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The need to mitigate the CO2 emissions deriving from the cement industry becomes imperative as the climate crisis advances. An effective strategy to achieve this is increasing the replacement level of cement clinkers by waste-derived supplementary cementitious materials (SCMs). In this study, the use of mechanochemically activated biomass ash for high-volume (up to 40%) substitution of cement is investigated. The effect of mineral carbonation treatment on the performance of the mechanochemically treated biomass ash as SCM was also examined. The results showed that the mechanochemically treated biomass ash was the most effective SCM, with the respective samples at 40% cement replacement reaching 63% of the strength at 28 days as compared to samples with 100% Portland cement, while only 17% of the strength was achieved in samples with 40% untreated biomass ash. As suggested by the isothermal calorimetry, XRD, FTIR, and TG analysis, the mechanochemical treatment enhanced the reactivity and the filler effect of the biomass ash, leading to improved mechanical performances of these mortars compared to those containing untreated biomass ash. Mineral carbonation reduced the reactivity of the mechanochemically treated biomass ash but still led to better strength performances in comparison to the untreated biomass ash. [ABSTRACT FROM AUTHOR]

Biomass ashes generated from the combustion process of timber materials have the capacity to be used as sustainable feedstock materials for CO 2 utilisation through mineral carbonation. However, the CO 2 uptake capacity and efficiency of biomass bottom ash are normally quite limited under ambient conditions due to the low reactivity of the materials. This study investigates the use of timber biomass bottom ash for direct mineral carbonation, and the effects of mechanochemical activation as a pre-conditioning treatment. The effects of different mechanochemical activation conditions (i.e., milling time, the ball to sample mass charge ratio, and the water addition content) were systematically assessed. The mechanochemically activated biomass bottom ash samples before and after carbonation were characterised using X-ray diffraction, Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and thermogravimetric analysis (coupled with mass spectroscopy). The results show that mechanochemical pre-conditioning can effectively improve both the mineral carbonation efficiency (kinetics) and capacity, most likely by increasing the reactivity of calcium (magnesium) silicate for mineral carbonation even at ambient temperature and pressure. The maximal CO 2 uptake capacity has doubled at the optimised mechanochemical treatment conditions. Comparison of performances reported in literature using biomass ash with similar chemical compositions was carried out, where mechanochemical activation pre-treatment exhibited superior performances. The outcomes of this study also suggest that mechanochemical activation might also be effective for improving the mineral carbonation capacity of other alkali industrial waste containing calcium (magnesium) silicates. • Mechanochemical activation can effectively improve the mineral carbonation efficiency and capacity of biomass ash. • In addition to milling time, ball to sample mass ratios and the addition of water play important roles during activation. • Mechanochemical activation improves the reactivity of calcium (magnesium) silicate at ambient temperature and pressure. • The developed processes can be applied to other alkali industrial waste containing calcium (magnesium) silicates. [ABSTRACT FROM AUTHOR]