Study On Preparation And Performance Of Spontaneous Combustion Coal Gangue Concrete

Spontaneous combustion coal gangue is a kind of solid waste associated with the coal industry,and it will cause certain harm to the environment.It is an effective way to solve the resource reuse by using spontaneous combustion coal gangue in the preparation of concrete.But in practice,due to the different degree of spontaneous combustion,most of spontaneous combustion coal gangue has different density levels and is between the light aggregate and ordinary gravel,the research of this kind of spontaneous combustion coal gangue for concrete preparation is relatively few,which restricts application of spontaneous combustion coal gangue in the concrete.In this paper,spontaneous combustion coal gangue with density grade is between light aggregate and ordinary gravel is used as coarse aggregate to prepare spontaneous combustion coal gangue concrete.Basis on the characterizing aggregate properties,mix design method,mechanical performance,resistance to chloride ion penetration,frost resistance performance and interface transition zone characteristics of spontaneous combustion coal gangue concrete are studied respectively.The main results follow:Through standard method for testing concrete aggregate,spontaneous combustion coal gangue test results are bulk density of 1260kg/m3,water absorption rate of 6.7%,crushing index of 12.2%,the strength is lower compares with the ordinary gravel.The basic experimental design,development regularity of mechanical performance is studied,the results show water cement ratio and water consumption is too large,the volume of sand rate is too large or too small,will have adversely affected for mechanical performance of C30 spontaneous combustion coal gangue concrete.During the mix design of spontaneous combustion of coal gangue concrete,standard deviation a of concrete strength is 4.4 by using the standard deviation calculate,correction factor of Bowromi formula is A=0.52,B=0.01 by Excel fitting.Based on the orthogonal experiment,the L9(34)orthogonal method is chosen,and the water to cement ratio,volume sand ratio and water reducer amount are affected,the optimal ratio of 28d compressive strength and resistance to chloride ion penetration of C40 spontaneous combustion coal gangue concrete are A1B2C3:water cement ratio of 0.35,volume sand rate of 37%,water reducing admixture of 1.8%,the factors affect order of significance are:water cement ratio>water reducing agent>volume sand ratio.The chloride ion permeation model is established,Q=2940.3X1+611.5833X2-31542.7778X3+729.3859,the electric flux is Q,unit is C;water cement ratio is X1;volume rate of sand is X2;water reducer amount is X3,fitting is 94.2%.Single factor experiment study shows the frost resistance performance of C40 spontaneous combustion coal gangue concrete increases along with the decrease of water cement ratio and increase of volume sand ratio and water reducing admixture.After 400 times of freezing and thawing cycles,its mass loss rate is within 5%,and the maximum loss rate of elastic modulus is only 25.5%.The micro hardness analysis shows that micro hardness increases with the decrease of water cement ratio and increase of aggregate pre wet time in the aggregate surface of spontaneous combustion coal gangue aggregate-cement matrix interfacial transition zone,but with the increase of distance from the surface of the aggregate,lower water cement ratio gradually lose the advantage of micro hardness.