Hybrid synthetic/natural fiber-reinforced strain-hardening magnesia-based composites

Abstract

Synthetic fiber-reinforced strain-hardening magnesia (MgO)-based composites (SHMC) are an emerging group of fiber-reinforced cementitious composites (FRCC) with ultra-high ductility and CO2 sequestration potential. However, the size of SHMC members is limited by the inadequate carbonation depth of the MgO matrix. In this work, hybrid synthetic/natural fiber-reinforced SHMC are developed containing different contents of PVA fibers (0-2 vol.%) and sisal fibers (0-4 vol.%). The new Hybrid-SHMC were experimentally studied on micro-scale and composite scale. On the micro-scale, the effect of cement matrix carbonation on the PVA/sisal fiber-to-matrix interfacial bonds and the matrix moduli were studied by single-fiber pullout test and local nano-indentation. On the composite scale, the effect of fiber dosage on the compressive/tensile behavior and carbonation profile of SHMC were studied. The effects of the carbonation-induced micromechanical enhancements on the composite behaviors were validated by a micromechanics-based fiber-bridging model. The results demonstrated that the new hybrid SHMC could achieve ultra-high tensile ductility (>2.5%) and uniform carbonation simultaneously (≥ 0.25g CO2/g MgO at different depths). In Hybrid-SHMC, the PVA fibers mainly contributed to the mechanical crack-bridging and thus strain-hardening, while sisal fibers with porous microstructure improved the carbonation depth and thus the fiber-matrix interfacial bonds, composite compressive, and tensile performances.