Methods to quantify the colour development of concrete exposed to fire

In this paper two techniques are discussed to measure the colour of concrete samples after fire exposure, namely a spectrophotometer and a calibrated flatbed scanner. These techniques are used to trace the temperature history of the concrete, from which the corresponding fire damage can be assessed. A spectrophotometer allows to measure colours in a fast and device independent way, resulting in absolute colours usable as a reference in both laboratory and field explorations. A flatbed scanner is less portable, but can be coupled to image analysis software by which focus is possible solely on the cement matrix. The alteration of the colour of traditional and self-compacting concrete is studied in both HSI and CIE Lab colour space. With increasing temperature not only a shift to red is considered, but also the development of a colour path.

► Colour changes of concrete exposed to fire are studied by a spectrophotometer and a calibrated flatbed scanner.
► In the a∗b∗ and –HS colour space, an elliptically shaped colour path is found.
► The effect of the colourful aggregates is minimized by blackening of the aggregates image analysis.