Mitigating Thermal Fluctuations in Flexible Pavements with Encapsulated Phase-Change Materials

Flexible pavement material systems used in Texas roadways have historically posed problems of rutting and cracking during periods of hot and cold weather, respectively. The costly restoration of asphalt pavements has driven the need to find long-term materials solutions. To address these problems, polymer-encapsulated phase change materials (PCMs) can potentially be incorporated into the surface layer of the pavements. PCMs are crystallizable, organic or hybrid materials that exhibit a high latent heat of fusion, which are widely used for thermal energy management. This investigation is aimed at limiting thermal fluctuations in roadways and reducing damage due to rutting and cracking. Compatibility tests of polymer-encapsulated PCM materials produced by Microtek Laboratories, Inc. were performed using two unmodified asphalt binders used by the Texas Department of Transportation, PG 58-28 and PG 64-22. The PCMs were mixed with these binders or binder/sand mixtures and tested for retention of thermal properties. The resulting blends were homogeneous, indicating that the PCM capsules are compatible with the asphalt.  A distinct inflection in the temperature heating profile near the melting point of the PCM, which produces a time lag in the heating, confirms that a significant portion of the polymeric capsules remained intact.  Asphalt concrete samples of thickness 4-5 inches containing PCM macrocapsules with polymeric encapsulants at 12.5% w/w were subsequently fabricated in a gyratory compactor.  Heat transfer test results from a test slab prepared with a conventional asphalt concrete formulation indicate that the PCM capsules survive the compaction process and provide the desired thermal effects.