Asphalt pavement! It’s everywhere you look. But what if you could have concrete for the same price? That’s the question that concrete pavement contractors are asking owners today, and often the answer is: “I’ll go with concrete.” This changing attitude marks the beginnings of a huge new market for concrete.
Designs and Materials
All types of concrete are currently being considered for commercial and industrial pavements, such as those used for trucking and freight facilities, intermodal facilities, shopping centers, and school parking lots. The three most common approaches are:
• Conventional concrete, designed and constructed according to ACI Committee 330 guidelines, either for unreinforced concrete paving (ACI 330.1-14, Specification for Unreinforced Concrete Parking Lots and Site Paving) or for industrial and trucking facilities (ACI 330.2R-17, Guide for the Design and Construction of Concrete Site Paving for Industrial and Trucking Facilities).
• Concrete overlays of asphalt, designed and built according to the Guide to Concrete Overlays of Asphalt Parking Lots by the National Concrete Pavement Technology Center.
• Roller-compacted concrete, designed and built according to ACI 327R-14, Guide to Roller-Compacted Concrete Pavements.
All of these approaches may be strongly considered as facility owners become more aware of the long-term cost of ownership. Many times, the realization of ongoing maintenance costs for asphalt pavement becomes a key factor in a decision to consider other options.
One factor in the increasing popularity of concrete pavements has been the attention the concrete construction industry has paid to industrial parking lot solutions over the past 10 years. Collaboration between the National Concrete Pavement Technology Center (CP Tech Center), and the National Ready Mixed Concrete Association (NRMCA)/American Society of Concrete Contractors (ASCC) Joint Paving Committee has greatly improved the odds when concrete goes against asphalt as a paving material. This group’s recently completed ASCC Paving Tool Kit includes guides, references, and case studies to help convince owners to go with concrete and to provide contractors and designers with the tools needed to do the job right. A resource that is advancing this effort is NRMCA’s Design Assistance Program (DAP) where an experienced engineer will design a concrete pavement free of charge for those working with NRMCA-member concrete producers. To access this program, go to ascconline.org/technical/paving-tool-kit.
An example of this newfound preference for concrete pavement is in two recently completed projects by Merlo Construction, Milford, Mich. In 2012, company CEO Ray Merlo began the lengthy process of convincing the developer of a 1 million-square-foot pavement for a FedEx Ground facility in Ohio to change from asphalt to concrete. It was a challenge most contractors would not take on, but Merlo and his team, with help from Ohio Concrete, persisted and got the job done. This was soon followed by a second FedEx facility in Pontiac, Mich. This effort paid off not only for Merlo, but the success of these projects served as an example for the developers of FedEx properties around the country who were now convinced they could have better, longer-lasting concrete pavement for their heavy-duty truck lots. “We’re working now to get concrete on the drawings in the first place rather than having to flip it,” Merlo says. “That will present us with fewer initial hurdles.”
Roller-compacted concrete pavement has also experienced substantial growth in many parts of the country. Placed with equipment typically more suited to asphalt, these industrial concrete pavements have replaced asphalt as the material of choice in intermodal facilities in Illinois, shipping container yards in California, and a variety of mixed-use applications throughout Texas.
Lastly, concrete overlays of existing asphalt parking lots are now another option for owners to consider for commercial/industrial pavement. Benefiting from the experience of overlaying airport runways that began over 50 years ago, and progressing to overlaying streets, local roads, and now sections of the interstate highway system, concrete overlays have a proven track record of long life and durability. Using the existing, in-place asphalt as base material, a new concrete pavement is placed directly on top of the asphalt.
The game-changer for overlaying parking lot pavement came along in the mid-1980s with the development of the laser-guided screed. Prior to that, all concrete overlays were placed with a slipform paver, which by its design runs in a straight line, being more conducive to straight, long runs of paving like a runway or highway. The laser-guided screed is much more appropriate for parking lot paving where large square or rectangular sections are common.
The newer 3D-equipped laser-guided screeds took this a step further—since they are not reliant on a stringline setup like slipform pavers and can easily maintain varying slopes, contours, and elevations—making them the ideal equipment for placing concrete overlays. “We do all our own grading work,” Merlo says. “About 300,000 cubic yards of soil moved on the Pontiac project. We integrate the dozers and the 3D screeds to the same model in order to get the right pavement thickness.” Merlo’s crews then broom the surface right behind the screed and spray on a curing agent, which was a challenge since the placements can be as much as 80 feet wide.
Calculations for load-carrying capacity based on the thickness of the old asphalt and the thickness of the concrete overlay ensure the right design for the application. Most people have driven on a concrete overlay on a highway but would not realize it is an overlay unless they pay close attention to the jointing of the concrete. Overlays will have more joints cut into the concrete than full depth concrete pavements, but that is the only visual sign of an overlay.
Thin Concrete Pavements
One recent development in concrete pavements that holds great promise is the Thin Concrete Pavement (TCP) system developed in Chile by Juan Pablo Covarrubias and advanced over the past few years by his son Juan Pablo Covarrubias V. Now this system is being represented in the U.S. by PNA Construction Technologies, which has dubbed it the TCP, Proprietary Paving Solution. With this system, contraction joints are cut typically on a 5- to 8-foot grid and the pavements are significantly thinner than those designed using the current pavement design methodologies.
The basic idea is that since only one wheel load will bear on a panel at any time, the smaller panels aren’t subjected to the bending stresses that would occur if two wheels were bearing on a single panel. The panels therefore don’t crack and the small panel size greatly reduces slab curling.
“It basically turns the pavement into large pavers,” says Jerry Holland, vice president and director of design at Structural Services Inc. “But since the macrofibers cross the joints, the pavers are connected and there’s significant shear transfer.” Holland points out that we have understood for a long time that small increases in joint spacing increase curling stresses exponentially, so reducing the panel size to 5 to 8 feet square reduces curling to a very small amount. “With this system we’re practically just using the concrete to keep the dirt off the truck wheels,” he says. “The load is going through into the soil support system. It seems odd to go thinner instead of thicker but it really makes sense and seeing some actual installations backs up the testing and analysis and the modeling that was performed at the University of Illinois.”
PNA uses TCP’s computer model, OptiPave, to analyze pavement projects. “The TCP, Proprietary Paving Solution is an all-encompassing design program that we are licensing to select contractors,” says PNA business development director Nigel Parkes. “Some of those we are working with currently include the Fricks Company, Lloyd Concrete Services, and Poppoff Inc.”
Parkes explains that when a contractor gets a project to bid, they come to PNA with the owner’s requirements for traffic and service life. Using the model, PNA evaluates the project and optimizes the design to account for such things as the soil support system, climate conditions, anticipated traffic, desired design life, and pavement materials. They go through an iterative process and provide the owner with options. “It’s a team approach,” Parkes says. “We do the initial analysis then have three external engineering companies that we work with to provide the contractor with a stamped design, so that for the owner it’s completely turnkey.”
Several projects using the TCP system have been built recently in the U.S., but many more have been completed in Central and South America. Most of these projects have been exterior industrial pavements and parking lots but there have also been highways and local roads where the thin pavement has also performed well.
A Walmart distribution center in Chile was paved using TCP in 2009 with a 6-inch concrete pavement atop a 6-inch granular base. This 600,000-square-foot facility handles nearly 500 heavy trucks per day and remains in nearly perfect condition. Four years after the distribution center opened, Walmart was so happy with the performance of TCP that they used it for an expansion of the original facility. In 2018, Walmart built another distribution center in Santiago, Chile. choosing TCP as its pavement solution—for 1.5 million square feet of pavement this time.
“What I like is that I can see installations with a tremendous amount of truck traffic, both in Chile and in Guatemala City,” Holland says. “In Guatemala, the tractor-trailers were coming and going and it was holding up very well.” He notes that one important piece of this system is a good soil support system and that he also favors a small amount of synthetic macrofibers in the concrete—about 4 pounds per cubic yard. He also recommends cutting the joints with a narrow blade on an early entry saw.
The PNA system is now being used across North America, although the company is being selective on projects in order to slowly grow this new approach.
