Effect of laboratory compaction on the viscoelastic characteristics of an asphalt mix before and after rapid freeze-thaw cycles

Abstract

Environmental conditions, the rate of loading and mixture properties are the most important factors that affect the complex modulus (|E*|) values. The effect of environmental freeze-thaw (FT) cycles on viscoelastic properties of asphalt base materials has not been investigated properly yet. At the bottom of the asphalt base layer in a pavement structure, there is higher tensile strain due to traffic, and it usually has a higher air voids content which is mostly due to a poor compaction during construction. Asphalt mixture with a nominal maximum aggregate size of 20mm, called “Grave Bitume” (GB20) which is normally used as a base layer in Quebec, was used in this study. The main objective of this study is to compare the complex modulus test results of the dry, partially saturated, and FT conditioned specimens with different compaction levels. Three different air voids (2%, 3.5%, and 7%) are targeted in this project. The saturated specimens are subjected to complex modulus test carried out using the Direct Tension-Compression test. The rheological model 2S2P1D is implemented to simulate the behavior of the mixes according to various temperatures and frequencies. The results indicate that the compaction level significantly affects the behavior of the mix after a large number of rapid FT cycles. The effect of FT cycles on viscoelastic behavior of the mix is added to the Witczak formula in order to improve the prediction of the service life of asphalt GB20 base mix. Comparison between the laboratory determined and predicted data indicate that the relative bias in the modulus prediction after 300 FT cycles, especially due to the high percentage of voids. This can be eliminated by applying the improved equation to the predicted values.