# Internal Curing Effect of Waste Glass Beads on High-Strength Cement Composites
## 3 Results and Discussion
### Cross-Sectional Analysis of Specimens  
Figure 10 shows the cross-section of a specimen mixed with WGBs at the age of 56 d, confirming the distribution of WGBs inside the specimen and the moisture inside WGBs. For S20, numerous white products were formed inside WGBs. These products were heterogeneous substances with gel-like aggregates. Some WGBs still had residual moisture, which could be confirmed with the naked eye. WGB pores were filled with hydrates by the moisture captured in WGBs. SEM analysis confirmed internal voids; a large amount of C-S-H gel was formed on the pore surface. For R20, moisture was confirmed to remain inside WGBs when the cross-section of the specimen was visually checked.  
Figure 9: Thermodynamic modeling of samples: (**a**) S20 and (**b**) R20 specimens.  
SEM and SEM-EDS analyses of WGBs confirmed that the intensity of the spectrum was lower than that for S20. These results were similar to those of thermodynamic modeling. Thermodynamic modeling confirmed the hydration tendency of paste except in the case of WGB; however, even in the case of WGB, hydration tendency can be considered similar to that inside the pores of paste and WGBs connected by micropores. In addition, when steam curing was performed and when the absorbed water in WGB was mixed, the hydration tendency inside WGB was higher. Therefore, microstructure hydration could be improved by combining the mixing of captured WGBs and steam curing to effectively improve the internal curing of HSCs. In addition, this trend was confirmed by the tendency for forming hydrates in pores similar to that of [PERSON] et al. and [PERSON] et al. [58; 59]. [PERSON] et al. identified the hydrate form and content level through SEM-EDS, which was similar to that found around R20 WGB analyzed in this study. S20 has high silica (Si) and the calcium (Ca), magnesia (Mg), and alumina (Al) contents are up to 3-fold higher than that in R20. It was found that there was a difference in the amount of hydrate formed in the surface pores of WGB as hydration was promoted by steam curing. A study by [PERSON] et al. confirmed the formation of abundant hydration products in the vicinity of LWA due to water released from LWA. This study found that the analysis results of the formation of hydrates generated around WGB and surface voids were similar to the results of thermodynamic modeling analyzed in Section 3.6. Accordingly, the curing water released by the WGB promotes hydration of the cement particles around it and makes the particle spacing denser.  
The experimental results of this study revealed that WGBs used in HSCs could improve internal hydration reactions. The curing method for HSCs mixed with WGBs was demonstrated to affect the number of hydration products based on age, which may also influence the extent of strength development. In the case of steam curing, strength development and internal hydrate formation levels at early ages were almost twice that of room temperature curing at the age of 56 d. Even after completing steam curing, the proportion of unreacted silica inside was partially reduced, and the internal moisture content was maintained at a certain level by pre-wetted WGBs. Therefore, WGBs could contribute to reducing unreacted hydrates inside HSCs.  
Figure 10: Cross sections of test specimens mixed with WGBs that confirm the state of the moisture trapped inside WGBs: (**a**) S20; and (**b**) R20 specimens.