Pore structure characterization of concrete mixtures with different aggregates using digital image processing and analysis

The presence of pores in a volume of concrete obviously affects the compressive strength of concrete (fc). Furthermore, characteristics of pores formed in concrete may vary, such as in shape, in size, in volume, and/or in its orientation tendencies. These characteristics also depend on the ingredient materials and the concrete casting process. In this research, three types of concrete in a form of cylindrical sample were analysed in order to investigate their pore structure characteristics. The first type of specimen is a core sample taken from a beam of an existing reinforced concrete structure building. It has 18 MPa of compressive strength. For the second type, an instant concrete with 40 MPa of designed compressive strength and 9 cm of slump test was chosen. The third sample is a concrete with Oil Palm Shell (OPS) as coarse aggregate substitution with 17 MPa of compressive strength. These three kinds of sample were scanned with a Bruker Micro-CT SkyScan 1173 device. The scanning process produced a set of projection images which were then reconstructed to obtain three-dimensional digital grayscale images. The pores inside the concrete sample are detected as dark pixels, which represent low-density structure. Based on the detected pores, the characteristics such as the volume distribution, the size distribution, the spatial distribution, as well as several structural descriptors such as shape, orientation and eccentricity of the pores were analysed. This study concludes that the type of aggregate greatly influences the characteristics of the pore formed in a concrete.