Residual performance of HPFRCC exposed to fire – Effects of matrix strength, synthetic fiber, and fire duration

This study investigates the effects of matrix strength, synthetic fiber content, and heating duration on the explosive spalling resistance and residual compressive and flexural properties of high-performance fiber-reinforced cementitious composites (HPFRCCs). Three different matrix strengths, ranging from 100 to 180 MPa; four different volume fractions of synthetic fibers, i.e., polypropylene (PP) and nylon (Ny) fibers, ranging from 0% to 0.6%; and three different fire durations of 1, 2, and 3 h under the ISO standard fire curve were adopted. Scanning electron microscope (SEM) images were obtained to evaluate the microstructural states of HPFRCCs and a mercury intrusion porosimetry (MIP) analysis was conducted to determine pore size distribution characteristics before and after fire exposure. The test results indicate that the addition of PP and Ny fibers is effective at enhancing the explosive spalling resistance, and higher amounts are required for higher strength matrices. The compressive strength of HPFRCCs decreased by more than 75% after the fire (≥950 °C), and higher residual compressive strengths were obtained with shorter fire durations and higher amounts of added PP and Ny fibers. The toughness was decreased by the fire more than the flexural strength, and the residual flexural performance were enhanced with higher amounts of synthetic fibers and matrix strengths. In particular, the residual flexural performance significantly decreased when the fire duration increased from 1 to 2 h, and only a minor change was observed thereafter. The effectiveness of higher amounts of synthetic fibers at improving the residual performance diminished with longer fire durations.