By: Larry Scofield, P.E., and Scott Haislip
When residents of the Rio Verde Community Association (RVCA) needed to repave their parking lot, they turned to a clean, bright concrete pavement to solve the problems of distressed asphalt. Rio Verde is a beautiful golf course community located 30 miles northeast of Phoenix with spectacular views.
The parking lot was old, cracked and showing signs of its age and poor condition. Because of the pavement condition, water was ponding in some areas of the parking lot. Also, some residents complained about tracking black asphalt oil from the parking lot and streets into their driveways, garages and homes. Asphalt oil is used to seal fresh asphalt pavement and then again repeatedly to maintain and repair cracks and other distresses that occur over time.
Elsewhere in the community, residents complained about the heat generated from asphalt streets. Residents typically would walk on the concrete golf cart paths, observing that it was much cooler than asphalt. In fact, concrete can be up to 8° to 15°F cooler than asphalt in hot weather. With the challenges presented by asphalt, it was time for change. Enter Marlin J. Knutson, P.E., retired president and CEO of the American Concrete Pavement Association, a civil engineer and a Rio Verde resident.
“Both aesthetic and housekeeping issues were main concerns of the community center patrons,” Knutson said. “Concrete pavement not only fit in with their cost allotment, but its clean surface also prevents tracking.”
Knutson, or “Knute” as he is known to friends, showed there was a better way. In fact, he did a 30-year life-cycle cost comparison and concluded that the community could save $80,000 by resurfacing the distressed asphalt with long-lasting concrete pavement. Knute also served as the project engineer and inspector.
“The life of the asphalt in our parking lot was past its prime, and we needed to remove and replace it,” said Doris Findling, executive director, RVCA. “Normally we would have repaved with asphalt, but Knute came in and showed the board of directors how an ultrathin concrete pavement could provide additional benefits. The board voted unanimously on the concrete option.”
Plenty of strengths
A 3-in. overlay (sometimes called ultrathin whitetopping) was placed over the distressed asphalt. This tried-and-tested technology dates to early 1988, when thin sections of concrete were placed over distressed asphalt in experimental projects in Kentucky, Iowa, Tennessee and many other states. Since these early test sections were placed, more than 1 million sq yd of ultrathin whitetopping has been placed nationally. These pavements are estimated to provide two to three times the life of similar asphalt overlays.
One of the secrets to the durability of thin concrete overlays is close joint spacings. Technicians cut the placed concrete into small panels—in this case 3-ft x 3-ft sections—to control cracking that would otherwise weaken concrete.
Typically in projects of this nature, a like amount of the underlying asphalt would be milled off prior to the placement of the concrete. In this case, however, the concrete was placed directly over the top of the old pavement. Remarkably, concrete has a strong affinity for distressed asphalt, which forms a tenacious bond to the concrete and thereby stabilizes the entire substrate.
Another key to success was the skills and cooperation among the various team members. Glendale, Ariz.-based RGG United Contractors co-owners Paul Ochs and Martin Rangel worked closely with the RVCA and others to assure success. Rinker Materials, which supplied the materials and provided testing services for the concrete, also was important to the success of the project. Saint-Gobain Specialty Reinforcements Group also was a key player. The close cooperation helped address several problems and also brought innovative solutions to the project.
“One of the major problems with the existing parking lot was standing water in the southeast corner after rainstorms,” said Ochs. “Working to ensure correct drainage made this project challenging.
“Survey shots were taken on 15-ft intervals and grade adjustments were made to ensure correct flow,” Ochs said. “However, working together with the various stakeholders in a partnering relationship produced a successful project that has met all of its intended purposes.”
Another key to the strength is the addition of alkali-resistant glass fibers. The glass fibers act as a bonding agent to the cement paste and absorb the stresses until the concrete has gained sufficient strength, according to James Patterson, national sales manager, Saint-Gobain Specialty Reinforcements Group, Peoria, Ariz.
“The new pavement looks great,” added Findling. “Residents have commented on the pleasing aesthetics of it and the lack of tracking. We’re looking forward to the potential for no maintenance costs in the near future.”
When the parking lot was completed, the RVCA’s board of directors voted to extend the contract to pave a short city street, cul-de-sac and curb section with concrete. A number of homeowners in the community also have replaced their asphalt driveways with concrete, in large part because of the aesthetically pleasing and durable parking lot.
Environment group of solutions
Beyond the Rio Verde project, the concrete overlay provides an environmentally friendly, cooler surface for streets and highways. Among the benefits:
- Concrete minimizes waste sent to landfills or incinerated. Concrete uses waste products such as fly ash (a byproduct of coal-burning power plants) and slag (a byproduct of steel manufacturing). These materials actually make pavements stronger and longer lasting and are completely neutralized when encapsulated in rigid concrete;
- Bright white concrete pavement reflects light, which means it stays cooler than asphalt, reducing ambient air temperatures in urban areas (also known as urban heat islands), which actually reduces the amount of air conditioning and the associated energy to cool homes and businesses;
- Compared with dark-colored asphalt, concrete’s inherently light color and natural reflectivity means fewer lights and less energy are required to light streets and parking lots;
- Concrete is made from an abundant supply of locally produced natural resources (essentially limestone, rock, water and other products that are in plentiful supply);
- Concrete can be colored and used in decorative applications, instilling civic pride. Faux brick crosswalks, stamped and colored artwork formed into concrete and colored concrete not only allow builders and designers to show a little flair, but also make people feel better about their community; and
- Concrete creates peace of mind. Focus group research by the American Concrete Pavement Association revealed some surprising results: Motorists are less stressed, have more time for important things in life and are able to focus better when driving on concrete. These results stemmed from the fact that there are fewer repairs and virtually no maintenance required by concrete.
About The Author: Scofield is director of environmental technology for the American Concrete Pavement Association, Mesa, Ariz. He can be reached at 480/775-0908, e-mail: [email protected]. Haislip is director of streets and local roads with the ACPA, Skokie, Ill. He c
