Three volumetric methods for measuring the vertical porosity distribution of pervious concrete pavement

This study comparatively investigated and evaluated three volumetric methods for vertical porosity distribution measurement of pervious concrete pavement: the incremental water displacement method (IWDM), slice-water displacement method (SWDM) with nondemoulding cutting, and computed tomography (CT) scanning method (CTSM). The regional porosity in pervious concrete consolidated by surface compaction increases with the vertical depth, with porosity differences of approximately 10.31%, 8.57%, and 8.80% between the top and bottom regions in the IWDM, CTSM, and SWDM, respectively. Capillary action in the IWDM increases the porosity of the bottom region 120-100 mm from the surface by approximately 0.76% and reduces the porosity of the top region 20-0 mm by approximately 0.75%, but it hardly affects the porosity of 4 other middle regions. The overall porosity determined with the SWDM is very close to that determined with the traditional water displacement method (WDM), with differences of <0.4%, indicating that the knockout effect is almost completely eliminated by the mould protection measure. The CTSM tends to yield a higher overall porosity than that determined with the IWDM, SWDM, and WDM, with average differences of 1.54%, 1.51%, and 1.58%, respectively. The results provide evidence to select the appropriate methods.