Bituminous Surface Treatment (BST) pavement treatment extends life, reduces cost
The City of Shoreline has 345 lane miles of paved surfaces with an estimated replacement value of $380 million. The Council has made maintaining this infrastructure a high priority, recognizing negative impacts of deferred maintenance over the long-term.
In the past, the City has largely relied upon the use of asphalt overlay applications to maintain City streets. However, with the cost of materials escalating significantly every year, the City’s ability to sustain the level of service in asphalting roads has been greatly diminished. It is critical to look toward maintaining the City’s roads through alternative means such as a pavement preservation program utilizing Bituminous Surface Treatments (BSTs).
BSTs used in Shoreline consist of a two-part application of asphalt emulsion and cover aggregate (small rock). BSTs are widely used to extend the life of a road, create a new wearing course and waterproof existing pavement. Costs are generally 75% less than the cost of a typical asphalt overlay, allowing for greater road coverage.
However, unlike an asphalt overlay, BSTs tend to have a coarser finished road surface. This can be controlled with the right combination of aggregate size distribution. Through testing, the City worked to ensure the right mix was found for Shoreline’s streets and that it closely matches what is seen with past overlays. Even so, residents may notice a difference.
The asphalt emulsion is a “rapid set” that promotes a quicker cure time and allows traffic back on the street within a few hours. The final sweeping and surface treatments happens a few days later. By using the BSTs, 5 to 10 miles are maintained and protected annually versus two to three miles, within the existing budget. With this approach, the City is able to stretch its resources while maintaining pavement quality.