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.

A high geo-stress environment severely damages tunnel structures owing to the large deformation of the surrounding rock, thereby threatening their safety. In this study, the Wushaoling highway tunnel group, which passes through a high geo-stress environment, is investigated as a case study. The spatial distribution of different types of tunnel cracks is analyzed based on the site observations. The lining crack variations, such as circumferential and longitudinal cracks, with the factors including grade of the surrounding rock, location of buried depth, and design type of the tunnel lining are investigated. Various structural reinforcement technologies are presented based on the damage degrees of the tunnel linings. Several finite element models of supporting structures are established to reveal the mechanism of tunnel crack control technology. The results show that longitudinal and circumferential cracks are the main characteristics of tunnel lining damage in high geo-stress environments, accounting for approximately 29.4 and 53.2% of the total cracks, respectively. SIVb-, SVc-, and SVd-type linings show numerous longitudinal cracks per kilometer. The longitudinal cracks appear primarily on the tunnel crown and hance. In terms of the lining support types in Grade V surrounding rocks, the number of longitudinal cracks per kilometer increases with the lining grade. The number of tunnel cracks per kilometer tends to increase with the buried depth. Four tunnel structure reinforcement treatment measurements for lining cracks in high geo-stress condition were innovatively proposed, which were proved effective in deformation controlling and strengthening the tunnel lining using numerical investigation. The key contribution of this research is to reveal the characteristics and evolution mechanism of tunnel lining cracks in high geo-stress condition, and provide effective treatments for the tunnel lining cracks. In addition, the findings from the study on the tunnel lining cracks also provide industry practitioners with a comprehensive guide regarding the characteristics and control techniques of the tunnel lining cracks, which can serve as a steppingstone to facilitate the construction technology development of the transportation industry.