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The type of steel furnace slag (SFS), including electric arc furnace (EAF) slag, basic oxygen furnace (BOF) slag, ladle metallurgy furnace (LMF) slag, and argon oxygen decarburization (AOD) slag, can significantly affect the composite properties when used as an aggregate or as a supplementary cementitious material in bound applications, such as concretes, mortars, alkali-activated materials, and stabilized soils. This review seeks to collate the findings from the literature to express the variability in material properties and to attempt to explain the source(s) of the variability. It was found that SFS composition and properties can be highly variable, including different compositions on the exterior and interior of a given SFS particle, which can affect bonding conditions and be one source of variability on composite properties. A suite of tests is proposed to better assess a given SFS stock for potential use in bound applications; at a minimum, the SFS should be evaluated for free CaO content, expansion potential, mineralogical composition, cementitious composite mechanical properties, and chemical composition with secondary tests, including cementitious composite durability properties, microstructural characterization, and free MgO content.

This study aims to investigate the possibility of using Linz-Donawitz (LD) slag as one of the cementitious materials for preparation of composite slag (having 8 and 15% LD slag), which will subsequently be used for manufacturing portland slag cement (PSC). PSC samples (having overall 4 to 9% LD slag) were prepared using LD slag from two sources in a laboratory ball mill. PSC samples were analyzed for various chemical characteristics and physical properties. Studies were conducted on concrete mixtures prepared at water-cement ratios (w/c) of 0.65 and 0.40. Fresh, hardened, and durability properties of concrete mixtures prepared using PSCs made with composite slag having up to 15% LD slag were found to be comparable to their corresponding control mixtures. Based on results, it was observed that composite slag having LD slag up to 15% of total slag can be used up to 60% for manufacturing PSC along with clinker and gypsum. The 3-, 7-, and 28-day compressive strength of PSC samples containing LD slags in different proportions were found to be comparable to control PSC samples and meeting the requirements of IS 455:2015. Even though the free lime content in LD slags was significantly higher (free lime content of 3.03 and 3.48%) in comparison to granulated blast-furnace slag (GBFS), it had almost a negligible effect on the PSC prepared using LD slag and soundness of experimental and control PSC was comparable because the maximum amount of LD slag added in overall PSC was restricted to 9%. The addition of LD slag in different proportions up to 9% in overall PSC does not seem to have any detrimental effect on performance of concrete in terms of sorptivity, carbonation depth, chloride penetration, and diffusion, which indicates its suitability for application in reinforced concrete structures. Keywords: composite slag; durability; granulated blast-furnace slag (GBFS); Linz-Donawitz (LD) slag; portland slag cement (PSC).

By-products from the non-ferrous industry are an environmental problem; however, their economic value is high if utilized elsewhere. For example, by-products that contain alkaline compounds can potentially sequestrate CO 2 through the mineral carbonation process. This review discusses the potential of these by-products for CO 2 reduction through mineral carbonation. The main by-products that are discussed are red mud from the alumina/aluminum industry and metallurgical slag from the copper, zinc, lead, and ferronickel industries. This review summarizes the CO 2 equivalent emissions generated by non-ferrous industries and various data about by-products from non-ferrous industries, such as their production quantities, mineralogy, and chemical composition. In terms of production quantities, by-products of non-ferrous industries are often more abundant than the main products (metals). In terms of mineralogy, by-products from the non-ferrous industry are silicate minerals. Nevertheless, non-ferrous industrial by-products have a relatively high content of alkaline compounds, which makes them potential feedstock for mineral carbonation. Theoretically, considering their maximum sequestration capacities (based on their oxide compositions and estimated masses), these by-products could be used in mineral carbonation to reduce CO 2 emissions. In addition, this review attempts to identify the difficulties encountered during the use of by-products from non-ferrous industries for mineral carbonation. This review estimated that the total CO 2 emissions from the non-ferrous industries could be reduced by up to 9–25%. This study will serve as an important reference, guiding future studies related to the mineral carbonation of by-products from non-ferrous industries. Graphical abstract

Increasing global cement and steel consumption means that a significant amount of greenhouse gases and metallurgical wastes are discharged every year. Using metallurgical waste as supplementary cementitious materials (SCMs) shows promise as a strategy for reducing greenhouse gas emissions by reducing cement production. This strategy also contributes to the utilization and management of waste resources. Controlled low-strength materials (CLSMs) are a type of backfill material consisting of industrial by-products that do not meet specification requirements. The preparation of CLSMs using metallurgical waste slag as the auxiliary cementing material instead of cement itself is a key feature of the sustainable development of the construction industry. Therefore, this paper reviews the recent research progress on the use of metallurgical waste residues (including blast furnace slag, steel slag, red mud, and copper slag) as SCMs to partially replace cement, as well as the use of alkali-activated metallurgical waste residues as cementitious materials to completely replace cement for the production of CLSMs. The general background information, mechanical features, and properties of pozzolanic metallurgical slag are introduced, and the relationship and mechanism of metallurgical slag on the performance and mechanical properties of CLSMs are analyzed. The analysis and observations in this article offer a new resource for SCM development, describe a basis for using metallurgical waste slag as a cementitious material for CLSM preparation, and offer a strategy for reducing the environmental problems associated with the treatment of metallurgical waste.

The amendment of cementitious binders with waste materials aids as a path to reduce the volume of waste and carbon emission. This review summarizes the current state of practice for cementitious binder fabrication in favor to the utilization of waste materials such as waste concrete powder (WCP), coal bottom ash (CBA) and steel slags. These materials have the potential to be employed as cementitious material, however much of the application is still up to the laboratory scale. This manuscript will serve as the support to understand the utilization of mentioned waste as nontraditional cementitious products. The highlighted areas likely need more refinement and research with indication on possible negative impact on application of wastes. The use of the aforementioned wastes for blending with OPC (ordinary Portland cement) can reduce carbon emissions from cement manufacturing. Additionally, it can also reduce the use of natural resources during clinker production.

The viscosity of high-titanium blast furnace slag with different TiO2 content, Al2O3 content, and basicity was measured at 1653–1773 K using the rotational cylinder method. The phase composition of the slag is measured by XRD. Phase diagram of the slags is calculated by FactSage software. Ionic network structure of the slags is analyzed by FT–IR. Results show that TiO2 depolymerizes the silicate network structure, reducing viscosity at high temperature, while increasing Al2O3 content generates a more complicated silicate, increasing viscosity. Basicity affects viscosity, with higher basicity resulting in lower viscosity above 1733 K. Perovskite significantly affects the viscosity of slag. This study provides an in-depth understanding of the relationship between the composition and viscosity of high-titanium blast furnace slag, which is very important for improving production efficiency.

Red mud (RM) is a solid waste material with high alkalinity and low cementing activity component. The low activity of RM makes it difficult to prepare high-performance cementitious materials from RM alone. Five groups of RM-based cementitious samples were prepared by adding steel slag (SS), grade 42.5 ordinary Portland cement (OPC), blast furnace slag cement (BFSC), flue gas desulfurization gypsum (FGDG), and fly ash (FA). The effects of different solid waste additives on the hydration mechanisms, mechanical properties, and environmental safety of RM-based cementitious materials were discussed and analyzed. The results showed that the samples prepared from different solid waste materials and RM formed similar hydration products, and the main products were C–S–H, tobermorite, and Ca(OH) 2 . The mechanical properties of the samples met the single flexural strength criterion (≥ 3.0 MPa) for first-grade pavement brick in the Industry Standard of Building Materials of the People's Republic of China-Concrete Pavement Brick . The alkali substances in the samples existed stably, and the leaching concentrations of the heavy metals reached class III of the surface water environmental quality standards. The radioactivity level was in the unrestricted range for main building materials and decorative materials. The results manifest that RM-based cementitious materials have the characteristics of environmentally friendly materials and possess the potential to partially or fully replace traditional cement in the development of engineering and construction applications and it provides innovative guidance for combined utilization of multi-solid waste materials and RM resources.

The demand for production of cements is ever increasing to meet the infrastructure development globally. The energy and emission factors available for cements in most of the life cycle assessment (LCA) databases may not exactly suit for all the geographical locations. The main challenge in Indian scenario is the absence of database for LCA study. This study attempts to develop the energy and emission factors for the manufacturing of cements in Indian context. In the present study, five different cement manufacturing plants located in north, south, east, west and central zones of India are considered to assess the energy dissipation and carbon dioxide emission involved during the production of ordinary Portland cement (OPC). Most of the data is collected from the field, so that the energy and emission factors determined will be suitable for the zonal study. The study is then extended to assess the energy consumption and carbon dioxide emission for three blended cements, viz. Portland Pozzolan cement (PPC), Portland slag cement (PSC) and composite cement (CC) with permissible known replacement levels of fly ash, granulated blast furnace slag and both fly ash and slag, respectively. The average energy use and carbon emission is found to be on higher side in India by 15.14% and 12.64%, respectively, compared to other countries in manufacturing of cements. An average energy consumption in manufacturing of PPC, PSC and CC is found to be respectively 24.5%, 35.3% and 43.13% less compared to that of OPC. The CO 2 emission intensity for OPC is found to vary between 893 and 940 kg/tonne of cement from five different zones, and an average of respectively 24.8%, 40.97% and 47.18% lower CO 2 emission was observed from PPC, PSC and CC compared to OPC. From the inventory results, CC has proven to be a more sustainable cement with low energy consumption and lower CO 2 emission compared to other cements.

Preparation of high acidity coefficient slag wool fiber with molten slag and modifying agents is considered to be a positive approach for value-added utilization of blast furnace slag. In order to achieve the multi-purposes of fiber-forming, energy saving, and waste heat recovery, the modifying agents that can improve the acidity coefficient of slag effectively, economically, and environmentally were investigated. Three agents with different acidity coefficients were adopted to modify slag and manufacture wool fibers. The effect of agent and slag proportion on the melting temperature and viscosity of molten slag was studied at a fixed acidity coefficient of 1.8 and 2.0. The results indicate that the sample modified with high acidity coefficient agent and high slag proportion has lower melting temperature and viscosity. The effect of agent and slag temperature on the fiber diameter was also investigated when the acidity coefficient of slag is 2.0. At a fixed slag proportion of 50 wt.%, the mean diameter decreases with increasing temperature and decreasing viscosity coefficient. Besides, the temperature drops caused by the addition of agents and energy consumption of samples for heating the slag were also analyzed.

Alkali-activated materials (AAMs) are a kind of hardened slurry produced by an alkali activation reaction between a silicate precursor and an alkali activator that is treated as an environmentally friendly cementitious material that can be used in place of ordinary Portland cement (OPC). However, some studies point out that the AAMs with a single precursor had some defects. To realize the high value-added utilization of phosphorus slag (PS), this paper mixed PS with granulated blast furnace slag (GBFS) to prepare alkali-activated composite cementitious materials. The workability, mechanical properties, and hydration of alkali-activated phosphorus slag—granulated blast furnace slag (AAPG) were characterized using fluidity, setting time, compressive strength, flexural strength, hydration heat, XRD, FTIR, TG-DSC, and SEM + EDS. The results show that GBFS can improve the fluidity of AAPG, but the slurry will flash set after exceeding 20% GBFS content. GBFS can rapidly hydrate to generate C-S–H to improve its early strength, but the later stage results in larger pores due to the uneven distribution of matrix products. The hydration generation products of AAPG are C-S–H and C-(N)-A-S–H dominated by the Q 2 unit, with some hydrotalcite by-products generated.