FRACTOGRAPHY OF FIBER-CEMENT COMPOSITES VIA LASER SCANNING CONFOCAL MICROSCOPY

Abstract

Fracture surface characteristics of pulp fiber-cement composites have been quantitatively evaluated by laser scanning confocal microscopy (LSCM) to examine the influence of fiber addition rate and matrix composition on mechanical behavior and fracture processes. A strong correlation was found between the fracture surface roughness and the post-cracking toughness in these composites. In addition, while not contributing to toughness, an inherent surface roughness, likely due to the inhomogeneous and porous microstructure of the hydrated cement paste, was apparent in both the roughness number and fractal dimension measurements. The fractal dimension of the fracture surfaces showed that matrix cracking was a contributing factor to increased toughness. Increased toughness of the composites was attributed to increased fiber pull-out, as compared to samples with minimal toughness which primarily failed by fiber fracture. The partial replacement of portland cement with supplementary cementitious materials did not have an observable effect of the fracture surface roughness.