Processing effects in cementitious composites: Extrusion and casting

There is growing interest in the effect of processing methods on the properties of cement composites. The present work compares two processing methods: casting and extrusion. The effects of high fly-ash content (70% by volume, replacement of cement) and different fiber lengths on the mechanical properties and microstructure characteristics are examined. Opposing trends are observed between the cast and the extruded composites. Increasing fiber length improves the mechanical behavior of cast composite, but it reduces the behavior of extruded composite (without fly ash). The use of fly ash had a negative effect on the mechanical performance of cast products, but a positive effect on the performance of extruded products (with long fibers). This contradictory behavior was explained by the differences in bond strength and matrix properties in the different systems, changing the mode of failure from fiber pullout to fiber fracture. It was concluded that the extrusion process improves the mechanical performance of cement composites. To achieve such improvement the properties and geometry of the fibers as well as the material ingredients and proportions should be chosen carefully and properly controlled.