Flexural behavior and microstructure of hybrid basalt textile and steel fiber reinforced alkali-activated slag panels exposed to elevated temperatures

Three-point bending tests were conducted after heating specimens to 400 °C, 600 °C, and 800 °C for durations of 1 and 2 h. The effects of thermal exposure on the matrix and the basalt fibers from the panels were investigated with scanning electron microscopy. Element and phase analyses of the matrix were performed after exposure to high temperatures via energy dispersive spectroscopy and X-ray diffraction, respectively. The first crack and peak flexural strength of the specimens not exposed to heat reached 8.9 and 20.5 MPa, respectively. Obvious decreases in flexural performance occurred as temperature and duration increased as a result of the decomposition of the alkali-activated slag mortar (AASM) matrix and the deterioration of the bonding performance between the basalt textile and the matrix. Changing of the Ca/Si ratio, the Al/Si ratio, and the crystalline phase of the AASM matrix indicated that phase transformation occurred after heat exposure at 800 °C.