Abstract
The presence of free lime and periclase in converter slag prevents it from directly being utilized as a source of concrete aggregate due to the deleterious expansion caused by reaction of free lime and periclase. In general, a six-month aging period is suggested in order to avoid any potential problems, but it is a tedious process that requires a long period of time. In this work, supercritical CO2 (SCD) was used to reduce the aging period down to one day or so. Since SCD creates a more aggressive environment for reaction, it can directly attack the surface of free lime and periclase to induce expansive reaction before using converter slag as concrete aggregate. According to the experimental results, the surface of converter slag was successfully carbonated by SCD, showing 7.80% of CO2 uptake by weight of converter slag. It was found that the mortar bar made of reacted converter slag reduced the amount of expansion. The 28-day compressive strength of mortar with converter slag was slightly reduced after reaction with SCD, but it was still 32% higher than mortar made of conventional sand.
Highlights
Introduction and Alexander SBrandAccording to the World Steel Association, the global crude steel production in 2019 was 1869.9 million tons, and it has been increasing every year [1]
This test procedure is designed to separate alkali reactive aggregate, the applicability of this test procedure to examine the expansion caused by free lime and periclase was proven by the earlier work [18] because the testing temperature is so high that it can accelerate the reaction of CaO and MgO
X-ray Powder Diffraction (XRD) analysis was performed to investigate the effect of supercritical carbon dioxide (SCD) on mineralogical changes of converter slag after reaction
Summary
The cement used was ASTM Type I Ordinary Portland Cement (OPC). The converter slag with unknown degree of aging was used for this work. Since there is no standard available for converter slag to be used as aggregate for concrete, the standard specification established for electric arc furnace oxidation slag was used for evaluation on chemical stability of converter slag. Sci. 2021, 11, 1918 crete Aggregate” [27], the electric furnace oxidation slag needs to contain a CaO content of 40% or less and a basicity (CaO/SiO2) ratio of 2.0 or less in order to be used as concrete aggregate. It was found that the converter slag used in this study did not satisfy both criteria. This indicates the converter slag that is used in this work is considered dangerous. To be used as aggregate for concrete if no additional separate treatment process is applied
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