The town of Twin Lakes, Wis., is about to become the proud owner of its first concrete roads. The happy occasion is the result of a progressive and proactive local concrete contractor working with a quality-oriented developer and open-minded village engineers.
Late last year Joe Swederski, vice president of Swederski Concrete Construction, Spring Grove, Ill., heard from a friend about a new residential development (known as Majestic Estates) just a few miles from the company's office. In talking with developer Robert Tomczak, Swederski learned that the original pavement design was for asphalt, as most local roads in the area have been for years. But Tomczak was very interested in the possibility of installing concrete roads to complement his plan for a high-class subdivision of relatively expensive homes.
Swederski Concrete has been steadily expanding the market for concrete parking lots and local concrete streets in northern Illinois and southern Wisconsin since it purchased its first Somero Laser Screed in 1999. Based on a proven track record, Swederski was able to show the developer how putting in concrete would reduce the roads' total life cycle cost. He also was able to trim the initial cost because less imported stone base was required with concrete than with asphalt.
With the total installed price for concrete approaching that of asphalt and the increase in property value that goes along with having concrete roads, Swederski's proposal was well received. However, convincing the developer was only the beginning. The remaining hurdles included convincing the design engineer and the village's engineering consultants.
The design engineer had worked on more than 200 subdivisions over 30 years, Swederski relates, but all of them had been asphalt. He was unfamiliar with, but not opposed to, light residential concrete road pavements.
Swederski's history of successful concrete road projects in the area provided a good starting point. But he also enlisted the help of Randell Riley, P.E., executive director of the Illinois Chapter of the American Concrete Pavement Association (ACPA). Riley previously had provided technical assistance on similar projects. His approach was to compare asphalt and concrete pavements for the development using the concept of equivalent single-axle loads (ESALs). This standardized unit represents the effect of an 18,000-pound single-axle load on pavement. The cumulative effect of traffic over the design life a pavement can be expressed in the total number of ESALs it will withstand.
The original pavement design was for a 1½-inch asphalt surface course atop 2 inches of binder and a 9-inch aggregate base course. Noting that the calculated concrete equivalent would be less than the ACPA recommended minimum, Riley analyzed the ACPA minimum instead—5 inches of unreinforced portland cement concrete atop a 4-inch granular base. He also analyzed the 6-inch pavement Swederski proposed to install on a 4-inch granular base.
To conduct the analysis, Riley used the WinPASS software developed by the ACPA. The program follows methods outlined in the 1993 “AASHTO Guide for Design of Pavement Structures,” which covers the design and evaluation of roadway pavement.
Riley's results showed that based on the AASHTO procedures, the asphalt road would carry only about 13,800 ESALs. However, the carrying capacity of the 5-inch concrete pavement he calculated would be 193,800 ESALs, or roughly 14 times the asphalt pavement's capacity. For the 6-inch concrete pavement Swederski proposed to use in the development, the carrying capacity came out to be 532,800 ESALs, roughly equivalent to 13 trucks per day—and 38 times the capacity of asphalt.
That engineering analysis combined with the contractor's performance record was enough to convince the design engineer that a concrete road would be sufficient. The village, however, still had concerns over both design and maintenance. Swederski turned to the ACPA Wisconsin Chapter for assistance, where regional engineers Reid Knutsen and Kevin Mc-Mullen provided a signed and sealed design detail cut and specifications for the project. The village's engineering consultant, Baxter & Woodman, accepted the design, explanation, and assurance of how little maintenance is required on a properly designed and constructed concrete road.