Waste into Construction Materials: Geopolymers from Recycled Sources

Summary

2.1. Chemical Resistance TestsWater, acid, and alkali resistance are important durability properties in construction materials [9,10], and their effects were investigated in this research work. Table 1 presents the weight loss for each sample, including commercial Portland cement, following immersion in tap water, 0.1 M HCl, and 0.1 M NaOH. At the same time, Figure 1 illustrates the average sample mass after immersion, normalized to the average initial mass (see Figure S1 for the average absolute masses).Sample 6, comprising 50 wt% of brick waste (B) and 20 wt% cement waste (C) geopolymerized with glass-derived silicate, exhibits the lowest weight loss (0.12%) in tap water immersion, indicating the highest resistance among the tested samples. In contrast, Sample 7, which has the same composition but is geopolymerized with commercial silica, shows the highest weight loss (0.30%) in water, indicating the lowest resistance. Portland cement displays a weight loss of 0.26%, comparable to most geopolymeric samples, except Sample 6, which outperforms it.In HCl, Sample 6 demonstrates the highest resistance, with a weight loss of 1.18%. Sample 3, produced from brick waste geopolymerized with commercial silica, exhibits the highest weight loss (2.96%) in this environment, indicating the greatest vulnerability to acidic conditions. Portland cement showed a weight loss of 2.66%, higher than most geopolymer samples except Sample 3, suggesting greater susceptibility to acid attack than the other geopolymeric materials. In fact, the orange coloring in Figure 2 indicates the formation of iron(III) oxide at the specimen surface, which may be attributed to the surface migration of Fe(III) ions from the tetracalcium aluminoferrite within the Portland cement clinker.Sample 6 again exhibits the lowest weight loss (1.11%) in NaOH, indicating strong resistance to alkali exposure. Conversely, Sample 3 shows the highest weight loss in NaOH (1.92%), consistent with its behavior in HCl, sugge...