The macroscopic mechanical properties and frost resistance durability of concrete are closely related to the changes in the internal pore structure. In this study, the two-dimensional and three-dimensional ICT (Industrial Computerized Tomography) pore characteristics of C30 concrete specimens before and after freezing and thawing in clean water, 5 wt.% NaCl, 5 wt.% CaCl₂, and 5 wt.% CH₃COOK solution environments are obtained through concrete frost resistance durability test and ICT scanning technology. The effects of pore structure changes on concrete frost resistance, durability, and compressive strength mechanical properties after freezing and thawing cycles in different salt solution environments are analyzed. This paper provides new means and ideas for the study of concrete pores. The results show that with the increase in the freezing and thawing times, the concrete porosity, two-dimensional pore area, three-dimensional pore volume, and pore number generally increase in any solution environment, resulting in the loss of concrete compressive strength, mortar spalling, and the decrease in the relative dynamic elastic modulus. Among them, the CH₃COOK solution has the least influence on the concrete pore changes; the NaCl solution has the greatest influence on the change in the concrete internal porosity. The damage of CaCl₂ solution to concrete is second only to the NaCl solution, followed by clean water. The increase in the concrete internal porosity from high to low is NaCl, CaCl₂, clean water, and CH₃COOK. The change in the pore volume of 0.1 to 1 mm³ after the freeze–thaw cycle is the main factor for reducing concrete strength. The test results have certain guiding value for the selection of deicing salt in engineering.

Solid waste silica fume was used to replace fly ash by different ratios to study the early-age hydration reaction and strength formation mechanism of concrete. The change pattern of moisture content in different phases and micro morphological characteristics of concrete at early age were analyzed by low field nuclear magnetic resonance (LF-NMR) and scanning electron microscope (SEM). The results showed that the compressive strength of concrete was enhanced optimally when the replacement ratio of solid waste silica fume was 50%. The results of LF-NMR analysis showed that the water content of modified concrete increased with the increase of solid waste silica fume content. The compressive strength of concrete grew faster within the curing age of 7 d, which means the hydration process of concrete was also faster. The micro morphological characteristics obtained by SEM revealed that the concrete was densest internally when 50% fly ash was replaced by the solid waste silica fume, which was better than the other contents.

Severe blockages of tunnel drainage systems greatly affect the lining structure of the tunnels, thus jeopardizing their stability and safety. In order to study the blockages of tunnel drainage pipes, the flow rate of a calcium carbonate crystal tunnel was measured in the mountainous area of Southwest China. According to the actual flow velocity results, numerical simulation was combined with finite element software (ANSYS Fluent). This analyzed the calcium carbonate crystallization near the interface of the tunnel drainage pipe. The results are as follows: (1) for both the Y-shaped three-way pipe and the T-shaped pipe, the values of maximum water velocity are similar but occur at different locations. At the interface of the transverse drainage pipes, flow velocity is the highest; (2) at the three-way joint segment, the water that flows in the longitudinal drainage blind tube is influenced by the water coming from the annular drainage blind tube. At the interface of the transverse drainage pipe, water flows at a lower speed in the Y-shaped three-way pipe than in the T-shaped pipe—the difference is about 3.75 times; (3) the smoothness of calcium carbonate deposition is correlated with water velocity and the content of calcium carbonate. The calcium carbonate crystal will occupy a larger space at locations with a higher calcium carbonate content and a lower flow velocity; (4) the drainage capacity of tunnel drainage pipes declines most when the volume fraction of calcium carbonate reaches 80%. Compared with the situation when calcium carbonate does not exist, the drainage capacity decreases by 84.78% for T-shaped pipe and by 77.64% for Y-shaped three-way pipe when the volume fraction of calcium carbonate is 80%.