Liu Jian-Bin, Zhang Zhong-Jian, Leung Anthony Kwan
Department of Civil Engineering, School of Engineering and Technology, China University of Geosciences (Beijing), No. 29 Xueyuan Road, Haidian District, Beijing, 100083, China.
Department of Civil and Environmental Engineering, School of Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong SAR, China.
Sci Rep. 2022 Sep 12;12(1):15308. doi: 10.1038/s41598-022-19655-x.
Thermal loading is an important factor that could lead to the weakening and deterioration of rock materials. Understanding the thermal properties of rocks and their evolution under different high temperatures is important in the post-fire-hazard evaluation and cultural heritage conservation. Yet it is challenging to understand the evolution of thermally-induced changes in rock properties and to quantitatively study degrees of thermal damage when samples are limited. This study investigates the effects of high temperatures (i.e., 200 °C, 400 °C, 600 °C, 800 °C, and 1000 °C) on a dolomitic marble using combined mesoscopic and macroscopic testing techniques. The test results show that increasing marble temperature led to a deterioration of physical properties (i.e., increasing open porosity and weight loss; but decreasing P-wave velocity) and mechanical properties (i.e., increasing axial strain corresponding with the peak stress; but decreasing uniaxial compressive strength, Young's modulus, and brittleness). There existed a threshold temperature of 600 °C, which marks different thermal damage mechanisms. Below the threshold, the rock deterioration was mainly caused by physical changes such as crack propagation and grain breakage, which can be characterized by mesoscopic parameters (i.e., linear crack density and mineral grain size distribution). On the contrary, when the temperature was higher than the threshold, the deterioration was caused by chemical changes, including mineral decomposition and re-crystallization, which was indicated by the changes in mineral compositions and relative atomic mass calculation. Based on the experimental results (e.g., mineralogical and physico-mechanical changes) and obtained relationships between the parameters in mesoscale and macroscale, a novel scheme for thermal damage evaluation is proposed to estimate thermally-induced changes in macroscopic parameters (e.g., Young's modulus) based on the corresponding mesoscopic parameters (e.g., particle size distribution and linear crack density).
热加载是导致岩石材料弱化和劣化的一个重要因素。了解岩石的热性质及其在不同高温下的演变对于火灾后危害评估和文化遗产保护至关重要。然而，当样本有限时，理解岩石性质热致变化的演变并定量研究热损伤程度具有挑战性。本研究采用细观和宏观测试技术相结合的方法，研究了高温（即200℃、400℃、600℃、800℃和1000℃）对白云质大理岩的影响。试验结果表明，大理岩温度升高导致物理性质劣化（即孔隙率增加和重量损失增加；但纵波速度降低）和力学性质劣化（即与峰值应力对应的轴向应变增加；但单轴抗压强度、杨氏模量和脆性降低）。存在一个600℃的阈值温度，它标志着不同的热损伤机制。低于该阈值时，岩石劣化主要由裂纹扩展和颗粒破碎等物理变化引起，这些变化可用细观参数（即线性裂纹密度和矿物粒度分布）来表征。相反，当温度高于阈值时，劣化是由化学变化引起的，包括矿物分解和重结晶，这通过矿物成分变化和相对原子质量计算得到体现。基于实验结果（如矿物学和物理力学变化）以及细观尺度和宏观尺度参数之间的关系，提出了一种新的热损伤评估方案，以根据相应的细观参数（如粒度分布和线性裂纹密度）估算宏观参数（如杨氏模量）的热致变化。
