The HMA control pavement was the standard for judging the performance of the OGFC sections. If the noise level on the OGFC section was more than 3 decibels lower than the control section it was considered to be an audible difference (a difference that is detectable by most human ears). If the difference was less than 3 decibels an audible difference would not exist and the OGFC would not be providing any noise reduction over the conventional HMA control pavement.
The graph below shows the history of the noise measurements on the I-405 Bellevue section. The numeric difference between the noise measurement on the HMA and OGFC sections was plotted against the age of the pavement. The black line at the 3 decibel differentiates between noise level differences that are audible and not audible. The red line at 0.0 decibels marks the level below which the OGFC is noisier than the HMA.
The graph shows that both OGFC-AR and OGFC-SBS were audibly quieter than the HMA control section for one month after construction. The OGFC-AR (green line) was audibly quieter for two additional readings in the first ten months. After the tenth month the OGFC-AR was not audibly quieter than the control section for the remainder of the 44 month study period. The OGFC-SBS (brown line) did not become audibly quieter than the control section after the initial reading.
The bar chart below shows the initial and final noise levels for the OGFCs and HMA control section.
How did the sections perform as pavements?
WSDOT use three criteria to rate pavement performance: smoothness, structural condition and rutting. Rutting due to raveling has been the major downfall of the other two quieter pavement sections. Currently there are no reports of any excessive raveling on this quieter pavement section. Final rutting measurements (average of all lanes) for the OGFC-AR section were 5.7 mm (7/32 inch), 4.5 mm (11/64 inch) for the OGFC-SBS, and 4.3 mm (11/64 inch) for the HMA.
Where were the sections on I-405?
The sections were installed on all lanes of the northbound direction of I-405. Average daily traffic in this location is about 165,500 vehicles (both directions).
- OGFC - Polymer (MP 10.60 – MP 10.93 and MP 12.06 – MP 12.40) 0.67 miles
- OGFC - Rubber (MP 10.26 - MP 10.60 and MP 11.76 - MP 12.06) 0.64 miles
- Control - HMA (MP 9.80 - MP 10.15) 0.35 miles
When were the sections installed?
The I-405 Bellevue test sections were paved during the day over the weekend of August 15 and 16, 2009.
Final Report with completed noise and pavement performance results: I-405 Bellevue Test Section
What were the mix design characteristics of each pavement?
|OGFC-AR ||OGFC-SBS |
|0.96 inches thick
||0.96 inches thick |
||PG 64-22 |
|3/8 inch maximum aggregate size
||3/8 inch maximum aggregate size |
|9.2 percent binder content
||8.6 percent binder content |
Fibers added to prevent draindown
How did the cost of OGFC pavement compare to conventional asphalt (HMA) on the I-405 Bellevue sections?
WSDOT uses life cycle cost analysis (LCCA) to compare the cost of different pavement types. LCCA is a method of economic analysis that takes into account the initial as well as discounted future costs. In the case of the OGFC and the HMA control section the future cost is the cost of repaving the roadway at the end the pavements life. The life cycle cost then becomes a function of how much it cost to pave the road and the time between each repaving of the road. Line item costs are necessary to perform a life cycle cost analysis. The I-405 was part of a larger design build contract; therefore, line item costs were not available.