ON THE USE OF POLARIZATION CAMERAS FOR THE DETERMINATION OF CONCRETE MOISTURE

Abstract. 3D concrete printing (3DCP) promises progress in the automation of the construction industry. The complexity and high quality requirements of 3DCP require automatic and digital control processes and systems that can continuously assess quality at any time and any place. In this paper, the relationship between the surface moisture of concrete and the degree of linear polarization (DolP) of light reflected from the concrete surface is investigated, which could serve as a basis for a camera-based control system. To proof this correlation, extensive practical investigations were carried out in which a mold-cast concrete specimen was illuminated with a white LED spotlight. The reflected light was recorded with a polarization camera, and the weight of the specimen served as a reference for the surface moisture. 14 experimental tests showed a high correlation between mass loss and DolP with a mean correlation coefficient of 0.994 in the last 60 minutes of the 180-minute observation period. The time series show an increasing DolP at the beginning of the observation period, which is probably due to the concrete bleeding and does not correlate with the mass loss. Further investigation into the factors influencing the DolP in the first part of the observation period needs to be carried out, either by testing influencing factors such as concrete bleeding or by finding a reliable method to measure surface moisture to correlate it with the DolP over the entire observation period. Nevertheless, the concept and methodology of data processing has been developed and prototyped, and a correlation has been demonstrated, that can provide a basis for the development of an operational camera-based concrete moisture monitoring system.