## 1 Introduction
[17] tested the mechanical properties of three groups of concrete specimens placed in a dry environment after 3, 7, and 28 days of standard curing, and they found that the compressive strength and the splitting tensile strength of concrete dried for 28 days after 3 and 7 days of standard curing were not significantly different from those after 28 days of standard curing. However, after 90 days, the compressive strength and the splitting tensile strength of concrete dried after 3 days of standard curing were 11% and 13% lower than those of concrete dried after 28 days of standard curing, respectively. [PERSON] et al. [18] found that, with the increase in drying temperature, the compressive strength of concrete showed a trend of decreasing first and then increasing, while the splitting tensile strength decreased. [PERSON] et al. [19] found that the compressive strength and the flexural strength of ordinary concrete and internally cured concrete exposed to a dry environment were both significantly reduced, which showed that the technology of internal curing could not significantly improve the cracking resistance of concrete, and the negative impact on the development of the properties and strength of concrete in a dry environment was significant. The erosion of concrete by saline soils is more severe in low-humidity environments with large temperature cycles. When the concrete produces defects such as cracks and pores due to temperature changes, on the one hand, the sulfate ions in the saline soil enter the concrete interior and react with the hydration products to produce expansive erosion products--ettrinigite(AFt) or gypsum [20]--or transform into bulky crystalline hydrates [21] and some sulfate crystals [22], which produces swelling stresses and leads to concrete cracking. On the other hand, chloride ions in saline soils enter the concrete interior and destroy the oxide film on the surface of the reinforcement, leading to corrosion of the reinforcement, which makes the bond interface between the reinforcement and the concrete swell and crack, leading to concrete cracking [23; 24; 25]. Among the methods used to investigate the macro-mechanical properties of concrete under conditions of different temperatures and humidity, most studies have used the fracture test method. [PERSON] et al. [26] used the shear test and beam test (three-point bending test) to investigate the effect of temperature and humidity on the bonding properties of composite materials, and the three-point bending test was effective in reflecting the bonding properties of the material. [PERSON] et al. [27] conducted a three-point bending test using notched beams in their study of the effect of different temperatures on the bonding performance and ultimate load-carrying capacity of strengthening composite systems at 100% humidity, which was more in line with the results of the single-lap or double-lap shear tests widely used in the study. Mineral admixtures such as fly ash and slag can partially replace ordinary silicate cement, which can improve the pore structure of concrete [28], improve the durability of concrete, reduce the risk of cracking [29], and reduce the amount of cement used and CO2 emissions during the generation of ordinary silicate cement [30]. [PERSON] et al. [31] found that fly ash and slag could decrease the total shrinkage of high-performance concrete significantly, but increased the self-shrinkage. [PERSON] et al. [32] prepared recycled concrete with 25%, 35%, and 55% of fly ash and found that the highest compressive strength and elastic modulus of concrete were achieved with 55% fly ash, which effectively improved the resistance of concrete to chloride ion penetration. Therefore, this study uses concrete modified by compound mineral admixtures (fly ash and slag) and a large temperature difference as the object of study, which is in line with the actual engineering conditions.