Crack Patterns in Direct Tension and Flexure of Ultra-High-Performance Fiber-Reinforced Concrete with Scale Effect

The crack patterns of ultra-high-performance fiber-reinforced concrete (UHPFRC) with size effect in tension and flexure were experimentally investigated. The investigated UHPFRC was blended 1.0 vol.% long twisted with 1.0 vol.% short smooth steel fibers. Flexural specimens and tensile specimens were designed with different scales of sizes as follows: 25×50×125, and 50×100×250 mm (thickness×width×gauge length) for the tensile specimens, 50×50×150, 100×100×300, 150×150×450 mm (width×depth×span length) for the flexural specimens. All tested specimens exhibited multiple micro-cracks during work-hardening responses. There was a clear scale effect on number of cracks appearing in UHPFRC specimens under tension and flexure, in addition to scale effect on strength, deformation, toughness. Besides, the model and the degree of scale effect on micro-cracks were shown and discussed.