Performance of Thin Concrete Overlays in South South Africa

Since 1970, several highways in South Africa were cujistructed in Portland cement concrete, the only design being used was the jointed unreinforced concrete pavements. Due to early deterioration as a result of alkali aggregate reaction, one section had to be overlayed In order to determine the last option, several experimental sections were built after proper evaluation and design. The evaluation and design process involved finite element modelling (nonlinear elastic materials and dynamic loading were part of the modelling) as well as heavy vehicle simulator testing. Continuously reinforced and jointed concrete sections of varying thickness were constructed. Subsequent monitonng for the past 13 years indicated relatively accurate predictions of types of distress and performance. This knowledge was also used to design and build a 170mm thick CRCP on a prominent freeway which is performing very well after eight years. The paper describes the modelling, prediction of performance, actual performance as well as the mechanistic evaluation of slab supportlload transfer at joints. Some guidelincs are suggested to be used in the design of thin concrete overlays on old concrete or flexible pavements.