# Physico-Mechanical Properties of Alkali-Activated Based Composites Using Recycled Fire Fibers
## 3 Results
### Mechanical Properties  
Figures 6 and 7 present the mechanical strength (Rf, and Rc) values for the mortars with siliceous and limestone aggregates (with and without TFs). Figure 5: FESEM micrographs of the selected mortars cured for 7 days at 65 \({}^{\circ}\)C: (**a**) the mortar with siliceous sand and 25% TFs; (**b**) the mortar with limestone sand and 25% TFs; (**c**) the mortar with 100% TFs. Figure 6: Mechanical properties of the mortars with siliceous and limestone aggregates incorporating TFs (0, 15, and 25% replacement by volume): (**a**) flexural strength (Rf) for the mortars cured at 65 \({}^{\circ}\)C; (**b**) compressive strength (Rc) for the mortars cured at 65 \({}^{\circ}\)C.  
In Figure 6, the Rf and Rc of the mortars cured at 65 \({}^{\circ}\)C (1, 3 and 7 curing days) sharply decreased as the amount of TFs increased, and this trend was in accordance with the dry density values. No significant differences for the Rc values were noted between curing days 1 and 7, and their strength value gradually increased or remained until curing day 7. This means that the development of the cementing matrix was optimum after 1 curing day. This behavior was described by [PERSON] [34], who measured the Rc and Rf developments of metakaolin-based mortars cured at 60 \({}^{\circ}\)C and 80 \({}^{\circ}\)C, finding that the mechanical properties were similar for 1, 3, and 7 curing days. [PERSON] et al. [35] also found a similar behavior: these authors measured the Rc values for mortars cured for 24 and 72 h, which were very similar. The same authors demonstrated that the curing at 20 \({}^{\circ}\)C was insufficient to yield Rc values higher than 10 MPa after 24 h curing. Figure 7 summarizes the results for the mortars cured at 20 \({}^{\circ}\)C (7, 28, and 90 curing days). The decrease in both fRf and Rc followed a similar pattern to those cured at 65 \({}^{\circ}\)C, which indicates a loss in mechanical strength as the amount of TFs increased. Figure 8 shows that curing at 20 \({}^{\circ}\)C for 28 days generally yielded better results than curing at 65 \({}^{\circ}\)C for 7 days. This was also observed for the control mortar, which indicates that curing significantly affects the AAC matrix [36]. Aggregate use in the mortars was indifferent to the obtained values, which were similar among the mortars with limestone and siliceous aggregates. The Rc values obtained for the control mortars at both 65 \({}^{\circ}\)C and 20 \({}^{\circ}\)C agreed with the results obtained by other authors, but with similar alkali-activated mortars [29]. Figure 7: Mechanical properties of the mortars with siliceous and limestone aggregates incorporating TFs (0, 15 and 25% replacement by volume): (**a**) flexural strength (Rf) for the mortars cured at 20 \({}^{\circ}\)C, (**b**) compressive strength (Rc) for the mortars cured at 20 \({}^{\circ}\)C.  
Figures 9-11 present the mechanical strength values (Rf and Rc) of the mortars with 100% TFs. Figure 9 shows a decrease in the Rf and Rc of the mortars cured at 65 \({}^{\circ}\)C when the binder quantity was reduced in relation to the TF volume. It generally depicts that the strengths reached at 1 curing day at 65 \({}^{\circ}\)C were similar to those for longer curing ages (3 and 7 days). This behavior means that geopolymeric binding matrix development is optimum for a short curing period, and it is not necessary to prolong the curing process, which reduces the energy use. Moreover, it highlights for the 1/1 composites that the mechanical properties are good for nonstructural purposes (e.g., masonry blocks for non-bearing walls [37]). Hence, the FCC and alkali activator uses are reduced, and consequently, so are the environmental and economic costs of composite production. Figure 8: Comparison of the Rc values of the mortars with siliceous and limestone aggregates cured at 65 \({}^{\circ}\)C for 7 days vs. 20 \({}^{\circ}\)C for 28 days.