A novel internal carbonation method for utilisation of steel slag-based binder : strength, microstructure, and in-situ carbon migration

Abstract

A novel internal carbonation method is proposed in this study for synthesising high-strength steel slag-based binder, using carbonated recycled concrete fines (CRCF) as calcium carbonate carriers and sodium meta-aluminate (SMA) solution as a chemical activator. The results demonstrate that the internal carbonation accelerates hydration and densifies microstructure of steel slag paste. The SMA-CRCF-activated steel slag (SSCRA) paste can achieve a setting time of around 1 h and a 28-day compressive strength of up to 32 MPa, showing a reduction of 84 % in setting time and a 5.4-fold increase in compressive strength compared to the SMA-activated steel slag (SSA) paste. During the process, the CRCF is rapidly dissolved upon activation of SMA solution, releasing carbonate ions to react with katoite and portlandite first and then the larnite in steel slag. After the internal carbonation, the main carbonated phases are Mc and calcite. The resulting C-A-S-H gel generated in the SSCRA paste is less polymerised than that in the SSA paste due to the incorporation of released Ca2+ ions from CRCF. Compared to accelerated carbonation curing, this method enables an easier fabrication process for steel slag products and eliminates constraints related to product dimensions, offering greater flexibility for field applications.