The purpose of this research is to probe the slaking property of the mudstone meeting with water. The elemental, crystalline, and morphologic changes in the mudstone with three different water contents were characterized using X-ray fluorescence spectrometer (XRF), semi-dynamic leach test, X-ray diffractometer (XRD), and scanning electron microscopy (SEM)/energy-dispersive X-ray analysis (EDAX) techniques. The XRF and chemical composition analyses indicated that the mudstone contains high concentrations of silicon and aluminum and low concentrations of calcium, iron, potassium, and sodium. The XRD examination showed large amount of quartz and illite, minor calcium aluminate hydrate and calcium silicate hydrate, and small amount of unidentifiable peaks. The result of semi-dynamic leach test showed that the release of sodium is very rapid initially and the released calcium species increase largely in the final subsequent extractions. The microanalysis using SEM/EDAX indicated that the petal-like structures increase with the moisture content of the mudstone. Thus, it was inferred that the possible mechanisms of the mudstone meeting with water to lead to the slaking phenomenon are stated as follows. The sodium sulfate will rapidly dissolve from the mudstone, and the sulfate species and calcium aluminate hydrate form the platelet-like solid solution of 3CaO-Al2O3-CaSO4·12H2O making the mudstone lose its cementing reaction.
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