## 4 Results and Discussion  
### Results of the Laboratory Experiments  
#### 4.1.1 Results of the Flexural Strength Test  
Figure 6 shows the FS values of mortar samples containing different WGP substituting ratios without adding chemical agents at 7, 14, and 28 days. Lower FS was observed in specimens containing 300 \(\upmu\)m WGP, which agrees with previous findings that coarse glass adversely affected mechanical characteristics [1,57]. In contrast, the mortar specimens containing 75 \(\upmu\)m WGP exhibited improved FS, compared to both 300 \(\upmu\)m WGP samples and the control one. This phenomenon illustrates the positive effect of mechanical activation in increasing FS. The 10% 75 \(\upmu\)m WG proportion showed the highest strength at 9.7 MPa (28 days), which was 26.63% higher than that of the control sample. Moreover, the FS of the sample containing 30% 75 \(\upmu\)m WGP was 7.6 MPa, which almost reached the same strength level as the ordinary mortar sample. This is mainly attributed to the bonding strength arising from WGP's pozzolanic reaction [11,58,59]. When glass's particle granularity shrank through physical grinding, its stable silica tetrahedron structure would be destroyed, leading to reduced crystallisation and increased reactivity. Meanwhile, the finer WGP had a larger specific surface area and simultaneously compacted the mortar structure through evenly distributed in the pores of the mortar. Therefore, it is effective to increase the FS of WGP mortars by applying a mechanical approach. Figure 7 compares the 28-day FS results of the mortar samples containing 300 \(\upmu\)m and 75 \(\upmu\)m WGP (10%, 20%, and 30%) under the chemical activation. When the WGP particle size was 300 \(\upmu\)m, the FS increase was only observed in samples containing activated WGP (2% Na\({}_{2}\)SO\({}_{4}\) and 2% alkali), compared to mortars with nonactivated WGP. Meanwhile, the FS in all the 300 \(\upmu\)m WGP mortars was less than that in the control sample, illustrating the limited chemical activation effect on coarse glass particles. The opposite phenomenon was observed when the WGP size was mechanically ground into 75 \(\upmu\)m. Figure 7c shows the highest FS value (around 9 MPa) on the mortar sample with 30% WGP (75 \(\upmu\)m) under the treatment of 2% Na\({}_{2}\)SO\({}_{4}\) and 2% alkali. It was both higher than the 30% nonactivated WGP sample (7.60 MPa) and the normal sample (7.66 MPa), indicating the positive efficacy of the  
mechanical-chemical activation. However, the FS was reduced provided that the 75 \(\upmu\)m activated WGP content was 10%, as shown in Figure 7a. This is mainly due to the excessive ASR expansion that exceeded the ASTM threshold (0.1%) shown in following chapters. The Na\({}_{2}\)SO\({}_{4}\) and alkali effect on the WGP-cement system is analogous to that on fly ash-cement system considering the slow pozzolanic reaction and similar chemical constituents for WGP and fly ash. According to the previous findings, the Na\({}_{2}\)SO\({}_{4}\) reacts with Ca(OH)\({}_{2}\) to generate gypsum and NaOH [60; 61]. The gypsum further reacts with the aluminate in cement to generate ettrinigite (AFt), and NaOH participates in the reaction with Ca(OH)\({}_{2}\) and WGP (or fly ash) to produce the additional gels [62; 63]. This results in more hydration products compacting the WGP mortar structure and improving the flexural strength. In addition, the Alite (C\({}_{3}\)S) hydration has been verified to be accelerated under the high concentration of dissolved sulphate ions [60]. Therefore, more calcium silicate hydrates and calcium hydroxide will be generated to further increase mechanical strength. Regarding the alkali (NaOH and Ca(OH)\({}_{2}\)) effect, it has been verified to effectively depolymerise WGP structure by destroying the chemical bond between the oxygen atom and silicon [64; 65]. Therefore, the WGP stable Silica tetrahedron units can be broken to accelerate the silica dissolution and WGP pozzolanic reaction, as illustrated by many researchers [66; 67].