Study On The Erosion Resistance Of Gangue Cement-based Materials Under The Action Of Dry And Wet Cycles And Sulfate

With the overall improvement of people’s living standards and quality in China,people pay more and more attention to environmental issues.The CPC Central Committee and the State Council have emphasized the development concepts of energy conservation and emission reduction,carbon peaking and carbon neutrality more than once at the 19 th and 20 th National Congresses.However,as a major coal mining country,more and more coal gangue mining,accumulation and spontaneous combustion have caused serious harm to the surrounding environment,which not only affects the utilization of land resources,but also pollutes the surrounding atmosphere and soil.In order to solve the problem of large accumulation of coal gangue in Xinjiang,this paper studies the influence of coal gangue type,content and curing conditions on the mechanical properties of coal gangue cement-based materials,and puts forward the best curing conditions in coal gangue cement-based materials.Then,according to the characteristics of multi-saline soil and changeable climate in Xinjiang,the corrosion resistance of coal gangue cement-based materials under the best curing conditions under the action of dry-wet cycle-sulfate was studied,and the corrosion resistance mechanism of coal gangue cement-based materials under the action of dry-wet cycle-sulfate was revealed.Spontaneous combustion and non-spontaneous combustion coal gangue were selected in the test.Coal gangue cement mortar specimens with grinding time of 15 min,30 min and 60min and content of 15%,30%and 45%were used for standard curing,steam curing at 90°C,steam curing at 80°C and steam curing at 70°C.The blank group without mineral admixtures with the same mix ratio was made for comparative test.In order to explore the erosion mechanism of coal gangue cement-based materials under dry-wet cycle-sulfate conditions,the flexural and compressive strength of mortar were measured by strength testing machine,and the phase composition of hydration products in coal gangue cement-based materials under different curing conditions was determined by SEM,XRD,TG and other modern microscopic testing techniques.The main conclusions are as follows:（1）The mechanical properties of spontaneous combustion coal gangue mortar specimens with grinding time of 30 min are the best.The flexural strength can reach 7.8 MPa and the compressive strength can reach about 45 MPa.The flexural and compressive strength of non-spontaneous combustion coal gangue mortar specimens with grinding time of 60 min is the highest,which can reach 10.1 MPa and 56.73MPa respectively.At the same time,the optimal steam curing system is to pre-raise for 2h,then heat up for 2h,keep constant temperature for 8h,and finally cool down for 2h,a total of 14h,and the constant temperature is set to（70±5°C）.（2）The incorporation of coal gangue will lead to a decrease in the flexural and compressive strength of cement-based materials,but it will increase the flexural-compressive ratio of the specimens,indicating that coal gangue cement-based materials have high crack resistance.Steam curing can improve the early strength of coal gangue mortar specimens,so that the 2d strength can reach 70%of 28d,and the incorporation of coal gangue can well resist the late strength shrinkage caused by steam curing.（3）The mortar specimens with spontaneous combustion coal gangue and non-spontaneous combustion coal gangue content of 15%and 30%respectively can well resist the erosion of dry-wet cycle-sulfate,but the mortar specimens with 45%spontaneous combustion coal gangue cement are the most seriously eroded.Through XRD and TG curve analysis,it can be seen that the content of Ca（OH）₂in the non-spontaneous combustion coal gangue specimen is higher,indicating that the content of the erosion product-ettringite is lower;the content of Ca（OH）₂ in the spontaneous combustion coal gangue specimen is almost no,indicating that the Ca（OH）₂ in the specimen is completely converted into ettringite,resulting in poor corrosion resistance.（4）The strength change of coal gangue cement-based materials in the process of sulfate attack shows the law of’repair-damage-repair-damage again’.Through micro-test technology,it is found that the strength increases because of the filling of micro-cracks and micro-pores by the generated erosion products.With the continuous generation of erosion products,the internal structure is destroyed again,so the cycle until the specimen is completely destroyed.