Effect of Fine Aggregate Particle Size on Physical, Mechanical, and Durability Properties of Ultra-High Performance Concret

Ultra-high performance concrete (UHPC) mixtures are typically developed using fine aggregate with a maximum size of 600 μm. From a sustainability point of view, use of larger size fine aggregate particles in UHPC mixtures should be investigated to reduce labor costs associated with sieving, to reduce wastage of sand, and to improve sustainability. This experimental research investigates the physical, mechanical, and durability properties of UHPC incorporating coarser fine aggregates with maximum particle size of 4.75 mm replacing fine sand. Both plain and fiber reinforced UHPC mixtures were developed with a target static flow of 200 mm (8 in.) and target compressive strength of 120 MPa (17,000 pounds per square inch). Three different curing regimens were investigated: moist curing, warm bath curing at 90°C, and heat curing at 90°C. Compressive and split tensile strengths, permeable porosity, and rapid chloride permeability tests were performed to study the effect of coarser fine aggregate sizes on these UHPC properties. Increasing the maximum fine aggregate particle size range did not affect the workability, compressive strength, permeable porosity, or chloride ion ingress; however, a limited decrease in split tensile strength was observed. A change in aggregate size may have a very large impact on fiber dispersion, embedment, and crack bridging. The experimental results highlight the potential of coarser fine aggregate used in UHPC.