Characterization of ferrochrome ash and blast furnace slag based alkali-activated paste and mortar. (11th January 2023)

• Record Type: Journal Article
• Authors: Omur, Tarik; Miyan, Nausad; Kabay, Nihat; Birol, Burak; Oktay, Didem
• Is Part Of: Construction & building materials. Volume 363(2023)
• Publication Date: 2023-01-11
• Subjects: Alkali-activation -- Ferrochrome ash -- Microstructure -- Rheology -- Physicomechanical properties; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2022.129805
• Languages: English
• ISSNs: 0950-0618

Abstract

Highlights: Effect of FCA replacement with BFS activated with various Na2 O dosage were studied. FCA addition reduced semi-adiabatic temperature, shrinkage, and modified rheology. FCA inclusion reduced compressive strength and slightly increased water absorption. C-ASH, CSH and MSH were identified as major reaction products by XRD analysis. Compressive strength results were well correlated with Ca/Si and Si/Al ratios. Abstract: Ferrochrome ash (FCA) is an industrial waste material which when disposed causes environmental pollution and health hazard. Therefore, in this paper, FCA replaced up to 30 % of blast furnace slag (BFS) to investigate its possible utilization by producing alkali-activated material. The effect of FCA content and varying Na2 O dosage on fresh, physicomechanical and microstructural properties was discussed. The addition of FCA improved the rheological properties of mixes by reducing plastic viscosity from 47.3 to 22.9 Pa.s and from 129.2 to 71.1 Pa.s and yield stress from 87.5 to 40.7 Pa and from 89.8 to 44.0 Pa for Na2 O dosage of 6 and 10 %, respectively. This allowed reduction of water content, which in turn resulted in similar or superior physicomechanical properties compared to the control mixtures. The setting time was prolonged with an increase in Na2 O dosage and FCA addition and was mainly governed by the initial molar ratio of SiO2 /Al2 O3 . The increase in FCA ratios consistently decreased semi-adiabatic peak temperature and time to reach the peak temperature. FCA addition decreased compressive strength and drying shrinkage of mortar mixes, whereas increase in Na2 O dosage significantly enhanced strength. The microstructural investigations revealed that the major reaction products of paste mixes were CSH, C-ASH, and/or MSH gels, along with minor phases such as forsterite, natrolite, brownmillerite, and spinel. The formation of MSH type gels was observed with an increased replacement ratio of FCA. In addition, the polymerization of main reaction products is found to be controlled by the Ca/Si and Si/Al ratios as revealed by microstructural analysis. The findings of this research point out the viability of producing BFS and FCA-based alkali-activated material with reasonable properties and their efficient utilization which may ensure sustainability.