Enhanced Gypsum Panels for Fire Protection

The fireproofing materials used to make firebreak systems are usually hydrated-calcium sulfate, i.e., gypsum or hydrated-calcium silicate panels. Gypsum presents a large latent heat due to its dehydration into hemihydrate and anhydrite. During a fire exposure, the gypsum panels are characterized by an isothermal stage on the unexposed side because of the latent heat effect. This dehydration induces cracks inside the panels, furthermore, the heat flow goes through these cracks and increases the temperature of the unexposed side. The dehydration leads to a large thermal shrinkage, due to the loss of bound-water molecules. In this study, a silica filler was introduced into the plaster. This filler modifies the thermal, physical, and mechanical properties of the gypsum panels and reduces the cracks’ formation. An optimum filler amount is identified. The thermal behavior of gypsum panels and commercially available calcium silicate products exposed to fire are then compared under a standard fire. Above a critical temperature (greater than $\mathrm{1,000}°\mathrm{C}$ ), a melting front diffuses through the material and affects its permeability, as well as its mechanical and geometric properties (thickness). Summing up, the development of new fireproofing materials (exhibiting a real high-temperature resistance) requires mastering high-temperature shrinkage, as shown in the example developed at the end of the paper.