## 4 Conclusions  
The aim of this paper was to conduct a comprehensive mechanical characterisation of gypsum-based mortars designed for passive fire protection. Testing involved five distinct compositions, including one commercially available variant, to assess the impact of varying binder and aggregate quantities, as well as the introduction of nano and micro silica particles, on mortar mechanical behaviour through both non-destructive and destructive tests. Additionally, physical characterisation tests were conducted on the specimens. The following encouraging conclusions emerged from this study:  
* Non-destructive testing revealed that the developed mortars exhibited uniform and homogeneous matrices;
* It was observed that higher binder dosages and lower aggregate dosages led to increased velocities/frequencies in non-destructive tests, correlating with higher mechanical strength and improved physical properties;
* The addition of short amounts of nano and micro silica particles in the mortars posed challenges to the mechanical and physical properties of such mortars;
* Compositions incorporating vermiculite demonstrated superior or comparable mechanical properties to the commercial composition, underscoring the potential for innovative material formulations. Conversely, compositions featuring perlite exhibited slightly lower mechanical properties compared to the commercial variant, yet this observation presents an opportunity for further optimisation;
* Notably, the study found a strong correlation between the mechanical properties studied (flexural and compression strength) and the physical properties (Young's modulus of elasticity and shear modulus) of the developed mortars, indicating robust material performance;
* These insights highlight the potential for continued advancements in mortar development for enhanced fire protection, paving the way for more resilient and reliable construction materials in the future. Based on the results obtained and given that compositions with different types of aggregates were used, further experimental tests will be conducted, taking into consideration the following parameters: (i) examining the distribution and dispersion of nano and micro silica particles within the gypsum paste; (ii) testing different water-to-binder (W/B) ratios to optimise both the hydration process and the mechanical strength of the mortar; (iii) assessing the compatibility and reactivity of these nano and micro silica particles with gypsum; and (iv) evaluating the effectiveness of various methods for incorporating the nano and micro silica particles into gypsum mortars. Conception and design of the study: H.C., L.V., A.R., A.S. and L.L. ; Acquisition of data: H.C., L.V., A.R. and E.M. Analysis and/or interpretation of data: H.C., L.V., A.R., A.S., L.L. and E.M. Drafting the manuscript: H.C. and E.M. Revising the manuscript: L.V., A.R., A.S. and L.L. Project administration and Funding acquisition, A.S. All authors have read and agreed to the published version of the manuscript. PTDC/ECI-EGC/31850/2017 (NANOFIRE-Thermal and Mechanical behaviour of Nano Cements and their application in steel construction as fire protection). FCT/MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB/04029/2020 ([[https://doi.org/10.54499/UIDB/04029/2020](https://doi.org/10.54499/UIDB/04029/2020)]([https://doi.org/10.54499/UIDB/04029/2020](https://doi.org/10.54499/UIDB/04029/2020))), and under the Associate Laboratory Advanced Production and Intelligent Systems ARISE under reference LA/P/0112/2020. Not applicable. The data presented in this study are available upon request from the corresponding author due to further ongoing studies.