aggregate is non-active. Within a certain range, coal gangue will not significantly reduce concrete anti-impermeability. With the increase of coal gangue, mechanical performance of concrete has not been reduced, but frost resistance of non-air entraining concrete has been reduced to some extent. Besides spacing factor of air void, water absorption of aggregate is another important factor for assessing frost resistance of concrete. Therefore, spacing factor of air void can accurately assess frost resistance of concrete combining with water absorption of aggregate. The interface structure between aggregate and hydrates of coal gangue concrete is different from ordinary concrete.For the coal gangue aggregate used in cement concrete, this study puts forward some suggestions on coal gangue content, water absorption, crushing index value, flaky and elongated aggregate content in order to improve the design quality and guarantee the structure safety.