The perception among building owners and specifiers is that a concrete parking lot may be better but it's considerably more expensive than asphalt. No matter how many times they hear about life-cycle costs or sustainability, the decision usually comes back to initial cost. Well, guess what—initial cost is no longer an issue.
Today, as asphalt prices have increased and technology has improved, the concrete industry has a great story and we need to tell it. What you need to make the case are some cold hard facts.
As important as the current cost of asphalt is to this discussion, just as important is the volatility of those prices and where the price is going in the future. Concrete materials are nearly all produced in the United States and are not as dependent as asphalt prices are on the value of the dollar or the price of a barrel of oil. “As long as the dollar is weak internationally and oil prices trend up, concrete is more cost effective,” says Greg Scurto, senior consultant of Scurto Cement Construction, Gilberts, Ill. “Sure, there are other factors, such as demand and energy supplies, but we believe that on an initial cost basis, concrete is becoming more and more competitive—and on a sustainability basis, it's far less expensive.”
An increasingly important factor in the cost of asphalt comes from the oil refining process. In a recent Webinar sponsored by the Silver Spring, Md.-based National Ready Mixed Concrete Association (NRMCA), Phil Kresge, senior director of national resources, noted that with the older topping refineries, 40% of a barrel of oil ended up as asphalt. Compare that to the today's catalytic cracking units where only 12% is asphalt or to the very new coker refineries that produce no residual asphalt only coke, which is sold to the steel industry or to the cement industry as fuel for kilns. All this leads to a dwindling supply of asphaltic binders. In addition, the asphalt that is available in the future will mostly go to highway department projects, not to commercial parking lots.
An important concept when comparing the cost of concrete parking lots to asphalt is the structural number. This is based on AASHTO's 1993 “Guide for the Design of Pavement Structures.” In that guide, 1 inch of the various materials used for pavement systems was assigned a coefficient based on its ability to support loads. This helps to show that 1 inch of concrete (with a coefficient of 0.5) has more strength than 1 inch of asphalt (with a coefficient of 0.2 to 0.4).
Say a project needs a structural number of 2.5, which is adequate for car traffic and the occasional truck. That would take 5 inches of concrete if placed directly on soil or 4 inches of concrete on 4 inches of subbase (with a coefficient of 0.12). An equivalent asphalt pavement with a coefficient of 0.3 would require 2½ inches of surface asphalt, 4 inches of asphalt base, and 4 inches of aggregate subbase.
Scurto emphasizes the importance of this approach. “You can't talk about concrete paving in the old way where everything is 7 or 8 inches thick by default. What you need to look at is your performance expectations for the asphalt and then design a concrete pavement for similar or slightly higher performance. Then you can compare apples to apples on a first cost basis,” he says.
He also notes that the total profile of the pavement needs to be factored into the calculation. “In the excavation bid, if there is haul off of soil, the profile of the concrete paving is so much thinner that the savings on the excavation makes it a no-brainer to go with the higher quality paving. Where an asphalt pavement might have a 16- to 19-inch profile, a concrete pavement system might only be 9 or 10 inches thick,” he says. “But you have to get in early so that the excavators can bid both options.”
Kresge also urges concrete contractors to encourage potential customers to quantify comparable pavements rather than looking at pavements of the same thickness. To assist with this, NRMCA has developed Concrete Pavement Analyst, a software package that allows users, as Kresge says, “to make an educated quantified comparison.” This package is free from NRMCA by contacting the concrete promotional group in your area. Go to www.concreteanswers.org/CPA_software.html for details.
Life-cycle cost is where a concrete parking lot, with its very low maintenance needs, has always had a big advantage over asphalt paving. “We give a three-year warranty as long as they allow us to use the sealer we want,” says Scurto. “I've got a parking lot that I placed in 1981 and only about 3% of the lot has been removed and replaced. An asphalt lot that old is called subbase.”