In this study, the influences of coarse aggregate to the electrical resistivities of concrete were investigated. Specifically, types and sizes of the aggregates were targeted as the studied parameters. Commercially available granites and marbles with various sizes of 4.75, 9.5, 12.5, and 19mm were used in the concrete mixtures, and the resistivities at the age of 28 days were investigated. Polarization induced resistivity growth during the electrical measurement were considered and experimentally nullified, such that the real bulk resistivities of concrete specimens can be obtained for comparison. Concrete specimens were made by cement mortars and several degrees (amounts) of coarse aggregates; with a fixed size of coarse aggregates used in a single specimen. Cement mortars were mixed with the water/cement ratio of 0.4, and the cement/sand ratio was held constantly at 1:1. The microstructures of certain specimen samples were obtained by Scanning Electron Microscopy so as to estimate the porosity of cement pastes, which is the primary conductive portion of cementitious materials. This was done to validate the resistivity observation. The results show that the electrical resistivities of concrete made with crushed granites were quite close to those that made with crushed marbles. Moreover, the particle size of aggregates seems to have no significant influences to concrete resistivities while it is to concrete strengths. As a partial study of nondestructive testing technologies to the performance estimations of concrete, further studies were required and we have drew a few comments.

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