| The performance of asphalt wearing courses in Costa Rica has been questionable for a long time, plastic deformation and moisture damage take place shortly after construction, followed by fatigue cracking in a few years of in-service performance. Apart from having highly variable raw materials, materials and construction specifications haven't been updated in a long time, and now the budget to implement effective pavement management is out of hand. This dissertation focuses on new types of mixes, such as gap graded and coarse dense graded, and asphalt binders, such as stiffer and polymer modified, as alternatives to current specifications, so that mixture performance can be optimized on user's demand.; Raw materials have been prepared and tested, and an appropriate mix design has been performed for every combination of aggregate and asphalt binder (total of 54 treatments). Mixes with optimum binder contents have been tested by plastic deformation, moisture damage and fatigue cracking, so that valuable information has been gathered and statistically analyzed. In addition, laboratory fatigue cracking transfer functions have been develop for Costa Rican materials.; Three aggregate sources have been extensively evaluated, as representative of the hot mixed asphalt production in the country, as well as four asphalt binders (two neat and two polymer modified ones). It has been found that performance is optimized by SBS modified binders together with coarse dense gradations, although optimum selection of gradation and binder has been found very aggregate source dependent. The benefit of SBS modification has been identified, since aggregate source, gradation and binder content become much less significant when SBS modified binders are used, and performance of mixes with SBS modified binders, specially with coarse dense gradations, has outranked the performance of mixes with neat binders. SMA mixes with neat binders have been found to perform better than current Ministry of Public Works' gradations with neat AC30 (only binder currently available at the country), although not as good as coarse dense graded mixes with SBS modified binders. A series of guidelines has been presented, were volumetric requirements are specified together with performance test requirements, for either top wearing courses or bottom fatigue resistance courses. |
