Evaluation of copper slag and stainless steel slag as replacements for blast furnace slag in binary and ternary alkali-activated cements

Abstract

Commonly used alkali activation precursors such as blast furnace slag and fly ash will soon become less available due to resource competition, and may cease to be produced in certain regions. This limitation in future supply is a main driving force for the investigation of alternative precursor sources, such as non-blast furnace slags and non-ferrous slags, to produce alkali-activated binders. The current study investigates the incorporation of copper slag (CS) and stainless steel slag resulting from electric arc furnace operations (EAFSS) as partial replacements for ground granulated blast furnace slag (GGBFS) in producing alkali-activated materials (AAMs), at paste level. Five binary alkali-activated mixtures with different replacement levels of GGBFS with CS, and three ternary mixtures with both CS and EAFSS as partial and total replacements for GGBFS, are activated by a sodium silicate solution. Replacing GGBFS with CS and EAFSS retards the reaction kinetics, resulting in improved fresh-state properties of the investigated AAMs, better retention of workability and longer setting times. The reaction of alkali-activated 100% CS shows minimal initial exothermic activity until 3.5 h, when a single intense peak appears, representing delayed dissolution and subsequent polycondensation. X-ray diffraction (XRD) data indicate that the main crystalline phases of CS and EAFSS are stable in these alkaline systems; it is the glassy components that react. The use of CS and EAFSS in blended AAMs causes a minor increase in porosity of ~ 1–3% with respect to GGBFS only, and a small reduction in compressive and flexural strengths, although these reach 80 MPa and 8 MPa, respectively, after 28 days, even at a replacement level over 65 wt. %. Conversely, the 100% CS mixture exhibits a one-day compressive strength of 23 MPa, with a negligible increase thereafter. This result agrees with both FTIR and SEM analysis which highlight only minor changes in binder development after two days. It is believed that the unusual behaviour of CS in the investigated mixtures is related to the low availability of calcium in this precursor material.

Why geopolymers and alkali‐activated materials are key components of a sustainable world: A perspective contribution

“…and activators which includes various mine tailing slags, red mud, biomass ashes, construction and demolition waste, calcined clays, and more. [50][51][52][53][54][55][56][57][58][59][60] The valorization of widely available, aluminosilicate-containing mine tailings to make geopolymers is also a rich area of potential research. While utilizing such industrial wastes for useful products is a positive aspect, they also introduce new mineralogical and chemical aspects and compounds that can significantly affect the alkali-activation process.…”

Utilization of Copper–Molybdenum Tailings to Enhance the Compressive Strength of Alkali-Activated Slag-Fly Ash System

“…Commonly used alkali activation precursors such as GBFS and FA will be less available due to resource pressures. Supply limitation is an important reason to research alternative precursors [22]. AAMs could consume vast quantities of industrial solid waste such as FA, iron ore tailings, and GBFS [23][24][25] and save up to 14% of the cost of replacing precursors and activators with industrial residues [26], making them one of the most promising green cementitious materials [27,28].…”

“…Utilizing synergistic effects between GBFS and other types of industrial solid wastes could lead to the production of high-performance, environmentally friendly construction materials [22]. A synergistic effect was exhibited within an alkaline environment between GBFS and red mud; when GBFS was partially replaced by red mud, its mechanical properties were comparable to or better than those samples without added red mud [33].…”

Impact of Ca, Al, and Mg on reaction kinetics, pore structure, and performance of Fe‐rich alkali‐activated slag

“…However, the reactivity of NFMS even with a fully amorphous phase is still lower, compared to commonly used precursors like GGBFS. In a study conducted by Stefanini et al, 24 they substituted GGBFS with NFMS and observed that this substitution slowed down the reaction kinetics. It also resulted in a slight increase in porosity (approximately 2% when fully replaced) and a reduction in compressive strength.…”