Study of the risk of instability in earthen bricks subjected to fire

The construction industry's growing demand for earthen materials faces a hurdle due to limited knowledge regarding their fire performance. The present work aims to assess the fire behavior of compressed earthen bricks, particularly focusing on spalling. Two influencing parameters were studied: the influence of cement stabilization and water content. To ensure equivalent compressive strength, compaction levels and cement content were thoughtfully chosen, as mechanical properties greatly influence fire behavior. In the material selection phase, unstabilized earthen bricks were compacted across a range of loading levels from 40 to 60 MPa. Subsequently, a loading level of 50 MPa was chosen for fire testing. Cement-stabilized earthen bricks were compacted at a Proctor level pressure with cement content varying from 2.5 to 10%. Additionally, Polypropylene fibers were incorporated into both types of bricks to assess their impact on fire behavior. Various water contents were tested, with samples maintained at hydric equilibrium through different curing conditions. Fire tests with a rapid heating rate (ISO 834-1 standard fire) were performed. Preliminary evaluation of the samples' fire behavior was based on their stability/instability during heating. Unstabilized samples exhibited thermal instability at intermediate water contents (50 and 75% RH), resulting in the detachment of their heated faces accompanied by a sound. However, they remained stable when dried or fully saturated. The inclusion of polypropylene fibers reduced the risk of instability. On the other hand, cement-stabilized bricks exhibited thermal stability, with no surface peeling observed, regardless of water content. The presence of cracks contributed to this stability.