The U.S. interstate system of highways celebrated its 50th anniversary this year. The majority of the interstate was originally built of concrete pavement. These pavements have served the traveling public well, with decades of quality service.
Today, concrete pavement technology is undergoing a season of innovation, optimization and rediscovery to meet the changing conditions and growing expectations of a new generation and a new age.
The National Concrete Pavement Technology Center at Iowa State University is partnering with the Federal Highway Administration, state departments of transportation and the concrete paving industry to develop, evaluate and advance concrete pavement innovations that:
- Minimize tire and pavement noise without compromising safety;
- Extend pavement durability; and
- Provide cost-effective rehabilitation options.
The following three research areas demonstrate the promise of concrete pavement technology to meet these challenges through improved surfaces, better mix designs and overlay solutions for a variety of rehabilitation needs.
Softening the drive
Using existing knowledge and conventional technology, the concrete paving industry has been capable of meeting individual desired pavement surface characteristics such as low noise and adequate friction. The challenge of today is designing and building pavements that balance all functional demands at the same time.
In the past, safety was often perceived to be the most important surface characteristic. Highway agencies therefore developed construction specifications that called for transverse tining. Transversely tined pavements indeed have provided the desired friction and corresponding safety; these pavements, however, are often noisier than other texture types.
Today, the public demands that pavements be both quiet and safe, without a compromise to either. New research indicates that a number of conventional concrete surfaces (such as drag textures and longitudinal tining) exist that can adequately balance a variety of surface characteristics. One key to using these surface textures successfully is to construct them consistently with good quality control.
In addition, several innovative concrete pavement surfaces, such as pervious concrete and exposed-aggregate concrete pavements, are being developed that hold the potential of even lower tire-pavement noise in the future.
A recent study by the National Concrete Pavement Technology Center recommends that consideration be given to diamond grinding some of the loudest existing concrete pavements (often with transversely tined surfaces).
Alternatively, many of these pavements could be resurfaced with a concrete overlay to address public concerns over noise. When properly selected, designed and constructed, a concrete overlay can add to a pavement’s load-carrying capacity and extend the pavement’s life, in addition to providing desired functional characteristics.
Void check
The air-void system of concrete (including air volume and distribution of air voids) is critical to providing adequate protection from freeze-thaw damage.
Existing methods of measuring the concrete air-void system have not provided the ability of real-time quality control. Fresh concrete methods measure only air volume, not size or spacing of voids.
The typically used hardened concrete test of the air-void system takes too long for control in the field. This testing also is destructive in that pavement cores have to be removed and refilled.
The air-void analyzer (AVA) provides a method of testing the complete air-void system of concrete in its plastic state. Research is currently developing means to minimize the influence of vibrations, such as those caused by passing traffic, on AVA testing in the field.
In addition, work is being done to improve the variability and precision of AVA measurements and to better understand AVA test results so that they may be meaningfully incorporated into construction specifications.
On another research front to improve the concrete air system, a concrete mix design is being developed that has the potential to provide self-consolidating concrete that can be used in slipform paving construction. Typically, vibrators are used to consolidate highway pavements. These vibrations often over-consolidate the concrete and negatively affect the concrete air-void system, leading to decreased freeze-thaw durability.
The new slipform paving self-consolidating concrete is expected to eliminate the need for vibration, which will in turn lead to improved pavement durability and decreased construction costs.
Overlays are overdue
Numerous states have successfully constructed concrete overlays over the years. In some cases, the overlays have provided over 30 years of good-to-excellent performance.
Different types of concrete overlays are capable of addressing a variety of rehabilitation needs. Ongoing research and trials continue to provide information and insights into the potential applications, restrictions and benefits of concrete overlays.
Many miles of existing pavements in the U.S. consist of an original concrete pavement that has had one or more asphalt resurfacing courses placed on top of it over the years. When these pavements are in need of their next rehabilitation, as many are today, a concrete overlay has been validated as a durable solution with a life-cycle cost that can be estimated over a long term.
Concrete overlays over composite pavements have performed well over time. Recent research from the National Concrete Pavement Technology Center provides design and construction guidelines for this type of rehabilitation.
In addition, ultrathin-bonded concrete overlays have shown themselves to be an effective resurfacing product on either an asphalt or concrete pavement with surface defects or noise issues, as long as the existing pavement is structurally sound.
Conventional concrete mixtures and a “get in, get out” construction approach can be used to minimize construction time and achieve opening to traffic within 24 hours in some cases.
These and other concrete pavement advancements are being developed and put into practice thanks to a collaborative spirit among members of the concrete pavement community.
A partnership among federal, state and local agencies, private industry, researchers and other stakeholders across the country is the basis of the CP Road Map, a 10-year plan for concrete pavement research.
The CP Road Map has recently gotten under way. The cooperative program promises accelerated implementation of promising new technologies through establishment of common priorities, strategic pooling of resources and effective communication of findings.
