Microscale investigation of fiber-matrix interface properties of strain-hardening geopolymer composite

This study reports the microscale investigation of a short fiber-reinforced fly ash-based strain-hardening geopolymer composite (SHGC), which possesses high tensile strength (4.7 MPa) and very high tensile strain capacity (4.3%). The investigation involved determination of the quantitative influences of the type of activator, water to geopolymer solids ratio and fiber surface oil coating on the microscale fiber-matrix interface properties using single-fiber pullout tests. The effects of the measured interface properties on the crack bridging σ(δ) relation of the composites were investigated using a micromechanics-based model to explain the experimentally observed macroscopic tensile ductility of the composites. The computed σ(δ) relation of fly ash-based SHGCs satisfied the necessary micromechanics-based conditions of steady-state flat crack propagation, which result in strain-hardening behavior. This research provides an in-depth understanding of fundamental fiber-matrix interaction properties and mechanisms, and their consequent effects on crack-bridging and tensile performance of the developed fly ash-based SHGCs. This understanding presents the rational basis for design of such cement-less composites.