Multiscale Chemo-physico-mechanical Characterization on the Modification Mechanism of Polyurethane Modified Porous Asphalt towards Enhanced Moisture Damage Resistance 

Porous asphalt (PA) with open-graded structure and large air void content is a functional pavement material, which offers various attractive benefits, such as reducing tire-pavement noise, decreasing water splashing and hydroplaning on rainy days, improving pavement surface friction, and alleviating urban heat island effects. However, as the pore structures of PA are often exposed to the moist environment, PA pavement usually has relatively short service life because of early-age moisture damage, which is mainly caused by the weakening effect of moisture diffusion on the asphalt mastic and aggregate-mastic interface, and the excessive pore-water pressure due to the coupling action of moisture and traffic load. To improve the resistance of PA to moisture damage, modification of the asphalt binder by a thermoset material, polyurethane (PU), has been found effective without compromising its functional properties. However, as a novel modification method, the fundamental interaction mechanism of PU and asphalt binder in moist environment has not been fully understood yet. To fill this gap and potentially apply PU modified porous asphalt (PUMPA) as a durable pavement material in Hong Kong, this study aims to investigate the interaction mechanism between PU and asphalt binder inside PUMPA under the combined effects of loading and water through a series of laboratory experiments and numerical simulations. A multiscale approach, which involves the investigation from the binder, to mastic and to mixture scale, will be adopted. The PU modification effect and mechanism at the binder scale will first be investigated through microscopic characterization of the physical and chemical interactions between PU and asphalt, and laboratory tests on the mechanical properties of PUMPA binder (PUMAB). Based on the enhanced understanding of the PU modification mechanism, an optimum PUMAB will be selected for characterizing the moisture-induced deterioration at both the mastic and mixture scales. Coupled chemo(binder)-physico(mastic)-mechanical(mixture) analysis will be conducted to understand the mechanism of PU modification comprehensively. Finite element models will be developed to simulate PUMPA’s performance under various loading and environmental conditions. Finally, the optimum conditions for applying PU as an asphalt modifier to produce durable PUMPA will be recommended, and guidance on the practical application of PUMPA will be developed. The outcomes of this study are expected to significantly enhance the fundamental understanding of the working mechanism of PUMPA and promote its wide application as a novel durable pavement material with multiple attractive functions, thus improving the sustainability of road networks both locally and worldwide.