Research On Properties Of Coal Gangue Aerated Concrete

Coal gangue produced by the coal mine industry has become the largest existing solid waste in China, and coal gangue heap caused many environmental and social problems. In recent years, many countries put huge amounts of coal gangue used in construction industry and achieve desirable results to solve the environmental problems caused by coal refuse pile effectively. At present, aerated concrete industry is developing vigorously in our country, then the preparation of aerated concrete block by taking use of coal gangue has important significance for environmental resources, social resources and scientific research field.The optimum mixture ratio within the test range of coal gangue aerated concrete matrix material is determined by the four-factor and three-level orthogonal experiment as coal gangue: lime: cement: gypsum = 60:18.5:18.5:3. Under the optimum mixture ratio, the average compressive strength for the coal gangue aerated concrete sample is 20.9 MPa.For the gangue aerated concrete slurry system, paste volume expansion is promoted by floating bubbles in the slurry. The bigger hydrogen bubble radius r and the shorter vertical distance h between two bubbles which are conducive to achieve the volume expansion of aerated concrete slurry. The slurry of coal gangue aerated concrete can be caused abnormal thickening by polycarboxylate superplasticizer agents. However, Polycarboxylate superplasticizer is unsuitable for regulating the slurry expansion degree of coal gangue aerated concrete.Based on the gangue material aerated concrete matrix optimum mixture ratio, a new orthogonal test with three factors and three levels is designed. In the new orthogonal test design, the C/S of elements and the content of aluminium are adjusted.Considering the mechanical and physical properties, the laboratory coal gangue aerated concrete optimal mix proportion is determined as coal gangue: lime: cement: gypsum = 54:23:20:3 in accompany with 1.3‰ aluminum contents. Meanwhile, watercement ratio is identified as 0.5 and the C/S of elements is 0.82. Coal gangue aerated concrete curing system in laboratory is determined: the curing condition is confined as 8 hours(1.1MPa, 187 ℃). XRD test results show that the autoclaved curing system enables coal gangue aerated concrete matrix material to generate CSH gel with tobermorite type.The study shows that the pore sizes in coal gangue aerated concrete are mainly between 0.5mm ~ 2mm, and there is a certain amount of connected pores. After 50 freezethaw cycles, the quality of coal gangue aerated concrete block increased and this phenomenon is due to the joint action of crack absorbent and hydration by gelling materials. Water absorption-time curves indicate calcium stearate can inhibit early absorbing water from materials effectively, however, it brings a defect that the compressive strength get decreased significantly and makes detrimental to frost resistance performance. Foam stabilizer can improve the frost resistance performance of coal gangue aerated concrete and make the block’s compressive strength increase significantly after 50 freeze-thaw cycle tests. Especially, comparing to the compressive strength increased by 15.5%, 26.5% and 30.4% for the initial slurry expansion is 250 mm, 290 mm and 320 mm, respectively.