# Microstructure and Mechanical Properties of Cement Mortar Containing Phase Change Materials
## 3 Results and Discussion
### Semi-Adiabatic Temperature Rise Test  
Figure 10 shows the history of the simple adiabatic temperature rise that is due to the mixing ratios of the OPC and PCMs. Figure 10a shows the experimental results for the cement mortar with PCM-Ba. As the PCM content increased by 3%\(\sim\)5%, the maximum hydration heat generation point was induced and the maximum temperature rise decreased. However, when 10%-15% PCM-Ba is mixed in, the PCM-Ba shows a similar tendency to the OPC and only the maximum temperature decreased. Figure 10b shows the temperature history of the cement mortar with PCM-Sr. For the PCM-Sr mixtures, the hydration heating rate decreased and the maximum hydration heat generation point decreased more obviously compared with the OPC. Specifically, the maximum hydration heat rate is slower than 3% at the mix ratio of 5% to 15%. This outcome indicates that the added PCM-Sr is not consumed. In the case of PCM-Sr, more than 3% addition is not likely to have a significant effect in reducing the hydration heat.  
Figure 11 shows the maximum temperature rise and development time according to the type of PCM and mixing percentage. The hydration heat reduction effect is 16.6% at the mix ratio of 3% PCM-Ba. As the mixing percentage increases, the hydration heat reduction percentages of 19.2%, 19.7%, and 20% are evident at mixing percentages of 5%, 10%, and 15%, respectively. The maximum temperature rise is shown to decrease according to the amount of the mixture with PCM-Ba, but the difference of maximum temperature rise is negligible. Therefore, the effective mix percentage for hydration heat reduction is less than 5% addition of PCM-Ba.  
The maximal temperature development time for 3% and 5% PCM-Ba shows hydration delays of 1.57 and 1.36 times, respectively, whereas the maximum temperature development times for the  
Figure 10: Effects of addition mix ratio of PCM on semi-adiabatic temperature rise—(a) cement mortar with PCM-Ba; (b) cement mortar with PCM-Sr.  
Figure 9: Effects of addition mixing ratio of PCM on compressive strength—(a) PCM-Ba; (b) PCM-Sr.  
mixing ratios of 10% and 15% show hydration delays of 0.86 and 0.79, respectively, which are faster results than for OPC. Therefore, the effective mixing rate for hydration heat reduction is less than 5% addition of PCM-Sr, which is based on the results of the maximum temperature rise tests and development time.  
When PCM-Sr is used, the mixing ratios of 3%, 5%, 10%, and 15% are reduced by 23.7%, 20%, 20.2%, and 21.5%, respectively, resulting in a higher hydration heat reduction rate compared to PCM-Br. However, unlike PCM-Ba, which shows a sequential decrease in hydration heat as the mixing percentage increases, 5% to 15% excluding 3% PCM-Sr decreases the reduction in hydration heat.  
When PCM-Sr is used, the maximum temperature expression time shows sequential hydration delays up to 1.6 times from the mix percentages of 3% to 15%. When the mix ratio is over 10%, the difference in delaying effects is insignificant. Therefore, considering the maximum temperature rise and the expression time, the effective mix ratio of PCM-Sr to reduce hydration heat is to be up to 3%. In short, the use of PCM-Ba is effective in reducing hydration heat and the use of PCM-Sr is effective in delaying hydration.