The effect of cement dosage on mechanical properties of concrete exposed to high temperatures

摘要

Although concrete is a non-combustible material, it is found that when exposed to high temperatures, such as fire, the physical, chemical and mechanical properties of concrete can drastically change. Thus, it becomes important to assess the relative properties of concrete under high temperatures in order to evaluate and predict the post-fire response of reinforced concrete (RC) buildings and structures. This paper assesses the effects of elevated temperatures and cement dosages on the mechanical properties of concrete. Two concrete mix designs were considered in this research in an attempt to study the effects of cement dosage (250 and 350 kg/m~3) on the post-fire response of concrete. Once cast, the test samples were first exposed to elevated temperatures ranging from 100 to 800 ℃, and then allowed to cool down slowly to ambient room temperature of 20 ℃ before being tested to failure. Several tests were then carried out to determine the mechanical properties of the cooled concrete specimens. The test results indicated that at temperature above 400 ℃, concrete undergoes significant strength loss when compared to the strength of non-heated concrete. In addition this strength reduction was found to be unaffected by the cement dosages. The experimental results were also compared with current European standard (BS EN 1992-1-2:2004 standard) strength equations and American Concrete Institute standard (ACI 216.1).