## 3 Results and Discussion
### Hardened-State Properties of Mortars
#### 3.2.5 Ultrasonic Pulse Velocity  
Ultrasonic pulse velocity (UPV) results at 91 days and 365 days of curing of the mortars are shown in Table 7. In general, an increase in UPV is observed in all mortars with curing time (Figure 7a). This is due to the fact that, as the curing time increases, the hydration products that are generated fill the internal pores of the cementitious matrices [47]. The UPV at 91 days of curing is between 4.2 and 4.5 km/s; these values are within the range (4.0-5.5 km/s) found for binary mortars containing other SCHs: fly ash, <30% [40], silica fume, <40% [48], limestone powder, <20% [49], and ternary mortars containing limestone powder and 20% to 30% of fly ash [18; 50]. Regarding the binary mortars, the incorporation of RC (5-10%) decreases the UPV between 2.5% and 2.8% compared to the conventional \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Physical Property**} \\ \cline{2-9}
**Motar** & \multicolumn{6}{c}{**Dynamic Modulus of Elasticity (GPa)**} & \multicolumn{6}{c}{**Ultrasonic Pulse Velocity (km/s)**} \\ \cline{2-9}  & **91 Days** & **CV 1** & **365 Days** & **CV 1** & **91 Days** & **CV 1** & **365 Days** & **CV 1** \\ \hline RM & 38.0 & 0.6 & 38.3 & 0.5 & 4.5 & 0.2 & 4.7 & 0.1 \\ M-5/0 & 36.2 & 0.4 & 38.0 & 0.8 & 4.4 & 0.3 & 4.6 & 0.1 \\ M-10/0 & 36.1 & 0.1 & 37.8 & 0.7 & 4.4 & 0.8 & 4.6 & 0.4 \\ M-0/10 & 36.6 & 0.6 & 38.1 & 0.4 & 4.4 & 0.5 & 4.6 & 0.2 \\ M-0/20 & 35.2 & 0.8 & 37.7 & 0.3 & 4.3 & 0.5 & 4.5 & 0.2 \\ M-5/10 & 36.8 & 1.0 & 38.3 & 0.8 & 4.4 & 0.4 & 4.7 & 0.2 \\ M-10/20 & 33.7 & 0.9 & 37.5 & 1.1 & 4.2 & 0.2 & 4.5 & 0.1 \\ \hline \hline \multicolumn{9}{c}{**Quantification of synergistic effects**} \\ \hline \hline \multicolumn{9}{c}{**Dynamic modulus of elasticity**} \\ \cline{2-9}
**Age** & \multicolumn{6}{c}{**\(\Delta\) with RC (\%)**} & \multicolumn{6}{c}{**\(\Delta\) with FA (\%)**} & \multicolumn{6}{c}{**\(\Delta\) with RC \(\times\) FA (\%)**} \\ \hline
**91 days** & \(-4.7\) & \(-4.9\) & \(-3.7\) & \(-7.4\) & \(-3.1\) & \(-11.3\) \\
**365 days** & \(-0.8\) & \(-1.4\) & \(-0.6\) & \(-1.6\) & \(-0.1\) & \(-2.1\) \\ \hline \multicolumn{9}{c}{**Ultrasonic pulse velocity**} \\ \cline{2-9}
**Age** & \multicolumn{6}{c}{**\(\Delta\) with RC (\%)**} & \multicolumn{6}{c}{**\(\Delta\) with FA (\%)**} & \multicolumn{6}{c}{**\(\Delta\) with RC \(\times\) FA (\%)**} \\ \hline
**91 days** & \(-2.8\) & \(-2.5\) & \(-2.4\) & \(-3.7\) & \(-1.9\) & \(-6.1\) \\
**365 days** & \(-2.4\) & \(-2.8\) & \(-1.7\) & \(-4.4\) & \(-0.3\) & \(-3.7\) \\ \hline \hline \end{tabular} Note. 1 CV: coefficient of variation in percent (%).  
\end{table} 
Table 7: Non-destructive mechanical and physical properties and the quantification of the synergistic effects of the mortars. Figure 6: Dynamic modulus of elasticity at 91 and 365 days as a function of the square root of the compressive strength (at the same age). mortar, and the use of FA (10-20%) leads to decreases between 2.4% and 3.7%. The simultaneous incorporation of RC and FA results in a reduction of the UPV between 1.9% and 6.9% with respect to the conventional mortar. Regarding the average increase of UPV between 91 days and 365 days of curing (\(\mathrm{UPV}_{91\mathrm{d}\to 365\mathrm{d}}\)), the highest one is found for ternary mortars that jointly incorporate RC and FA (-6.0%), while for the binary mortars with RC or with FA, the increases were circa 3.9%, which is similar to what was observed for the reference mortar (-3.8%). This behaviour is associated with the increased reactivity of FA in the presence of RC, causing the microstructure of ternary mortars (with FA and RC) to become denser compared to their binary counterparts that only incorporate RC or FA. These findings are consistent with the results for compressive strength (Section 3.2.2) and for the dynamic modulus of elasticity (Section 3.2.4), as shown above. Some authors ([51; 52; 53]) consider UPV values greater than 4.5 km/s to denote excellent quality mortars, and values between 3.6 km/s and 4.5 km/s correspond to good quality mortar.