Color and Material Property Changes in Concrete Exposed to High Temperatures

When a concrete structure is exposed to heat such as a fire, its material properties, such as weight, compressive strength and elasticity, are degraded. The exposure also accompanies cracking, spalling and color changes. Therefore, a structure′s quantitative damage assessment is very critical in determining whether to dismantle or strengthen the structure after a fire. The purpose of this study is to consider the color change of heat exposed concrete as a major parameter in conjunction with material property changes, such as weight loss and compressive strength degradation, for the purpose of identifying the relationship between concrete color change and material property changes at high exposure temperatures. For this purpose we manufactured concrete samples with varying water-to-cement ratios and heated them to target temperatures of 100, 200, 300, 400, 500, 600, 700 and 800°C in an electric oven, whereupon their color changes, weight losses and residual compressive strengths were measured for analysis. Experiment results show that the color change into red in concrete samples exposed to higher temperatures has a consistent relationship with weight loss rate and residual compressive strength. This result indicates that measuring the hue value in a concrete material can enable assessment of its material property changes.