Steel structures are vulnerable to fire due to the degradation of their mechanical properties at high temperatures, making it necessary to protect them when exposed to high temperatures. This paper presents the results of an experimental research work to characterise the mechanical properties of gypsum-based fire-resistant mortars with and without nano and micro silica particles by destructive and non-destructive tests at ambient temperature. Five compositions were studied: one commercial composition was used as a reference and four were developed in the laboratory. Two were based on gypsum with perlite or vermiculite, and the other two included nano and micro silica particles. Twenty specimens underwent ultrasonic pulse velocity, flexural, and compression tests, while five specimens were tested by the impulse excitation of vibration. Young's modulus, shear modulus, and Poisson's ratio were assessed by non-destructive tests, and the flexural and compression strengths were assessed by destructive tests. Additional tests included density and porosity assessments, thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy. Results indicated that adding nano and micro silica particles posed challenges to the mechanical and physical properties. Despite this, vermiculite compositions showcased superior or similar properties to the commercial composition, while perlite compositions exhibited slightly lower properties.
