This research will help to improve our understanding of the fracture properties of ECC at low temperatures (long-term low temperatures, freeze–thaw) and evaluate the safety properties of ECC under low-temperature conditions. Three levels of saturation (saturated, semi-saturated, and dry), four target temperatures (20, 0, −20, and −60 °C), and the effect of the coupled of the two on the mode I fracture properties of ECC were investigated. Then, we compared and analyzed the fracture properties of ECC loaded at 20 and −20 °C, after different freeze–thaw cycles (25, 50, 100 cycles), which were compared with saturated specimens without freeze–thaw at the four target temperatures to analyze the differences in low-temperature and freeze–thaw failure mechanisms. Temperatures and saturation have a significant effect on the fracture properties. Low temperatures and freeze–thaw treatments both decreased the nominal fracture energy of ECC. Distinct differences in matrix and fiber-matrix interface damage mechanisms have been discovered. Low temperatures treatment transforms ECC from a ductile to a brittle fracture mode. However, even after 100 freeze–thaw cycles, it remains ductile fractured. This study complements the deficiencies of ECC in low-temperature theoretical and experimental applications, and it sets the stage for a broad range of ECC applications.

A new temperature stress test machine (TSTM) was developed to improve temperature control accuracy and efficiency. As there is no uniform standard for the threshold value of TSTM, quite different threshold values are used in the test, which results in the influences of the threshold value on the evaluation of thermal stresses and crack risk of concrete not being determined. To illustrate the importance of an appropriate threshold value, different threshold values were used to evaluate the influences on the thermal stresses and cracking resistance of concrete specimens under a complete restraint test with semi-adiabatic temperature development. The results show that the maximum compressive stress of a concrete specimen with a threshold value 3 με was slightly larger than that of 1.5 με when the growth rate of tensile stress of the concrete specimen with the threshold value 3 με was slightly greater than that of concrete specimen with the threshold value 1.5 με. Based on the combination of crack risk coefficient and restraint degree, a new system for evaluating the crack resistance of concrete was proposed, in which different threshold values were used to estimate their influences on the crack risk of concrete. Thus, an appropriate range of threshold values could be determined.

The chemical debonding energy, initial interfacial frictional bond strength and slip-hardening coefficient between polyvinyl alcohol (PVA) fibres and an engineered cementitious composite (ECC) matrix were obtained by means of single PVA fibre pull-out tests. The effect of three moisture states (fully saturated, semi-saturated and fully dry) on the bonding properties between the PVA fibre and ECC matrix at three target temperatures (25°C, 0°C and −20°C) was investigated. It was found that, at 25°C, the bonding properties decreased with an increase in moisture content. At 0°C and −20°C, the bonding properties increased with an increase in moisture content. At −20°C in the fully saturated state, the bonding load was too large to cause fibre rupture. The bonding properties were found to increase with decreasing temperature in the fully saturated and semi-saturated states and decrease with decreasing temperature in the fully dry state. This study of the effect of low temperature and moisture state on the bonding properties between PVA fibres and ECCs provides theoretical support for how to ensure good ductility when ECCs are in service at low temperature.

The emergence of strain-hardening cementitious composites (SHCCs) improves brittle cracking of concrete materials. SHCC has the characteristics of strain hardening and multiple cracking under tensile load. In this study, 10 groups of SHCC were developed by incorporating polyvinyl alcohol (PVA) fiber into cement-based materials with high-content fly ash. Testing variables included water/binder ratio, sand/binder ratio, fly ash and cement content, and sand particle. The tensile test on the thin-plate specimen and compression test on cylindrical specimen were carried out. In addition, the double-edge notched plate specimens with relative notch lengths of 0.2, 0.4, and 0.6, respectively, were tested. The results showed that the average ultimate tensile strain of SHCC was 403 times that of ordinary concrete, and the peak compressive strain was about four times higher than ordinary concrete. The ultimate tensile strain of SHCC with high-volume fly ash ratio is generally higher than the low-volume fly ash ratio group. The failure mode of SHCC was ductile with good energy dissipation. Also, SHCC compressive strength is mainly adversely affected by the water/binder ratio and the ratio of cement to fly ash. With the increase of compressive strength, the angle of the failure face was reduced under compression. The acoustic emission (AE) activity captured the initiation and development of cracks at the three stages in the notched specimens under tension. With the increase of the notch length, the fracture energy calculated by the tensile stress–crack mouth opening displacement (CMOD) curve decreases.