Durability of Bitumen-Stabilized Materials

ABSTRACT Bitumen-stabilized material (BSM) technology has been developed to stabilize base layers with bitumen to become flexible and durable (moisture resistant) with less than half of the application rate of bitumen that would be used in asphalt. This technology enables bitumen to be dispersed in meniscal droplets among the aggregates of the base layer. Dispersion takes place along with moisture and active filler but without heating the components. Given the need for flexible base layers with moderate stiffness that are not prone to cracking, conventional bases come up short. Cemented bases have high and sometimes variable stiffness, are brittle, and crack; unbound bases have low stiffness, are porous, and rut; whereas asphalt bases are temperature sensitive but, more importantly, are economically and environmentally expensive. The ideal base would be a load-spreading interlayer with intermediate stiffness between that of the surfacing and subbase, i.e., a balanced pavement. The “noncontinuously bound” nature of a BSM results in only partially coated aggregates above the size of 0.300 mm, whereas the majority of the bitumen produces a mastic of finer aggregates (active filler and bitumen) that produce flexible spot welds within the matrix. The hydrophobicity of the bitumen provides robust durability and moisture resistance. In addition, the composition of a BSM base, i.e., approximately 50 % stiffness of asphalt, provides that necessary balance. This state-of-the-art paper identifies the key durability properties that need to be addressed, with the objective of a pavement structure that achieves an adequate lifespan. A number of factors need to be considered and understood, i.e., the role of all components (aggregate, bitumen, active filler, and moisture) and their volumetrics, compaction, permeability, and performance test methods and limits all play a role in satisfying BSM durability.