## 3 Results and Discussion
### Strength
Figure 9 shows the strength of the cement mortar after compounding with \(\beta\)-CD and CA. It can be seen from the figure that the strength decreases after the two are mixed, and the strength does not increase significantly in the first 7 days. When the content of \(\beta\)-CD is 0.3% and the content of CA is 0.5%, the 7 d flexural strength increases to 3.95 MPa and the compressive strength increases to 20.8 MPa; obviously, there is still a big gap compared with the blank group. However, compared with other dosages, the strength of this dosage increased more significantly. According to the 28 d strength, when the content of \(\beta\)-CD and CA are both 0.3%, the flexural and compressive strengths are the highest, which are 8.1 MPa and 34.5 MPa, respectively. According to the situation that the above two retarders are added separately, with a dosage of 0.3% to 0.9%, the strength of the first 3 d is basically the same, and the strength of 7 d has increased. However, the 7 d strength of the composite of \(\beta\)-CD and CA was essentially the same compared to its 3 d strength. This shows that after the two retarders are mixed together, the hydration of cement is inhibited together, the retardation effect is more significant, and the hydration is slower. Figure 8: Effects of PCE compound B on mechanical properties of HBCSA: (**a**) flexural strength and (**b**) compressive strength. Figure 9: Effects of PCE compound \(\beta\)-CD and CA on mechanical properties of HBCSA: (**a**) flexural strength and (**b**) compressive strength. The strength of composite component B and \(\beta\)-CD also showed a decreasing trend compared to the blank group, as shown in Figure 10. The strength of the cementitious sand increased with the amount of \(\beta\)-CD, with the highest strength at 0.9% and a strength of 37.4 MPa at 28 d. The results show that the higher the amount of B, the more favorable the development of the strength of HBCSA cement within the dosing range. Based on the development pattern of the strength of HBCSA cementitious sand after the addition of different retarders (except for single admixture B) mentioned above, it can be found that the strength of cementitious sand will decrease substantially in the early stage. Taking Figure 11 as an example, Figure 11a shows the damage interface of the pure high-pelite sulphoaluminate cement mortar sample; it can be clearly seen that the specimen has a dense structure inside the surface at 3 d, with only some tiny holes. In contrast, with the breaking interface between the flexural and compressive breaking of the cementitious sand specimen at 3 d after the addition of 0.3% \(\beta\)-CD to the cement (Figure 11b), it can be seen that the specimen appears to have more holes and a looser structure, and the damage is more severe after the specimen is compressed. As the strength of cement stone is increased by promoting the dissolution of cement and the precipitation of hydration products to accelerate the hydration of the slurry, however, when the retarder is added, the rate of formation of hydration products is slow and inconsistent, the distribution is not uniform, and the bond between the layers is poor when stacked closely, resulting in a loose structure and slow strength development of the cementitious sand specimen. When these retarders have a good retarding effect, they inhibit the hydration of the cement, and the strength at all ages is lower than that of the blank group, meaning that the flexural strength of the cementitious sand decreases sharply.