Microstructural characterization of high performance fiber reinforced cement composites

Effects of fiber length and sand addition on the mechanical performance of cast and extruded PVA fiber reinforced cement composites were investigated. Microstructural characterization, image analysis, and statistical tools were used to study the influence of processing, fiber length and sand addition on fiber-matrix bond, fiber dispersion, fiber orientation and matrix porosity in the composites. Effect of fiber dispersion is later investigated in detail to understand its effect on the mechanical behavior.; In the extruded composites, shorter fibers (2 mm) improved the mechanical performance. In the cast composites, longer fibers (6 mm) gave the best mechanical performance. This contradictory trend was found to be a result of differences in fiber failure mechanism, fiber distribution and fiber orientation. Microstructural observations indicated a strong matrix-fiber bond for the extruded composites. Statistical quantification of image analysis on fiber dispersion and alignment indicated that shorter fibers in extruded composites were evenly dispersed and aligned along the extrusion direction.; The addition of sand increased the strength of the plain cement paste, but decreased the mechanical performance of the fiber reinforced cement composites. Fiber clumping, an increase in the size and number of fiber free areas and higher matrix porosity were observed in the composites when sand was used.; Effect of fiber dispersion on the mechanical performance was found to be one of the major parameters which needed further investigation. The Electronic Speckle Pattern Interferometry technique was used to record the location of crack initiation, sequence of the development of multiple cracks and the corresponding cracking stresses. Fiber dispersion at each crack location was statistically quantified by the theory of point processes. The size of the fiber free areas and fiber clumping were quantified at the crack cross-sections. By using Linear Elastic Fracture Mechanics, fracture toughness of the matrix was calculated. A strong relation between the cracking stress and the fiber free areas in the composite was observed. It is shown that the toughness of the composite depends on the fiber clumping at the first crack cross-section.