Investigating the underlying causes of thermal instability in compressed earth bricks

Abstract

Earthen materials are extensively researched for modern construction, but their high-temperature behavior remains poorly explored. This paper addresses the thermal behavior of compressed earth bricks at high temperatures. Two types of earthen materials with similar compressive strength are studied: unstabilized earth bricks compacted at 50 MPa and cement-stabilized earth bricks compacted to the Proctor level. The materials are tested to characterize their mechanical, thermal and permeability properties at different water contents and temperatures up to 600 °C. The results show that the properties of unstabilized material are more prone to variations with water content and temperature than the cement-stabilized material. While the unstabilized earth material has higher residual mechanical properties and permeability after high-temperature exposure, which can improve fire resistance, its lower thermal conductivity could lead to higher thermal gradients and a greater risk of thermal instability. Subsequent complementary fire tests, with thermocouples embedded in the materials, allow detailed tracking of thermal gradient evolution at high temperature, supporting the identification of the origins of thermal instability. The residual material properties dataset helps to identify the post-fire behavior of earthen materials and serves as input for future fire behavior modeling and analysis. Meanwhile, thermal gradient data provides insights into the internal temperature evolution of earthen materials, highlighting key influencing factors that may contribute to their thermal instability.