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

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 con-ducted. 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 con-taining 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.

Automated summary

This study explores the valorization of high volume-converter steel slag in green composites and achieves the production of steel slag-based building materials with high compressive strength and CO2 uptake ability through alkali activation and carbonation curing methods.