Micromechanics of high-strength, high-ductility concrete

This paper reports the microscale investigation of a new fiberreinforced cementitious composite, high-strength, high-ductility concrete (HSHDC), which possesses a rare combination of very high compressive strength (166 MPa [24.1 ksi]) and very high tensile ductility (3.4% strain capacity). The investigation involved experimental determination of fiber/matrix interaction properties using single-fiber pullout tests. A new mechanism of inclinationdependent hardening in fiber pullout-unique for a high-strength cementitious matrix-is discovered. The existing fiber-pullout analytical model for strain-hardening cementitious composites (SHCCs) is modified to incorporate the new mechanism. The modeled fiber-pullout behavior is used in a scale-linking model to compute the crack bridging (σ-δ) relation of HSHDC, which is also empirically verified through single-crack tests. The σ-δ relation of HSHDC satisfies the micromechanics-based necessary strength and energy conditions of steady-state flat crack propagation that prevent localized fracture. The microscale investigation of HSHDC in this research thus demonstrates the rational basis for its design combining both high compressive strength and hightensile ductility.