Microstructural characterization of limestone exposed to heat with XRD, SEM and TG-DSC
Highlights: • The microstructure of limestone (25 °C–800 °C) was analyzed by XRD, SEM and TG-DSC. • The microstructural properties of the crystal are anisotropic in different crystal plane directions. • Microstructure controls the macroscopic properties of limestone. - Abstract: Limestone is a common rock used in many buildings and found in underground engineering projects. After exposure to heat, for example, the occurrence of fires, the stability of limestone structures is mostly affected, which may have safety repercussions. Therefore, the impact of thermal effects on the microstructure of limestone is investigated in this study, in which 8 groups of limestone samples are exposed to different temperatures (25 °C, 100 °C, 200 °C, 300 °C, 500 °C, 600 °C, 700 °C and 800 °C), after which X-ray diffraction, differential scanning calorimetry and scanning electron microscopy are carried out. The mineral composition and the microstructure of the samples are numerically modeled, in which the diffraction peaks, full width at half maximum, integral breadth, microstrain, average domain size and dislocation density are analyzed. The macroscopic properties obtained from the results in other works in the literature including porosity, compressive strength, damage coefficients and modulus of elasticity are also compared with the parameters above. The changes in the crystal structure of two minerals, calcite and dolomite, are found to be anisotropic in the different crystal plane directions. It is also found that the limestone microstructure affects the macroscopic properties. A temperature between 200 °C to 300 °C is the critical temperature at which both the macroscopic properties and macrostructure demonstrate significant changes.