Effective approach to improve pavement drainage layers

The objective of this study was twofold: (1) quantify the benefits of a specially designed geocomposite membrane [a low modulus polyvinyl chloride (PVC) layer sandwiched between two nonwoven geotextiles] to act as a moisture barrier in flexible pavement systems; and(2) quantitatively measure the moisture content of unbound granular materials nondestructively. The geocomposite membrane was installed over half the length of a pavement test section at the Virginia Smart Road, while the other half of the test section consisted of the same design without the interlayer system. An air-coupled ground penetrating radar (GPR) system with 1 GHz center frequency was used to monitor and detect the presence of moisture within the pavement system over different periods of time corresponding to different levels of water accumulation. Results of GPR data analysis indicated that the use of the geocomposite membrane reduced water infiltration to the aggregate base layer by as much as 30% when measurements were performed after rain. It was also found that the moisture content underneath the interlayer was almost constant and therefore independent of the amount of rainwater, which is the primary source of moisture in pavement systems that have a low water table. The impact of moisture in the granular layers was investigated using the results of a deflection monitoring program. The results indicate that the area with the geocomposite membrane always showed less deflection than the area without the interlayer. The study recommends that any pavement drainage layer must be backed by an impermeable interface, given that the water table is low.