Effect of Drying on Clay Clogging of Pervious Concrete

Pervious concrete, extensively applied in sustainable urban drainage systems, is prone to clogging. From the perspective of the clogging particle size relative to the pore size, clay particles easily pass through pervious concrete. However, drying may increase the potential of clay clogging. A laboratory study was performed to examine the effect of drying on clay clogging of pervious concrete and the mechanism of clay clogging. Five slurries of different clay concentrations were prepared to clog pervious concrete specimens under two exposure methods, namely, drying and no drying, which were applied after the clay slurry was added to the specimen. After clogging, 30 pressure washing cycles were applied to each specimen, and the permeability was measured after each washing cycle. Moreover, the dried clay-clogged specimens were scanned by computed tomography (CT) before the 1st washing cycle and after the 30th washing cycle. The measurements revealed that more than 80% of the total retained particles were within the depth range $20–70\mathrm{mm}$ below the specimen surface, and the most highly clogged layer was found in this range. The permeability of specimens clogged with undried clay almost recovered to the initial value after only five washing cycles. Clay drying may cause difficult-to-recover clogging due to two factors, namely, drying increases particle-to-particle cohesion and particle adhesion to pore walls, and drying causes particles to shrink to form aggregates that are larger than the pore size. This study facilitates the development of effective pavement maintenance strategies.