In 1978, an experimental two-layer concrete pavement was opened to traffic on SR-45 near Fort Myers, Florida. The experimental pavement included a series of two-layer concrete pavement sections with various design features placed over either a granular or a cement-treated subbase. These sections consisted of a 3-in. (7.5-cm) portland cement concrete (PCC) surface over a 9-in. (23-cm) lean concrete (commonly referred to as econocrete) layer. The control section consisted of a standard PCC 9 in. (23 cm) thick with joints spaced at 20 ft (6 m) on a cement-treated subbase. After 30 years of service, the sections constructed over a granular base performed better than those placed over a cement-treated subbase. The distresses on the two-layer concrete pavement sections built on the granular subbase were minimal, regardless of their slab lengths. In contrast, the control section experienced greater cracking, greater corner deflections, and moderate-to-severe spalling. The findings validate several features of Florida's current design policies, such as limiting joint spacing to 15 ft and prohibiting cement-treated subbases directly below concrete pavements. Furthermore, this project has demonstrated that a two-layer concrete system consisting of a relatively thin high-quality PCC surface over a lower-quality econocrete layer and a granular subbase can be a sustainable and long-lasting pavement design alternative.
