Effect of steel fibers and thermal cycles on fracture properties of ultra-high-performance concrete

The advent of ultra-high-performance concrete (UHPC), a new generation of cementitious material having excellent material properties, has generated a great deal of interest in the field. In this study, the fracture properties of UHPC mixtures reinforced with steel fiber (fiber content varying from 0 to 6.2 % by weight) and subjected to thermal cycles were investigated to examine the effect of heat-cool cycles. The standard prism of 100 × 100 × 400 mm³ with a central notch was used in a three-point bend test to determine fracture properties that include critical stress-intensity factor (K_ic), critical crack tip opening displacement (CTOD_c), energy release rate, and total fracture energy. All specimens were water-cured for 28 days. Two exposure conditions were used: a 6-month thermal cycling and a 6-month laboratory exposure for further selfcuring. The thermal cycling comprised heating in an oven at 60°C for 2 days and then cooling them at room temperature for the next 2 days over a period of 6 months. Test results show that UHPC reinforced with 6.2 % steel fiber exhibited excellent fracture properties with significant ductility. Both thermal cycling and prolonged self-curing of water-cured UHPC specimens enhance fracture properties because of more complete hydration of cement in UHPC. This improvement in properties signals an additional advantage of water-cured UHPC for its application in hot climatic conditions. Copyright