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| Study on the weightless-expansion mechanism of red-layer mudstone by heat treatment temperature |
| XIE Zhuowu1，LING Sixiang1，LIAO Xin1，WU Xiyong1，ZHAO Siyuan2，CHEN Ming3，DUAN Qian4 |
| (1. Faculty of Geosciences and Environmental Engineering，Southwest Jiaotong University，Chengdu，Sichuan 611756，China；2. College of Water Resources and Hydropower，Sichuan University，Chengdu，Sichuan 610065，China；3. The 4th Engineering Co.，Ltd. of China Railway 12th Bureau Group，Xi'an，Shaanxi 710024，China；4. School of Mathematics，Southwest Jiaotong University，Chengdu，Sichuan 611756，China) |
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Abstract In this study，drying experiments at different temperatures were conducted to study the variations in the quality，fracture，pore，microstructure and expansion of upper-Shaximiao Formation red mudstone in eastern Sichuan Province. Field emission scanning electron microscope(SEM)，N2 adsorption measurement and digital radiography(DR) were used to evolution micro-structure，meso-pore and macro-fracture of rock samples during heat treatment，aiming to obtain the mass loss and expansion rules of rock samples reveal the influence of heat treatment on the expansion mechanism of red mudstone. The results show that：(1) The mass loss of rock samples presents two patterns as "rapid water loss-slow water loss" and "slow water loss" with the increase of heat treatment temperature. The complete water loss of the red mudstone requires a heat treatment temperature greater than 130 ℃；(2) Clay minerals exhibit interlayer opening and cracks along layers after high-temperature heat treatment，while they mainly show intralayer cracks after low-temperature heat treatment. The contribution of heat treatment temperature to macro cracks after heat treatment is low less than primary fissure；(3) The fine particles (0.5～2 nm) in rock pores increase significantly with the decrease of heat treatment temperature，and the number of these particles reaches the peak at 110 ℃. Heat treatment temperature has an obvious effect on the micro-pore sizes of rocks. Compared with the "single peak" distribution of pores in natural state，the pore distribution after the high temperature heat treatment presents a bimodal type. (4) The expansion pattern under the low temperature treatment is mainly controlled by macro-fractures，while the expansion pattern under high temperature treatment is dominantly controlled by the macro-fractures and micro-pores. In addition，increasing the heat treatment temperature can significantly increase the curve slope and final expansion in the “rapid expansion” stage. The results reveal the characteristics of micro-structures and micro-pores and the development of macro-fractures under different heat treatment conditions and discuss the influence of heat treatment temperature on the expansion processes of upper-Shaximiao Formation red mudstone，which may provide a new insight into predicting the drying degree of mudstone and provide a reference to the correction of final expansion rate under specific heat treatment conditions.
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