Abstract
In this study, the effects of heating rate and compressive strength on the spalling behavior of single-sided heated ring-restrained concrete with compressive strengths of 60 and 100 MPa were investigated. The vapor pressure and restrained stress inside the concrete were evaluated under fast- and slow-heating conditions. Regardless of the heating rate, the concrete vapor pressure and restrained stress increased as the temperature increased, and it was confirmed that spalling occurred in the 100-MPa concrete. Specifically, it was found that moisture migration and restrained stress inside the concrete varied depending on the heating rate. Under fast heating, moisture clogging and restrained stress occurred across the concrete surface, causing continuous surface spalling for the 100-MPa concrete. Under slow heating, moisture clogging occurred, and restrained stress continuously increased in the deep area of the concrete cross-section owing to the small internal temperature difference, resulting in explosive spalling for the 100-MPa concrete with a dense internal structure. Additionally, while the tensile strength of concrete is reduced by heating, stress in the heated surface direction is generated by restrained stress. The combination of stress in the heated concrete surface and the internal vapor pressure generates spalling. The experimental results confirm that heating rate has a significant influence on moisture migration and restrained stress occurrence inside concrete, which are important factors that determine the type of spalling.
Highlights
The internal structure of high-strength concrete is denser than that of normal-strength concrete. This increases the likelihood of spalling in high-strength concrete when it is exposed to high temperatures, such as temperatures caused by fire
It is necessary to investigate spalling by examining the vapor pressure and thermal stress in concrete subjected to single-sided heating and considering the heating rate and compressive strength
When concrete with compressive strengths of 60 and 100 MPa were subjected to single-sided heating, the vapor pressure due to the temperature difference inside the concrete was measured, and the restrained stress by the ring-restrained condition was calculated to examine the influence of thermal stress
Summary
The internal structure of high-strength concrete is denser than that of normal-strength concrete. Choe et al [25] examined the effect of heating rate on high-strength concrete spalling They reported that the heating rate significantly affects moisture migration and vapor pressure accumulation in concrete. They found that moisture migration does not occur under slow-heating conditions owing to the similar temperature distribution in concrete They reported that explosive spalling caused by boiling liquid expanding vapor explosion (BLEVE) may occur in high-strength concrete with a high-density matrix. It is necessary to investigate spalling by examining the vapor pressure and thermal stress in concrete subjected to single-sided heating and considering the heating rate and compressive strength. When concrete with compressive strengths of 60 and 100 MPa were subjected to single-sided heating, the vapor pressure due to the temperature difference inside the concrete was measured, and the restrained stress by the ring-restrained condition was calculated to examine the influence of thermal stress. The bottom of the ring was insulated to prevent the ring from being directly heated
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