Parameters affecting high-performance response in fiber-reinforced concrete

High perfonnance fiber reinforced cement composites (HPFRC) are defined as the materials which exhibit a postpeak strain hardening type of response with a multiple crack pattem. Such a ductile behavior makes the HPFRC an ideal material to be used in structural repair and retrofit for dimensional stability, tensile-load carrying capacity, impact resistance, flexibility and long tenn impetmeability. The critical parameter for continuous fiber reinforced cementitious materials to obtain the high performance response is the minimum fiber volume ratio with well dispersed fibers. As long as continuous fiber composites have a sufficient number of fibers to bridge the cracks, strain hardening and multiple cracking can always happen. However, there is no single dominant parameter which can control the multiple cracking process in discontinuous fiber composites. Various parameters can affect the postpeak response of discontinuous fiber reinforced cementitious materials. They are related to fibers, matrix and the processing methods. Parameters relating to the reinforcement include the type of fiber, fiber length, fiber volume ratio, fiber orientation, state of fiber dispersion and the degree of adhesion to the matrix. These primary variables are in tum influenced by selection of the matrix type, presence of additives, and the processing conditions. The latter acts through controlling the state of dispersion, establishing a fiber orientation pattem and enhancing the adhesive bond between fiber and matrix. To design a high performance fiber reinforced cementitious repair material, the approach in which the repair will be carried out should be considered simultaneously.