Influence of matrix constituents and properties on fiber-matrix bond behavior of strain-hardening ultra-high performance concrete

Strain-hardening ultra-high performance concretes (SH-UHPC) reinforced with high-density polyethylene fibers have recently attracted much interest due to their unique combination of compressive strength and tensile strain capacity. This study investigates the effects of matrix compressive strength (f_c′), type and content of supplementary cementitious materials (SCMs), and cumulative particle size distribution modulus (q) on the fiber-matrix interfacial bond properties of SH-UHPC. These effects are examined using a response surface design of experiments with three different groups of mixtures, each group made with a different SCM (microsilica, slag, or fly ash). While significant correlations were identified between the interfacial frictional bond and independent variables (f_c′, SCM type and content, and q), significant effects of interactions between the independent variables (e.g., between the SCM content and q) on the fiber-matrix frictional bond were also discovered. The results of these experiments were used to develop a simplistic inverse analysis method to determine the fiber-matrix interfacial parameters from single-crack tests instead of highly variable and more tedious single-fiber pullout tests.