Hygrothermal effects on tensile and fracture properties of epoxy filled with inorganic fillers having different reactivity to water

The study investigated the effects of ageing on the tensile properties and fracture behaviour of an epoxy filled with inorganic fillers having different reactivity to water, such as fly ash, calcium carbonate (CaCO3), and Portland cement. CaCO3 is insoluble in water, whereas fly ash and cement are reactive to water; however, fly ash is less reactive than cement. The water absorption, tensile properties, and mode-I fracture toughness of the epoxy containing 7 wt% of filler were compared after ageing the composites in distilled water at 50 °C. Gravimetric analyses showed that compared to neat epoxy, CaCO3 slightly decreased the equilibrium water uptake of the filled epoxy, whereas fly ash and cement increased the equilibrium water uptake. Compared to the other fillers, the tensile strength of CaCO3-filled epoxy was inferior in both dry and wet conditions. However, in dry condition, the elastic modulus of CaCO3-filled epoxy was slightly higher. Overall, the fly ash-filled epoxy showed better tensile and fracture properties in both dry and wet conditions although it absorbed more water than the other fillers did. Scanning electron microscopy revealed that crack deflection played a dominant role in the toughening of filled epoxies in both dry and wet conditions.