Investigation of dynamic fracture properties of steel fiber-reinforced potassium magnesium phosphate cementitious composites after high-temperature exposure

Potassium magnesium phosphate cement (MKPC) is well known for its exceptionally high-temperature resistance. However, the inherent brittleness of MKPC becomes more pronounced after exposure to high temperatures, resulting in significantly reduced dynamic fracture properties. This study reinforced the dynamic fracture toughness (K_IC) of MKPC by incorporating microfine steel fibers (MSF). The effects of temperature, MSF dosage, and loading rate on MSF-reinforced MKPC (MSF-MKPC) were systematically investigated, with the underlying mechanisms elucidated through microstructural characterization by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The main findings are as follows: (1) The K_IC of MSF-MKPC initially increases with increasing temperature, subsequently decreases, and eventually slightly recovers. The deterioration in the dynamic fracture properties is caused primarily by the dehydration of the MSF-MKPC matrix at elevated temperatures. (2) Following high-temperature exposure, the K_IC of MSF-MKPC increased with increasing MSF dosage, peaked, and then decreased. In Particular, the incorporation of MSF improved the fracture toughness of MSF-MKPC more effectively after high-temperature exposure than at room temperature, with an optimal dosage of 2%. (3) The K_IC of MSF-MKPC was positively correlated with increasing loading rates; however, the growth rate progressively decreased as the loading rate increased. (4) An empirical formula was established to evaluate the K_IC of MSF-MKPC, which demonstrated strong fitting performance and offered a reliable basis for the evaluation and optimization of material properties.