Structural Integrity Assessment of Plastic Sand Blocks under Thermal and Mechanical Stresses

This study presents a comprehensive evaluation of the fire performance of plastic-sand blocks (PSBs), addressing a key gap in understanding their safety under extreme conditions. Fire endurance, thermal insulation, and postfire hose-stream tests were conducted to assess their structural integrity and resistance to heat exposure. The equivalent thickness method was applied to determine the fire rating of the combustible PSBs and to benchmark their performance against conventional cement-sand blocks. In addition, both mechanical strength and thermal behavior were examined under fire conditions. The results reveal important performance trading-offs: compressive strength declined significantly from 7.8 MPa at ambient conditions to 3.2 MPa after fire exposure, and the thermal insulation capacity was lower than that of conventional blocks, indicating limitations in their structural fire performance. Empirical results demonstrated a stark contrast in fire resistance: the control cement specimen achieved a fire rating of 4 h 25 min, whereas the PSB failed rapidly at just 21 min. Furthermore, the plastic-sand composite significantly reduced the water absorption rate by 1.8% compared with the control, which showed a 4.2% increase. The postfire hose-stream test showed inward then outward wall deflection, highlighting key failure mechanisms and providing valuable data for assessing the structural safety of this alternative material.