The Mechanistic-Empirical Pavement Design Guide (M-EPDG) is a state-of-the-practice tool for pavement analysis and design. M-EPDG has been incorporated into the AASHTOware Pavement ME Design software program, and local calibration is necessary for optimal performance. To support NCDOT in use of the Pavement ME Design software for design and analysis of portland cement concrete (PCC) pavements, as well as to meet the need to support the decision to move forward with PLC concrete specifications for future NCDOT projects, a variety of PCC pavement mixtures were developed, batched, and tested. Mixtures included several coarse aggregates, Type I/II ordinary portland cement (OPC), PLC, fly ash from two sources, and fine aggregates (manufactured sand and a natural sand) used in North Carolina (NC). PLC used in these mixtures were produced by intergrinding with one of the OPCs used in the study. Tests to determine the mechanical and thermal properties of the concrete mixtures, as well as several durability performance tests were performed. A catalog of PCC characteristics for use as inputs in the Pavement ME Design software was prepared, and the impact of the new suggested inputs on NC concrete pavement design were evaluated.
The cement type (OPC or PLC) used does not highly influence the results for the suite of tests used to determine the concrete inputs for M-EPDG. Comparable performance of the PLC provides incentive to NCDOT for use of this more sustainable alternative to OPC. Although the type of coarse aggregate utilized in this study did not highly influence the laboratory test results supporting the recommended M-EPDG PCC inputs, the fine aggregate type utilized in the mixture (manufactured sand versus natural sand) did have a significant influence on two thermal PCC inputs: coefficient of thermal expansion (CTE) and thermal conductivity. A sensitivity analysis was performed to identify the changes in predicted distresses for a range of each PCC input. Several typical North Carolina concrete pavements were analyzed using previous and newly suggested PCC inputs using the original design constraints. Findings offer insight into the potentially longer service life of concrete pavements designed and constructed in the past by NCDOT. Use of the new PCC input values may result in the design of slightly thinner concrete pavements in the future. Thinner pavements will reduce the amount of materials used in pavement construction, resulting in lower costs and environmental impact of concrete pavement. The benefits of deciding to reduce PCC thickness should be weighed against the risks associated with under-prediction of traffic or section loss associated with one or more diamond grinding treatments during the service life of the pavement, as well as the service life benefits that could be obtained by using a thicker PCC pavement.
As expected, results indicate use of fly ash in pavement concrete should improve durability performance. Use of PLC alone (without fly ash) did not provide distinct durability performance advantages, when compared to OPC. However, if PLC is utilized with fly ash in concrete mixtures, enhanced durability performance could be anticipated. Due to the delayed strength gain of fly ash mixtures, use of 28-day compressive strength as a PCC input in MEPDG may be unsuitable. A strong correlation was found between surface resistivity test results and rapid chloride permeability test (RCPT) results for all mixtures included this study. Findings of a limited LCA offered insight into the decrease in predicted total criteria air pollutant emissions associated with increased use of fly ash and PLC, providing confidence to NCDOT that use of PLC and fly ash in concrete infrastructure should provide environmental and sustainability benefits, as mandated by the MAP-21 legislation.
