CO2 activated steel slag-based materials: A review

Highlights

• Kinetics of steel slag CO₂ activated-based materials are presented and discussed.

• Composition, fineness of the slag and CO₂ uptake are critical kinetic parameters.

• CO₂ activated steel slag-based materials are suitable for structural construction applications.

• CO₂ uptake can reach 1.76 tonnes for each 10 tonnes of Slag CO₂ activated binder.

• Further research on kinetic conditions and industrial feasibility prospects is needed.

Abstract

World sustainable development concerns finding new solutions for mitigation of waste accumulation on landfills and global warming increase. New clean technologies, which can reuse pollutant materials and sequestrate industrial waste and greenhouse gases, are potential solutions to mitigate global environmental threats. The feasibility of developing cement-free steel slag-based construction materials activated by carbonation was reviewed in this study, by analysing different steel slag, its chemical composition and carbonation reaction. The influence of carbonation conditions by controlling parameters such as humidity, carbon dioxide concentration, partial pressure, compacting pressure, slag fineness, temperature and carbonation duration was also reviewed. Good compressive strength and carbon dioxide uptake results demonstrated that slag-based materials activated by carbonation are potential for replacing precast Portland cement-based materials, they are also an environmentally friendly solution against Global Warming.

Introduction

Global Warming is caused by production accumulation of Green House Gases (GHGs); therefore, finding efficient methods for reducing its production, implementing its capture and storage systems is compulsory. GHGs include carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulfur hexafluorocarbon (F₆C). Nowadays, the most abundantly emitted GHGs are CO₂ (56%) and CH₄ (18%) (Zoundi, 2017).

Global Warming exceeded its limits in 2015, mainly due to a high content of carbon dioxide (CO₂) in the atmosphere (Szulejko et al., 2016). CO₂ emissions of 4,45 billion tonnes of CO₂-equivalents in 2015 (Eurostat, 2017a) from a spectrum of industrial processes pose negative impacts on the environment and human health.

Regarding CO2 production, fossil fuel power plants are the largest sources (40% of total CO2 emissions). Other sources of CO₂ arise from transportation and general industry (Eurostat, 2017a). Regarding the construction Sector, the Portland cement industry is responsible for emitting 15% of the indirect CO₂ emissions from non-energy use moreover, its production process consumes a huge amount of energy (Huang et al., 2018).

Waste from European economic activity and households produced 2.5 billion tons in 2014. Most of this waste was dumped in landfills resulting in potential long-term public health problems, soil and water contamination (Eurostat, 2017b). This waste management behaviour results in accumulation of large amount of mineral waste deposited in fields which leads to environmental pollution and serious landscape impacts which affect the quality of life of local population. Preventive measures typically involve the use of earth/rock dams or lagoons to store waste. Unfortunately, potential collapse of such structures could have serious impacts on the environment and human health and safety (European Commission (EC), 2009). The steel industry has steel slag as its main by-product which is produced at large scale. The steelmaking process uses three different furnaces. The basic-oxygen furnace (BOF) is used at the first steel refinement of the steelmaking process with molten iron, steel scraps plus lime or dolomite as input. The electric-arc furnace (EAF) has a similar steel refining process but uses high-power electric arcs to produce high quality steel from recycled steel scrap. After being refined by the BOF or EAF, the steel can be refined again through a secondary steel making operation which aims to achieve a specific chemical composition. This secondary operation uses the ladle furnace which is similar to the EAF and has ladle slag as by-product (Jiang et al., 2018). The steel slag annual production worldwide is about 130 million tons which are mainly Electrical Arc Furnace (EAF) and Basic Oxygen Furnace (BOF) slags (van Zomeren et al., 2011). Most part of this production is disposed on landfills however; the slag is also used as aggregates for different construction purposes such as ready-mix concrete, asphaltic concrete, road bases and surfaces, and fills (Piatak et al., 2015).

There are numerous studies about carbonation of Portland cement-based materials such as the review where Ashraf summarized relevant information of these carbonation features and highlighted areas where further investigation could be taken (Ashraf, 2016). Besides this general approach, Jang et al. focused the research on CO₂ sequestration (Jang et al., 2016) and Zhang et al. analysed the application of carbonation by its curing mechanism, achieved properties and feasibility (Zhang et al., 2017).

Steel slag used as an alternative recycled raw material activated by CO₂ is being recently studied and considered as a solution for storing CO₂, reducing GHG emissions, as well as recycling and valorising steel industry waste. A challenge on the steel slag-based carbon dioxide cured/activated materials is related with the variety of its chemical composition which depends on the steel manufacturing specification. Different benches of slag have a different chemical composition and structure, making the carbonation reaction more difficult to model and understand (Mahoutian et al., 2018).

Recently, studies have shown that the steel slag will react with aqueous CO₂
under controlled conditions to form complex carbonates
which have binding capabilities. The compressive and flexural strength of the analysed
cement-free binder systems increase with the carbonation duration; moreover, the systems exhibit mechanical properties
that are comparable to ordinary Portland cement systems, which are commonly used as the binder in the construction industry (Mo et al., 2017).

Therefore, apart from the cement-based, this review aims to emphasizes the current research status on steel slag-based construction materials activated by carbonation. This review also covers the reaction, carbonation conditions, carbon dioxide uptake, carbonation products, compressive strength, materials properties, different construction material applications and research needs. Information was obtained from well-known journals and researchers which have been recently working with slag-based carbon dioxide activated materials.