*4.3. EDX Analysis*

The analytical method of energy-dispersive X-ray spectroscopy (EDX) was also used to determine the elements (elemental composition) present on any given material sample. In addition, when used in combination with SEM, allows for the analysis of near-surface elements and their amount at different positions providing a map of the sample [25]. Since the glassy layer is the zone directly affected by laser irradiation, this study investigated the changes in the chemical composition of cement-based materials by analyzing two zones, (1) the non-processed zone and (2) the processed zone (glassy layer), as shown in Figure 7. The decrease in calcium and the increase in silicon percentage are the two major changes in the specimens when comparing the chemical composition of the glassy layers and non-processed zones in the CM series, respectively. The most significant change in calcium element was observed in sample CM0.6, where the percentage of calcium element in the non-processed zone was 81.75% and decreased to 39.77% in the processed zone. In addition, at specimen CM0.8, the percentage of silicon element in the non-processed zone

increased from 8.75 to 40.59% in the processed zone. Since the evaporation temperature of calcium is 1484 ◦C and that of silicon is 3265 ◦C, a part of the calcium has evaporated after solidification, which can explain the above-mentioned phenomenon. As a result of calcium evaporation, the percentage of silicon has increased while the percentage of calcium has dropped.

**Figure 7.** Energy dispersive X-ray (EDX) analysis of chemical composition change.

EDX mapping was also exploited to determine the distribution of silicon and calcium composition in non-processed and processed zone. Before the EDX mapping process, the specimens were ground after cross section cutting to achieve a high surface quality. Figure 8 shows the EDX mapping images of 2 main chemical components of silicon and calcium in each sample. The chemical mapping in non-processed zone in each sample shows the distribution of silica sand and cement paste. Meanwhile, the heat effect of laser irradiation generated a glassy layer whose major components were silica sand and cement paste, which was melted and resolidified. As a result, the heat effect of laser irradiation caused the redistribution of the element composition between the processed and non-processed zone. Furthermore, the mixing of silicon and calcium component is the obvious difference between the processed and non-processed zone. Under the direct effect of the laser beam in the processed zone, the sample components which included cement and silica sand were melted and redistributed. Thus, silica sand particles were not found in the processed zone. As can be observed in Figure 8, there is a mixing of silicon and calcium components in the processed zone. In contrast, there is no mixing or redistribution of silicon and calcium components in the non-processed zone. Silica sand particles with silicon as the major component could be detected. In addition, the chemical redistribution is significantly greater in high silica sand proportion samples such as CM0.8 and CM1.5 than in CM0.2 and CM0.4 samples. Furthermore, when comparing the distribution of silicon and calcium, the density of silicon was densely distributed in non-processed zone as the proportion of silica sand increased in high silica sand proportion samples such as CM0.8 and CM1.5.

**Figure 8.** Elemental mapping for Ca and Si on the specimens after the laser scabbling.
