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Previous experimental studies on concrete under high temperatures have mainly concentrated on the reduction of stiffness and strength properties. Various experimental parameters have been examined such as maximum temperature, heating rate, types of aggregates used, various binding materials, and loading paths (that is, mechanical loading applied before, during, and after high temperature testing). There exist few data on strength, stiffness, and permeability of concrete considering cooling rate after fire damage, however. Particularly, the increase of permeability severely affects the durability properties of concrete and reduces the remaining service life of the concrete structure. The purpose of this study is to investigate strength, stiffness, and permeability properties of concrete cylinders that are subjected to various heating and cooling scenarios. The thermal diffusivity, weight losses, color changes, and cracks of the specimens are also reported.
Keywords: permeability; stiffness; strength; temperature.
INTRODUCTION
Fire is a great risk to human life, especially in the aftermath of vehicular, earthquake, and other extraneous accidents. When a concrete structure is exposed to fire, the concrete experiences large volume changes resulting from thermal dilatation of aggregate, shrinkage of the cement paste, and spalling due to high thermal stresses combined with internal pore pressure buildup. During a fire, the concrete structure suffers from severe degradation of mechanical and transport properties that may lead to expeditious reduction of the remaining service life. The level of thermal damage depends on the size of the structural member and the spatial and temporal fire conditions such as maximum temperature, heating rate, exposure time, and cooling rate. Therefore, it is very important to study the residual mechanical and transport properties after the concrete was subjected to high temperatures with different heating and cooling rates. A better understanding of these degradation effects will provide essential information to the concrete industry to improve the fire resistance of concrete and to quantify the level of fire damage in the remaining structure.
Extensive experimental studies on various properties of concrete under high temperature have been conducted with an emphasis on the effect of high temperature on the stiffness, strength, and thermal expansion of concrete.1-21 Very little research has been performed on the reduction of transport properties after concrete is exposed to high temperature, which is very important to the residual durability of...