Correlating the amorphous phase structure of vitrified bauxite residue (red mud) to the initial reactivity in binder systems. (March 2022)

• Record Type: Journal Article
• Authors: Hertel, Tobias; Van den Bulck, Amy; Blanpain, Bart; Pontikes, Yiannis
• Is Part Of: Cement & concrete composites. Volume 127(2022)
• Publication Date: 2022-03
• Subjects: Bauxite residue -- Red mud -- Glass -- Vitrified -- Reactivity -- Binder; Composite-reinforced concrete -- Periodicals; Concrete -- Periodicals; Composite materials -- Periodicals; Composites de ciment -- Périodiques; Béton -- Périodiques; Composites -- Périodiques; Béton léger -- Périodiques; Cement composites; Composite materials; Composite-reinforced concrete; Concrete; Lightweight concrete; Periodicals; Electronic journals; 620.135
• DOI: 10.1016/j.cemconcomp.2022.104410
• Languages: English
• ISSNs: 0958-9465

Abstract

Abstract: The initial reactivity in cementitious systems (i.e. alkali-activated and blended cement systems) of three slags produced using bauxite residue (BR) as the main raw material were assessed; these slags ranged from semi-vitrified to fully amorphous. Additions of C, SiO2 and CaO to BR decreased the liquidus, therefore, firing at 1200 °C was performed and slags with different amorphous contents were achieved after quenching. Results demonstrated that the content of amorphous phase (50–98 wt%) and composition of the amorphous phase, and thus the degree of polymerisation, vary significantly, depending on the amount and type of the additions. Some crystalline phases were detected, which, very beneficially, are able to incorporate potentially unwanted elements. The results of simplified heat flow reactivity tests that simulated alkali-activated binders (Na-silicate-solution as activator) and reactivity tests that modelled the situation in blended cements (reactivity assessment according to the RILEM-TC-267-TRM, rapid, relevant and reliable – R 3 test ) coincided and demonstrated a correlation between the structure of the amorphous phase of the slags (i.e. degree of polymerisation) and reaction kinetics. The lower the degree of polymerisation of the amorphous phase, the faster the dissolution of the slag. The content of amorphous phase did not seem to have an influence on this early reactivity of the BR derived slags. As the results of both calorimeter tests demonstrated the same trend, it is likely that the R 3 reactivity test can also be used for Fe-rich slags and potentially as a tool to determine the reactivity of Fe-rich slags in alkali-activated systems. Highlights: Production of three semi-vitrified to fully amorphous slags from bauxite residue Crystalline phases incorporate potentially toxic elements, such as Cr Correlation between the structure of the amorphous phase and reaction kinetics The lower the degree of polymerisation, the faster the dissolution of the slag