Study On Chloride Penetration Resistance Of Recycled Aggregate Thermal Insulation Concrete Based On Pore Structure

Recycled aggregate thermal insulation concrete(RATIC)achieves the purpose of combining "construction waste recycling" and "self-insulating concrete",which not only helps to solve the problem of reuse of construction waste,but also gives structural concrete new functions.It provides a new idea for the promotion and use of recycled aggregate concrete.Durability is an important indicator that affects whether building materials can be widely used.As an important durability performance of concrete,resistance to chloride ion penetration has an important impact on whether concrete materials can be used normally for a long time.The addition of recycled coarse aggregate and thermal insulation aggregate makes the internal structure of concrete more complex and the interface structure more diverse.At the same time,with the development of science and technology,the research scale of scholars on concrete has gradually changed from macro-scale to micro-scale,and has gradually carried out research between multiple scales.Studying the structural characteristics of concrete pore structure is of great significance for analyzing concrete failure mechanism,improving concrete production process and improving certain macroscopic properties of concrete.Based on the above background,in order to systematically understand the resistance to chloride ion penetration and microscopic pore structure of RATIC and explore the relationship between the durability and microscopic pore structure of RATIC,this paper uses electric flux method,nuclear magnetic resonance method(NMR),grey correlation theory and multiple regression analysis to reveal the influence of recycled coarse aggregate and thermal insulation aggregate on the chloride ion penetration resistance and pore structure characteristics of RATIC,and determined the quantitative relationship model between the strength and pore structure,the diffusion coefficient of chloride ion and the pore structure.The specific research contents and main results are as follows:(1)The electric flux method was used to study the effect of the replacement rate of recycled coarse aggregate and the content of thermal insulation aggregate on the resistance to chloride ion penetration of RATIC.By comparing with the test results of ordinary concrete,the effect of two kinds of aggregates on the chloride ion corrosion resistance of concrete was revealed.The research results show that with the increase of the replacement rate of recycled coarse aggregate,the resistance to chloride ion penetration of RATIC is gradually weakened.It can be seen that recycled coarse aggregate is not conducive to the enhancement of the resistance to chloride ion penetration of RATIC.However,the thermal insulation aggregate can effectively improve the chloride ion penetration resistance of RATIC,and the a chloride ion penetration resistance of RATIC increases with the increase of thermal insulation aggregate content.(2)The nuclear magnetic resonance(NMR)method was used to explore the microscopic pore structure characteristics inside the RATIC,and the effect of the replacement rate of recycled coarse aggregate and the content of thermal insulation aggregate on the pore structure of the RATIC was analyzed.The proportion of various types of pores in RATIC is ranked from large to small: harmless pores,more harmful pores,less harmful pores and harmful pores.The higher the replacement rate of recycled coarse aggregate,the greater the total porosity of recycled thermal insulation concrete and the less harmful pores inside it,but the more harmless pores,harmful pores and more harmful pores,especially the increase of harmful pores is the largest.The higher the amount of thermal insulation aggregate,the greater the total porosity of the recycled thermal insulation concrete,the less harmful pores inside it,and the more harmless pores,more harmful pores and less harmful pores,of which the most harmful pores increase.(3)The most important factors affecting the compressive strength(28 d)and resistance to chloride ion penetration of recycled thermal insulation concrete are calculated and analyzed based on the grey relational theory.On this basis,through the method of multiple regression analysis,the multi-factor quantitative relationship models between the strength of RATIC and pore structure parameters,chloride ion diffusion coefficient and pore structure parameters are established.The results of grey correlation analysis show that the main factor affecting the 28-day compressive strength of RATIC is the total porosity,and the main factor affecting its resistance to chloride ion penetration is the harmful porosity.The results of univariate analysis show that the compressive strength of RATIC has a strong linear correlation with the porosity and average pore size,and the chloride ion diffusion coefficient of RATIC has a strong linear correlation with the porosity of harmful and harmless pores.Based on the results of single factor analysis,a multi-factor model of strength and pore structure was constructed: σ=f(porosity,pore size distribution),and a multi-factor model of chloride ion diffusion coefficient and pore structure was constructed: D=f(porosity of harmful pores,porosity of harmless pores).