Abstract
The use of electric arc furnace slag (EAFS) as sole precursor to produce alkali-activated mortars has been experimentally investigated. EAFS, a by-product of the steel recycling industry, is a coarse material with unevenly distributed and size-extensive particles. Milling of EAFS was required to achieve a cement-like sized powder before it could be used as precursor. Different combinations of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) were used, by varying the Na2O/binder concentration (4%, 6%, 8%, 10%, 12%) and SiO2/Na2O ratio (0, 0.5, 1.0, 1.5, 2.0, 2.5) to maximize the mechanical performance. The alkaline solutions were prepared 24 h prior to mixing to unify temperatures for all mixes. The results showed that the SiO2/Na2O ratio and strength development are directly proportional. The maximum 28-day compressive strength obtained, after being subjected to an initial 24 h thermal curing at 80 °C, was 9.1 MPa in mixes with 4% Na2O/binder and 2.5 SiO2/Na2O. However, after an additional 28 days of accelerated carbonation, the maximum compressive strength (i.e., 31 MPa compared to 3.9 MPa in uncarbonated mixes, corresponding to an 800% increase) was obtained in mixes with 12% and 1.0 for Na2O/binder and SiO2/Na2O, respectively, thus showing an alteration in the optimal alkaline activator contents.
Highlights
The world’s annual population is continuously increasing by 1.05% on average, with an increase of 81 million people in 2020 [1]
The results revealed that concrete specimens containing properly ground electric arc furnace slag (EAFS) showed better microstructure, higher compressive strength, lesser porosity and better durability performance compared to the reference blast furnace slag blended cement specimens
fly ash (FA) showed a wider peak at 20 μm and a lower distribution percentage at 0.35 μm compared to EAFS and cement
Summary
The world’s annual population is continuously increasing by 1.05% on average, with an increase of 81 million people in 2020 [1]. It is a well-known fact that for each one tonne of cement produced, around 0.5–0.6 tonnes of CO2 (0.59 according to IEA, 2020 [4]) are being released into the atmosphere, meaning that in 2016, the cement industry itself released nearly 2.5 billion tonnes of CO2, which accounted for 8% of the global CO2 emissions of the same year [5,6] Solving this issue cannot be done by cutting the production of cement alone; other cementreplacing materials need to be found to meet the growing demand for this vital building material. One contender is the electric arc furnace slag (EAFS), as the steel industry is shifting from new steelmaking to a recycling system, reducing the amount of GGBFS. It has an aluminosilicate-rich chemistry giving it the possibility to be the cement-replacing AAM used in concrete. It is being used mostly as an aggregate substitute for road base course layers and asphalt pavements [11,12], which is a downcycling process from what they can offer
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