ABSTRACT

Inadequate subsurface drainage of pavement systems has contributed to many premature pavement failures. If there is inadequate subsurface drainage, premature pavement distresses are likely to occur. In case of concrete pavements, the following major distresses are experienced due to excess water: pumping, faulting, slab corner breaks, curling/warping, punch outs and D-cracking. An unstabilized permeable base consisting of non-stabilized aggregates is placed over a previously constructed aggregate or geotextile separator layer. Aggregate material should be hard, durable and angular. The preference is 100% crushed aggregate. Los Angeles abrasion should not exceed 45%. The aggregate is placed with an asphalt laydown machine in compacted lift not exceeding 100 mm. Compaction should consist of one to three passes of a 4.5 to 9 metric ton smooth steel-wheeled power roller. Over rolling can cause degradation of the aggregate material resulting in loss of permeability. The grade of asphalt binder should be the same as that used for overlying asphalt courses.