# Fracture Properties of Concrete in Dry Environments with Different Curing Temperatures
## 5 Conclusions  
In the current research, the fracture properties of concrete in dry environments with different temperatures were investigated using the wedge splitting specimens. Four different temperatures (5 \({}^{\circ}\)C, 20 \({}^{\circ}\)C, 40 \({}^{\circ}\)C, and 60 \({}^{\circ}\)C) were considered, which represented cold, normal, hot, and extremely hot weather, respectively. The complete load-CMOD curves of specimens were obtained at 3, 7, 14, 28, and 60 d. The key fracture parameters of concrete were also evaluated. The following conclusions can be drawn from the experimental data:  
1. In a dry environment, the gain in fracture energy of the concrete strongly depended on the curing temperature. An elevated temperature was beneficial to the rapid development of concrete  
Figure 7: The fracture surface of concrete at different temperatures: (**a**) at 5 \({}^{\circ}\)C; (**b**) at 60 \({}^{\circ}\)C.  
fracture energy at an early age. However, this situation did not hold at later ages, in which a higher value of the fracture energy at a later age was obtained by concrete stored at lower temperatures, and vice versa. Generally, at 60 d, the fracture energy of concrete cured at 60 \({}^{\circ}\)C was only larger 7.7% and 3.2% when comparing concrete stored at 5 \({}^{\circ}\)C and 20 \({}^{\circ}\)C, respectively, and even was smaller 2.8% when comparing concrete stored at 40 \({}^{\circ}\)C. Considering the early growth rate and later-age value of fracture energy, the optimum curing temperature for fracture energy of concrete under dry condition was around 40 \({}^{\circ}\)C.
2. In the case of the dry condition, the effective fracture toughness improved significantly as the increase of curing temperature in the early stage, but the influence of temperature on the concrete fracture toughness reversed after 28 d, wherein a relatively small ultimate value of effective fracture toughness was measured by the samples stored at the higher temperature. The temperature crossover effect was observed in concrete effective fracture toughness. From the temperature investigated, the most suitable curing temperature for the development of effective fracture toughness of concrete in dry environments was still 40 \({}^{\circ}\)C.
3. For a given curing condition, both the effective fracture toughness and fracture energy improved speedily with age at the beginning. After the growth rate reached their maximum value, these two fracture parameters increased slightly with age at a reducing rate, and eventually tended to their stable values as the age was further extended. Further, the effective fracture toughness and fracture energy tended to stabilize in a shorter time with the increasing temperature.  
It should be noted that the aforementioned conclusions are only valid for the concrete studied in this paper, and the general conclusions for other types of concrete need further study.  
Conceptualization, Z.M.; formal analysis, Z.M.; funding acquisition, Q.L. and Y.H.; investigation, Z.M.; methodology, Z.M.; project administration, C.L. and Y.Q.; resources, C.L. and Y.Q.; supervision, Y.H.; writing--original draft, Z.M.; writing--review and editing, Q.L. and Y.H. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Natural Science Foundation of China (51979145, 51839007), the Fundamental Research Funds for the Central Universities, CHD (300102219305), the Open Research Fund Program of State Key Laboratory of Hydroscience and Engineering (sklhse-2020-D-01), and the Research Projects of China Three Gorges Corporation (Contract numbers: BHT/0806 and WDD/0427).  
The authors declare no conflicts of interest.