*3.2. Density*

The density of the samples was measured, and the results are demonstrated in Figure 7. The measurement revealed the density of 2354, 1769, and 987 kg/m<sup>3</sup> for C.S, E50, and E100 respectively. It shows the density of E50 and E100 decreased 30% and 65% respectively in comparison to the CS, which is attributed to the very low density of EGA and its porous structure. In addition, the densities of CT, E50T, and E100T were 2%, 3%, and 6% higher than CS, E50, and E100 respectively. It can be concluded that the increase in density was attributed to the lower porosity in the cement matrix due to the incorporation of nTiO2. It is noteworthy that E100 with density of 987 kg/m<sup>3</sup> was classified as a lightweight mortar that can be used for production of lightweight concrete. Figure 8 illustrates the cross section of CS and E100 samples.

**Figure 7.** Density and water absorption of mix specimens.

## *3.3. Water Absorption*

The water absorption test was completed on all mixes and the results are shown in Figure 7. The water absorption of 4.19% obtained for control sample (CS) however a higher water absorption rate was obtained for the mixes containing EGA. The water absorption of E50 and E100 mixes were 7.47% and 14.74% respectively, which shows a 78% and 252% increase in the permeability of the matrix, compared to the control sample. The increase in water absorption is due to the high porosity of EGA in comparison to NA. The results revealed that the water penetration increased by increasing the EGA content. The water absorption rate obtained for the E100 (values of approximately 14%) was higher than the acceptable range (<10%) [43,44]. The addition of nTiO2 reduced the water absorption value by 28%, 17%, and 2% for samples containing 0%, 50%, and 100% EGA respectively. The decrease in water absorption upon the inclusion of nTiO2 coincides with previous studies [45] and aligns with the density results. The reduction in water absorption was attributed to the filling effect of nTiO2 and reducing the porosity of the cement matrix. It is worthy to note that the sonication process resulted in tiny bubbles of air uniformly distributed in the mortar. These small bubbles are like entraining air that improves the workability of the mixes. Indeed, nTiO2 acted as nanofillers in mortar and improved the resistance to water penetration of the cement composite [46].

**Figure 8.** Cross-section of (**a**) the control sample (CS) and (**b**) E100 mixtures samples with uniform distribution of EGA in the cement matrix.
