## 4 Discussion of Results
### Flexural Behaviour  
The flexural responses obtained were adjusted to exclude the initial deformation for small loads due to the accommodation of the loading device and the supports. The approach used is schematically represented in Figure 10 and allowed us to acquire more realistic values by disregarding the initial parasitic deflections [37; 56]. After the occurrence of the first crack, the onset of matrix cracking, the load-deflection curve deviates from linearity; for plain mortar, the load-deflection curve drops suddenly, leading to failure. In the case of an FRM, the addition of fibres significantly influences the composite's behaviour after cracking, leading to deflection-softening (load decay with the increase in deflection), or alternatively to deflection-hardening (load increases with the deflection) [19; 57].  
Figure 9: Compressive behaviour of mixtures in two different curing environments: (**a**) compressive strength; (**b**) elastic modulus.  
After adjusting all flexural stress vs. deflection responses, representative curves for each fibre fraction were selected and are plotted in Figure 11a,b. The effect of adding fibres to the matrix is clear, even for 0.25% of fibres. By increasing the fibre fraction, the toughness of the material gradually increases and the flexural response gradually shifts from a typically brittle fracture to a deflection-softening response for lower fibre fractions, and a deflection-hardening response for higher fibre volume fractions.  
Figure 11: \(Cont.\)  
Figure 10: Schematic representation of the flexural response and approach adopted to correct the experimental setup adjustments during loading [37].  
The values of the modulus of rupture (_MOR_), and of the limit of proportionality (_LOP_) were computed according to the RILEM Technical Committee 49 TFR [58] recommendations:  
\[MOR=\frac{3F_{max}L}{2 bd^{2}} \tag{2}\]  
\[LOP=\frac{3F_{crack}L}{2 bd^{2}} \tag{3}\]  
These are plotted against the fibre volume fraction in Figure 12a,b, respectively. The _MOR_ was obtained from the maximum load, \(F_{max}\), and the _LOP_ by finding the load at which the first non-linearity is observed in the force-deflection relationship, \(F_{crack}\), see Figure 10.  
Figure 11: Typical flexural stress vs. displacement responses obtained from flexure tests: (**a**) specimens cured in 60% RH; (**b**) specimens cured at 85% RH.  
Figure 12: RH 60 and 85% curing conditions: (**a**) modulus of rupture; (**b**) limit of proportionality.  
The values of the \(MOR\) and \(LOP\) obtained for both curing environments show a clear increasing trend with the fibre volume fraction. The specimens cured at 85% RH showed, for all fibre fractions, a higher MOR. Regarding the \(LOP\), no clear trend was observed, and for the higher amounts of fibres, 0.75 and 1.00%, the \(LOP\) values obtained for 85% RH were lower or similar to the ones obtained for 60% RH. The increase in \(LOP\) with the fibre fraction indicates that fibre reinforcement started contributing for the flexural capacity of the mortar at a very early stage of the micro-cracking propagation. As expected, the influence of fibre fraction was more pronounced on the increase in \(MOR\), since at this load level, meso-cracks are already formed, being the fibres crossing these cracks which are more active in arresting their propagation.