Enhancing the recyclability of air-cooled high-magnesium ferronickel slag in cement-based materials: A study of assessing soundness through modifying method

The air-cooled ferronickel slag is already selected as a raw material (aggregate) in concrete manufacturing, while the using as supplementary cementitious materials is still limited because of the high magnesium content. The objective of this study focuses on the practicality of air-cooled high-magnesium ferronickel slag (HMNS) blended Portland cement pastes, providing experimentally criterion for aircooled HMNS's application. The different fineness on compressive strength and soundness of mixtures were investigated comprehensively. To be compared with the actual expansion of the HMNS blended Portland cement pastes, the mixtures containing MgO expansive agent addition (on the basis of the MgO content in the HMNS blended mixtures) were especially produced for autoclave expansion test. An optimum strength in practical application was obtained when the dosage of HMNS and its particle size were 20% and less than 50 mu m respectively. The expansions of all mixtures were not only quite small (scattered around 0.09%) by traditional autoclave test, but the HMNS blended mixtures also exhibited the lower expansion when autoclave time is 6 h and 12 h. However, the expansive values of MgO expansive agent blended mixtures express more expansion than that of the HMNS blended mixtures in all autoclave times. This phenomenon was attributed to the form of magnesium in HMNS, where the primary phase of magnesium was clinoenstatite (MgSiO3) or forsterite (Mg2SiO4) and those phases showed inactive in this system by XRD, TGA and BSEM-EDS analyses. Therefore, HMNS used as supplementary cementitious material could not bring volume expansion, and this conclusion may present a great benefit to the recycling of HMNS in the field of construction materials. (C) 2020 Elsevier Ltd. All rights reserved.