Influence of Exposure Conditions on the Carbonation and Durability of ISSA-Modified Cementitious Materials

Abstract This study explores how exposure conditions affect the carbonation process of cementitious materials that include incinerated sewage sludge ash (ISSA), to evaluate ISSA’s potential as a sustainable additive in cement-based construction materials and its role in CO₂ sequestration. Hardened cement pastes with different amounts of ISSA (0 %, 20 %, 25 %, 30 %, and 35 %) were subjected to two carbonation experiments: indoor and outdoor in a natural environment. The carbonation process was tracked using phenolphthalein tests, scanning electron microscopy (SEM-EDS), X-ray diffraction (XRD), and calcium carbonate content measurement. Results show that ISSA-modified cement pastes have increased carbonation potential, especially at 20–25 % ISSA, with a rise in CaCO₃ formation and diverse calcite morphologies. However, higher ISSA levels (>30 %) led to decreased carbonation efficiency. The outdoor experiment revealed the significant influence of temperature and humidity changes on carbonation rates, resulting in slower CO₂ absorption compared to laboratory conditions.