Evaluating the residual properties of masonry units and mortar at elevated temperature conditions and its compliance with Sri Lankan building fire safety guidelines

Abstract

Masonry structures are valued for their strength and durability, and the properties of masonry materials under ambient conditions have been studied widely. The behaviour of masonry materials under fire conditions has also been investigated; however, studies on their residual performance after fire exposure remain limited. As the post-fire capacity of masonry walls is uncertain, studying their residual behaviour is important for improved fire safety. Therefore, this study evaluates the residual properties of masonry units commonly used in Sri Lanka, including clay bricks and cement–sand blocks as conventional units, and compressed stabilized earth blocks (CSEBs), foam concrete blocks, and autoclaved aerated concrete blocks as alternative units. Three specimens of each unit type, along with mortar samples, were heated to 200 °C, 400 °C, 600 °C, 800 °C, and 1000 °C, and then assessed for mass loss, crack propagation, and compressive strength, with ambient-condition specimens serving as references. Wall strengths were calculated using the experimental results. The results showed a unique behaviour in solid clay bricks, which recorded a 29% increase in compressive strength at 200 °C before reducing at higher temperatures. All other masonry units and mortar exhibited a continuous decrease in strength, with reductions ranging from 1% to complete loss depending on temperature. Solid cement–sand blocks and their corresponding walls performed best among the tested units, satisfying load-bearing and non-load-bearing strength requirements up to 800 °C. CSEBs were unsuitable at elevated temperatures and lost all capacity by 800 °C, showing weaker residual performance. Mass loss varied between 0% and 20% across units. Cracks were observed only in solid clay bricks and CSEBs, with CSEB cracks exceeding 3 mm after 800 °C, resulting in a complete loss of strength. Based on the findings, the study highlights the importance of incorporating material-specific fire-performance data into building design regulations to improve fire safety.