The present research is concerned about how different the W/C ratio and the pore volume are between the upper paste and the lower paste of coarse aggregate in concrete. The value of color difference in hardened concrete was measured with a color difference meter. Each specimen contained a certain amount of red ink. Since the value of color difference in hardened concrete was proportional to the quantity of water with red ink in it, it was confirmed that the value of color difference can be used as an index which shows how much of water transfers as the concrete hardens.
Firstly, the results showed that the W/C ratio increased partially near the lower surface of coarse aggregate in concrete. Secondly, the comparison of the volume of hardened paste near the upper surface of coarse aggregate with that near the lower surface by using a porosimeter showed that the total pore volume of hardened paste was larger near the lower surface of coarse aggregate than near the upper surface.