Thermal degradation of fiber reinforced extruded materials

Abstract An experimental investigation regarding the mechanical properties of four different types of cement-based fiber reinforced extruded materials is presented, with consideration to the extrusion direction and the type of fibers (all types of fibers are industrial by-products). Using the three-point bending test, a variation of both the nominal bending strength and the fracture energy is observed as a consequence of a thermal treatment up to a maximum temperature of 500 °C. In particular, for a given mix, by testing specimens of different dimensions, it is shown how the decay of the nominal bending strength in the damaged (thermally treated) material is significantly different than in the undamaged one, due to fracture initiation being characterized by a larger dissipative zone. The change in the microstructure of the materials is confirmed by micrographs obtained through scanning electron microscopy and by the results of mercury intrusion porosimetry tests. As a consequence, the ratio between the strength of the heat treated and the undamaged specimens, i.e. the reduction in nominal strength as a function of temperature, is size dependent.