Cost-effective Pavement Preservation with Lightweight Aggregates

Pavement preservation not only ensures a road is smooth and safe, but it can also economically prolong a pavement’s overall service life. In fact, both the Federal Highway Administration and the National Park Services have cited that every dollar spent on pavement preservation saves between six and 10 dollars in future maintenance. Asphalt surface treatments can help maintain roadways while also improving safe driving conditions immediately and in the long-term.

However, not all asphalt surface treatments provide the same benefits. As several Departments of Transportation (DOT) across the country have discovered, using expanded shale, clay and slate (ESCS) lightweight aggregate supports cost-effective maintenance due to its high retention rate and ability to reduce the amount of emulsion necessary to reseal a road. These benefits along with its ability to contribute to long-term skid resistance can help DOTs plan more efficient pavement preservation strategies.

Create High-Friction Asphalt Pavement for Safer Roads

To produce ESCS lightweight aggregates, raw materials are heated a rotary kiln. During this process, air bubbles form within the expanding material. These air bubbles remain as a network of unconnected voids throughout the cooled aggregate. The material can then be crushed and sorted into highly regulated particle size.

The voids within ESCS create a surface with a skid resistance that is significantly above limestone aggregate, approximately 65 for chip seal (compared to limestone’s 50) and 44 for hot mix (22 for limestone). Given the material is easy to ship and widely available, it can contribute to a high friction surface treatment (HFST) that is more economically feasible than traditional materials.

Support Road Longevity With Improved Skid Resistance and Adhesion

In addition to providing a HFST upfront, lightweight aggregates do not readily polish as they wear. This creates a relatively stable amount of skid resistance over the pavement’s service life. While some degree of polishing is inevitable in application, ESCS lightweight aggregate resists polishing to extend the level of safety an asphalt can provide over its lifetime.

Further, the voids within the aggregate increase the adhesion between the stone and the emulsion, which translates to less chipping and aggregate loss over the course of the pavement’s life. As a result, when used in asphalt chip seal, ESCS lightweight aggregates contribute to approximately a 40 percent longer service life than chip seals that use conventional aggregates. And in residential areas, the asphalt pavement’s service life may extend up to 14 years to contribute to cost-effective pavement preservation strategies.

Preserve Pavement More Easily and With Minimal Costs

ESCS lightweight aggregates also support asphalt crews. ESCS aggregates are lighter than conventional rock and so provide greater square yards of coverage per ton. The material can also provide retention rates of up to 99 percent, compared to the average 60 percent retention rate for natural aggregates. In a 2017 report from Carbon County, the DOT found that their oil use was reduced by 12% when they switched to lightweight aggregate.

All of these qualities contribute to a lower material cost for resurfacing. Likewise, the higher retention rate and greater coverage per ton supports faster resurfacing. On the one hand, this reduces labor costs. On the other, it also reduces road closure times, which minimizes the strain put on local communities.

Extend Asphalt Pavement Benefits to Constituency

Lightweight aggregates can provide many benefits to DOTs looking for cost-effective ways to preserve pavements. This material not only improves a road’s skid resistance and service life, but it can also support more efficient pavement preservation efforts.

That said, lightweight aggregates can also benefit commuters directly. Its higher-than-average adhesion rates resist chipping to reduce instances of vehicular damage caused by flying stones. And if the asphalt pavement does chip, ESCS’s lowered density reduces overall damage caused by chipped pavement. In fact, representatives from the Utah Department of Transportation (UDOT) report zero claims of vehicular damage on interstate projects that utilize ESCS chips. DOTs that are interested in using ESCS lightweight aggregates for asphalt surface treatments can contact a local producer to learn more about how to incorporate this material more readily into their pavement preservation plans.