Why Permeable Asphalt is Not Popular in the U.S.

Introduction to Permeable Asphalt

The term ldquo;permeable asphaltrdquo; can describe two different pavement structures commonly used in the United States. One type consists of open graded friction courses (OGFC), polymer-modified prime layer membranes (PFLMs), and porous friction courses (PFCs). These are typically used as the top layer on highways and allow water to penetrate only the surface, draining to the side of the road rather than over it. The other refers to a full-depth permeable pavement system, often found in large parking lots, where water can drain completely through the structure back into the soil. This alternative can significantly impact water management and soil health, adjusting to the native soil conditions.

Use of Permeable Asphalt on Highways

While permeable asphalt is not as widely used in all states, some transportation agencies have mandated its use on specific highways, particularly interstates. This indicates a localized popularity among certain state transportation agencies. However, questions arise regarding whether it should be used everywhere, considering its benefits and drawbacks.

Cost and Durability Issues

The primary reasons why permeable asphalt is not more popular in the U.S. are associated with cost and durability. These mixes often incorporate polymer-modified asphalt binders, which are more expensive than non-polymer-modified (NPM) binders. This higher cost is compounded by the need for specialized training and handling, limiting the number of contractors willing to produce them. In some markets, the requirement for specific aggregate types and importation of these materials further adds to the expenses.

In addition to cost, durability is a critical factor. Permeable asphalt structures are vulnerable to freeze-thaw cycles, particularly in colder climates, which can reduce their effectiveness over time. Furthermore, the open void structure of these pavements can result in less overall strength and durability compared to conventional dense-graded asphalt mixes. Rim scarring from trucks and snowplows can severely damage these areas, leading to potential future maintenance issues.

Current Application and Benefits

Despite the challenges, permeable asphalt serves a valuable function as a premium product that enhances road safety and functionality. It provides skid resistance, prevents hydroplaning, and reduces traffic-pavement noise. However, its structural value is a matter of debate. Some states do not assign it any structural value, treating it as a surface application for aesthetic or performance purposes. For these states, permeable asphalt is used to enhance the driving experience by addressing specific concerns.

The decision to use permeable asphalt ultimately lies with individual transportation agencies, each weighing the costs against the benefits. While it offers unique advantages, such as improved water management and reduced noise pollution, its higher costs and potential durability issues must be carefully considered.

Overall, permeable asphalt represents a promising approach to sustainable highway pavements. As technology advances and awareness increases, it is likely that more states and transportation agencies will adopt this solution, leveraging its benefits while addressing the challenges associated with its implementation.