A structural capacity of asphalt concrete overlays on concrete pavements has been evaluated by loading tests on the test pavements. Based on the results, two calculation methods of thicknesses of asphalt concrete overlays on concrete pavements, of which slabs can fulfill their function as slabs, have been developed. Main conclusions are as follows;
(1) Deflections of overlay pavements and strains in concrete slabs decrease with increase of overlay thickness. Moreover, effeciency of load transfer of joint in exsisting concrete slabs (Eff) affects behaviors of overlay pavements, so the deflections and strains very with the positions in a slab.
(2) In order to calculate the thicknsses of asphalt concrete overlays on concrete pavements, two types of methods have been proposed. One is by multi-layered elastic theory, and another is by finite element method as composite pavement. Both take into consideration the effect of Eff of existing concrete pavements to overlay thicknesses. Overlay thicknesses by these two methods are extraordinarily thinner compared with those by the present method in Japan.