## 3 Results
### Compressive Strength  
Figure 4 shows the values for the average compressive strength of the polysulfide polymer concrete specimens at various curing times. From the figure, it can be seen that the compressive strength of polysulfide polymer concrete increases continuously with curing time. In particular, the compressive strength increases drastically within the first 24 h, beyond which it continues to increase gradually. To analyze the strength development characteristics of polysulfide polymer concrete in detail, the rates of development of compressive strength were evaluated based on the compressive strength at 672 h (i.e., 28 days, which is considered the standard time for complete development of the compressive strength of cement concrete). The evaluation results showed that approximately 27% of the compressive strength of polysulfide polymer concrete at 672 h is developed after 6 h of hardening. In contrast, approximately 70% and 80% of the compressive strengths at 672 h are developed after 24 h (1 day) and 168 h (7 days), respectively. These results indicate a more rapid development of strength than that exhibited by cement concrete, in which 20% and 80% of its compressive strength develops after 24 h (1 day) and 336 h (14 days), respectively [34]. Rapid hardening of materials used in the construction of bridges and buildings can allow structural members to resist the large stresses induced by traffic and work operations after a shorter interval of time. Because of the short hardening time of polysulfide polymer concrete, it can be applied to structural members at nighttime and the members can be strong enough to handle traffic flow the next day. Note that, as shown in Figure 4, the compressive strength of the polysulfide polymer concrete used in this study complies with the value, over 34 MPa within 24 h and over 7 MPa within 3 h, recommended in the ACI 548.9 guideline [35]. Figure 5 shows the development of the compressive strength of polysulfide polymer concrete at various curing temperatures. This figure illustrates that the compressive strength of the concrete is strongly dependent on the curing temperature. The lower the curing temperature, the higher the compressive strength, and vice versa. Such a correlation between the curing temperature and compressive strength is not observed for cement concrete, in which the compressive strength decreases with either increasing or decreasing curing temperature from an optimum temperature somewhere in between extremes [29]. Notably, curing cement concrete at temperatures below \(-4\)\({}^{\circ}\)C or above 25 \({}^{\circ}\)C is absolutely prohibited in concrete buildings [36] because outside of this temperature envelope the development of compressive strength is either too slow or too fast; as a result, the final strength is considerably lower than the design strength. However, in the case of the polysulfide polymer concrete used in this  
Figure 4: Effect of curing time on average compressive strength. study, the specimen cured at \(-10\)\({}^{\circ}\)C exhibited the highest compressive strength of all of the specimens cured at various temperatures. This phenomenon can be theorized to be caused by the rate of chemical reaction of the polymer concrete. The chemical reaction of polymer concrete progresses slowly in the beginning stages of curing, but continues more rapidly in the later stages, so it was found to have the maximum final strength at a sub-zero curing temperature. This behavior has been confirmed in previous research by others as well [37]. The behavior of the polysulfide concrete used in this study confirms the above fact that even below the freezing temperature, continuous chemical reactions occur in polymer concrete, leading to the development of compressive strength. Interestingly, a higher curing temperature has a positive effect on the initial strength of polymer concrete by increasing the rate of the chemical reactions, but it has a negative effect on the final strength.