Comparison of technical and short-term environmental characteristics of weathered and fresh blast furnace slag aggregates for road base applications in South Africa

This study investigated chemical, physical-mechanical and environmental characteristics of weathered blast furnace slag (WBFS) and freshly produced slag (FBFS) for their potential utilisation as granular road base and subbase aggregates. The X-ray fluorescence analysis revealed that each material exhibited a strong CaO-SiO2-MgO-Al2O3 chemical system. The X-ray diffraction analysis detected the major mineral phases in WFBS as akermanite, gehlenite and monticellite that accounted for 91.4% of the total mineralogical phase composition. Akermanite and gehlenite accounted for 91% of the total mineralogical phase composition in FBFS. Both slags have weak cementitious properties. The aggregate crushing value, 10% fines aggregate crushing value, flakiness index, plasticity and compaction characteristics of both slag aggregates complied with the South African specifications for crushed stone base and subbase aggregate materials. Soaked California bearing ratio (CBR) values of 153% and 128% for WBFS and FBFS respectively meet the bearing strength requirement for their use in base and subbases. The two materials may also be considered as solid waste with low-risk environmental pollution. Low long term expansion values of 0.32% and 0.39% were observed for WBFS and FBFS respectively. The investigated characteristics indicate that these slags are suitable alternative materials for granular road base construction. Keywords: Chemical characteristics, Mineralogical characteristics, Hydraulicity, Low-risk solid waste, Physical characteristics, Mechanical characteristics, Volumetric expansion