Impact of Local Calibration on Pavement Design in Michigan

The global Pavement-mechanistic-empirical (ME) transfer functions have been calibrated using the long-term pavement performance (LTPP) pavement sections at the national level. These functions may need calibration for local conditions for reliable performance predictions. Several calibration studies have been conducted for local conditions, but limited research is available on the impact of calibration on pavement design. This study calibrates and validates the Pavement-ME transfer functions using version 2.6 for Michigan. A total of 256 flexible and 113 rigid sections have been selected based on the performance and availability of Pavement-ME inputs. The authors obtained the Pavement-ME inputs using construction records, plans, job mix formula (JMF), and material testing results. In contrast, the performance data was obtained from the Michigan Department of Transportation (MDOT) pavement management system (PMS) database. The calibrated models were then used for pavement design to estimate the impact of calibration and for comparison with AASHTO93 designs. The paper identifies the controlling distresses for pavement design. A total of 44 new flexible and rigid sections were designed based on the newly calibrated coefficients. The results show a significant improvement in performance prediction after local calibration. A comparison between AASHTO93 and Pavement-ME designs showed a reduction in hot-mix asphalt (HMA) and plain cement concrete (PCC) slab thicknesses for the latter approach. On average, the surface thicknesses using locally calibrated coefficients were thinner by 0.22 in. (0.56 cm) and 0.44 in. (1.12 cm) for flexible and rigid pavements, respectively. Critical design distresses for flexible pavements include bottom-up and thermal cracking. Conversely, transverse cracking and international roughness index (IRI) control the designs for rigid sections. Evaluating the impact of locally calibrated models on pavement designs is essential to obtaining practical and cost-effective design thickness.

This study provides a framework for the local calibration. Several factors affect the local calibration process, including the field performance data. The recorded performance data may have irregularities due to measurement errors, limitations in distress identification, and conversion to the Pavement-ME units. Therefore, the authors recommend analyzing the raw performance data and filtering it (if required) for practicality. Pavement design is one of the most crucial calibration process steps and is often not considered in practice. It is worth mentioning that pavements were designed based on calibrated models, and based on MDOT feedback, the calibration improved the designs. The authors recommend that the calibration results should not be based only on statistical parameters (SEE, bias, etc.) but also on practical engineering judgments. By understanding which distress types are most relevant to their region, agencies can develop mitigation and maintenance strategies leading to longer pavement service lives. For example, MDOT can mitigate the occurrence of thermal cracking, a critical distress, by using modified and improved binders.