01515140

Component

Durability of asphalt mixtures immersed in water at 60°C for up to 70 days were investigated to better under the moisture-damage phenomenon. Moisture-damage in asphalt mixtures can be defined as the loss of adhesion between the aggregate and asphalt mastic bond or the loss of cohesion within the mastic in the presence of moisture that leads to loss of durability. The mixtures investigated comprised a limestone aggregate, two mineral fillers (granite and limestone), and a 40/60 pen bitumen and were compacted to three nominal air void levels (4, 6, and 8 percent) using a gyratory compactor. Durability of the asphalt mixtures was estimated using indirect tensile stiffness as a function of moisture conditioning time. Stiffness generally decreased with conditioning time (and consequently water content) except at low exposure times where low water content was associated with a slight but repeatable increase in stiffness. Mixtures containing granite filler and/or high air voids were less durable than similar mixtures containing limestone. The effect of moisture exposure on durability was found to be reversible as moisture conditioned asphalt mixtures that had lost up to 80% of the initial stiffness upon drying fully recovered. The reversible nature of the moisture-induced stiffness degradation suggests a plasticization process whereby the bulk mastic is softened and the critical stress concentration location is moved from the interfacial region of the aggregate-mastic bond into the bulk mastic. Estimates of mastic thickness and length of diffusion paths obtained from image analysis of micro-CT scans of the asphalt mixtures internal structure suggest moisture diffusion was mainly restricted to the bulk mastic and not the aggregate-mastic interface. The results suggest cohesive rather than adhesive failure dominate the durability of asphalt mixtures under the long-term moisture exposure used in this study.

This paper was sponsored by TRB committee AFK40 Characteristics of Asphalt-Aggregate Combinations to Meet Surface Requirements.

01503729

14-0127

English

16p

2014

Transportation Research Board 93rd Annual Meeting

Digital/other

Figures; Photos; References; Tables

Asphalt mixtures; Durability; Limestone aggregates; Mastic asphalt; Moisture content; Tensile strength; Thickness

Highways; Materials; I33: Other Materials used in Pavement Layers

Transportation Research Board Annual Meeting 2014 Paper #14-0127

TRIS, TRB, ATRI

Jan 27 2014 2:09PM