## 5 Conclusions  
The need to strengthen a vast number of existing masonry structures that are frequently under the effect of dynamic actions determine the importance of studying metrics that allow us to assess the performance of FRMs used as strengthening overlays. These metrics cannot be limited to maximum resistance or deformability; instead, they must be oriented to distinguish materials with a higher energy dissipation capacity.  
In this work, a new NHL-FRM material was developed to be used as an economically and environmentally sustainable strengthening overlay. The use of metrics geared towards the assessment of toughness and ductility led to the identification of a material that is compatible with the application and meets its requirements.  
The main conclusions from this study are as follows:  
* The inclusion of PAN fibres in an NHL matrix changed the fresh and hardened behaviour of the mortar, even with minimal fibre addition of 0.25%.
* A fibre content of 1.00% resulted in deficient workability for overlay application. Utilizing admixtures like superplasticizers may enhance workability without compromising mechanical properties.
* The target values of compressive strength at 28 days, 10 \(<f_{c}<\) 15 MPa, were achieved for F0.50 \(\_\)RH60 and F0.75 \(\_\)RH60 and for all mortars cured at RH85.  
Figure 23: Flexural strength vs. flexural toughness ratio from FRM [28; 30; 32; 34; 35; 36; 37; 38; 40; 41].  
* The flexural strength target values, \(5<f_{\_}{\_}{\textit{ff,tl}}<7.5\) MPa, were achieved for F0.75_RH85, F1.00_RH60 and F1.00_RH85.
* The compressive and flexural toughness of the FRM substantially increase with the adding of fibres. There was an important variation in the capacity to dissipate energy, even for lower amounts as 0.25%; this capacity was maximized at 1.00% of fibres.
* The correlation between the mechanical properties in compression and flexure and the respective toughness ratios showed opposite trends. While the toughness ratio in compression increased for lower compressive strength values, the toughness ratio in flexure increased for higher flexural strength values.  
Both the developed NHL-FRM with PAN fibres and the mechanical assessment approach used can be advantageous for overlay strengthening design and application in masonry elements, with the possibility of achieving interesting mechanical performances as well as good compatibility and sustainable formulations.  
Conceptualization, J.A.P.P.A., E.N.B.P. and J.A.O.B.; methodology, J.A.P.P.A., E.N.B.P. and J.A.O.B.; formal analysis, J.A.P.P.A. and E.N.B.P.; investigation, J.A.P.P.A.; resources, E.N.B.P. and J.A.O.B.; Writing--Original draft, J.A.P.P.A.; writing--review and editing, J.A.P.P.A., E.N.B.P. and J.A.O.B.; supervision, E.N.B.P. and J.A.O.B.; project administration, E.N.B.P.; funding acquisition, E.N.B.P. All authors have read and agreed to the published version of the manuscript.  
Not applicable.  
The data presented in this study are available from the corresponding author, J.A.P.P.A., upon reasonable request.  
The authors are very grateful to the companies SECIL and EUROCALCIO for the material provided.  
The authors declare no conflicts of interest.