Study On Durability Of Spontaneous Combustion Coal Gangue Aggregate Geopolymer Concrete Under The Coupling Action Of Freeze-thaw And Sulfate Attack

Using alkali-activated fly ash to prepare geopolymer as cementitious material and spontaneous combustion coal gangue as coarse aggregate to prepare spontaneous combustion coal gangue aggregate geopolymer concrete can reduce CO₂emission caused by cement production and save natural sand and gravel resources,which has great energy conservation,environmental protection and engineering application value.After the spontaneous combustion coal gangue aggregate geopolymer concrete is put into use,it is in a complex environment.SO₄^2-of surface water and groundwater has corrosive effect on concrete,and it will be affected by the freezing and thawing cycle caused by temperature change in northern China.Therefore,it is of great scientific research value and practical significance to study the durability of spontaneous combustion coal gangue aggregate geopolymer concrete under the coupling effect of sulfate attack in value and practical significance to promote the engineering application of this new type of green concrete.The main research contents and conclusions of this study are as follows:（1）The effects of replacement ratio of spontaneous combustion coal gangue aggregate（Replacing 0%,20%,40%and 60%natural coarse aggregate with equal mass）on the workability and cube compressive strength of concrete were systematically studied.The test results show that the slump of concrete is negatively correlated with the replacement rate of spontaneous combustion coal gangue aggregate.The strength of concrete mixed with spontaneous combustion coal gangue aggregate is significantly lower than that of natural gravel aggregate concrete.With the increase of the substitution rate of spontaneous combustion coal gangue,the cube compressive strength of concrete increases first and then decreases,and the cube compressive strength of concrete is the best when the substitution rate is 40%.（2）Using the concrete mass loss rate and compressive strength loss rate as the damage indicators,freeze-thaw tests were carried out under different spontaneous combustion coal gangue coarse aggregate replacement rates,sulfuric acid under different spontaneous combustion coal gangue coarse aggregate replacement rates and Na₂SO₄solution concentrations.Salt erosion test and durability test of spontaneous combustion coal gangue aggregate geopolymer concrete under the coupling action of freeze-thaw and sulfate erosion at different spontaneous combustion coal gangue coarse aggregate replacement rate and Na₂SO₄solution concentration.The test results show that:compared with natural aggregates,spontaneous combustion coal gangue aggregates have larger pores and lower strength,and are susceptible to freezing and thawing and sulfate erosion.The durability of gangue aggregate geopolymer concrete is gradually weakened.（3）Combined with scanning electron microscope and energy spectrum analysis,the internal mechanism of concrete performance deterioration under different erosion environments is discussed,especially the weak link of concrete—the microscopic damage of the interface transition zone is analyzed.The results show that the microscopic damage in the transition zone of CGPC（Spontaneous combustion coal gangue aggregate geopolymer concrete）interface is larger than that of NGPC（Natural aggregate geopolymer concrete）under different erosion environments.Compared with other erosion environments,sulfate erosion has little effect on the microscopic damage in the transition zone of the NGPC interface,while the coupled environment of freeze-thaw-sulfate erosion accelerates the damage of the microstructure in the transition zone of the CGPC interface.（4）A binary surface regression model of mass loss rate,compressive strength loss rate,freezing and thawing times and substitution rate of spontaneous combustion coal gangue aggregate geopolymer concrete under a single freezing and thawing environment was established,and a multiple regression model was further established combined with the concentration of sodium sulfate.Based on this,the durability life of spontaneous combustion coal gangue aggregate geopolymer concrete under complex environment was predicted.The regression accuracy of the model is judged by analyzing the residual diagram.The results show that the regression model has high fitting accuracy,which can provide reference for the durability life prediction of spontaneous combustion coal gangue aggregate geopolymer concrete in complex environment.