Temperature-induced slaking characteristics of mudstone during dry-wet cycles

Abstract

As the determinant of thermal propagation velocity and temperature field distribution within rocks, the effective thermal conductivity is not only influenced by the structure characteristics of medium (e.g. mineral compositions, porosity and micro cracks), the multiphase flow characteristics (e.g. saturation and water vapor content), and temperature, but also deeply affected by the multi-field coupling within rock masses. Mudstone contains non-clay minerals and clay minerals, which split apart from each other owing to the difference in thermal expansion coefficient. With the aim to analyze the temperature effect on the slaking characteristics of mudstone during dry-wet cycles, this paper performs the sieving test on air-dry fragments obtained from the dry-wet cycle test. With a customized test device, three dry-wet cycles are conducted on five samples at 60°C, 90°C, 105°C, 120°C and 180°C, respectively. The grains are divided into 4 categories: coarse grains (d15mm), medium grains (7mmd15mm), fine grains (0.075mmd7mm) and particles (d0.075mm). The mass percentage, number of fragments, specific surface area and fractal dimension are calculated after the drywet cycle test. The test results show that: the mass percentage of coarse grains decreases but that of medium and fine grains increases as temperature rises, indicating that higher temperature causes higher fragmentation and finer grains; the number of medium and fine grains grows, while that of coarse grains increases firstly and then decreases with the rise of heating temperature, and the fragmentation becomes more obvious after the temperature reaches 120°C; the specific surface area and the fractal dimension of the samples increase with the increase of temperature. The difference in mudstone fragmentation is mainly attributed to mineral composition and pore-fracture structure. The high temperature environment is conducive to mudstone fragmentation and the dry-wet cycles act as the driving engine of the rapid disintegration of mudstone.

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