Influence of limestone powder on water film thickness and plastic viscosity of UHPC

In this paper, the influence of micro scale and nanoscale limestone powder (LP) on plastic viscosity of ultra-high performance concrete (UHPC) mixture was investigated. Moreover, a novel method for analyzing water film on particle surfaces has been presented based on low-field nuclear magnetic resonance technology (LF-NMR). Results showed that approximately 95% of free water in UHPC slurry is adsorbed on the surface of particles, while the rest is filled in capillaries and macropores. Moreover, rheological properties of UHPC are related to particle size of limestone powder. Micro scale limestone powder (LP1) could reduce the heat release during early hydration of UHPC, increase the fluidity, but has no significant effect on the water film thickness. The plastic viscosity of UHPC mixed with 10% mass fraction of LP1 will decrease by 22.8%, the flowability will increase from 235 mm to 270 mm, and the compressive strength will remain unchanged at 160 MPa. However, nanoscale limestone powder (LP2) increases the heat release of UHPC and significantly reduces its fluidity. A 10% mass fraction of LP2 will reduce the water film thickness of the UHPC by 23.5%, increase the plastic viscosity by 38.5%, and reduce the flowability to 210 mm. Meanwhile, the compressive strength of UHPC will decrease if the mass fraction of LP2 exceeds 5%.