Mechanical properties of hybrid cement-based composites

Tensile and flexural properties of cementitious composites reinforced with carbon and alumina whiskers are studied, in addition to polypropylene (PP) fibers. Significant strength increase is observed by the addition of short carbon and alumina whiskers. Due to the inability to bridge the macrocracks, the whisker's contribution is limited to increasing the ultimate strength and marginal postpeak toughening. Fracture toughness may be increased by the addition of PP fibers to produce hybrid composites. Pullout of PP fibers from the matrix is the main reinforcing mechanism and results in significant energy dissipation. Hybrid composites are shown to have superior strength and toughness properties due to the interaction of reinforcing fibers. Various procedures to characterize the tensile and flexural fracture of these composites are evaluated. A method to obtain the experimental R-curves is discussed. This approach provides the most suitable means of characterizing the fracture response of FRC materials.