Macro Performance And Micro Pore Structure Characteristics Of Solid Waste Admixture Mold Bag Concrete

In this paper,fly ash from Baotou Power Plant in Inner Mongolia,waste silicon powder from Wulatqianqi Jade Yard in Bayan Nur City,two kinds of solid waste,and other quality were used to substitute part of cement as raw materials for molding bag concrete.The concrete cube compressive strength test,freeze-thaw cycle test and pore structure nuclear magnetic resonance test were combined to study the macro performance deterioration and micro pore damage characteristics of concrete.The early mechanical properties and the deterioration mechanism of frost resistance and durability of solid waste admixture mold bag concrete were investigated from the aspects of pore fractal characteristics,one-dimensional Wiener process modeling and two-parameter Weibull probability distribution function modeling,etc.,which provided some theoretical basis for the study of mold bag concrete suitable for service environment in Hetao irrigation area of Inner Mongolia.The main research results are as follows:(1)Solid waste admixture(fly ash,industrial waste silicon powder)is beneficial to improve the early mechanical properties and pore development of mold bag concrete.The compressive strength of the bag concrete with appropriate reinforcement waste admixture is obviously better than that of the reference group(FA20S0).Among them,FA15S4 group(fly ash replacement rate is 15%,silica powder replacement rate is 4%)has the best mechanical properties for 28 d,and the structure of the connection between cementing material and coarse and fine aggregate has stronger load bearing capacity than the existing mold bag concrete group.Its failure morphology shows only many vertical cracks,and the spalling of aggregate and cement slurry is not obvious.The internal pores of molded bag concrete have good fractal characteristics,and the fractal dimension of NMR is segmented.The fractal dimension can be used to better characterize the development and change characteristics of the internal pores of concrete,and can also indirectly reflect the compressive strength of molded bag concrete.(2)The freeze-thaw cycle test results under different freeze-thaw media(clean water and Yellow River water)show that FA15S4 has the best freeze-thaw resistance,and FA20S20 group has the worst freeze-thaw resistance.Solid waste admixture can effectively improve the freeze-resistance and durability of bag concrete.Under the action of freeze-thaw cycle of the Yellow River water,the freeze-thaw damage of the mold bag 5concrete with the same proportion is more serious,and some small pores change to large pores after freeze-thaw.The influence of the Yellow River water freeze-thaw on the internal pore structure of the specimen is more serious than that of plain water.Adding the waste reinforcement admixture to the mold bag concrete can optimize the salt-freeze resistance of the concrete,reduce the damage degree,and improve the pore structure.(3)After freeze-thaw cycle,the fractal dimension of micro-pores decreased,while that of large pores increased.After freeze-thaw cycle,the fractal dimension of large pores in group FA15S4 only increased by 0.043,which was the smallest increase,which was consistent with the conclusion that this group had the best freeze-thaw resistance.The fractal dimension of NMR can characterize the pore structure changes of bag concrete before and after freeze-thaw to a certain extent.(4)Two freeze-thaw damage models of bag concrete based on mass loss rate and relative dynamic elastic modulus were established by means of unvariable Wiener random process and two-parameter Weibull probability distribution function.Wiener model predicted that the life of FA15S4 group was the longest,which could be freeze-thaw cycles324 times in clear water and 239 times in Yellow River water,respectively.The life of active mold bag concrete was the shortest,which could only be freeze-thaw cycles 258 times in clear water and 212 times in Yellow River water.The addition of fly ash and waste silicon powder is beneficial to prolong the service life of mold bag concrete.The prediction conclusion of Weibull probability distribution function model is consistent with that of Wiener model,but the predicted life of Weibull probability distribution function model is generally higher than that of Wiener model.