This study investigates the effects of thermal treatment and exposure time on the physico-mechanical properties related to the mineralogical and structural changes of clayey rocks at temperatures of up to 1000 °C. Vitric-crystal tuffs were studied because they show different engineering behavior than most rocks at high temperatures. The samples were heated at the rate of 10 °C/min, exposed to the desired temperatures for 2 h, and cooled at room temperature. Then a series of geo-mechanical tests was performed, thin sections and SEM images were prepared, and XRD and DTA analyses were carried out. Depending on the increase in the high temperature, the strength increased by 50% in the samples exposed to 400 °C, and a higher strength value was recorded than the initial strength even at 600 °C. Thin sections and SEM images showed that while the primary void ratio decreased until 400 °C because of the melting and expansion of clay-sized particles, new micro-cracks formed at the boundaries of quartz and plagioclase. Although the secondary micro-crack ratio increased, the sintering, cementation, and fusing between clay minerals were the main reasons for the increase in strength until 600 °C. After this temperature, the strength suddenly decreased due to the transformation of minerals, especially the formation of muscovite, and the development of secondary glasses. These changes were observed in DTA peaks and XRD analysis results. The unit weight decreased until 600 °C due to dehydration of absorbed water and hydroxylation reactions of the clay minerals and then remained constant. Despite the decrease in strength, the filling of primary voids by molten clay minerals and the formation of high-density minerals like clinoptilolite and muscovite prevented decreases in unit weight after 600 °C. In addition, the investigation of the exposure time showed that 90% of the strength loss occurs within the first 20 min at the threshold temperature, after which time does not affect the change in strength.

中文翻译：

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矿物学和微结构变化对热处理后粘土岩物理和强度特性的影响

本研究调查了热处理和暴露时间对与粘土岩在高达 1000 °C 的温度下的矿物学和结构变化相关的物理力学性质的影响。研究了玻璃晶凝灰岩，因为它们在高温下表现出与大多数岩石不同的工程行为。将样品以 10 °C/min 的速率加热，在所需温度下放置 2 小时，然后在室温下冷却。然后进行了一系列地质力学测试，制备了薄片和SEM图像，并进行了XRD和DTA分析。取决于高温的增加，暴露于 400°C 的样品强度增加了 50%，并且即使在 600°C 下也记录到比初始强度更高的强度值。薄片和 SEM 图像表明，虽然由于粘土大小的颗粒的熔化和膨胀，初级孔隙率下降到 400 °C，但在石英和斜长石的边界处形成了新的微裂纹。虽然次生微裂纹率增加，但粘土矿物之间的烧结、胶结和熔合是直到600℃强度增加的主要原因。在这个温度之后，由于矿物的转变，特别是白云母的形成，以及二次玻璃的发展，强度突然下降。在 DTA 峰和 XRD 分析结果中观察到这些变化。由于吸附水的脱水和粘土矿物的羟基化反应，单位重量下降到600°C，然后保持不变。尽管实力下降，熔融粘土矿物对原始空隙的填充以及斜发沸石和白云母等高密度矿物的形成防止了 600°C 后单位重量的下降。此外，对暴露时间的调查表明，90% 的强度损失发生在阈值温度的前 20 分钟内，此后时间不会影响强度的变化。