Pavement data collection: plan vs. actual
How well do actual pavement conditions match what was planned? A pilot project was conducted last year to find out.
County engineers submit their “NEEDS Report” to State Aid every year, said Rich Sanders of Polk County. The report estimates the construction cost required to improve a state-aid system to standards adequate for future traffic on a uniform basis. The data—including the year graded, year surfaced, type of surfacing, design strength, functional class, proposed section, and relative cost to improve—form the NEEDS database.
What isn’t collected, however, is the actual structure in place—in other words, what was constructed (materials and thickness) versus what was planned. Other unknowns are the types of road users (important with increasing truck traffic) and how well the roads are performing.
For the pilot, 341 sites and nearly 1,300 total miles were analyzed, said Cameron Kruse of Braun Intertec, one of the consultants selected by State Aid to conduct the work. Testing included:
- Falling weight deflectometer, to calculate pavement strength, capacity, and remaining life
- Ground penetrating radar (GPR), to provide a picture of pavement structure and to analyze WD data
- Coring, to calibrate GPR data
- Traffic data (volume and classification)
Coring, GPR, and traffic data were compared to reported (historical) values, and the data were used to back-calculate pavement strength, capacity, and remaining life, Cruse said.
Five percent of the CSAH system was tested in the first year. Preliminary results found that the difference between cored and reported thickness in 15 percent of cases was plus or minus 3 inches. “This suggests an opportunity to improve in that area,” Cruse said.
The pilot did not cover concrete, he added.
—Pamela Snopl, LTAP editor