Developing Mineral Foam Blocks from Oil Shale Byproducts through Accelerated Carbonation

This study explores the impact of accelerated carbonation curing (ACC) on the production of sustainable mineral foam blocks (MFBs) for wall applications. MFBs were prepared with varying proportions of cement (CEM-I 42.5R) and oil shale ash (OSA), achieving 70–85% residual resource integration. Aluminum powder acted as a pore-forming agent to create the foamed structure. ACC conditions (100% CO₂, 1 bar, ∼65% RH) enhanced performance metrics, which were evaluated by compressive strength, density, porosity, and CO₂ uptake values. OSA incorporation can offer advantages in thermal properties of MFBs, yet without ACC treatment, the strength development of MFBs was primarily governed by cement hydration. Carbonated samples exhibited higher compressive strength (2.5–5.7 MPa) than uncarbonated ones (1.1–3.4 MPa). The analyses revealed partial carbonation of certain hydrated calcium-silicate and ettringite phases, while portlandite formed during hydration reactions was nearly fully converted to calcite. This conversion maximized CO₂ sequestration (∼140 kg/ton), while maintaining a balanced strength. The role of anhydrite was found to be primarily pH dependent, participating in secondary reactions that enhanced the microstructure and integrity in conjunction with calcium silicate hydrates (C–S–H), calcium–silicate(aluminum)-hydrate (C–S(A)–H), ettringite, and gypsum. Mineralogical and microstructural analyses confirmed the formation of CaCO₃ in various morphologies. Carbonation-induced densification, primarily driven by CaCO₃ precipitation and transformation of amorphous phases, resulted in a more compact microstructure with reduced porosity. These findings demonstrate that ACC treatment improves MFB performance, optimizing high-volume OSA use while achieving significant CO₂ mineralization, advancing sustainable construction.