Abstract
Microwave heating potentially reinforces the muddy intercalation to eliminate slope failure. Montmorillonite has the worst water resistance among the muddy intercalation components, which is a primary facet of inducing muddy intercalation failure. This study investigates the mechanism of shear strength and water stability enhancement of montmorillonite heated by the microwave oven and muffle furnace from room temperature to 800 °C. Results show that montmorillonite mineralogical evolution can be divided into three stages: room temperature-300 °C, 300-600 °C, and 600-800 °C. Microwave heating is more efficient in montmorillonite heat treatment than muffle furnace heating and makes the montmorillonite dehydroxylated earlier. It is worth noting that hot spots formed inside the montmorillonite specimens during the microwave heat treatment. Microwave significantly promotes the shear resistance of montmorillonite, where the maximum increases are 39.94% of cohesion at 600 °C and 20.54% of internal friction angle at 700 °C. This enhancement is due to the rough surfaces and large particles produced by dehydroxylation and Mg-Al spinel synthesis, and the significant degree of disorder state of MMT after dehydroxylation also plays a vital role. The microwave-heated montmorillonite over 500 °C presents good integrity in the water immersion test over 24 h. Considering the shear behavior and water stability, we believe the most reasonable heating interval for microwaves is 500-600°C.
Highlights
The muddy intercalation is a weak material between the upper and lower rock layers in the argillaceous slope, consisting of quartz, clay minerals, calcite, and feldspar[1,2,3]
The first stage is from room temperature to 196 °C
This study investigates the mechanism of shear strength and water stability enhancement of montmorillonite heated by the microwave oven and muffle furnace from room temperature to 800 °C by evaluating the mineralogical composition, micromorphology, shear behavior, and water stability
Summary
The muddy intercalation is a weak material between the upper and lower rock layers in the argillaceous slope, consisting of quartz, clay minerals, calcite, and feldspar[1,2,3]. The shear failure of muddy intercalation under the water function is mainly due to the clay minerals swelling and softening[5,6,7]. The clay minerals take account for 60% of muddy intercalation[2,3,8], and among which the montmorillonite (MMT) presents the worst water resistance[9,10]. Ameliorating MMT properties probably reinforces muddy intercalation to prevent structural failure from heavy rainfall or high groundwater content. The MMT crystal has a unique 2:1 layered structure that two inward-pointing tetrahedral sheets sandwich one octahedral sheet[11]. This structure absorbs the environmental water and swells[12,13].
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