Experimental study on methods for carbonation depth measurement of alkali-activated foam pastes for carbon dioxide storage

Alkali-activated foam pastes (AAFPs) have significantly different hydration and carbonation mechanisms compared with ordinary Portland cement (OPC) pastes. An accurate determination of the carbonation depth of AAFP is crucial for evaluating their carbon dioxide storage potential. The main objective of this study was to determine whether detection methods for carbonation depth developed for OPC are applicable to AAFP. An AAFP was prepared using fly ash, ground granulated blast-furnace slag, sodium hydroxide solution, waterglass solution and hydrogen peroxide as the main raw materials. The applicability of the phenolphthalein–alcohol solution method (PASM) and the layer-by-layer grinding pH method (LGPM) for measuring the carbonation depth of AAFP was analysed using rapid carbonation tests, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy and other characterisations of AAFP samples. The results showed that the carbonation depth and carbonation rate coefficient of the AAFP measured using the LGPM were, respectively, 1.42–1.65 and 1.64 times higher than those measured using the PASM. The LGPM was able to determine the carbonation depth of the AAFP more accurately, enabling the precise identification of the AAFP into three carbonation zones: a fully carbonated zone (pH ≈ 9.50–9.88), a partially carbonated zone (pH ≈ 9.88–12.12) and an uncarbonated zone (pH ≈ 12.12–12.62). For a more accurate evaluation of the carbonation process and carbon dioxide sequestration capacity of AAFP, it is thus recommended to use the LGPM to determine the carbonation depth.