Regulating asphalt pavement temperature using microencapsulated phase change materials (PCMs)

The use of phase change materials (PCMs) to regulate pavement temperatures has been previously studied, with the most successful studies using porous aggregates to stabilize the PCMs. However, this technique can lead to issues with PCM leakage and low PCM content. A less studied method is the use of PCM microcapsules, which also presents challenges since most microcapsules are not strong nor stable enough to survive the high temperatures and compressive forces experienced during asphalt mixture production and placement. This work presents a study of the properties of a new commercial microcapsule type with robust walls and high thermal stability, that are expected to overcome the aforementioned issues. Results from differential scanning calorimetry and thermogravimetric analysis confirmed the microcapsules exhibited high latent heats (200 J/g) and are thermally stable below 400 °C. Additionally, approximately 90% of the capsules remained unbroken after being milled at 140 °C for 20 min, suggesting they are capable of withstanding the mixing and compaction stages of asphalt pavement construction. When PCM microcapsules were added to HMA, thermal cycling experiments showed that specimens containing 10 and 20 vol% PCM exhibited temperature lags of 5 to 10 °C from the control mixture, as they approached the PCM melting/freezing temperature. These results confirm the ability of microencapsulated PCMs to regulate asphalt pavement temperature. However, results from measurements conducted at 40 °C and 1 Hz showed a 75% reduction of the dynamic modulus in specimens containing PCM microcapsules, which could indicate that the addition of these materials also affect asphalt mixture stiffness.