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Abstract
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Cement-based grouts have been commonly used for chemical ground improvement due to their adequate mechanical and rheological properties, availability, and low cost. However, over-reliance on cement has adverse environmental impacts. To comply with policies on CO2 emission reductions and align with United Nations Sustainable Development goals (SDG), research is currently developing innovative grouting materials used as full or partial replacement of cement grout. This study assesses CO2-induced carbonate minerals as novel injectable materials for treating sand and peat soil using carbonate solutions directly synthesised by CO2 absorption. Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD) analyses attested the formation of siderite (FeCO3) and calcite (CaCO3) carbonate minerals, which precipitated in the soil voids, bridging soil particles. Sand samples treated with siderite grout exhibited the highest Unconfined Compressive Strength (UCS) of 70 kPa at 11% siderite content; those treated with calcite grout reached 53 kPa at a calcite content of 16%. Peat samples stabilised with siderite grout attained a maximum UCS of 36 kPa at 20% siderite content, i.e. a threefold UCS improvement as UCS of untreated peat was 12 kPa, while peat samples treated with calcite grout achieved approximately 23 kPa at 19% carbonate content. Life Cycle Analysis (LCA) assessment of the environmental performance of carbonate grout mixtures using conventional cement-based grout as control showed a dramatic reduction in the global warming potential and improvements in 13 and 14 out of the 18 impact categories assessed for calcite and siderite grout respectively; possible ways of further reducing the environmental impacts are discussed. Overall, the findings give promise that carbonate minerals synthesised using CO2 can be a suitable alternative to Portland cement for grouting applications, complying with several green chemistry principles and SDGs, as discussed in the paper, and having the potential advantage of consuming captured CO2 from industrial sources.
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