Experimental Research On The Effect Of Mineral Admixtures On Mechanical Properties And Chloride Permeability Of Concrete

The cement industry is one of the representative industries with high pollution and high energy consumption in China's industrial system.With the increasing public awareness of environmental protection,it has become a trend to reduce cement consumption and recycle industrial waste to prepare concrete in the construction industry.The advanced treatment of industrial waste(such as fly ash,coal gangue,etc.)requires a lot of financial and material resources,and random stacking will invade cultivated land and seriously pollute the environment.However,some industrial wastes have pozzolanic properties and have the potential to become supplementary cementitious materials.Therefore,many scholars have used industrial waste as mineral admixtures to explore their comprehensive utilization value in the construction of reinforced concrete structures.In the existing research,the discussion on the influence of single mineral admixture,such as fly ash,on the properties of concrete is relatively comprehensive.However,as a supplementary cementing material,coal gangue's resistance to chloride ion penetration and frost and its binding capacity are still of little concern.In addition,the effects of double-doped fly ash and coal gangue on the mechanical properties,chloride diffusion process and chloride binding capacity of concrete are also to be studied.In order to explore the above issues,this paper carries out the following research work:(1)The compressive strength test is carried out based on the cement replaced partially with fly ash,coal gangue or both mineral admixtures.The compressive strength at the age of 7,28 and 90 days of mineral admixture concrete with different mixing ratios is measured.After comparative analysis,considering the mechanical properties of 90 d,the ratio of cement substitution of 20% and the mass ratio of fly ash to coal gangue of 50/50 and 40/60 are recommended as the optimal ratio of cement substitution and the optimal ratio of fly ash to coal gangue,respectively.(2)The artificial ocean tidal simulation device independently developed by our research group is used to simulate the real-time tidal fluctuation process.Based on this,the chloride ion diffusion test of fly ash and coal gangue concrete specimens is carried out.Through the laboratory testing,the chloride ion concentration of concrete specimens with different fly ash and coal gangue ratios at different exposure times and different depths can be obtained under different cement substitution ratios.By the regression analysis of chloride ion concentration,the corresponding chloride ion diffusion coefficients are obtained to evaluate the effect of the fly ash,coal gangue or both mineral admixtures on the diffusion characteristics of chloride ions in concrete.After comparative analysis,the ratio of cement substitution of 20% and the mass ratio of fly ash to coal gangue of 40/60 are recommended as the optimal ratio of cement substitution and the optimal ratio of fly ash to coal gangue,respectively.(3)The effect of fly ash on the chloride ion binding capacity of concrete is still controversial.The influence of coal gangue on the chloride ion binding capacity of concrete has rarely been studied.Based on the above chloride ion diffusion test,the total chloride ion concentration of concrete specimens with different fly ash and coal gangue ratios at different exposure times and different depths can be obtained under different cement substitution ratios.The effect of fly ash and coal gangue on the chloride ion binding capacity of concrete is investigated using linear binding isotherms.Through comparative analysis,fly ash and coal gangue have a positive effect on improving the chloride ion binding capacity of concrete,whether binary or ternary.(4)The volcanic ash effect is the key to turning mineral admixtures into good use,and this effect is deeply affected by the fineness of the admixture.Based on the optimal cement substitution ratio determined by the above compressive strength test,the compressive strength,freeze-thaw cycle and chloride ion diffusion tests are carried out.The study was carried out with coal gangue of different fineness in the case of cement substitution ratio of 20%.After comparison and analysis,it is recommended that 2000 mesh be the optimal fineness of coal gangue.(5)Considering the mechanical properties and the resistance to chloride ion penetration of mineral-containing concrete,the final recommended cement substitution ratio is 20%,and the optimal ratio of fly ash to coal gangue is 40/60.It can be found that China's 2017 cement output is 2.32 billion tons.Based on this optimal ratio,using fly ash and coal gangue to replace cement will reduce cement production by 464 million tons per year,consume 185.6 million tons of fly ash and 278.4 million tons of coal gangue,which will greatly reduce the occupation of cultivated land and various pollution,improve the health of our citizens,and vigorously promote the construction of a resource-saving and environment-friendly society.