Quantification of Thermal Uniformity for Asphalt Paving Using the Thermal Segregation Index

Thermal and mechanical segregation are significant asphalt paving issues that affect the quality of asphalt pavements. Both types of segregation can be caused by inadequate mix material production, material delivery, and paving operation. Severe segregation results in lower in-place asphalt densities, which affect pavement performance. Measuring thermal segregation with technology such as paver mounted thermal profiling (PMTP) is critical to ensuring pavement quality. PMTP can continuously measure surface temperature profiles behind the trailing edge of a paver screed with an infrared sensor or photogrammetry. PMTP can also track paver speeds, stop locations, and stop durations. The differential range statistic (DRS) was created in the 2000s to evaluate thermal segregation. However, the DRS does not always adequately capture narrow bands of longitudinal thermal segregation caused by poor auger extension setup, mix building up beneath the reverse auger box and/or slat conveyors, worn deflector plates, and so forth. This paper introduces the thermal segregation index (TSI), which combines overall 2D sublot thermal uniformity and lateral thermal uniformity to overcome DRS’ shortcomings. The TSI combines the transverse semivariogram index (TSVI) and standard deviation (StDev) for sublots of 45.7 m (150 ft) in length. TSVI represents the lateral thermal uniformity in the transverse direction, while StDev represents the overall sublot temperature variation and is comparable with the DRS method. The TSI method was validated with an extensive thermal profile database and implemented in the Veta software allowing agencies and contractors to identify thermal segregation reliably and timely to conduct adequate corrective actions to resolve mix and paving issues.