Abstract: In this study, the porosity assessment of cement mortars containing Precious Slag (PS) Ball – an industrial waste produced by rapid cooling of slag generated from steel making process by Slag Atomizing Technology (SAT) – is done by backscattered electron (BSE) image analysis. PS incorporated mortars were prepared. And tested for strength at different ages. Later, the BSE analysis was done by employing the pore segmentation method. Binarization on the images using Otsu’s thresholding method was done followed by the porosity determination. As the interfacial attributes was the primary concern, the porosity was determined from the aggregate surface to the 100μm width. A total of 24 sections were analysed and the mean values were plotted. Although the PS Ball incorporated mortar exhibited 10% lower strength at 28-day age, it showed stronger and less porous interface between aggregate and paste matrix (from particle surface up to 35μm width) as compared to that of normal mortar containing sand, which is justifiable by the chemical composition of PS Ball attributed to the potential chemical binding. Further, the porosity decreased as the distance from aggregate surface increased. While the use of PS Ball is environmental friendly, its enhanced interfacial properties with a meagre strength loss of cement mortars when used as 100% sand replacer, encourage its use in sustainable construction materials.