Strength properties of Bayer red mud stabilized by lime-fly ash using orthogonal experiments

Bayer red mud (RM) was produced from aluminum ore according to Bayer process. In order to study the feasibility of stabilized Bayer RM for use in road construction, strength properties of RM stabilized by lime-fly ash using orthogonal experimental method were evaluated. In test design, the normalized orthogonal table of L-9 (3(4)) was adopted. The influence of ratio of lime-ash, the dosage of lime and fly ash, and the type of Bayer RM (Two kinds of Bayer RM from different producers) on the unconfined compressive strengths (UCS) of 7-day and 28-day curing age were studied. The experimental results showed that these factors significantly influenced the UCS. The principal factors influencing 7-day UCS was ratio of lime-ash, followed by chemical compositions of Bayer RM and the dosage of lime and fly ash in last. The principal influencing factor of 28-day UCS was chemical compositions of RM, followed by ratio of lime-ash and the dosage of lime and fly ash in last. Then the optimum proportion for the UCS was determined through the orthogonal analysis. The X-ray fluorescence (XRF) showed that chemical compositions and contents of two types of RM were significantly different in iron, silicon and calcium. The microscopic analysis of the raw material and stabilized material employed X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) showed that DA(Ca3Al2O6), C2S, and calcium carbonate increased under the optimal conditions of lime-fly ash stabilization, and hydrated silica aluminate and CSH were gradually generated. The stabilization mechanism of Bayer RM by lime-fly ash is related to hydration like aluminate cement. There is no essential difference in reaction mechanism for two kinds of Bayer RM and the difference in the strength properties is essentially originates from the active material content. (C) 2018 Elsevier Ltd. All rights reserved.