Effects of moisture on the mechanical and viscoelastic behavior of asphalt mixture under repetitive cyclic loading

Abstract

Moisture exposure of the asphalt pavement leads to the loss of internal strength of the mixture and exacerbated distresses such as cracking and rutting. The moisture has a long-term aging effect on the bitumen binder and bitumen mastic (loss of cohesion) and stripping of bitumen from the aggregate surface (adhesion fail). Understanding the process of moisture damage in asphalt is very crucial because of its significant consequences on pavement life. However, its effect is very complex and there is no single theory to explain the damage processes. Currently, employing moisture sensitivity tests according to EN 12697-12 have the advantage to compare moisture sensitivity after short-term conditioning for 3 days at 40 °C between different materials. However, the test procedures consider a single load application, which is far from the actual repeated vehicular loads in the pavement life. To understand the effects of moisture under repetitive loads, this research follows the cyclic load indirect tensile fatigue test (ITFT) with a stress-controlled mode of loading. Three different aggregate sources combined with two types of bitumen binders were employed to prepare 100mm cylindrical specimens cored from laboratory prepared slab using a steel roller compaction. To study the moisture effects on self-healing (stress recovery) of the asphalt, a rest period was introduced at a predefined number of load cycles. The short-term moisture conditioned samples show that moisture has influenced the stiffness modulus, elastic horizontal strain, self-healing effects, and the fatigue life of the asphalt mixture. Moreover, the effect of aggregate and bitumen sources influences moisture sensitivity of asphalt mixture under cyclic loading. The addition of a surfactant additive has also shown the advantage to decrease the effects of moisture in asphalt mixture made with quartzite aggregate.