Role of matrix structure and flaw size distribution modification on deflection hardening behavior of polyvinyl alcohol fiber reinforced engineered cementitious composites (PVA-ECC)

The multiple cracking and deflection hardening performance of polyvinyl alcohol fiber reinforced engineered cementitious composites (PVA-ECC) under four-point flexural loading have been investigated. Matrices with different binder combinations and W/B ratios (from 0.44 to 0.78) providing satisfactory PVA fiber dispersion were specially designed. Effect of pre-existing flaw size distribution modification on deflection hardening behavior was comparatively studied by adding 3 mm diameter polyethylene beads into the mixtures (6% by total volume). Natural flaw size distributions of composites without beads were determined by cross sectional analysis. The crack number and crack width distributions of specimens after flexural loading were characterized and the possible causes of changes in multiple cracking and deflection hardening behavior by flaw size distribution modification were discussed. Promising results from the view point of deflection hardening behavior were obtained from metakaolin incorporated and flaw size distribution modified PVA-ECCs prepared with W/B=0.53. The dual roles of W/B ratio and superplasticizer content on flaw size distribution, cracking potential and fiber-matrix bond behavior were evaluated. Flaw size distribution modification is found beneficial in terms of ductility improvement at an optimized W/B ratio.