Yüksek Sıcaklığın Yapı Malzemesi Olarak Kullanılan İgnimbiritlerin Fiziksel ve Mekanik Özelliklerine Etkisi
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Date
2024Author
Şahiner, Nuryıldız
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One of the factors that causes significant changes in the physical and mechanical
properties of rocks is high temperature. This effect results in permanent damage to the
rocks, leading to their deterioration and consequently a reduction in their strength. During
a fire, temperatures can reach very high values over time. Experiments conducted
considering the post-fire condition are typically performed on samples that are first heated
and then cooled, evaluating the effects of temperature. However, studies investigating the
temperature-dependent physical and mechanical properties of certain rock types used
solely as building stones in our country are quite limited. This study aims to assess the
changes in physical and strength properties and long-term durability of ignimbrites used
as building stones when exposed to high temperatures, and to determine the threshold
stress values of crack progression stages. For this purpose, ignimbrite samples with
different colors and textures produced as building stones in the Cappadocia Region (7
different ignimbrite building stones) were collected. These samples were subjected to
various temperatures ranging from room temperature (without any thermal effect) up to 1000°C and then slowly cooled to room temperature. The physical and mechanical
properties of all samples were determined and evaluated. During the strength tests, the
Acoustic Emission (AE) technique was used to determine the threshold stress values
associated with crack progression stages due to stress increase. Additionally, Scanning
Electron Microscope (SEM) examinations were conducted on selected ignimbrite
samples to observe mineral changes and crack development related to temperature.
According to the results obtained from the study, although there were minor fluctuations,
the unit weight decreased with increasing temperature, while the specific gravity did not
show significant changes with temperature. Specifically, at 800°C, the uniaxial
compressive strength of each sample decreased compared to 600°C, but increased again
at 1000°C. The elastic modulus values obtained from the stress-strain curves were found
to be consistent with the behaviors observed in the uniaxial compressive strength tests.
The changes in the initial crack initiation and crack coalescence threshold stress levels
with temperature, determined using the Acoustic Emission technique, were found to be
parallel to the changes in UCS values, with these levels being approximately 18% and
55% of the UCS values, respectively. SEM images revealed that at 1000°C, there was no
change in the minerals of the samples, but melting in the ash matrix occurred, which is
thought to affect the rock's strength indirectly by causing weakening. At 800°C, crack
development was observed, while at 1000°C, cracks deepened and spalling occurred in
the ash matrix.