Electric heat treatment is a widely used concrete curing method during the winter. Through direct and indirect heat exchange, the electric heating system tracks and controls the temperature of the heating medium based on a positive temperature coefficient (PTC) effect. In this study, to standardize the application of this treatment in the winter curing of concrete, the thermal energy conversion of an electric heating system and the heat-transfer characteristics of concrete have been studied. Based on the theoretical derivation, a calculation model of the relationship between the thermal energy of the electric heating system and the temperature of the concrete is established. The model is verified using the concrete heating and curing test results. The numerical analysis program COMSOL is used to analyze the effects of various factors on the concrete temperature field, including the electric heating power (e.g., the surface temperature of the electric heating system), concrete casting temperature, thermal conductivity, and heat release coefficient. The results show that decreasing the surface exothermic coefficient and increasing the heating temperature will significantly increase the peak temperature of the concrete. When the heat source temperature increases by 20 °C, the peak temperature could increase by approximately 13 °C. When the heating stops, the concrete volume increases temporarily, particularly in the region where the heating cable is buried. Consequently, an excessive heating power increase may cause cracks on the concrete surface. Compared with the factors of thermal conductivity and surface exothermic coefficient, the ambient temperature has the most significant effect on the concrete cooling rate when the heating stops. When the ambient temperature decreases by −20 °C, the cooling rate of concrete increases by 0.72 °C/h. The role of concrete insulation materials needs to be strengthened to reduce cooling rates during power outages and form removal. The findings from the study provide industry practitioners with a comprehensive guide regarding the specific applications of the electric heating system in early-age concrete curing.

When the early-age concrete is exposed to a negative temperature environment, the internal relative humidity will continue to change under the action of ambient temperature and humidity, affecting its physical properties, which in turn leads to changes in the performance of the concrete structure. Based on this, the variation law of relative humidity at different depths from the upper surface of the concrete with different initial humidity under sealed and unsealed conditions of early-age concrete in cold regions was studied by experiments. The results show that the influence of ambient temperature on the internal relative humidity of concrete is greater than that of ambient humidity. The temperature-relative humidity change process of each specimen during the test can be divided into five stages. For the same initial humidity of the specimen, the closer to the upper surface, the greater the relative humidity change, the greater the impact of the environment; At the same depth from the upper surface, the higher the initial humidity, the greater the relative humidity change, and the greater the environmental impact.

With China actively promoting the construction process of “sponge cities”, permeable concrete urgently needs further development. This article obtains the macroscopic effective porosity and permeability coefficient through macroscopic permeability tests, and the microscopic effective porosity and permeability coefficient through microscopic X-CT tests. Fit the experimental results to obtain the relationship between macro effective porosity and permeability coefficient function, and the relationship between micro effective porosity and permeability coefficient. Based on the constant uniform pressurized laminar flow pipeline model and the Blick nonlinear laminar flow pipeline model, the relationship formula obtained from the validation fitting is reliable. Through analysis, it is concluded that the critical value of seepage state change inside pervious concrete is that the area proportion of nonlinear seepage holes should reach 75 %, and the number proportion of nonlinear seepage holes should exceed 11 %. Under this condition, a nonlinear laminar flow system similar to network structure will be formed inside pervious concrete, thus significantly improving the permeability.