Effect of Moisture Content and Freeze-Thaw Cycles on Bearing Capacity of RAP/Natural Aggregate Mixtures
Last modified: 2017-02-28
Unbound granular base layer plays a significant role in the overall performance of the pavement structure. It provides structural support for the upper pavement layers, contributes to load distribution and acts as frost protection layer. Traditionally this layer is built with high quality natural aggregate. However, as the sources of natural aggregates are becoming increasingly scarce, engineers are examining the possibilities of using recycled materials. The most widely used recycled material in pavement construction is reclaimed asphalt pavement (RAP) and its possible application in unbound granular base layer has been investigated since the mid-1990s. Previous studies confirmed that RAP can be a suitable replacement for natural aggregate, but there is major concern regarding the impact of seasonal variations in environmental factors on its properties. The paper analyses effect of changing moisture conditions and freeze-thaw cycling on bearing capacity of natural aggregate (limestone and gravel) and its mixtures with varying RAP percentages (20, 35 and 50%). Bearing capacity was determinate by laboratory CBR tests on samples prepared by modified Proctor compaction at optimal moisture content. Three samples for each mixture were prepared and tested after different curing conditions. First sample was tested immediately after compaction, second after 96 hours soaking in water and third after 14 freeze-thaw cycles. Base on the obtained results it can be concluded that the impact of changes in moisture content and freeze-thaw cycling is largely depended on the type of natural aggregate. Increasing RAP content for mixtures with limestone decreases their sensitivity to changes in moisture content and freeze-thaw cycling. For mixtures with gravel increasing RAP content increases their sensitivity to changes in moisture content and does not affect their sensitivity to freeze-thaw cycling.
unbound granular layer; bearing capacity; reclaimed asphalt pavement; moisture content; freeze-thaw cycling