Potential of finely ground limestone powder to benefit ultra-high performance concrete mixtures

•The use of limestone powder as an inert filler in UHPC is proposed.•Limestone powder reduces health hazards associated with silica powder in UHPC.•Minor replacements of cement with limestone do not negatively affect performance.•Full replacement of silica powder does not significantly impact UHPC performance. Ultra-high performance concrete is a specialized class of cementitious materials notable for very high compressive strength, increased toughness, and improved durability relative to conventional concrete. Due to its high cement content and the use of very finely ground crystalline silica, ultra-high performance concrete has a greater cost and CO2 footprint than normal concrete. Potential health concerns can also arise due to repeated inhalation of crystalline silica powder during production. Finely ground limestone powder was hypothesized as a potential filler to help minimize these negative aspects when used as either a partial or full mass replacement of similarly sized cement and silica powder. Limestone powder was shown to have a positive effect on fresh properties of the composite including mixing time and workability. Small replacements of cement were shown to have beneficial effects on compressive strength. Scanning electron microscopy showed that limestone powder replaced unreacted materials without significantly impacting hydration reactions.