Measurement of time-dependent colour variation in concrete.

Abstract

The phenomenon of colour variation in finished concrete has become a contentious issue in recent years as engineers and designers strive, not only for blemish free finishes, but crisp “white” concretes with uniformity throughout. Three factors determine what colour an observer perceives: (i) the light source, (ii) the object surface and (iii) the observer himself. Several methods have been identified for the evaluation of colour yet in most cases in the absence of suitable measuring equipment; it is the observer who will decide. Given that colour variation may present differently depending on aspects such as the viewing distance, the ambient light and the viewing angle, this typically results in a subjective assessment devoid of any quantitative metrics. This paper presents the results from an experimental programme aimed at developing a robust and repeatable quantitative methodology for concrete colour measurement. Controlled concrete specimens have been studied over a 3 year period, for 3 different exposure conditions. Initially the exposure conditions are evaluated against each other but, more importantly, changes, monitored over time have also been recorded.