Effect of Thermal Treatment on the Dynamic Behaviors at a Fixed Loading Rate of Limestone in Quasi-vacuum and Air-filled Environments

Abstract

Thermal damage in rock engineering occurs in the air-filled and quasivacuum environments of rock mass located near or far from the free surface. Meanwhile, dynamic loads are encountered frequently in engineering practice. In this study, 39 limestone samples are prepared, and a series of laboratory tests, including split Hopkinson pressure bar SHPB , nuclear magnetic resonance NMR and optical microscopy analyses, are conducted to investigate the effects of temperature and the environment on the dynamic mechanical properties of limestone. The results show that the macro-physical and dynamic mechanical properties of limestone after thermal treatment can be divided into two stages by a critical temperature of 450°C, at which the thermal damage factor is 0.71 and 0.75 in the quasivacuum and air-filled environments, respectively. In the first stage, with temperatures varying from 25°C to 450°C, the thermal damage due to expansion and fracturing slightly influences the related parameters, except the P-wave velocity. However, in the second stage, with temperatures ranging from 450°C to 900°C, the thermal damage caused by mineral decomposition and hydration leads to a remarkable decrease in the dynamic bearing and anti-deformation capacities. The environment plays a negligible role in the first stage but an important role in the second stage, and the dynamic compressive strength and modulus of samples after thermal treatment in the air-filled environment are much lower than those in the quasi-vacuum environment. Both the temperature and environment of thermal treatment should be considered in engineering practice, especially when the temperature exceeds 450°C.

Damage Characteristics of Thermally Deteriorated Carbonate Rocks: A Review

“…However, the increasing temperature gradually depreciated the elastic phase and enhanced the yielding phase up to the failure point under brittle-ductile transformation in which rock can withstand greater strain at minimum stress. The same results were also reported by Yu et al [91] while testing thermally treated limestones (25-900 • C) under quasi-vacuum and air-filled environments. The failure modes of limestone subjected to dynamic compression were observed as chip-shaped fragmentation and axial splitting with shear cracks.…”

“…Researchers have studied the dynamic behavior of different rocks under destructive and nondestructive dynamic loadings [8,[89][90][91][92][93][94][95][96][97][98][99]. They found that an increasing loading rate appreciably affects the dynamic response of rocks.…”

“…They heated the limestone from its ambient temperature to 900 • C and found a 70% reduction in dynamic elastic modulus at 600 • C. This temperature was considered as a critical temperature after which limestone started to change its behavior from brittle to ductile. [91] Damping Ratio, Damping Capacity, & Loss Factor…”

Experimental Study on Mechanical Property and Pore Distribution of Limestone Specimens after Heat Treatment under Different Heating Conditions

“…For some special rock issues, such as underground gasification of coal, tunnel fire, and gas explosion, the heating process of rock usually occurs in the environment with low concentration of air. Yu et al [33] conducted split Hopkinson pressure bar (SHPB) tests on limestone specimens heated in quasi-vacuum and air-filled environments, respectively, and found that the heating environment played a remarkable role between 450 and 900°C. Uniaxial compression tests were conducted by Su et al [34] on marble specimens to investigate the influence of thermal environment on mechanical behaviors.…”

Thermal cycling effects on the dynamic behavior of granite and microstructural observations

“…The dynamic behaviors of rock after thermal treatments have been extensively studied (Zhang et al 2001;Li et al 2012;Huang and Xia 2015;Yu et al 2018;Wang et al 2019a). A series of dynamic behaviors, mainly including the dynamic compressive strength (Li et al 2020a), dynamic tensile strength (Mardoukhi et al 2017), and dynamic fracture toughness (Yin et al 2018), are commonly tested using the split Hopkinson pressure bar (SHPB) system.…”