Slag cement, also called ground granulated blast furnace slag (GGBFS), is the cement that enhances traditional concrete benefits of strength and durability while reducing waste, energy use, and greenhouse gas (GHG) emissions. It is used in construction applications in conjunction with traditional Portland cement, as part of blended cement, or as stand-alone cement. It usually replaces some percentage of the Portland cement in concrete mixes.
Slag cement’s constituent components are slag, clinker, and gypsum. Slag is a blend of iron ore, limestone, and dolomite heated in an iron blast furnace at up to 1,450-1,500ºC. It is essentially a non-metallic product comprising more than silicates and alumina-silicates of lime replacing 90% glass. As slag is a by-product of steelmaking, slag cement is largely produced by integrated steel-cement manufacturers. Slag application reduces the overall cost of cement production and, thus, slag cement is cheaper than other cement types, such as Ordinary Portland Cement (OPC) and Plain Cement Concrete (PCC). According to estimates, slag cement is 24% cheaper than OPC and 17% less costly than PCC. This makes it ideal for use in mass construction projects, such as dams. The overall composition of slag cement is blast furnace slag (75%), clinker (20%), and gypsum (5%).
Slag cement improves the workability, placement, and consolidation of concrete and provides higher compressive strength to concrete compared to OPC. Slag cement-based concrete shows higher flexural strength for a given compressive strength. Higher compressive strength (achievable with slag cement) enhances structural stiffness while minimising load deflections.
The additional calcium silicate hydrate and the dense slag cement paste reduce pore size and cement permeability. Lower permeability, in turn, reduces the ingression of harmful substances (chlorides, sulphates etc.) and water availability catalyses harmful chemical reactions within the concrete mix. Minimum tricalcium aluminate content in slag cement makes it suitable for mass concrete because of its low heat of hydration and low-temperature differential.
One of the most important aspects of slag cement is its ability to drive emission reduction in the cement industry. Slag cement production requires lower clinker consumption, which results in lower GHG and CO2 emissions. Slag cement also lowers landfill burden and reduces steel plant emissions compared to the traditional air-cooling process. Moreover, slag cement production requires 50% less energy compared to OPC, which further reduces carbon emissions.
Slag cement sales are expected to record an 11.8% CAGR over 2020-26 to c.USD41bn by 2026. The industry will likely primarily be driven by use in residential buildings, as rising disposable incomes and reductions in borrowing costs are expected to drive the demand for residential units. Growing regulatory curbs on carbon emissions and rising carbon taxes and penalties are also expected to drive the market in the forecast period (2000-2006).
Slag cement is expected to play a key role in the energy transition journey. There is a renewed focus on slag cement today as cement producers become more conscious of sustainable production. Slag cement not only provides high-quality concrete but also addresses global warming, natural resource conservation, and minimisation of landfill pollution.
