Phase Change Materials in Asphalt Cut Pavement Temps by 1.5°C in Lab Tests

Asphalt pavement covers the vast majority of high-grade roads in China and worldwide, yet asphalt is inherently temperature-sensitive. Above approximately 55°C, the dynamic stability of asphalt mixtures plunges, triggering rutting, deformation, and accelerated aging. Conventional solutions — rutting-resistant binders, reflective coatings, water-retention surfaces — address symptoms rather than the underlying thermal energy accumulation. This study explored a fundamentally different approach: embedding latent-heat phase change materials (PCMs) directly into the asphalt mix so that the material itself absorbs excess thermal energy during phase transition, buffering dangerous temperature spikes.

The researchers selected polyethylene glycol with a molecular weight of 1500 (PEG1500) as the phase change core material, chosen for its phase transition temperature range compatible with summer pavement conditions and its chemical compatibility with asphalt binders. Calcium alginate — formed by reacting sodium alginate with calcium chloride — served as the encapsulation wall, preventing liquid-phase leakage during the solid-to-liquid transition and providing thermal stability up to the 150–190°C range required for hot-mix asphalt construction. The preparation involved dissolving sodium alginate and calcium chloride separately in deionized water, blending liquid PEG1500 into the sodium alginate solution at 80°C, then dripping calcium chloride solution into the mixture and allowing it to stand for 8 hours. The resulting dry composite was a white granular solid with an apparent density of 1.08–1.21 g/cm³.

For laboratory validation, the composite PCM was incorporated at varying dosages into SMA-13 Marshall specimens — a stone mastic asphalt mix commonly used for surface layers in China. Specimens were placed in an oven set to 60°C, and internal temperatures were monitored over time. At a doping level of 2.4% composite PCM by weight, specimen internal temperatures were reduced by approximately 1.5°C compared to unmodified controls. This modest but meaningful reduction reflects the latent heat absorption during the solid-to-liquid phase transition of PEG1500, which effectively delays the rate of temperature rise within the mix.

To translate these laboratory findings to real pavement structures, the team constructed a three-layer finite element model in COMSOL Multiphysics software representing a typical Chinese highway surface structure: 4 cm SMA-13 (top layer), 6 cm AC-20 (middle layer), and 8 cm AC-25 (bottom layer). The model incorporated summer solar radiation boundary conditions and thermal properties measured from the specimens. Simulations were run with and without 2.4% PCM in the top and middle layers. Results showed that adding PCM to both the top and middle surface layers kept temperatures in all pavement layers outside the critical range where asphalt dynamic stability sharply declines — a threshold associated with rutting onset at temperatures above approximately 55°C.

The study's implications are primarily for infrastructure durability in hot climates. By keeping pavement temperatures below the rutting threshold, PCM-modified asphalt could meaningfully extend road service life and reduce maintenance costs. The approach is additive-based and compatible with existing hot-mix construction processes, lowering the barrier to adoption. However, the temperature reduction observed in lab conditions (1.5°C) is relatively modest, and real-world performance under sustained solar loading, traffic-induced heating, and multi-year thermal cycling remains to be validated through field trials. The study does not report long-term mechanical performance data or cost-benefit analyses, which will be essential for practical deployment decisions.