Role of Cyclic Thermal Shocks on the Physical and Mechanical Responses of White Marble

Yujie Feng,Honghui Zhao,Haijian Su,Yinjiang Nie

doi:10.3390/machines10010058

Yujie Feng, Honghui Zhao + Show 2 more

Open Access

https://doi.org/10.3390/machines10010058

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Abstract

Marble is a common rock used in many buildings for structural or ornamental purposes and is widely distributed in underground engineering projects. The rocks are exposed to high temperatures when a tunnel fire occurs, and they will be rapidly cooled during the rescue process, which has a great impact on the rock performance and the underground engineering stability. Therefore, the role of cyclic thermal shocks on the physical and mechanical properties of marble specimens was systematically investigated. Different cyclic thermal shock treatments (T = 25, 200, 400, 600, 800 °C; N = 1, 3, 5, 7, 9) were applied to marble specimens and the changes in mass, volume, density and P-wave velocity were recorded in turn. Then, the thermal conductivity, optical microscopy and uniaxial compression tests were carried out. The results showed that both the cyclic thermal shock numbers (N) and the temperature level (T) weaken the rock properties. When the temperature of a thermal shock exceeds 600 °C, the mass loss coefficient and porosity of the marble will increase significantly. The most noticeable change in P-wave velocity occurs between 200 and 400 °C, with a 52.98% attenuation. After three thermal shocks, the cyclic thermal shock numbers have little influence on the uniaxial compressive strength and Young’s modulus of marble specimens. Shear failure is the principal failure mode in marble specimens that have experienced severe thermal damage (high N or T). The optical microscopic pictures are beneficial for illustrating the thermal cracking mechanism of marble specimens after cyclic thermal shocks.

Highlights

To ensure the stability and safety of rock engineering, it is critical to understand the physical and mechanical properties of rock
Underground coal gasification (UCG), geothermal energy exploitation, nuclear waste disposal, fire hazards in underground tunnels and the maintenance/restoration of stone-built heritage following fire exposure are among examples of rock engineering applications that involve high temperatures [1,2,3,4,5]
In the past few decades, some researchers have studied the effects of thermal damage on the physical and mechanical properties of marble rocks under post-high temperature conditions by laboratory testing [17,18,19,26,31,32]

Summary

Introduction

To ensure the stability and safety of rock engineering, it is critical to understand the physical and mechanical properties of rock. In the past few decades, some researchers have studied the effects of thermal damage on the physical and mechanical properties of marble rocks under post-high temperature conditions by laboratory testing [17,18,19,26,31,32]. Ozguven and Ozcelik [31] heated the marble and limestone specimens up to 1000 ◦C and investigated the effect of the thermal gradient on physical and mechanical properties such as density, porosity, uniaxial compressive strength and tensile strength. Their results demonstrated that the apparent porosity increases with temperature, probably due to capillary cracks caused by heat. The two end surfaces of the specimens were polished to control the flatness and parallelism within ±0.02 and ±0.05 mm according to the ISRM suggested method [33]

Cyclic Thermal Shock Treatment

Testing Procedures

Effects of Temperature Level

Microscopy Observation

Findings

Conclusions