Abstract
Many physical processes in the field of rock physics are influenced by
the presence of fractures and microcracks. Therefore, intact rock
samples are often used for reproducible experimental studies, and cracks
are artificially created by various methods. For this, one possibility
is the use of thermal treatments. In this work, twelve thermal
treatments, differing in the applied maximum temperature and the applied
cooling condition (slow versus fast cooling) are experimentally studied
for dry Bianco Carrara marble under ambient conditions. Two sizes of
cylindrical core samples are investigated to identify a potential size
effect. As effective quantities on the core-scale, the bulk volume, the
bulk density, and the P- and S-wave velocities, including shear wave
splitting, are examined. To obtain a three-dimensional insight into the
mechanisms occurring on the micro-scale level, micro X-Ray Computed
Tomography (µXRCT) imaging is employed. For both cooling conditions,
with increasing maximum temperature, the bulk volume increases, and the
propagation velocities significantly drop. This behavior is amplified
for fast cooling. The bulk volume increase is related to the initiated
crack volume as µXRCT shows. Based on comprehensive measurements, a
logarithmic relationship between the relative bulk volume change and the
relative change of the ultrasound velocities can be observed. Although
there is a size effect for fast cooling, the relationship found is
independent of the sample size. Also the cooling protocol has almost no
influence. A model is derived which predicts the relative change of the
ultrasound velocities depending on the initiated relative bulk volume
change.