## 4 Discussion of Results  
### Compressive Behaviour  
The compressive behaviour of representative specimens cured for 28 days in a climatic chamber at 20 \({}^{\circ}\)C and 60% RH and 85% RH is shown in Figure 8a,b, respectively, were the average axial compressive strain is the average displacement of the three LVDTs divided by the length of the specimen. The initial slope of the compressive stress--strain responses, as expected, was marginally influenced by the addition of fibres, showing essentially  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & \multicolumn{8}{c}{**RH85\_20**} & \multicolumn{8}{c}{**RH60\_20\_28**} \\ \cline{2-10}  & \multicolumn{3}{c}{**7 Days**} & \multicolumn{3}{c}{**28 Days**} & \multicolumn{3}{c}{**90 Days**} & \multicolumn{3}{c}{**28 Days**} & \multicolumn{3}{c}{**90 Days**} \\ \cline{2-10}  & \(f\) & \(d_{f,max}\) & \(f\) & \(d_{f,max}\) & \(f\) & \(d_{f,max}\) & \(f\) & \(d_{f,max}\) & \(f\) & \(d_{f,max}\) \\
**Specimen** & **MPa (\%)** & **mm (\%)** & **MPa (\%)** & **mm (\%)** & **MPa (\%)** & **mm (\%)** & **MPa (\%)** & **mm (\%)** & **MPa (\%)** & **mm (\%)** \\ \hline R\_01 & 2.02 & 0.16 & 2.78 & 0.12 & 3.91 & 0.12 & 2.02 & 0.16 & 2.49 & 0.17 \\ R\_02 & 2.02 & 0.15 & 3.18 & 0.19 & 4.19 & 0.13 & 2.02 & 0.15 & 2.21 & 0.12 \\ R\_03 & 2.57 & 0.18 & 3.25 & 0.18 & 3.5 & 0.11 &similar slopes for different fibre fractions. However, the peak stress and the post-peak behaviour of the mixtures were clearly influenced by the fibre content. The peak stress presented the tendency to increase for lower fibre fractions and to decrease when higher fibre fractions were used, while the post peak behaviour improved for higher fibre fractions. These changes suggest that the increase in the fibre fraction led to the expected increase in ductility and the ability to dissipate energy after cracking, due to the contribution of the PAN fibres to restrain crack propagation. However, above a certain limit, higher fibre fractions may have contributed to the reduction in the solid skeleton compactness and strength, along with the reduction in workability.  
Figure 8: Typical compressive stress vs. average axial compressive strain responses obtained for mortars with different fibre fractions: (**a**) specimens cured in 60% RH; (**b**) specimens cured at 85% RH.  
Figure 9 shows the main results obtained for the compressive strength at 28 days of curing after casting, for both curing environments. The specimens cured at 85% RH show, in all cases, higher compressive strength than the ones obtained for specimens cured at 60% RH; see Figure 9a. The compressive strength shows a small variation, with the increase in the fibre content for both curing conditions. In the case of 85% RH, the maximum compressive strength was achieved for a fibre fraction of 0.25%, and at 60% RH the maximum compressive strength was achieved for a fibre fraction of 0.50%. This variation would not occur in the case of Portland cement FRM, as concluded by [PERSON] et al. [54] by studying the pore morphology of mortars in different curing conditions. However, in the case of NHL-FRM, the binder's hardening is influenced by hydration reactions and additional carbonation reactions [55]. For NHL 5.0 from Secil, Table 1 shows that there is a minimum of 15% free line available for carbonation reaction. The availability of free lime simultaneously with higher porosity and favourable curing conditions, 60% RH in a ventilated climatic chamber, may justify the slight increase in the strength due to carbonation.  
The same trend can be observed for the elastic modulus, as shown in Figure 9b. The values of the elastic modulus and compressive strength are in accordance with the ones expected for an NHL mortar.