Abstract
The effectiveness of the subsurface drainage system is a primary factor influencing long-term pavement performance. Pavement research indicates that pavement drainage systems increase pavement life and lower maintenance costs by minimizing the risk of subgrade softening and differential frost action. For rigid pavements, optimum transverse joint performance is achieved when the concrete pavement overlies a highly permeable base layer, promoting subsurface drainage, as well as a layer that is structurally stable, providing uniform support to the slab. This type of slab support eliminates the potential for loss of slab support from fine migration from pumping action over time. The Ministry of Transportation of Ontario (MTO), Canada, recognizes the benefits of high-performance pavement drainage systems and several years ago adopted open graded drainage layers (OGDLs) for design of freeways. The MTO OGDL has an open void structure with a laboratory-determined permeability on the order of 10-2 cm/s by using aggregate with a very low fines content. To achieve stability, 100 percent crushed bedrock aggregate is specified, and since the late 1980s, MTO has specified the use of an asphalt-treated OGDL with 1.8 percent asphalt cement to facilitate placement. The material development and subsequent construction and quality control activities completed during construction of test sections on a major freeway in southern Ontario in 1996 and 1997 are outlined. The work conducted along with the trials established that a portland cement-treated OGDL placed with conventional asphalt paving equipment is a viable alternative to asphalt-treated OGDL on the basis of costs and drainage properties.
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