Study on the Color Changes of Blast-Furnace Slag Concrete subjected to High Temperatures using Photo Image Analysis

사진분석법을 이용한 고온에 노출된 고로슬래그 콘크리트의 색상변화도 평가

When reinforced concrete is subjected to high temperatures in a fire, there is a deterioration in its properties. It is very important to know loss in compressive strength, loss of elastic modulus, cracking and spalling of the concrete. To determine whether a structure can be repaired rather than demolished after a fire, an assessment of structural integrity must be made. To assess the remaining bearing capacity of the structural elements after fire, information of the temperatures reached inside the elements is necessary. On heating, a change in color from normal to a pink/red is often observed and this is useful since it coincides with the onset of significant loss of concrete strength. The purpose of this study is to quantify changes in color for blast-furnace slag concrete using photo image analysis and to identify the relationship between color change and increasing temperatures. For this purpose, we manufactured concrete samples with varying water-to-binder ratios and heated them to target temperatures of 100, 200, 300, 400, 500, 600, and $700^{\circ}C$ in an electric oven, whereupon their color changes in photos of the specimen were measured using photoshop program. The result of this study shows that color changes in a concrete exposed to high temperature have a consistent relationship with several variables according to RGB, HSB, and Lab color coordinates. Therefore, it is possible to estimate how much temperature the specimen was exposed considering these results of color change.