Effects of hydrated lime and quarry dust dosage and aging on the relaxation modulus of bituminous mastics

Bituminous mastics are essential in influencing the stiffness and viscoelastic behaviour of asphalt mixtures, as the binder–filler matrix governs stress transfer and deformation resistance in pavements. Understanding the stress relaxation behaviour of mastics is crucial because it indicates the ability of the material to dissipate stresses induced by traffic loading. This experimental study evaluated the stress relaxation behaviour of bituminous mastics prepared with hydrated lime and quarry dust as fillers at three dosage levels (20%, 30%, and 40%). Stress relaxation experiments were performed at temperatures ranging from 40, 50, and 60 °C under a constant strain level of 10%, considering both unaged and aged conditions (10, 50, 100, and 200 h). The results showed that hydrated lime mastics shown a higher relaxation modulus compared to quarry dust mastics. Under unaged conditions at 40 °C, the peak relaxation modulus rose from 4.46 × 10⁶ Pa for HLM20 to 5.51 × 10⁶ Pa for HLM30, indicating a rise of about 23%, and then decreased to 4.95 × 10⁶ Pa for HLM40. Conversely, quarry dust mastics showed a gradual increase in modulus with filler dosage, rising from 4.71 × 10⁶ Pa for QDM20 to 5.30 × 10⁶ Pa for QDM40 at 40 °C. Aging further increased the modulus of both mastics, with HLM30 reaching 7.86 × 10⁶ Pa after 100 H of aging, indicating a significant stiffening effect. Master curve analysis also showed that the modulus of hydrated lime mastics increased by more than 100% from HLM20 to HLM30 under aged conditions, confirming the improved stiffness and stress resistance at this dosage. Overall, the results indicate that 30% hydrated lime provides the optimum filler dosage, offering a better balance between stiffness and relaxation behaviour compared with quarry dust mastics.