Representation Functions to Predict Relaxation Modulus of Asphalt Mixtures Subject to the Action of Freeze-Thaw Cycles

Abstract

This paper provides computational analyses using three representation functions (generalized power law function, Prony series function, and Burger model–based representation function) to determine relaxation moduli of asphalt mixtures subject to the action of freeze-thaw (F-T) cycles. Freeze-thaw cycles have been a severe concern on asphalt pavements in most dry freeze regions. The major damage of F-T cycling to the pavement is because of its volumetric expansion that pushes the pavement system upward thus causing the pavement to crack. Based on current pavement design criteria, the effect of F-T cycles on the performance of asphalt pavements has not been taken in to consideration in the stage of design and construction. The objective of the paper is to provide better understanding on mechanical behavior of asphalt mixtures under the F-T cycles using the three representation functions. Asphalt mixtures were sampled from an asphalt paving project located in Flagstaff, Arizona where mixtures collected from the job site were compacted using a Superpave gyratory compactor on specimens (15 mm in diameter and 11 mm in height). A series of F-T cycle tests (, 1, 15, 2, 25, and 3) were undertaken on all specimens using an ASTM-approved apparatus with modifications in sizes of asphalt specimens. After a desired F-T cycle was completed, specimens were removed for testing low-temperature properties of asphalt mixtures using a bending beam rheometer (BBR) in accordance with the newly released AASHTO standard. Creep compliance data obtained from BBR tests were used (1) to determine a relation between the stiffness value decrease and number of F-T cycles, and (2) to perform linear viscoelastic (LVE) analysis to predict relaxation moduli of asphalt mixtures at the selected F-T cycles. Based on the results of F-T cycle tests associated with numerical analyses, a single-term exponential model has better description with an exponential decay trend in the stiffness decrease of asphalt mixtures subject to the action of F-T cycles. In addition, LVE analyses indicate the initial relaxing capacity of asphalt mixtures drops approximately 6% after 3 F-T cycles. The paper concludes that Prony series function appeared to have better prediction than other two functions in fitting raw creep compliance data of asphalt mixtures at , 1, 2, 25, and 3 F-T cycles as well as showing promising results in predicting the relaxation modulus of asphalt mixtures subjected to F-T cycles.