Germany has been using nonwoven geo textile as an interlayer between cement layers that results in improved pavement performance. The German highway authorities have over 25 years of experience using nonwoven geotextiles as an interlayer. Federal Highway Administration (FHWA) of USA decided to conduct research experiments akin to Germany. The use of geotextiles in the construction of concrete pavements in USA is not a new concept, but use of a nonwoven geotextile between cementitious layers is. Geotextiles are commonly incorporated into pavement systems as a filtering layer between the base (or subbase if there is one) and the subgrade. German engineering, however, has demonstrated that nonwoven geotextiles can be placed between a concrete pavement surface and cement stabilized base. There, it provides a layer of separation, reduces water ingress, and minimizes bearing stresses. Typical US practice for providing a separating layer requires a layer of thin hot-mix asphalt (HMA) be constructed between the concrete surface and a cementitious stabilized base layer. Initial recommendations for material specifications and better construction practices have been developed. This information, along with a summary of recent field trials in Missouri and Oklahoma, is summarized below. Proper specifications for a nonwoven geotextile used as an interlayer between cementitious layers are based on optimizing pavement performance. The material properties of interest, their function, and how they affect pavement performance include: • Separation, which prevents the surface and base layers from bonding to one another and further helps to minimize discontinuities (cracks or joints) in the underlying cementitious layer from reflecting to the surface layer. To function as an effective separation layer, the material must possess a degree of resilience to accommodate the anticipated movements in the base layer. Effective separation between cementitious layers can promote durability and longevity. • Drainage, which allows water to migrate away from the base and subgrade layers. Water that penetrates the surface and filters down to the interlayer should drain into the interlayer, and then proceed along the cross-sloped surface to the pavement edge. German practice requires that the geotextile either terminate next to a drainage layer or be daylighted (allowing the egress of water). The drainage function requires that the geotextile have enough permeability (and transmissivity) to allow a minimum flow rate in three dimensions. The benefit to proper drainage of infiltrating water minimizes loss of base and subgrade support reducing the potential for premature failures. • Cushioning layer which reduces bearing stresses and the effects of dynamic traffic loads. This function also requires a geotextile material to meet specific specifications. The benefit of cushioning is increased longevity as a result of a reduced potential for premature failures due to heavy traffic loads. Benefits identified because of the field trials include the following: • Lower costs for material and installation when compared to conventional HMA interlayers. • Reportedly equivalent performance, at least for separation of cement bases and new concrete pavements. • Ease of installation, requiring a minimum of training and equipment. • Rapid installation, with firsthand observations revealing installation rates exceeding that of paving. (Source: geosyntheticsmagazine.com)