Experimental Study On Durability And Pore Structure Of Bag Concrete Under Dry-Wet-Freeze-Thaw Cycle

Due to environmental factors,the existing formwork concrete lining of Hetao Irrigation District often faces seasonal freeze-thaw and dry-wet cycles,resulting in durability damage such as cracks on the surface of the concrete lining of the bag.Based on the ratio of the existing bag concrete,the solid waste materials such as fly ash and silica fume and fly ash and marble powder are used to replace the cement,and the different mineral admixtures are applied to the molded bag concrete.The effects of mechanical properties and microscopic pore structure,while simulating the actual service environment of the molded bag concrete,establishing a reasonable dry-wet-freeze-thaw cycle system,and studying the effects of the coupling of dry-wet-freeze-thaw cycles on the durability and microscopic porosity of the molded bag concrete.The optimized mix ratio of the concrete lining of the molded bag in the Hetao Irrigation District is obtained,which lays a foundation for the promotion and application of the molded bag concrete in the Inner Mongolia Hetao Irrigation District and even the northern region.The main research results are as follows:(1)The macroscopic mechanical property test results show that the appropriate amount of double-mixed fly ash and silicon powder,fly ash and marble powder can improve the compressive strength of the molded bag concrete.When the double admixture substitution rate is about 20%,the early compressive strength of the molded bag concrete lining is better than other groups,and the F10S8 and F10D10 sets have the best compressive strength.(2)The microscopic pore characteristics show that the proper amount of double-doped mineral mixture is beneficial to improve the pore structure,and the improvement of pore structure by double-mixed fly ash and silica powder is better than that of double-mixed fly ash and marble powder.When the substitution rate of double admixture is about 20%,with the increase of silicon powder replacement rate,the replacement rate of fly ash decreases,the porosity decreases gradually,and the pore size also changes from harmful holes to less harmful holes and harmless holes;(3)The durability test under the coupling of dry-wet-freeze-thaw cycle shows that the proper amount of fly ash and silica powder and the incorporation of fly ash and marble powder are beneficial to improve the durability of the molded bag concrete.The blending ratio of 10%fly ash 10%marble powder and 10%fly ash double 8%silica powder is optimal.The XRD and electron microscopy analysis of the dry-wet-freeze-thaw cycle showed that the main damage of the internal structure of the double-blend form bag concrete was affected by the ice-water phase transition and the erosion of salt ions in the Yellow River water.(4)Using the grey correlation degree in the grey theory to analyze the correlation between the damage degree of the bagged concrete under the dry-wet-freeze-thrust coupling and the pore washing characteristics and the pore size distribution,and the specific surface area,average radius and 0-200?m were found.The correlation between the chord length distribution and the damage degree of the molded bag concrete is the highest.