Influence of thermal exposure scenarios on the residual mechanical properties of a cement-based composite system

Cement-based composite materials have emerged as effective solutions for strengthening and retrofitting reinforced concrete (RC) structures, but their behaviour at elevated temperatures remains a critical concern. This research addresses the impact of thermal exposure time and thermal cycles on the residual mechanical properties of a PBO (short of polyparaphenylene benzobisoxazole) FRCM (Fabric Reinforced Cementitious Mortar) composite system through a combination of experimental studies and theoretical analyses. The experimental investigation included tests on specimens exposed to various temperatures (20 ◦C, 100 ◦C, and 200 ◦C), exposure time duration (1 and 8 hours), and thermal cycles (up to 5 cycles). Mechanical tests, including tensile, compressive, flexural, and single lap direct shear tests, were performed on both the PBO FRCM composites and their constituent materials. The experimental results showed that at 200 ◦C, both residual bond and tensile properties of the PBO FRCM composites are significantly affected by the elevated temperature. Tensile strength and bond capacity decreased by approximately 44 % and 23 %, respectively, at 200 ◦C compared to specimens tested at ambient temperature (20 ◦C). The duration of thermal exposure significantly affected the residual mechanical properties of the PBO FRCM system; specimens exposed to 200 ◦C for 1 hour showed a 20 % reduction in tensile strength and a 17 % decrease in bond capacity, indicating less degradation compared to those exposed for 8 hours. Thermal cycling had minimal impact on tensile strength and bond capacity, with variations in both properties similar to those observed in specimens exposed to 200 ◦C for a single cycle. The experimental results were then used as input data to define local bond-slip laws, which were then incorporated into finite element (FE) models to simulate the experimental bond tests. The numerical simulations demonstrated a relatively good accuracy compared to the experimental results, validating the effectiveness of the defined local bondslip laws.