Iron tailing powder in cement-based composites: Evaluating filling effect from particle-size distribution

Iron tailings, a significant hazardous waste, can be put to use as mineral admixtures in concrete, but the mechanism by which they function requires elucidation. In this study, we define a filling-effect coefficient δ for iron tailing powder (ITP) based on the Horsfield and Andreasen closest-packing theories. Four intervals of the particle size are selected to show how the distribution of ITP affects the pore structure of cement-based composites (CBCs). Experimental measurements of the activity of ITP show that by using δ, the activity indices of ITPs with different fineness values can be calculated without time-consuming mortar tests. Our analysis indicates that ITP particle sizes < 5 µm are essential for the filling effect. However, the contribution of the filling effect to the activity index is limited: Excessive increase in the fineness of ITP does not further enhance their activity. The overall correlation coefficient between δ and the 28 d activity index of ITP with different fineness values is 0.9076. An evaluation formula of the activity index of ITP is established to quantitatively calculate the activity index of ITP with different fineness without mortar test.