The iron and steelmaking industry is undergoing significant transformation to meet the rising demand for steel and its components. Generally, the production of steel is a continuous process carried out by using various furnaces, including blast furnaces (BF), basic oxygen furnaces (BOF), integrated furnaces (BF and BOF), and electric arc furnaces (EAF), with distinct operating conditions. Among these, the EAF has emerged as a sustainable solution for steel production due to its utilization of recycled steel scraps and alloys. However, the processing of steel using EAF generates waste industrial slag that requires appropriate reuse to prevent environmental contamination. The EAF slag contains heavy toxic metals such as zinc (Zn), manganese (Mn), nickel (Ni), cadmium (Cd), chromium (Cr), aluminium (Al), posing risks to water and soil if disposed of in landfills, while incineration is both energy-intensive and costly. Therefore, a sustainable and cost-effective solution is imperative. Geopolymer concrete, made from waste materials, offers numerous advantages in terms of strength and durability. Despite this, there is a lack of literature on the effects of EAF slag on geopolymer concrete. The EAF slag has the potential to be utilized as aggregates or as a pozzolanic material in geopolymer composites. Recycling EAF slag in geopolymer composites not only promotes environmental sustainability but also reduces greenhouse gas emissions. This comprehensive review explores the application of EAF slag in geopolymer composites, examining its synergistic effects on the mineralogical composition, morphological characteristics, environmental consequences, and management, as well as its impact on the hardened properties of geopolymer composites.

Calcium carbide residue (CCR), a calcium-rich industrial waste, shows promise in improving mechanical properties of weak soils when used alone or in combination with pozzolanic materials and alkaline activators. This study comprehensively investigated the mechanical performance and stabilisation mechanism of CCR, CCR-fly ash, and alkaline-activated CCR-fly ash on kaolin clay, aiming to clarify their differences in mechanisms, identify their limitations, and promote effective application. The contribution of CCR, fly ash, alkaline activator, and initial water content of soil on enhancing soil strength was quantitively assessed through signal-to-noise ratio and analysis of variance (ANOVA) based on the Taguchi method. The stabilisation mechanism of different CCR-based materials was investigated by assessing the morphological and mineralogical features of stabilised samples. Taguchi analysis revealed that the development of soil strength was primarily influenced by initial water content in the early curing stage, while the contribution of fly ash became larger over time. Variation in CCR content had a limited effect on soil strength across all curing periods, as indicated by low contribution values and low statistical significance in ANOVA. The microstructural analyses revealed a low degree of formation of C-S-H and CA-H gels in soil stabilised with CCR alone and CCR combined with fly ash, while alkaline activated CCR-fly ash stabilised soil exhibited the coexistence of C-A-S-H and N-A-S-H gels. Taguchi superposition model was effectively used to estimate compressive strength results and supported the determination of suitable CCR-based materials for specific strength requirements.

Expansive soil poses significant challenges for engineering due to its susceptibility to swelling and shrinkage. This study aims to explore effective methods for improving its mechanical properties using single alkaline activators, single slag, and their combination. Laboratory experiments were conducted to evaluate the unconfined compressive strength (UCS) and analyze curing mechanisms through X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results demonstrate that all three treatments enhance soil strength, with the combination of alkali-activated slag being the most effective, followed by the single alkaline activator and single slag. Optimal dosages were determined as 15% for the activator and slag individually and 15% activator combined with 20% slag, yielding the densest structure and highest UCS. The activator's modulus of 1.5 was found to be optimal, and strength improved further with extended curing time. A microscopic analysis revealed that alkaline activation formed gel-like substances and dense needle-like structures, while slag generated CaCO3 and Ca(OH)2. The combination produces a synergistic effect, creating substantial amounts of C-S-H, C-A-S-H gel, and dense needle-like structures, which enhance soil compactness and strength by binding particles and filling voids. These findings provide insights into the curing mechanisms and offer practical solutions for improving expansive soil in engineering applications.

Guided by the solidification of loess contaminated with heavy metal ions (HMs), a natural inorganic diatomite (NID) was developed as curing agent under an alkaline activator (AA). The curing time, NID content and AA type on the mechanical properties of contaminated soil and solidification effect of HMs were investigated. The solidification source was analysed by microstructure measurement. As curing time increased, the solidification effect increased, with an optimum curing time of 28 days. The higher the content of NID, the stronger the solidification ability. Nevertheless, the strength showed a tendency of initial increase and subsequent decrease. The strength was maximum when NID content reached 10%. The AA created an alkaline environment to promote solidification. In comparison to Na2SiO3 solution, NaOH solution is more effective in the adsorption of HMs. The larger ionic radius of Pb2+ relative to Cu2+, limited HMs migration ability, thereby facilitating solidification.