## 3 Results  
### Effects of the Environmental Humidity on Strength  
#### 3.1.1 Compressive Strength  
The compressive strength of the cement paste was evaluated under different humidity conditions. The results are shown in Figure 1. With an increase in the further hydration time, the compressive strength increased under all humidity conditions.  
Under the conditions of the sealing state, RH50% \(\pm\) 5%, RH \(\geq\) 95%, and water soaking at 20 \({}^{\circ}\)C, the compressive strength of the cement pastes after 180 d of further hydration increased by 10.1%, 15.3%, 22.6%, and 17.1%, respectively, compared to that before further hydration. After further hydration for 14 d, considering the sealing state, RH50% \(\pm\) 5%, RH \(\geq\) 95%, and water soaking at 20 \({}^{\circ}\)C, the increase in strength under the aforementioned conditions was equal to 3.0, 3.2, 4.2, and 5.3 MPa, respectively, compared to that before further hydration. After further hydration for 90 d, the increase in strength was 7.2, 9.2, 12.0, and 6.2 MPa, compared to that evaluated after 14 d of further hydration. After further hydration for 180 d under the conditions of the sealing state, RH50% \(\pm\) 5%, RH \(\geq\) 95%, and water soaking at 20 \({}^{\circ}\)C, the strength increased by 1.0, 1.6, 4.5, and 4.2 MPa, respectively,compared to that measured after 90 d of further hydration. Evidently, among the four humidity environments, RH \(\geq\) 95% exerted the most significant influence on the compressive strength of the cement pastes. Under the water-soaking conditions at 20 \({}^{\circ}\)C, the highest and lowest strength increments were observed during the early (between 0 and 14 d) and middle stages (between 14 and 90 d) of further hydration, respectively, and a relatively large increment in strength was observed during the late stages of further hydration (between 90 and 180 d).  
In the sealing state, large autogenous shrinkage deformations of cement pastes occurred, and the tensile stress on the surface of the cement pastes led to cracking. Meanwhile, the cement hydration rate was the lowest. Therefore, the rate of increase in strength in the sealing state was the lowest. Under RH50% \(\pm\) 5% conditions, external water entered the specimen through diffusion, which reduced the degree of autogenous shrinkage and drying shrinkage. Meanwhile, under RH50% \(\pm\) 5% conditions, the cement hydration was accelerated to a certain extent, yielding a higher rate of strength increase compared to that obtained in the sealing state. Under the conditions of RH \(\geq\) 95% and water soaking at 20 \({}^{\circ}\)C, a satisfactory supply of water vapour and water from the external environment accelerated the further hydration process, and the further hydration products continued to fill the internal pores of the cement pastes. This increased the rate of increase in the compressive strength. Under the conditions of water soaking at 20 \({}^{\circ}\)C, the cement paste was exposed to an adequate supply of water during the early stage of further hydration, which enhanced the further hydration reaction, yielding the maximum increment in strength. The further hydration reaction during the early stage resulted in a high degree of pore filling, limiting the diffusion of external water in the cement paste and resulting in the minimum increment in strength. During the late stage of further hydration, the available space in the cement paste gradually decreased. When the remaining space could not accommodate further hydration products and the expansion stress of the products exceeded the tensile strength of the cement paste, the microcracks generated in the cement paste provided a new channel for water diffusion. Therefore, a large increment in strength was maintained.