Experimental investigation on the confining effect of fibers in SHFRCC

Strain Hardening Fiber Reinforced Cementitious Composites (SHFRCC) comprise of a mix design that differs from normal concrete mixes. Fibers act as mass reinforcement leading to large deformation capacities, bridging of the cracks and transferring stresses through cracked regions, delaying or even entirely mitigating cover splitting. This contribution is interpreted as an intrinsic “confining effect”. To characterize the confining effect, an experimental program was undertaken, including a series of specimens comprising either SHFRCC or plain cementitious matrix of the same composition (PC), subjected to various levels of confinement of known intensity (steel stirrups and FRP jacketing). A triaxial state of stress is found to develop in the SHFRCC, where the internal stresses supported by the fibers are related to classical constitutive models for plain concrete with FRP jackets or steel stirrups. The lateral and volumetric behavior of the composites is investigated and related to the tensile strength of SHFRCC, measured through a variety of tests. Overall, it was concluded that the fiber reinforced composites respond in a manner that is entirely consistent with commonly understood confined concrete behavior.