Quantitative characterization and evaluation of key physicochemical characteristics of steel slag

Abstract

Steel slag is considered to improve the road performance of cold mixed asphalt (CMA) due to its superior physicochemical characteristics. To realize the potential application of steel slag in CMA pavement, the alkalinity, hydration activity, pore characteristics, and three-dimensional (3D) morphology were quantitatively characterized and evaluated based on the X-ray fluorescence (XRF), mercury intrusion porosimetry (MIP), 3D laser scanning, and 3D structured light measurement, respectively. The results show that the alkalinity of steel slag can not fully reflect its hydration activity. Most steel slag has high alkalinity with an alkalinity value greater than 2.5, while the activity index (AI) is generally less than 1.0. The pores of steel slag are mostly "ink-bottle" shaped, in which macropores are the most developed, and small pores and micropores are the least developed. The total pore volume of macropores is the largest, while the total pore area of small pores is the largest. The porosity of porous, less porous, and dense steel slag is 12.05%, 6.88%, and 1.28%, respectively. The adsorption and accommodation capacity of porous steel slag for fluids is the largest, followed by less porous and dense steel slag. All three steel slags have good 3D shapes, and their shape factor (SF), sphericity (S), needle degree (ND), and flake degree (FD) have distribution intervals of 0.81–1.19, 0.70–0.99, 1.01–1.90, and 1.01–1.51, respectively. Porous steel slag shows richer apparent morphology than less porous and dense steel slag. Their apparent morphology characterization indicators Ra, Rq, Rp, Rv, and Rt show a good linear positive correlation with porosity, which can be regarded as the classification criterion for apparent morphology. This study will help enrich the theoretical basis and control indicator system for applying steel slag in CMA pavement.