In specific parking areas, a specialized porous pavement mix was placed with roughly 20 percent air voids to quickly drain stormwater to a subsurface collection basin that slowly releases the water to retention ponds.
flexible inner layer to keep the joint between the asphalt and concrete impermeable. Low permeability — A void-filling emulsion was applied to all pave- ment surfaces. The emulsion (RPE) is designed to permeate into any interconnected voids of the surface mix, thereby making it imperme- able. The unique penetrating qualities of this emulsion, along with careful application, is intended to leave little product on the surface and not adversely affect pavement friction. Porous pavement design — In specific parking areas, a specialized porous pavement mix was placed with roughly 20 percent air voids to quickly drain the water. These porous layers have a subsurface col- lection basin that slowly releases to retention ponds. This eliminates flooding from stormwater runoff. No bird baths — Before the surface lift was paved to all roads and parking areas, a survey was conducted to assess the ability to drain without ponding. A small milling machine was used to correct slope where needed to enable water to drain. Only a few small areas needed to be milled before the final surface lift was placed. Conclusion Too often, little attention is given to designing and constructing pave- ments for commercial properties. This can lead to early distresses, requiring crack filling and other repairs that are a poor reflection on the business. Innovative engineering and the use of premium materials should not just be reserved for highways. The design and construc- tion of the pavements at Heritage Group’s new Innovation Center and Research Laboratory is an example of how long-term performance can be achieved, resulting in low maintenance and outstanding life-cycle costs long term. MARK BUNCHER, PH.D., P.E. , is director of engineering at the Asphalt Institute (www.asphaltinstitute.org). TONY KRIECH is vice president of Research and Development at the Heritage Research Group (http://hrglab.com/rd.html). This article is reprinted with permission from the spring 2018 issue of Asphalt magazine, published by the Asphalt Institute.
Unique features The center’s final pavement designs utilized materials and features not typical of commercial parking lots or even roads. Structural design — The roads were designed at 8 inches of com- pacted 36-mm top size aggregate base, with 4 inches of 19.0-mm Superpave hotmix asphalt (HMA), and two, 1-inch lifts of steel slag SMA 4.75 mm. The steel slag SMA 4.75 mm mix is identical to the current racing surface placed on the main oval of the Indianapolis Mo- tor Speedway, but with improved binder properties. The parking areas were constructed using 6 inches of compacted #53 aggregate base, 3 inches of 19.0-mm Superpave HMA, and a 1-1/2-inch lift of 9.5 mm with dolomite. Polymer Modified Asphalt (PMA) — Two polymer asphalt systems were selected. The roads used a PMAwith a unique polymer combina- tion that graded as a PG 82-22 (true grade 82-26) in the top two 1-inch steel slag SMA lifts. The parking areas used a PMA that graded as a PG 70-22 (true grade 74-24) in the 1.5-inch surface lift of 9.5 mm. Mix performance testing — Performance testing was conducted on the surface mixtures, including IFIT (low-temperature cracking) and Hamburg (high-temperature rutting). Results were favorable. Longitudinal joint sealant — Parking lots contain many longitudinal and transverse joints. The area around these joints tends to have higher air void levels, making them more prone to permeability, cracking, and raveling. An innovative technique to seal these joints from the bottom- up is called Longitudinal Joint Sealant (LJS) — named by the Illinois DOT. The Heritage Group’s VRAM product is placed typically at a width of 12 or 18 inches on the underlying pavement by either a handheld drag box, push cart, or in-line spray bar, prior to the surface lift being placed. The heavily modified sealant is designed to wick up into the surface mix, thereby filling the voids around the joint, reducing perme- ability, increasing durability, and keeping the joint from opening up over time. Sealant was also applied along the concrete curb to create a
54
csengineermag.com
may 2018
Made with FlippingBook Annual report