Effect of nanoclay and conventional flame retardants on asphalt mixtures fire reaction

Fires in highway tunnels produce high temperatures, heat radiation, low visibility, and several toxic and dangerous gases. Thus, materials used in tunnel structures should be designed in order to limit such problems. The present work addresses the formulation of asphalt mixtures with fire retardant properties based on: (i) the substitution of traditional mineral filler with specific flame retardants (FR) like aluminium hydroxide (ATH) and magnesium hydroxide (MH); (ii) the use of asphalt binders nano-modified with organo-clays. The fire behaviour and the smoke release properties of the mixtures were evaluated by means of cone calorimeter test. Among the FR fillers, ATH gave the most encouraging results in terms of heat and smoke releases. The simultaneous use of FR and nanocomposite asphalt binder gives a synergic effect which significantly changes and improves the fire behaviour of the mixtures.