Experimental Study On The Frost Resistance And Photocatalytic Performance Of TiO₂ Concrete Under Single-sided Freeze-thaw

The small size and nucleation effect of nano-TiO₂ promotes the hydration of cement and effectively fills the pores between the C-S-H（hydrated calcium silicate）matrix,improving the mechanical and frost resistance of concrete.In addition,the incorporation of nano-TiO₂ into the concrete matrix gives it photocatalytic activity,which in turn degrades a range of pollutants.When concrete is subjected to freeze-thawing,its apparent morphology and internal pore structure will change significantly,affecting its frost resistance and photocatalytic performance.Therefore,the research on the anti-freezing performance and photocatalytic performance of nano-TiO₂ concrete after freeze-thawing is of great practical significance to promote the engineering application of nano-TiO₂ concrete.This paper analyses the evolution pattern and mechanism of the anti-freezing performance and photocatalytic performance of nano-TiO₂ concrete from macroscopic and microscopic perspectives.The main research contents and conclusions are as follows:（1）Four dosing levels of nano-TiO₂ concrete were prepared by selecting 0%,2%,4%and 6%nano-TiO₂ of equal mass instead of cement for single-sided freeze-thaw cycle tests.The results showed that the accumulated mass loss rate of each specimen increased and the compressive strength decreased gradually with the increase of freeze-thaw cycles.The relative dynamic modulus decreases slowly at the beginning of freeze-thaw,but with the increase of the number of freeze-thaw cycles,the decreasing trend is obvious.During the whole freeze-thaw cycle,the frost resistance of concrete dosed with 2%nano-TiO₂ is optimal.（2）Based on the NMR technique,the changes of T₂ spectrum distribution,pore size percentage and other pore parameters of TiO₂ concrete with different doping levels after freeze-thawing were analysed,and the relationship between pore structure parameters and compressive strength was explored.The results show that the peak and area of the T₂distribution curve of nano-TiO₂ concrete increase to different degrees with the increase of the number of freeze-thawing times and the trend of shifting to the right is obvious.The greater the number of freeze-thaws for each dose of TiO₂ nanoconcrete specimens,the greater the porosity.Faster rise in porosity curves of concrete specimens with various doses of TiO₂ nanoparticles under salt freezing compared to water freezing.During the whole freeze-thaw cycle,the compressive strength of nano-TiO₂ concrete continues to decrease with the increase of porosity and permeability.（3）The effects of different light duration,number of freeze-thaw cycles and evolution of pore structure on the photocatalytic performance of nano-TiO₂ concrete were tested by photocatalytic experiments.The results showed that the photocatalytic degradation efficiency of each dose of nano-TiO₂ concrete specimens increased with the increase of light duration.It keeps decreasing with the increase of the freezing and thawing times.The efficiency of photocatalytic degradation of pollutants on the surface of concrete specimens increases as the amount of TiO₂ nano-doping increases.The decrease in efficiency of photocatalytic degradation of nano-TiO₂ concrete is more pronounced in salt-freezing environments than in water-freezing.（4）The gray entropy method was used to analyze the correlation degree of test conditions,pore structure parameters and each pore size distribution on the photocatalytic degradation efficiency.And the reaction mechanism of photocatalytic degradation of pollutants was summarized and discussed.The results showed that the most influential factors of freeze-thaw conditions,pore structure parameters and pore size distribution on the photocatalytic degradation efficiency were nano-TiO₂ doping,bound water saturation and the number of micropores,respectively.