Evaluation of zero-stress temperature prediction model for Portland cement concrete pavements

The current mechanistic-empirical pavement design guide (MEPDG) postulates that zero-stress temperature (ZST) has substantial effects on the behavior and performance of Portland cement concrete (PCC) pavements. To date, the only available ZST prediction model for PCC pavements is the one proposed by the MEPDG, which was quite simplified with a function of only two input variables: cementitious content and mean monthly temperature for the month of construction. In this study, the feasibility of the current ZST prediction model in the MEPDG was assessed by comparing the ZSTs evaluated from a series of field tests with the ones estimated from the MEPDG model. In order to find ZSTs in actual PCC pavements, accurate evaluations of early-age concrete stress developments were essential. To achieve this aim, non-stress cylinders (NCs), which directly measure stress-independent strain in the field concrete structures, were employed. Once the stress-dependent strain history was estimated based on the measured total and stress-independent strain histories, it was converted to the stress history using a step-by-step numerical method considering creep and modulus developments of concrete. The results of this study showed that about 4.5-7.7 °C of differences existed between the measured and predicted ZST values. This finding strongly suggests a need for development of a more advanced ZST prediction model with reasonable assumptions and diverse parameters.