Whether you’re installing a new roadway, trail, or parking lot, drainage is one of the most important aspects of the paving process. The correct drainage for your new pavement area will keep it looking fresh and staying strong for years to come.


Here are five reasons why drainage for asphalt pavement is so important!

Water & Asphalt Don’t Mix

Water is one of asphalt’s “natural enemies.” Puddles of water on an asphalt pavement will slowly break it down, causing a pothole to form.


Water deteriorates asphalt by breaking the bonds between the asphalt binder and the rocks and sand. Asphalt binder is a by-product produced from crude oil during gasoline production, and water and oil don’t mix.


Water below the asphalt pavement is also an issue. Poor drainage below the pavement can saturate and weaken the supporting materials in the aggregate base and subgrade, allowing traffic loading to cause excess damage to the asphalt pavement.

Freeze-Thaw Cycles

During winter, water can get into cracks in the pavement and expand when freezing. This causes the cracks to widen and grow.


In addition, water can freeze and expand in large “ice lenses” below the asphalt pavement layer. These ice lenses cause the asphalt to heave upward and then become potholes when the ice melts in the spring, which is a result of freeze-thaw cycles.

Less Water Puddles Means Less Surface Wear & Tear

The slope of the pavement is crucial to keep water from pooling on the surface of the pavement.


A pavement with little to no grade for drainage will quickly develop puddles (future potholes). Bituminous Roadways recommends constructing new pavements with at least a 1% grade.


For existing pavements, routine maintenance is crucial to protect pavements from water damage. Cracksealing, patching, and sealcoating will all extend the life of your pavement by reducing the damage to the pavement caused by water.

Drainage Happens on More Than Just the Surface

Proper drainage on the surface can still mean moisture will find its way underneath. However, with proper subsurface drainage, water will keep moving under the top layers.


Installing an aggregate base with quality class-5 aggregate will allow your base layer to be strong, stable, and quickly drain water away from the pavement, but this is not always enough. A subgrade made of mostly clay may prevent the water from draining.


In some situations, it is best to install a 12 to 18-inch sand layer below the aggregate base layer to improve the drainability of the supporting materials.


Another solution to improve subsurface drainage is to install drain tile below the pavement. Drain tile is a channel built below the pavement using geofabric as a filter, round river gravel, and a perforated pipe connected to a catch basin or stormwater pipe.

Protects Buildings Near the Pavement

With proper drainage, water will be directed away from the building towards the catch basins and into the sewer system. This can help improve the life of your building as less moisture will accumulate near the foundation, which can lead to water damage over time.

Choose Bituminous Roadways for Twin Cities Asphalt Paving

When you need maintenance on your existing pavement or require a new installation, go with the most trusted asphalt paving contractor in the Twin Cities: Bituminous Roadways!


Get a free online consultation or give us a call at 651-686-7001.