## 3 Results and Discussion
### Concrete Environmental Performance Comparison  
Considering the analysis of environmental impact for 1 m\({}^{3}\) of a manufactured hollow-core slab, a reduction in the environmental impact with partial cement replacement was achieved for all LCIA methodologies evaluated (Figure 14). Additionally, the maintenance or the increase in the concrete compressive strength in the samples tested was noted. Figure 13: Environmental impact per 1 kg of material: (**A**) global warming potential (GWP) indicator; (**B**) cumulative energy demand; (**C**) total environmental impact (IMPACT 2002+). [PERSON] et al. [25] evaluated glass waste in concrete as a partial replacement for cement and its environmental impact. They identified that, as the strength of the concrete increased, the environmental impact increased, contrary to what was identified in the present research. On the other hand, [PERSON] et al. [26] identified that the incorporation of glass waste was environmentally advantageous, including impacts similar to the glass recycling process. In research by [PERSON] et al. [25], for the analysis of conventional concrete (310 kg/m\({}^{3}\) of cement) an impact of 290 kg CO\({}_{2}\) eq. was found. The authors also considered glass waste of 20% replacement (62 kg/m\({}^{3}\)), which resulted in 260 kg CO\({}_{2}\) eq. In the present contribution, the conventional concrete uses 302.85 kg/m\({}^{3}\) of cement, totaling 475 kg CO\({}_{2}\) eq (Figure 14A), and with the replacement of 20% of the total cement by glass powder (49.57 kg/m\({}^{3}\)), the total is 414 kg CO\({}_{2}\) eq. According to [PERSON] et al. [25], concrete with the addition of glass waste reduced 0.48 kg CO\({}_{2}\) eq for each kg of waste incorporated into the material as pozzolanic material. This research, however, showed that the environmental gain in global warming potential can reach 1.23 kg CO\({}_{2}\) eq. Using the same methodology for energy use, [PERSON] et al. [25] reported 3.23 MJ saved with each kilogram of glass waste used to make concrete, while this study found around 8 MJ (Figure 14B). Therefore, with the use of the glass powder, gains related to the reduction in the emission of potential gases for GWP and reduction in EE were noted. Regarding the total impact (Figure 14C), it was found that the most expressive impact for the manufacture of 1 m\({}^{3}\) of the slab was damage to human health. Additionally, replacing cement by the waste up to 20%, either considering the milling or without this additional step, produced equivalent reductions. The milled residue, however, had better performance regarding its mechanical properties. It is also important to highlight that resistance to compression was maintained after 20% cement substitution with glass waste powder after 28 days. After 56 and 91 days, the mixture with 20% ground glass powder (GP2-20) had results slightly higher than those of the control mixture. These results can be explained by the physical effect of pore-filling, where the empty pores left by the cement paste are filled by the glass particles, reducing  
Figure 14: Compression strength versus environmental impact: (**A**) GWP; (**B**) embodied energy (EE); (**C**) total impact indicator (TI). the porosity and contributing to the retention of the mixture water, enhancing the cement hydration process. Another process that may have contributed to the compressive strength gain was the possible pozzolanic effect of the glass waste. This possible chemical reaction between the glass powder and the cement (due to the formation of more stable compounds, such as the production of C-S-H originated from the reaction of calcium hydroxide and water) diminished the empty spaces in the transition zone between the paste and the aggregates [17; 18]. Additionally, chloride penetration resistance was also evaluated (Figure 15). The ASTM C 1202 [41] test was adopted in which the results indicated that after 28 days, with a 20% cement replacement, moderate chloride penetration was found.