Rheology and hardened properties of eco-friendly ultra-high performance concrete paste: Role of waste stone powder fillers

Waste stone powder is the largest by-product generated during the production of manufactured sand, which causes environmental pollution and resource wastage due to its large accumulation and landfill disposal. In this study, the effectiveness of basalt powder (BP) was evaluated against that of limestone powder (LP) to verify its potential for use as a functional and environmentally-friendly filler in Ultra-High Performance Concrete (UHPC) compositions. The theories of wet packing density (WPD) and water film thickness (WFT) are introduced to investigate the effect of stone powder on hardened and rheological properties of UHPC. Results indicate that the WFT of the solid particle system (cement and stone powder) exhibits a direct correlation with the increase in stone powder content (up to 20 %). As the WFT increases, the shear resistance between particles is reduced, leading to a nonlinear decrease in the yield stress and plastic viscosity of the UHPC paste, thereby enhancing its flowability. More superplasticizer is adsorbed on the surface of BP, which weakens the gain effect of the superplasticizer in reducing the yield stress. Due to the increased WPD, a near-linear enhancement in the compressive strength of the paste is observed. Supplementary nucleation sites for C-S-H are provided by the surface of the stone powder, thus accelerating the early hydration kinetics of the UHPC paste and facilitating development of strength at an early age. When 20 % of cement is replaced by LP and BP, the carbon emission index of UHPC paste is reduced by 34.9 % and 21.7 %, respectively. [Display omitted] •Basalt stone powder shows potential as a mineral admixture.•Water film thickness is increased due to stone filler effect.•Additional C-S-H nucleation sites are provided by stone powder.•Negative correlation between water film thickness and yield stress.