## 3 Results and Discussion
### The Effects of PSA Emulsions on the Mechanical Properties of Modified Mortar  
The mechanical properties of the polymer-modified mortar were characterized based on compressive strength, flexural strength, and the compressive-flexural ratio. The test results in Figure 5 show that for all the PSA emulsions, the compressive strengths of the modified mortars continuously decrease with increasing P/C ratios at different ages and curing methods. When the P/C ratio is 15%, the compressive strength of the modified mortars is nearly 50% lower than that of the blank mortar. Furthermore, there is also a correlation between the compressive strength of the modified mortars and the composition of the PSA emulsions: the compressive strength of the modified mortars is relatively higher for the PSA emulsions with a higher content of the hard monomer St. Comparing the  
Figure 4: The hydration heat release rate of PSA emulsion-modified paste: **(a)** different emulsions with the same dosage; **(b)** SA4 emulsion with different dosages. compressive strengths of the modified mortars at different ages shows that the compressive strength of the blank mortar M0 increases from less than 50 MPa at the curing age of 7 days to about 72 MPa at the curing age of 28 days. For the five types of mortars modified with PSA emulsions, the growth rate of the compressive strength decreases significantly with the increase in the P/C ratio as the curing age increases. In particular, when the P/C ratio is 15%, the increase is less than 10 MPa. This may be due to the following two reasons: (1) The incorporated PSA emulsion replaces part of the cementitious material, and the more emulsion is added, the larger the proportion of the replaced cementitious materials. This leads to a smaller increase in the later strength of the modified mortar. (2) The PSA emulsion hydrolyzes under the alkaline conditions after cement hydration [31], forming carboxyl groups that combine with Ca\({}^{2+}\), thus reducing the generation of other hydration products. Moreover, more hydrolyzed groups are produced and the amount of other hydration products decreases as the dosage of the PSA emulsion increases, resulting in an unobvious increase in the compressive strength. The five PSA emulsions had different effects on the compressive strength of the mortar under different curing conditions. Under mixed curing conditions, the compressive strength of SA5M was approximately 7 MPa higher than under standard curing; in contrast, there was no significant change in the compressive strengths of the modified mortars of the other four PSA emulsions. This is mainly due to the fact that SA5 emulsion has the highest minimum film-forming temperature, which is slightly lower than the mortar curing temperature and is easily affected by the curing method. Mixed curing includes dry curing, which is conducive to the film formation of polymer emulsion. This, in turn, influences the properties of the latex film after it has formed. As a result, different curing methods significantly impact the compressive strength of the modified mortar. However, the minimum film-forming temperatures of the other four types of PSA emulsions are much lower than the curing temperature. Consequently, the influence of different curing methods on their film-forming properties is limited, and thus the impact on their compressive strength is also limited. The curves of the variations in flexural strength with P/C of the modified mortars with PSA emulsions are shown in Figure 6. For the five types of PSA emulsions, the flexural strengths of the modified mortars produced for different periods under different curing conditions decrease with increasing P/C ratios. This may be because the content of BA in the PSA emulsion is too high, resulting in excessive chemical reactions during cement hydration and leading to a decrease in strength. There is no obvious relationship between the flexural strength of the mortars modified with different PSA emulsions and the composition of the PSA emulsions.