Evaluation of the damage of an asphalt mix under repeated freeze-thaw cycles

Abstract

Asphalt mixtures are temperature sensitive and have viscoelastic characteristics, so the performances of an asphalt mixture are often affected by nature phenomenon. In Canada, like in many other northern countries, freeze-thaw cycles are a common phenomenon. Also, it is believed that the number of freeze-thaw cycles is increasing with the influence of the climate change. Because of that, the actual methods to predict the pavement distress may overestimate the pavement life. Fatigue distress is a fracture mechanism generated by repeated applications of tensile strains that creates stresses which are less than the strength of the materials. It is initiated at the bottom of the asphalt base layer that is mostly built, in Quebec, with GB20 mix. GB20 is a rutting resistant mix with low binder content that makes it sensitive to fatigue damage. On the other hand, during thaw period, the melting of snow induces bearing capacity loss. The loss of structural support from underlying layers creates a significant increase in tensile stresses at the bottom of the asphalt layers. In addition, there is another possibility of increased tensile stresses due to temperature variations and water expansion/contraction which causes an increase in early fatigue cracking. The effect of temperature and moisture at the bottom of the asphalt layer is totally neglected so far. The thermal variation and moisture contraction/expansion can produce horizontal strains that induce fatigue damage. The effect of environmental freeze-thaw cycle test on the evolution of fatigue cracking has not investigated properly yet. In this research, an asphalt mixture commonly used in the province of Quebec mostly as a base course is studied (GB20). The expansion and contraction of tested specimens are generated by the environmental chamber and measured by strain gauges. Direct Tension-Compression (DTC) equipment is used for the analysis of fatigue, and complex modulus tests. Rapid freezethaw cycles have been implemented to the conditioned specimens in the lab to simulate the daily rapid freeze-thaw cycles. The results demonstrated that the compaction level significantly affects the behavior of the GB20 mix after a large number of rapid freeze-thaw cycles. The effect of rapid freeze-thaw cycles on viscoelastic behavior of the mix was added to the Witczak formula to improve the prediction of the service life of this type of mix. Considering the results of the complex modulus analysis, it was found that the influence of freeze-thaw conditions on the stiffness behavior of the mix is higher with increasing the number of cycles. Regarding fatigue test results, the reference mixture (no freeze-thaw cycles) was more resistant to fatigue cracking than the conditioned mix (mix conditioned with 300 rapid freeze-thaw cycles). The results also indicated that the addition of Aramid Pulp Fiber (APF) could increase the performance and durability of the GB20 asphalt base mix.

Date	26 Oct 2018
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Alan Carter (Supervisor) & Guy Doré (Co-supervisor)