# Deterioration Process of Cementitious Material Properties under Internal Sulphate Attack
## 3 Results and Discussion
### Expansion Measurements  
Figure 10 shows the swelling rate of cement mortar specimens with different SO\({}_{3}\) content in the aggregate at 20 \({}^{\circ}\)C. The results show that the greater the SO\({}_{3}\) content in the aggregate, the greater the swelling rate of mortar specimens. When the SO\({}_{3}\) content in the aggregate was 0.6% and 1.2%, the expansion rate of mortar specimens at 360 d did not exceed 0.1% and no longer had a significant expansion trend. The expansion rates were 0.029% and 0.094% at 360 d. When the SO\({}_{3}\) content in the aggregate was 2.4%, the expansion rate of the specimens reached 0.33% at 360 d, and the expansion trend slowed down; and when the SO\({}_{3}\) content in the aggregate was 4.8% and 7.2%, the swelling rate of the specimens at 360 d was 0.55% and 0.61%, respectively, and the swelling had not yet stabilized. From XRD Figure 5, we know that the gypsum in the mortar specimens with SO\({}_{3}\) content less than or equal to 2.4% in the aggregate at 360 d has been consumed, and the mortar specimens with SO\({}_{3}\) content of 4.8% and 7.2% in the aggregate have remaining unreacted gypsum. This indicates that when the gypsum admixture is small, the amount of calcium alumina generated by ISA is limited and the volume deformation caused to the specimens is limited; instead, calcium alumina is used to fill the cement paste pores [27]. Figure 10: Expansion of mortars with different SO\({}_{3}\) content in aggregate. Figure 9: Phase content of cement mortar added with 7.2% SO\({}_{3}\). Figure 11 shows the expansion rates of mortar specimens with 4.8% SO\({}_{3}\) content in the aggregate at different curing temperatures. From Figure 11, it can be seen that the expansion of the mortar specimens maintained at 20 \({}^{\circ}\)C grows linearly with age, the mortar specimens maintained at 40 \({}^{\circ}\)C and 60 \({}^{\circ}\)C expand rapidly within 14 d, and then the expansion development slows down, where the expansion of the mortar specimens maintained at 40 \({}^{\circ}\)C continues to grow at a lower rate, and the expansion of the mortar specimens maintained at 60 \({}^{\circ}\)C tends to stabilize after 14 d, with little expansion enhancement. The expansion rate of the mortar specimens maintained at 20 \({}^{\circ}\)C was the smallest before 85 d, and its expansion exceeded that of the mortar specimens maintained at 60 \({}^{\circ}\)C and 40 \({}^{\circ}\)C at 86 d and 150 d, respectively; at 360 d, the expansion rates of the mortar specimens maintained at 20 \({}^{\circ}\)C, 40 \({}^{\circ}\)C and 60\({}^{\circ}\)C were 0.55%, 0.37% and 0.15%, respectively. From the next section, we know that the higher the maintenance temperature, the higher the strength of mortar specimens. In maintenance of mortar specimens at 60 \({}^{\circ}\)C with fast strength development, the higher the maintenance temperature, the faster the rate of gypsum dissolution reaction to generate calcium alumina, as the strength limits the expansion of calcium alumina; while in maintenance of the specimens at 20 \({}^{\circ}\)C with slow strength development, the gypsum dissolution to generate calcium alumina rate is slow. The swelling value law is 40 \({}^{\circ}\)C \(>\) 20 \({}^{\circ}\)C \(>\) 60 \({}^{\circ}\)C. From XRD analysis in Figure 11, we know that the gypsum in the mortar specimen with 4.8% SO\({}_{3}\) content in the aggregate is sufficient, which is higher than the gypsum content in the net mortar specimen with 4.8% SO\({}_{3}\) cement, which will generate more calcium alumina; thus, after 150 d, the swelling rate of the specimen maintained at 20 \({}^{\circ}\)C exceeds 40 \({}^{\circ}\)C.  
Figure 12 shows the expansion rates of mortar specimens with 4.8% SO\({}_{3}\) content in different gypsum particle size aggregates at 20 \({}^{\circ}\)C maintenance. From Figure 12, it can be seen that the swelling of mortar specimens mixed with gypsum sand of particle size \(<\) 0.3 mm, 0.3-1.18 mm and 1.18-2.36 mm grows linearly with age and the swelling has not yet stabilized.