Viscoelastic characterization of cold recycled bituminous mixtures

This study demonstrates the time (loading frequency), temperature and stress dependent behavior of the cold recycled mixtures treated with foamed bitumen. The behavior of these Foamed Bitumen treated Mixes (FBMs) was evaluated in terms of the dynamic modulus which is a critical input for many pavement design methods including AASHTO and Austroads. Tests were performed at multiple temperatures and loading frequencies that typically encounter in pavement structures. Two FBMs; one with 1% cement and other without cement were prepared using the gyratory compactor and dynamic modulus tests were performed at three different temperatures (5, 20 and 40 degrees C), five different loading frequencies (0.01, 0.1, 1, 5 and 10 Hz) and different deviatoric stresses ranging from 50 kPa to 300 kPa. The test results suggest that the FBM response depends on stress level along with frequency and temperature even at lower stress levels unlike in Hot Mix Asphalt (HMA) which tends to show stress independent behavior at lower stress levels. The dynamic modulus of FBMs increased with increase in deviotric stress indicating the stress hardening behavior of these mixes. The study also proposed an approach to construct stress dependent master curves so that all the parameters such as temperature, loading frequency and stress level that influence the stress-strain behavior of FBMs into a single model. Stress-dependent master curves were constructed by shifting the laboratory data both horizontally and vertically conferring to the time-temperature superposition principle to create a single master curve from which the viscoelastic response of the FBM mixtures can be obtained. It was found that the proposed stress dependent model predicted the dynamic modulus of FBMs to good accuracy. (C) 2018 Elsevier Ltd. All rights reserved.