Whitetopping is a very similar process to full-depth concrete paving and the mix designs are interchangeable. The major difference is depth - whitetopping is usually applied at a thickness anywhere between 2 to 6 inches, whereas full-depth paving is usually 4 to 8 inches thick. On this particular project, the whitetopping was poured at an average of 4 inches throughout the lot. In addition, whitetopping requires less surface preparation than a full-depth concrete paving job. For this particular job, Docken's crews filled potholes with concrete base course. Other prep work included removing the asphalt around drains and areas where it was necessary in order to achieve the correct pitch and slope. The lot was swept clean before the concrete was poured.
Docken Concrete worked with its ready mix supplier, LYCON Inc., to choose the correct mix for the job. The mix contained 564 pounds of cement without fly ash or slag so early strengths could be achieved in order to allow traffic back on the parking lot so all businesses at the mall could remain open during the project. The mix included 3 pounds per cubic yard of Propex FiberMesh 650, a fiber reinforcement. Fiber reinforcement is optional in whitetopping, but some industry experts and associations recommend it. The mix was air entrained, used ASTM C33 #67 coarse aggregate and placed at a 4-inch maximum slump.
Docken Concrete employed the use of its Somero Laser Screed® with 3-D Profiler System. Docken explains this equipment was instrumental in making this project a quick and easy job, especially in regards to achieving proper slope around drains. "We were able to lay our first pour at 100 feet wide," he says. "The Laser Screed also eliminates the forms you would need with a truss screed and a lot of the labor over other methods." Docken thinks with his equipment he can work about twice as fast as a contractor doing a similar job with a truss screed.
It's not necessary for contractors to perform a concrete paving job with a 3-D-capable Laser Screed, however. Alternative methods include truss screed and wet screeding with a roller screed. With these other methods contractors set their grades with lasers. To achieve proper slope they may have to pave in smaller sections, but they still reach the same end.The lot was constructed in eight separate pours. Between the pours, Docken Concrete used Greenstreak Speed Dowels at 2 feet on center at construction joints.
Throughout the lot in areas with existing concrete curb, Docken poured a 4-inch tack-on curb. Where the parking lot met the sidewalk in front of the strip mall there was a 5-inch curb dropping off to the old asphalt lot. With Docken pouring 4 inches of concrete, it would have left only a 1-inch curb. As a remedy, the owner decided to make his entire lot leading up to the sidewalk handicap accessible. So Docken added an extra inch leading up to the sidewalk and gradually sloped out the area into the rest of the lot in order to eliminate the curb and make the entire sidewalk accessible by wheelchair. Where the whitetopping met the sidewalk, Docken placed polyethylene foam expansion joints.
Saw cuts 1 1/4 inches deep were performed the same day of the pour with an early entry saw. The joints were cut in a 10-foot by 10-foot pattern, with special care taken around curb islands.
"Because we poured over existing curb islands, we isolated those with saw cuts to prevent random cracking," Docken explains. "Because the concrete and asphalt met in those spots, there could have been cracking without those cuts because of the cold joint."The parking lot was finished with a broom finish after the screed and Docken applied Tamms Cure 500W, a white pigmented curing compound. The company sealed the lot a few months later with Baracade Silane 40 from Euclid Chemicals. The water repellent sealer offers defense against deicers and salts for Wisconsin's snowy winters and should last eight to 10 years depending on traffic wear patterns.
The whitetopping job took one week from start to finish. Docken says the project ended with positive results, it was done at a competitive price and sees whitetopping as a new source of business for his company.