Load Transfer through Aggregate Interlock: Crack Width, Aggregate Type and Performance

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It is well known that performance of plain jointed concrete pavements depends on aggregate interlock to transfer load from the one slab to the next. In order to quantify the relative contribution of crack width and the strength of the aggregate to the long-term performance of a plain jointed pavement, experimental sections of road were built using different aggregates types. These sections were subsequently loaded to failure using the Heavy Vehicle Simulator (HVS). Some typical sections of interstate-type highways, which had been under traffic for between ten and twenty years were also investigated using FWD testing and determination of changes in crack width with changes in temperature. Detailed asbuilt information including concrete mix characteristics was available for all these sections. This paper discusses the prediction of crack width using the RILEM model which predicts early age shrinkage. The model was modified to include the effects of aggregate type, environmental conditions and age. The change in load transfer at the joints and cracks, as indicated by relative vertical movement under dynamic loading as a result of temperature variation and humidity, is reported on. It was found that a change in load transfer occurred under increased loading and that this could be related to the crushing characteristics of the coarse aggregate. This paper presents the final outcome of the study in terms of theoretically based equations that were adjusted using regression techniques to fit the field experience. These equations have now been incorporated into a mechanisticallybased design method for concrete pavements, cncPave.