Technologies behind the concrete pavements used on the U.S. nation’s roads and highways have been around for a while, but new developments in equipment and admixtures have opened up the market for some of them, making them the latest trends in concrete paving: concrete overlays, roller compacted concrete, and full-depth reclamation.
CONCRETE OVERLAYS:
Because of the lack of a long-term highway funding bill, little new construction has been going on, so pavement preservation has become a priority for most agencies and municipalities. This is an area where concrete overlays are showing great promise. Bill Davenport, Vice-President of Communications-American Concrete Pavement Association (ACPA) said, “Concrete overlays have been around for a while, but within the last seven to eight years in particular, we’ve seen a tremendous growth in the use of the [concrete overlay] technology. Agencies don’t have the money to do everything they’d like to do or everything they need to do, they are required to do more with less, so concrete pavement overlays come into play.”
“As an industry, we’re trying to educate agencies and contractors about the benefits of concrete overlays, as well as make them aware of potential applications,” Davenport said. ACPA staff engineers, affiliated associations, and the National Concrete Pavement Technology Center (CPTech Center) are working together to provide information and technical assistance, but Davenport says there’s still work to be done. There are several types of concrete overlays that fall into two categories—bonded or unbonded. Within these categories, overlays are:
- Placed over distressed asphalt: One of the most common applications where generally the top 2 to 5 inches of the asphalt wearing course is milled off then replaced with concrete. The thin concrete overlay goes down quickly in comparison to complete road replacement, allowing the road to be opened to traffic much quicker.
- Concrete: Stringless technology can play a big part in concrete overlays, making them easier to construct. It uses computerized electronic guidance systems and laser technology to control overlay thickness and smoothness, and make adjustments as it moves along. Davenport said, “Stringless technology is taking hold with many contractors, as it makes the work site safer and helps improve final smoothness results when applied correctly. As we move forward, it is going to increase production and reduce some of the inconvenience to motorists.”
- Roller-Compacted Concrete Pavements: Roller compacted concrete (RCC) is not a new technology, but it is still new to many people. Wayne Adaska, P.E., Director of Pavements-Portland Cement Association (PCA) stated, “Roller compacted concrete competes well with asphalt paving on cost and speed of construction. The zero-slump concrete, which uses no forms or reinforcement, is placed with asphalt-type pavers and then compacted to a high density using vibratory rollers.” The key to RCC’s speed of construction is that it is placed in much thicker layers than asphalt—as asphalt is placed in multiple layers of 3/4 to 2 inches, RCC is placed in a single layer of up to 9 inches. Within the past five years, RCC has been embraced by many paving contractors as asphalt has experienced sharp increases in cost.
FULL-DEPTH RECLAMATION (FDR):
As preservation and rehabilitation have been on the minds of public agencies, there has been a renewed interest in FDR. It is one of the most sustainable paving products in the market place, since it preserves everything in place. This 30-year-old technology has been revolutionized in today’s market by larger, more powerful equipment. Reclaimers/pulver mixers have been the key component in revitalizing the market by expediting construction and making FDR economical. Reclaimers can pulverize the asphalt and granular base in just one pass, as deep as 18 inches. Cement is then spread, then the material is remixed, water added if necessary, compacted, and cured. The result is a strong durable base that is constructed quicker and more economically, and is much more sustainable than removing and replacing the existing road. The base is suitable for concrete or asphalt pavement surfaces.
MAINTENANCE OF TRAFFIC: An emerging focal point for the concrete pavement industry is maintenance of traffic in construction work zones. Increasingly, contractors are required to keep traffic moving around work zones and avoid disrupting and delaying road users to the greatest extent possible,” Davenport says. “This is an area where the national association, along with local chapters, state paving associations, and contractors will work together with agencies to find additional solutions.”
To read the “Equipment World Online News” article and for more information about these technologies online and in print, please go to: http://www.equipmentworld.com/some-old-concrete-pavement-technologies-are-making-a-comeback-and-giving-asphalt-a-run-for-its-money/. (Home page photo: Credit to Equipment World Online News link above).