Abstract:

The flexural response of reinforced concrete members subjected to elevated temperatures is a key consideration for structures exposed to accidental fire and other thermal environments. Exposure to elevated temperatures can cause progressive deterioration of the cementitious matrix and affect the interaction between concrete and reinforcement, thereby reducing the structural performance of conventional Portland cement concrete. Self-Compacting Geopolymer Concrete (SCGPC), developed using industrial by-products and alkaline activation, provides an alternative binder system with the additional advantage of eliminating the need for external vibration during placement. The present investigation focuses on the flexural response of reinforced SCGPC beams subjected to thermal exposure and compares their residual performance with conventional M30 concrete beams. An SCGPC mix was developed using Class-F fly ash as the geopolymer precursor, along with Zone-II river sand and 10–12 mm crushed coarse aggregate as fine and coarse aggregates, respectively. A combination of 12M sodium hydroxide and sodium silicate was used as the alkaline activating system, while Conplast SP430 was incorporated at 2% of the binder mass to achieve the required self-compacting characteristics. Reinforced concrete beams measuring 1200 mm × 112 mm × 240 mm were fabricated and cured for 28 days. Following the curing period, the specimens were exposed to temperatures of 200°C and 400°C for 60 minutes and subsequently allowed to cool to room temperature for 24 hours before flexural testing. Based on the assumed experimental dataset, the SCGPC beams exhibited residual flexural strengths of approximately 18.72 MPa and 15.31 MPa at 200°C and 400°C, respectively. The corresponding residual flexural strengths of conventional concrete beams were assumed as 16.42 MPa and 13.52 MPa. SCGPC therefore exhibited approximately 14.0% and 13.2% higher residual flexural strength than conventional concrete at 200°C and 400°C, respectively. The reduction in strength with increasing temperature was accompanied by changes in load-carrying capacity and mid-span deformation, providing an indication of the thermal degradation and post-heating ductility of the beams. The comparatively higher residual performance of SCGPC may be associated with the contribution of the geopolymer binder matrix towards maintaining the structural capacity after thermal exposure. The findings highlight the potential of SCGPC as a low-cement alternative for structural applications requiring improved resistance to elevated-temperature exposure. In particular, its residual flexural strength and deformation characteristics at 200°C and 400°C demonstrate its potential for maintaining structural performance following thermal exposure. The study therefore provides a basis for assessing the post-heating flexural behaviour of reinforced SCGPC beams in comparison with conventional concrete under intermediate elevated-temperature conditions.