Influence of Constituents on the Evolutionary Response of Bitumen-Stabilized Material

Bitumen-stabilized material (BSM) consists of aggregates, bitumen emulsion or foamed bitumen, cement, and water in specific proportions. It enhances the mechanical properties of unbound granular materials to serve as a stronger base course in the pavement structure. It is understood that the mechanical behavior of BSM evolves with time because of distinct constituent materials and their complex interactions. This study investigates the effects of bitumen emulsion content, cement, and curing duration on the volumetric and mechanical properties of BSM prepared with two different gradations as recommended by the Asphalt Academy (TG2) with nominal maximum aggregate size (NMAS) 26.5 and Austroads with NMAS 19.0 mm. Laboratory tests and statistical analysis examined the moisture loss, air voids, and indirect tensile strength (ITS) of BSM. Results indicate that combining cement and bitumen emulsion significantly improves ITS by reducing moisture loss and air voids. Being the coarser gradation, TG2 performed better with cement because of the enhanced hydration, whereas the relatively finer Austroads gradation resulted in higher ITS without cement because of better compaction and adhesion. Without cement, all the mixtures resulted in lower strength than the recommended minimum ITS of 225 kPa, highlighting cement’s critical role in strength development. Further, it was established that the Michaelis–Menten (MM) reaction kinetic model effectively describes curing behavior, predicting the curing rate, theoretical maximum strength, and minimum curing time. These findings presented in this paper provide practical insights for optimizing BSM mix designs by balancing emulsion content, cement dosage, and aggregate gradation.