Study On The Effect Of Activated Coal Gangue Powder On The Performance Of Coal Gangue Coarse Aggregate Concrete

Coal gangue is one of the largest industrial solid wastes in China.It is an effective way to use coal gangue in cement-based materials.The optimum activation temperature of undisturbed coal gangue in Xuanhua Mine of Zhangjiakou was determined by X-ray diffraction analysis,thermogravimeter differential analysis and cement mortar strength test.Then the coal gangue powder（CGP）activated by the optimum temperature was used as admixture and mixed with coal gangue coarse aggregate to form coal gangue coarse aggregate concrete.Different activated coal gangue powder content and different CGA replacement rate were selected as variables to conduct compressive,tensile and flexural mechanical properties tests and chloride ion penetration durability tests on coal gangue concrete.At the same time,nitrogen adsorption method（BJH）,mercury injection method（MIP）and scanning electron microscopy（SEM）were used to investigate the influence mechanism of CGP on pore structure,interface transition zone（ITZ）and microstructure of coal gangue coarse aggregate concrete.Experimental results show that:（1）The main phase composition of undisturbed coal gangue from Xuanhua Mine in Zhangjiakou is kaolinite,quartz,dolomite,albitite and microcline.Combined with the analysis results of XRD and TG-DSC,it can be seen that when the thermal activation temperature is 500℃,the layered structure of kaolinite in coal gangue mineral composition has a complete transformation of thermodynamic metastable state.And the cement mortar（30%wt）replaced at this temperature has the maximum compressive and bending strength,so the optimal activation temperature of the original coal gangue of Xuanhua Mine in Zhangjiakou is 500℃.（2）The higher the replacement rate of CGA is,the more obvious the mechanical properties of coal gangue coarse aggregate concrete specimens are reduced,when the CGA replace rate was 0%,30%,50%,the damage form of specimens are mainly in mortar and natural coarse aggregate interface transition zone is given priority to,mixed with CGP caused the intensity of the secondary hydration contribution is lower than the strength loss caused by clinker reduce,The mechanical strength is reduced.When the CGA substitution rate is 100%,the failure mode of the sample mixed with CGP shows more fracture of coal gangue coarse aggregate.Due to the high water absorption rate of coal gangue coarse aggregate,the water film attached to its surface does not participate in the hydration reaction,resulting in the formation of more interfacial pores.The incorporation of CGP consumes Ca（OH）₂ in the pores.The generated C-S-H gel filled the interfacial capillary pores,the compactness of internal structure of coal gangue concrete is enhanced.（3）The chloride ion diffusion coefficient of coal gangue coarse aggregate concrete increases with the increase of CGA substitution rate,while the incorporation of CGP reduces the chloride ion diffusion coefficient,reduces the channels of chloride ion diffusion,and improves the chloride ion permeability resistance of coal gangue concrete.Combined with the results of mechanical strength,it can be seen that the incorporation of appropriate amount of CGP can reduce the concentration of alkali ions in the hydration system and promote the hydration reaction of cement clinker.If the incorporation amount is too low or too high,the secondary hydration will be delayed.The adaptive dosage of CGP is 15%.（4）Combined with nitrogen adsorption method（BJH）and mercury intrusion method（MIP）the result of analysis shows that a moderate amount of CGP with decreased in all the light-weight aggregate concrete specimens of porosity and average pore diameter and its pozzolanic effect caused by filling the inside the specimens of stoma,optimize the structure of the internal hole of the specimens,the harmless,less harm to the increase in the number of holes,The number of harmful and harmful holes is reduced.Scanning electron microscopy（SEM）observed that a large number of granular and reticular C-S-H gels were filled in the mortar pores and interfacial transition zone due to the addition of appropriate amount of CGP,which was consistent with the results of pore structure analysis.