# Development of Passive Fire Protection Mortars
## 1 Introduction  
There is a growing interest in developing alternative and sustainable construction materials with enhanced properties. As metals are infinitely recyclable, this type of construction is part of a future of \"green construction\", thus contributing to a sector of the economy with low environmental impact [1; 2; 3]. However, steel structures show some weaknesses, especially their structural behaviour when subjected to fire [4; 5; 6; 7; 8; 9]. Due to the high thermal conductivity of the steel, the high section factor of the members, and the rapid degradation of the steel mechanical properties, with the increase of steel temperature, rapid change in the stiffness and mechanical resistance may be noticed in the structure. Its resistance and stability may be compromised, leading to the collapse of some elements or even of the entire structure [10; 11; 12; 13; 14; 15]. The thermal protection of these structural elements is crucial. The fire protection of structures can be achieved by combining active and passive fire protection systems and management systems (smoke exhaust systems, communication and evacuation procedures, fire detection systems, and compartmentation [16]). Active fire protection can consist of systems or items such as fire extinguishers, standpipes, sprinkler systems, and fire blankets [17]. It is required that these systems have a quick response capacity in extinguishing or controlling the development of a fire in its initial phase [18]. However, implementing these systems has high installation and maintenance costs, and their results can have low functional reliability and unsatisfactory operational results [19]. In turn, when applying passive protection, it is almost sure that it will be operational during a fire event. Passive systems include the fire resistance of structural or nonstructural members of a building, such as columns, beams, walls, and ceilings. This purpose ensures adequate evacuation times, minimum safety conditions for firefighting and rescue operations and minimises property, economic, and life losses [20]. The most common method to protect a member from exposure to extreme temperatures is to apply insulation materials around the structural members. Insulation materials used as fire protection in structural steel members can be: board systems (gypsum board or calcium silicate), insulating blankets (ceramic, rock, and glass wool), spray systems, or intumescent coatings [21]. These materials should be cheaper than the steelwork, easy of application, safe (i.e., not be hazardous during the application and in service, or toxic in the event of fire), and should insulate and remain undamaged during the fire attack (with limited detachments and fractures during the required fire resistance) [22]. One solution that meets these protection requirements is the coating with enhanced fire-resistant mortars due to the introduction of nanosilica particles and thermally stable and porous aggregates [23]. With the emergence of nanomaterials (silica nanoparticles, titanium dioxide nanoparticles, alumina nanoparticles, and carbon nanotubes, etc. ), their incorporation in pastes, mortars, and other cement-based materials has appeared as a possibility to improve their mechanical and thermal properties: higher durability, better resistance to corrosion and better fire resistance [24; 25; 26; 27; 28], with the silica nanoparticles being the most studied nanomaterial in cement [26]. However, little attention has been given to other properties, such as thermal conductivity at elevated temperatures [29]. When subjected to high temperatures, perlite and vermiculite have been incorporated in cement mortars to improve their thermal performance [30]. Perlite consists of a siliceous volcanic rock with 2% to 6% water combined. However, when small perlite grains are subjected to high temperatures (870 \({}^{\circ}\)C), they strongly increase their volume with numerous tiny, sealed air cells, like popcorn giving rise to lightweight expanded perlite.