20.500.12556/DiRROS-29286 Effect of alkali-activation pre-treatment of sintered aggregates from biomass fly ash on microstructural and mineralogical evolution The increasing demand for lightweight construction materials and the depletion of natural aggregates highlight the need for circular solutions based on industrial residues. Co-incineration biomass ash (BA), despite its high availability, carbon content, and variable composition, remains underutilised in high-value applications. This study explores a previously unexamined valorisation route through the production of sintered alkali-activated aggregates using sodium-silicate-assisted pre-treatment. Two BA mixes with different Na2O dosages (7.57 and 5.44 wt% Na2O) were pelletized and thermally treated between 700 and 1200 ◦C. The alkali activation pretreatment simultaneously improved the granulation efficiency, enabled the formation of alkali-activated gel, and supplied Na2O as a flux, significantly influencing the crystalization, melting, and sintering behavior. Comprehensive characterisation using mercury intrusion porosimetry, dilatometry, X-ray diffraction, Fouriertransform infrared spectroscopy, thermogravimetry–differential thermal analysis, and scanning electron microscopy revealed a coherent thermal sequence: from gel deterioration and a macroporosity development below 800 ◦C, to the crystallization of Ca–Mg silicates and the formation of an akermanite-dominated matrix at 800–1000 ◦C, followed by partial melting and sintering in the presence of a liquid phase above 1000 ◦C. A higher alkali content promoted earlier densification and strength development. Aggregates with higher Na2O content (BA1) exhibited an earlier onset and higher intensity of sintering shrinkage, reaching a compressive strength of 4.53 MPa at 1100 ◦C, corresponding to more than a fourfold increase compared to thermally untreated aggregates, whereas the lower-alkali mix (BA2) remained below 0.26 MPa at the same temperature. Open porosity of BA1 aggregates increased to 78.8% after heating to 800 ◦C due to deterioration of the alkali-activated gel, followed by densification accompanied by akermanite-dominated crystallization and pore coalescence, resulting in 73.1% porosity and a bulk density of 1.28 g/cm3 at 1100 ◦C. The results identify BA as a promising precursor for lightweight or dense SAA and demonstrate alkali-activation-assisted thermal treatment to be a technically applicable circular-economy pathway for converting co-incineration BA into value-added construction materials. alkali-activated materials biomass ash sintered aggregates lightweight aggregates alkalijsko aktivirani materiali biomasni pepel sintrani agregati lahki agregati true false true Elsevier Angleški jezik Slovenski jezik © 2026 The Authors Neznano 2026-05-06 11:24:43 2026-05-06 11:31:03 2026-05-07 03:51:13 0000-00-00 00:00:00 2026 0 0 str. 19392-19407 part B issue 12 May 2026 0000-00-00 Zaloznikova Objavljeno apc 0000-00-00 0000-00-00 2026-03-04 54 1873-3956 10.1016/j.ceramint.2026.03.041 271010307 https://www.sciencedirect.com/science/article/pii/S0272884226010709 0 6bf00323-492d-11f1-8a5a-001a4af901a5 https://dirros.openscience.si/Dokument.php?lang=slv&id=43836 http://hdl.handle.net/20.500.12556/DiRROS-24254 0 6d018c21-492d-11f1-8a5a-001a4af901a5 https://dirros.openscience.si/Dokument.php?lang=slv&id=43837 RAZ_Tesovnik_Anze_2026.pdf RAZ_Tesovnik_Anze_2026.pdf 1 55B775D115F6AEC2F1E4EA5132674BF0 d973b2b0757c08a3beba0a835528917a117c2ac9dff8e59fa7c72eddd125b699 195fcd04-492e-11f1-8a5a-001a4af901a5 https://dirros.openscience.si/Dokument.php?lang=slv&id=43838 Zavod za gradbeništvo Slovenije Dataset for alkali-activation pre-treatment of sintered aggregates 0 0 0