With limited dollars allocated for new road construction and repair of existing streets, guaranteeing the longevity of asphalt surfaces is essential. A new tool that uses radio waves to evaluate asphalt integrity provides an accurate assessment of air voids and compaction quality with offering money and time-saving benefits.
Asphalt milled in preparation for new asphalt overlay with new overlay partially applied on Idaho Street. Source: User Famartin via Wikipedia Commons
The success of road rehabilitation work depends upon the quality of the asphalt work.
Even though the American Society of Civil Engineers (ASCE) gave roads in the US a “D” grade on its 2013 Infrastructure Report Card, the Center for Budget and Policy Priorities reports that infrastructure spending is currently at a 30-year low. For civil engineers, this means competition for road and bridge projects is fierce and successful completion of these jobs is essential for securing future contracts. A critical factor in evaluating the quality of road and highway rehabilitation and construction is the longevity of the asphalt used to pave the surface of the roadway.
According to an article on the website Civil and Structural Engineering, the factors indicative of the integrity of asphalt include the following:
- If the number of the air voids present in the asphalt is greater than or equal to 8% or fewer than 3%, the asphalt will deteriorate more quickly than anticipated. This will lead to a diminished lifetime for the roadway.
- If the density of the asphalt is less than optimal due to poor compaction techniques, such as suboptimal temperature or faulty rolling pattern, the asphalt will degrade rapidly.
Currently, the most commonly used tools for measuring asphalt integrity only assess a small sample of the road surface and require a significant amount of labor and maintenance expenditure. This means a higher likelihood that the asphalt will fail as compared to asphalt that has been thoroughly evaluated. What are the alternatives to the asphalt measuring devices currently on the market?
The Drawbacks of Nuclear and Electrical Density Gauges
A density gauge being used to ensure proper compaction for the foundation of a school construction project. Source: Wikipedia (Public Domain)
Traditional means of non-destructive asphalt testing tend to be inefficient, labor-intensive, and costly.
For obvious reasons, non-destructive means of evaluating the quality of asphalt are preferred to coring, which is a destructive means of determining the air space in the asphalt as well as its density. Destructive assessment of asphalt is also time-consuming and provides only a small sample size, so the accuracy of this type of measurement is very limited in terms of accuracy. The two most widely used devices for asphalt assessment along streets and highways are nuclear density gauges and electrical density measurement devices.
Nuclear density gauges emit a burst of radioactive particles and then its sensors capture the number of particles scattered by the asphalt. The reading provided by this device is the percent of particles reflected back to the sensor, which can be used to determine the structure and density of the asphalt.
The drawbacks of using nuclear density gauges include:
- The device must remain stationary for a discreet amount of time, which makes the measurement process lengthy and labor intensive.
- Since measurements are typically taken at 100-foot intervals, there is a risk that an area of comprised asphalt may be missed.
- As with all nuclear devices, users must undergo highly specialized training to operate nuclear density gauges.
- The units require specialized transportation vehicles and highly secured storage facilities.
- Re-licensing, maintenance, and recalibration costs are approximately $2,000 each year.
While electrical density gauges offer the advantage of requiring less money to credential operators, store, transport, and maintain than nuclear density gauges, they share drawbacks in terms of accuracy and labor expense.
Innovative Radio Wave Density Gauge Offers Improved Accuracy and Reduced Expenses
This photograph shows the north side of Morrisville Carpenter Road in Morrisville, North Carolina. Opposite this street is an urban apartment subdivision. Source: Nader Moussa – Wikipedia
Properly compacted asphalt provides a long-lasting roadway surface.
A team working at the Strategic Highway Research Program at Texas A & M University recently announced their development of an asphalt density gauge that uses an innovative application of radio wave technology. The device uses ground penetrating radar to determine the air space present in asphalt as well as the quality of the asphalt mix and its compaction. One advantage of this new gauge is that it takes measurements at 6-inch intervals, which significantly improves the accuracy of the readings provided by the device. Additionally, the tool can be mounted on the back of a vehicle, which decreases the labor cost involved in determining the integrity of the asphalt used to pave a road.
What is your experience using density gauges? Do you think you would want to try a device that uses radio waves?