Valorization of converter steel slag in sustainable mortars by a combined alkali and carbonation activation

Abstract

Converter steel slag is the main by-product in steel-making industries, which is difficult to be utilized in building materials manufacture due to the poor hydraulic reactivity. This study aims to explore the valorization of high volume-converter steel slag in green composites by applying an innovative curing strategy, which provides a possibility to produce steel slag-based building materials with a high CO2 uptake ability and satisfied mechanical performance. The high volume of converter steel slag (CSS) containing mortars based on alkali activated ground granulated blast furnace slag (GGBS) activated a combined carbonation curing was designed and proposed. The activation mechanism was investigated by characterizations of reaction products, reaction heat, mechanical performance, and shrinkage behavior of GGBS-CSS mixtures. X-ray diffraction, thermogravimetric analysis, FTIR test, isothermal calorimeter test, compressive strength test, phenolphthalein test, and shrinkage test were conducted. The results indicated that the GGBS-CSS mortars can be efficiently activated by alkali activation (7 days) and carbonation (21 days), the highest compressive strength (50.21 MPa) was achieved by the mixtures containing GGBS and CSS with 50:50, and activated by 2M sodium hydroxide solution. The main reaction products after combined activations included calcium carbonates (vaterite, aragonite and calcite) and C-(A)-S-H gels. CSS content and activator dosage were addressed as the main factors to control the activation processes. The CO2 uptake potential of GGBS-CSS mixtures all exceeded 100 kg/ton binder.