Clinker-free carbonate-bonded (CFCB) products prepared by accelerated carbonation of steel furnace slags: A parametric overview of the process development

[Display omitted] •CaCO3 precipitating during accelerated carbonation can be engineered into binder.•No conventional binder required. Water, alkaline residues, and CO2 are sufficient.•In addition to permanent CO2-sequestration, product will offset OPC production.•The process can also remediate industrial residues against environmental leaching.•Upscaling in UK, Belgium, Portugal, Canada, Japan, and China are discussed. Clinker-free carbonate-bonded (CFCB) products are construction materials produced by co-utilizing CO2 and alkaline industrial residues (AIR) in water-AIR systems, without any clinker components. The cementing properties of the CFCB products rely almost entirely on the cementing capability of the Ca-rich carbonates resulting from accelerated carbonation, and do not depend on the formation of any conventional binder (e.g., C-S-H). The CFCB technology involves preparation of a wet mix of particulate AIR (step 1), followed by preparation of a shaped precursor (step 2), followed by accelerated carbonation (step 3). Each of these steps involves several (interdependent) parameters. The parameters that are discussed in this overview include: (a) types of AIR, (b) control of the physical properties of the starting material, (c) compositional screening of the particulate materials, (d) pre-hydration of the particulate materials, (e) liquid to solid ratio of the shaped precursor, (f) particle packing in shaped precursor, and size of the shaped precursor, (g) process CO2-availability, (h) process temperature, (i) process carbonation duration, (j) process pH, and (k) post-carbonation curing. Since steel furnace slags (SFS) have been the most popular AIR used for the production of CFCB products, this overview is focused on them. However, utilization of other AIRs (like incineration ashes), as well as pure minerals like ɣ-C2S and Ca(OH)2 are also mentioned at appropriate places. Ongoing upcycling efforts across the world are also discussed with reference to several producers in Europe, North America, and Asia.