Study on the Water Stability of Polyurethane Concrete from Perspective of Polyurethane-Aggregate Interface

Since the conventional asphalt concrete will release many harmful gases including greenhouse gas in the construction process and it is prone to early diseases leading to long-term performance deficiencies, in recent years, polyurethane (PU) has been gradually considered to replace the asphalt binder used in road due to its excellent performance, such as mechanical properties, durability, elasticity, environmentally friendly, low energy, etc. However, the PU concrete has been found to have poor water stability due to the poor moisture damage resistance of the PU-aggregate interface. To improve the water stability of PU concrete, the evolutions in the moisture damage resistance of PU-aggregate interface subjected to water immersion and freeze-thaw cycle were investigated, and the technique to improve its moisture damage resistance was preliminarily explored. For this purpose, a method for evaluating the PU-aggregate interfacial bonding property was first proposed. Under the two aging conditions of water immersion and freeze-thaw cycle, both the interfacial tensile strength and shear strength decreased rapidly in the early stage of aging, followed by a steady and incredible great degradation ratio. In contrast to interfacial tensile strength, interfacial shear strength is more sensitive to freeze-thaw cycle than water immersion. The decrease of moisture damage resistance of PU-aggregate interface is mainly ascribed to the destruction of the weak van der Waals forces caused by the invasion of water, plasticization of PU binder, hydrolysis of –NHCOO– and possible incomplete curing, among which the first two factors are inescapable. The best way to improve the moisture damage resistance of the PU-aggregate interface is to develop a PU that can be highly cured in a short time at ambient temperature and does not readily hydrolyse. The present research provides a solid theoretical basis for the research and development of PU suitable for pavement.