1593 3.3 Properties of the solidified slurry Two years after completion of the injection trials, cored samples of the solidified slurry were recovered by borehole drilling (Figure 6). The properties of core sample were evaluated by uniaxial compressive strength test. For comparison with the field cores, laboratory specimens were prepared by mixing blast furnace slag (BFS) with CO₂ MNB water at a water-to-slag ratio of 2.0. The specimens were cured in air for 28 days. In addition, thermogravimetric analysis (TG) was conducted to quantify the amount of CO₂ fixed in the samples, based on the decomposition of chemically bound CaCO₃ into CaO and CO₂ at temperatures of approximately 600°C. As shown in Figure 7, both the laboratory-prepared specimens and the field-recovered core samples exhibit distinct weight loss in the temperature range of 600–850°C in their TG–DTG curves. Therefore, the amount of fixed CO₂ was calculated from the mass loss within this temperature interval. The UCS and CO₂ fixation results for the field cores and the 28-day cured laboratory specimens are summarized in Figure 8. The UCS of the field cores (73.0 MPa) was substantially higher than that of the laboratory specimens (9.9 MPa). Similarly, the CO₂ fixation capacity of the field cores (13.28 kg CO₂/ton) exceeded that of the laboratory specimens (6.54 kg CO₂/ton). These results demonstrate that CO₂ was effectively fixed within the solidified slurry. Furthermore, the significantly enhanced mechanical strength and CO₂ fixation observed in the field cores suggest that the solidification reaction such as hydration and carbonation reactions were promoted under pressurized in situ conditions. This finding confirms the effectiveness of CO₂ fixation in the goaf environment. Figure 6 – Cored samples of the solidified slurry
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