Keywords: porosity, concrete, image processing.

In this paper an image processing technique is use to determine the porosity of a simple concrete specimen. In this material the resistance is considered the most important property, giving an indication of the concrete quality, being directly connected to the structure of the hydrated cement paste. The automatization of the methods that determine the concrete porosity is the goal of a variety of recent research. The majority of these methods work with high quality images (microscopy and high resolution scanner) and use image processing programs.

The present work goal is to calculate concrete porosity value from images obtained from commercial scanners, which are inexpensive and easy to obtain, using pixel and morphology mathematic processing techniques. Therefore, the surface images of the concrete specimen obtained were separated into two HSV layers using a MATLAB® program. The V layer was adjusted in contrast, binarized and filtered using the erosion operation with a circular structuring element to remove isolated points, interpreted as noise. In the resulting image the empty spaces are counted to determine the porosity. The porosity value and the percentage of the gap of each sample were calculated using the average of the acquired images. The value obtained is compatible with porosity values known for this type of concrete. These values must be adjusted with real values, measured by other methods, to obtain values of adjustment and correction.

On the continuation of this work, we intend to obtain values of the porosity index of simple concrete samples and high performance concrete obtained from cylindrical specimens molded. This procedure will allow the assessment of the method, once that a comparison between the digital results and experimental results is made with samples of the same concrete. The experimental results will be obtained from the traditional method prescribed in the ABNT-NBR 9778 [1] standard through tests. Although this study is still in its initial phase, the results obtained are shown to be promising, with values obtained with the same magnitude and with small difference in relation to the index obtained experimentally by other authors.

1

Associação Brasileira de Normas Técnicas, ABNT-NBR 9778, "Argamassa e concreto endurecidos - determinação da absorção de água por imersão - índice de vazios e massa específica", Rio de Janeiro, Brazil, 1987.

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