Study of Iowa PCC Thermal Properties for Mechanistic-Empirical Pavement Design

The present research was designed to determine thermal properties, such as coefficient of thermal expansion (CTE) and thermal conductivity, of portland cement concrete (PCC) used in Iowa pavements. These properties are required as input values by the AASHTO Mechanistic-Empirical Pavement Design Guide (MEPDG). In this research, a literature survey was conducted to determine the major factors that significantly affect thermal properties of PCC. CTE tests of various lab and field samples were performed. The variations due to the test procedure, equipment used, and consistency of field batch materials were evaluated. The test results showed that the variations in CTE values due to test procedure and batch consistency were relatively small (<5%), while the variation due to the different equipment was relatively large (<15%). Concrete CTE values were significantly affected by different types of coarse aggregate. The CTE values of Iowa concrete made with gravel-limestone, quartzite, dolomite, dolomitelimestone, and limestone were 7.27, 6.86, 6.68, 5.83, and 5.69 microstrain/°F (13.08, 12.35, 12.03, 10.50, and 10.25 microstrain/°C), respectively, which were all higher than the default value of 5.50 microstrain/F (9.90 microstrain/°C) in the MEPDG program. In addition, the thermal conductivity of a typical Iowa PCC mix and an asphalt cement concrete (ACC) mix (both with limestone as coarse aggregate) were tested. The thermal conductivity was 9.24 Btu•in/h•ft•°F (1.33 W/m•K) for PCC and 14.52 Btu•in/h•ft•°F (2.09 W/m•K) for ACC, which are different from the default values (15.0 Btu•in/h•ft•°F or 2.16 W/m•K for PCC and 8.04 Btu•in/h•ft•°F or 1.16 W/m•K for ACC) in the MEPDG program. Results indicated that appropriately documenting concrete thermal properties is essential for updating the typical material input values and providing rational concrete pavement design in future.