Effect Of Substitution Rate And Seam Height Ratio On Fracture Properties Of Spontaneous Combustion Coal Gangue Coarse Aggregate Concrete

With the continuous increase of environmental protection at the national level,the development of green buildings has become the trend of the times.The “solid waste” aggregate is used to replace the natural aggregate to prepare concrete.The “grain consumption” is large,which reduces environmental pollution and saves natural resources,which is favored by the industry.However,due to the different causes of coal gangue,physical and chemical properties and mechanical properties have entered a large scale,and no unified industry standard has been formed.At present,spontaneous combustion coal gangue aggregates are widely used in road engineering,but most of them are used as aggregates in base mixes,and there are few reports on road surface cement concrete aggregates.Therefore,it is very necessary to carry out research on fracture toughness of spontaneous combustion coal gangue coarse aggregate concrete.In this paper,the spontaneous combustion coal gangue coarse aggregate concrete is prepared by replacing the natural coarse aggregate with the mass of 25%.Firstly,the influence of substitution rate on the basic mechanical properties of spontaneous combustion coal gangue coarse aggregate concrete was studied.Then the fracture rate test of three-point curved incision beam was used to study the effect of substitution rate on concrete fracture toughness.The brittleness and deformation ability of concrete were measured by characteristic length and ductility index..Based on the image processing technology,the distribution and failure characteristics of coarse aggregates on the fracture section of the specimen were analyzed,and the mechanism of the spontaneous aggregate gangue coarse aggregate on the brittle failure of concrete was revealed.Finally,the seam height ratio was studied on the spontaneous combustion coal gangue coarse.The effect of fracture properties of aggregate concrete three-point bending beam was studied.Based on SEM scanning electron microscopy,the microstructure of the material was characterized and the mechanism of the effect of spontaneous coal gangue coarse aggregate on the fracture toughness of concrete was revealed.The main findings are as follows:(1)With the increasing replacement rate of spontaneous combustion coal gangue coarse aggregate,the compressive strength,tensile strength and flexural strength of concrete gradually decrease.(2)The fracture properties of concrete gradually decrease with the increase of substitution rate.The substitution rate has little effect on the resistance of concrete cracks before cracking,but it has a great influence on the ability of concrete to resist external forces after critical instability.The coarse aggregate of spontaneous combustion coal gangue makes the fracture energy of concrete gradually decrease,but with the increase of substitution rate,the relative energy consumption of concrete increases gradually.From the characteristic length and ductility index,when the substitution rate is more than 25%,the brittleness of concrete increases and the deformation ability gradually decreases.(3)With the increase of substitution rate,the fracture ratio of mixed coarse aggregates on concrete fracture section increases obviously,the section tends to be flat,and the fractal dimension gradually decreases.The distribution density and disorder of the micro-defects of spontaneous combustion coal gangue aggregates are large,resulting in an increase in the substitution rate,an increase in the degree of disorder of the microstructure of the concrete,and an increase in the fracture toughness of the concrete due to the size effect.Therefore,it is feasible to quantitatively describe the fracture characteristics of spontaneous combustion coal gangue coarse aggregate concrete by using fracture ratio and fractal dimension.(4)The effect of seam height ratio on the instability fracture toughness of spontaneous combustion coal gangue coarse aggregate concrete under different substitution rates is not obvious,but with the increase of seam height ratio,the fracture fracture toughness tends to increase,and the fracture energy The decline is obvious.The degree of influence of size effect on fracture toughness increases with the increase of the replacement rate of spontaneous aggregate coal gangue coarse aggregate,but the decline of ductility index decreases gradually.The paper has 29 figures,15 tables,and 91 references.