## 3 Results and Discussion  
### Effect of Loading on the Mechanical Properties of Cementitious Materials Subject to Sulfate Erosion  
Figure 2 illustrates the influence of load and sulfate coupling on the cementitious materials' properties of cementitious materials. It is evident from Figure 2a-d that both the compressive and flexural strengths of the mortar and concrete, subjected to varying flexural loads, exhibit a general trend characterized by an initial increase followed by a subsequent decline. The peak values for the flexural and compressive strengths were achieved after completing 60 days of wet-dry cycles.  
Figure 2: Mechanical properties of cement-based materials influenced by load and sulfate coupling: (**a**) Rupture strength of concrete; (**b**) rupture strength of mortar; (**c**) compressive strength of concrete; and (**d**) compressive strength of mortar.  
This observed phenomenon can be attributed to water evaporating from within the specimen during the drying cycle, leading to the formation of sulfate crystals formation, as depicted in Equation (1). Simultaneously, the wet cycle promotes the infiltration of sulfate ions into the specimen. Furthermore, once these sulfate ions penetrate the sample, they react with cementitious material to generate plaster. As erosive aging progresses, this plaster further interacts with the calcium aluminate and calcium hydroxide present in the cementitious matrix, resulting in the formation of calcium alumina compounds, as illustrated in Equations (2)-(6).  
\[\text{Na}_{2}\text{SO}_{4}+10\text{H}_{2}\text{O}\text{$\rightarrow$}\text{ Na}_{2}\text{SO}_{4}\cdot 10\text{H}_{2}\text{O} \tag{1}\]  
\[\text{CH}+\text{Na}_{2}\text{SO}_{4}+\text{H}_{2}\text{O}\text{$\rightarrow$} \text{CSH}_{2}+2\text{NaOH} \tag{2}\]  
\[\text{C}\text{-S-H}+\text{Na}_{2}\text{SO}_{4}+\text{H}_{2}\text{O}\text{$ \rightarrow$}\text{CSH}_{2}+2\text{NaOH} \tag{3}\]  
\[\text{C}_{4}\text{ASH}_{12}+2\text{CSH}_{2}+16\text{H}_{2}\text{O}\text{$ \rightarrow$}\text{C}_{6}\text{AS}_{6}\text{H}_{32} \tag{4}\]  
\[\text{C}_{3}\text{A}+3\text{CSH}_{2}+26\text{H}_{2}\text{O}\text{$\rightarrow$} \text{C}_{6}\text{AS}_{6}\text{H}_{32} \tag{5}\]  
\[\text{C}_{4}\text{AH}_{13}+3\text{CSH}_{2}+14\text{H}_{2}\text{O}\text{$ \rightarrow$}\text{C}_{6}\text{AS}_{6}\text{H}_{32}+\text{CH} \tag{6}\]  
where CH is calcium hydroxide, C-S-H is calcium silicate hydrate, CSH\({}_{2}\) is gypsum, C\({}_{4}\)ASH\({}_{12}\) and C\({}_{6}\)AS\({}_{32}\) are natural gas hydrates of calcium sulfoaluminate (AFt), C\({}_{3}\)A is a tricalcium aluminate hydrate, C is calcium oxide, A is aluminum oxide, S is silicon dioxide, and \(\overline{S}\) is sulfur trioxide.  
The influence of the bending load on sulfate erosion manifests as an increase in the number of cracks on the specimen's surface and the width of micro-cracks within the specimen, facilitating sulfate ingress through these fissures. Furthermore, after 28 days of curing, the cement remains incompletely hydrated; thus, applied loads expedite sulfate penetration into the cementitious material while simultaneously promoting hydration processes in certain components. This interaction results in an initial increase in both the flexural and compressive strengths. However, following this peak, a gradual decline in the flexural and compressive strengths is observed due to the expansion forces generated by significant product accumulation, which ultimately leads to the specimens.