Continuing Research on the Sound Reduction Benefits of Rubberized Asphalt

1
Continuing Research on the Sound Reduction
Benefits of Rubberized Asphalt

• Prepared for the
• Arizona Public Works Association
• 2003 Statewide Conference

2
History of Rubberized Pavement

• Pioneered by the City of Phoenix, ADOT, and
  CALTRANS
• Significant increase in usage during the 1990s
• Technology improvements
• Performance data
• Competitive cost
• Primary use continues to be on resurfacing
  projects
• Increasing use on new/reconstructed roadways

3
Pavement Definition

• Portland Concrete Cement Pavement (PCC)
• Asphalt Concrete Pavement (AC)
• Asphalt Rubber Pavement (ARAC)
• Asphalt Concrete Friction Course (ACFC)
• Asphalt Rubber Friction Course(ARAC-FC)

4
Benefits of Rubberized Asphalt Pavement

• Service Life
• Skid Resistance
• Cracking
• Rut Depth
• Smoothness

• Ride Quality
• Maintenance
• Pavement Markings
• Sound Reduction

5
Traffic Generated Sound

• Three primary sources
• Engine compartment
• Exhaust system
• Tire/pavement interaction

6
Traffic Generated Sound

• Even distribution among the 3 sources from
  automobiles at low speeds (25-30 mph)
• Engine and exhaust sources dominate with heavy
  vehicles at low speeds
• Tire/pavement source dominates at higher speeds
  (gt50 mph)
• Distribution on a typical arterial roadway
  (40-45 mph) ..?

7
Tire/Pavement Generated Sound

• Produced by tire vibration and air
  compression/expansion within the contact zone
• Tire vibration low frequency, not very audible
• Decreases with smooth, flexible pavement
• Air compression/expansion frequencies well
  within audible range
• Increases with smoother, less porous pavement
• To maximize sound reduction smooth, flexible,
  and porous pavement is desirable

8
Properties of Sound

• Noise is unwanted sound
• Perception varies by the individual
• Measured using logarithmic scale, dBA
• 10 dBA is a doubling of loudness
• 3 dBA is a 50 increase in loudness
• Human ear cant typically distinguish sounds with
  less than 3 dBA difference
• Traffic generated sound ranges from 40 to 80 dBA
• Typical arterials are around 65 dBA

9
Sound Level Studies on Pavement Types

• Volpe Transportation Research Study

10
Sound Level Studies on Pavement Types

• City of Sacramento Study

0 mo
0 mo
0 mo
4 yr
Loudness
5 yr
-0 dBA
1 mo
16 mo
6 yr
6 mo
1 mo
-3 dBA
-4 dBA
-5 dBA
-5 dBA
-2 dBA
-6 dBA
ARAC
AC
ARAC
11
Sound Level Studies on Pavement Types

• City of Scottsdale Study

68.3 dBA
Before After Measurements
67.5 dBA
66.0 dBA
65.4 dBA
65.6 dBA
65.0 dBA
64.7 dBA
Loudness
63.3 dBA
-2.7
-2.5
61.3 dBA
-2.7
60.3 dBA
-3.4
-5.1
Res. 30 mph
Minor 40 mph
Minor 35 mph
Res. 35 mph
Major 45 mph
12
Pima County Experience

• Rubberized Asphalt Pavement use has been adopted
  by ADOT, Pima County, COT, and Oro Valley
• Resurfacing typically uses 1-11/2 ARAC-FC
• New/Reconstruction typically uses 2 top lift of
  ARAC
• Agencies use it due to its performance and
  maintenance characteristics
• Sound reduction benefits not well understood

13
More Questions Than Answers

• What are the difference in sound reduction
  between ARAC and AC?
• The differences between ARAC and ARAC-FC?

14
More Questions Than Answers

• How long do the sound reduction benefits from new
  ARAC last?
• From new conventional AC?

15
More Questions Than Answers

• Are the sound reduction benefits affected by
  traffic volume?
• By traffic speed?
• By percentage of heavy vehicles?

16
The On Going Process of Monitoring New Pavements

• Arterial roadways within Pima County
• Reconstructed or overlayed roadways since late
  2001
• 40-50 mph typical speeds
• 5,000-60,000 vehicles per day
• 1 hour Leq measurements annually
• Normalized sound measurements to account for
  traffic volume variations using the FHWA Traffic
  Noise Model

17
Initial Results

• Rancho Vistoso Boulevard - Oro Valley
• 4 lane divided, 40-45 mph, 5,000 ADT
• 550 vehicles per hour, 3 heavy vehicles
• Milled and overlaid with 2 ARAC

18
Rancho Vistoso Boulevard
Site 1
Site 2
Loudness
-3.2 dBA (0.1)
-3.3 dBA
-4.1 dBA (1.3)
-5.4 dBA
Worn AC
ARAC 1 Mo
ARAC 1 yr
Worn AC
ARAC 1 Mo
ARAC 1 yr
19
Initial Results

• Oracle Road (SR 77) - ADOT
• 6 lane divided, 45-50 mph, 60,000 ADT
• 3,500 vehicles per hour, 2 heavy vehicles
• Milled and replaced with 1/2 ARAC-FC on 3 AC

20
Oracle Road (SR 77)
Site 1
Site 2
Loudness
-2.7 dBA
-1.9 dBA
-2.3 dBA (-0.4)
-4.0 dBA (-1.3)
Worn AC
ARAC 1 Mo
ARAC 9 mo
Worn AC
ARAC 1 Mo
ARAC 9 mo
21
Initial Results

• First Avenue - Pima County
• 3 lane, 40-45 mph, 19,000 ADT
• 925 vehicles per hour, 1 heavy vehicles
• New 2 AC overlay on worn surface

22
First Avenue
Site 1
-1.8 dBA (1.3)
Loudness
-3.1 dBA
Worn AC
New AC 1 Mo
New AC 11 mo
23
Discussion of Initial Results

• New ARAC or ARAC-FC provides an initial sound
  reduction of about 3 dBA versus worn AC pavement
• New AC provides a similar initial sound reduction
  versus worn AC pavement

24
Discussion of Initial Results

• It appears that higher volumes and speeds may
  diminish sound reduction benefits
• It is unclear if a ½ ARAC-FC will provide the
  same level of sound reduction benefit as 2 ARAC
• Continued monitoring on a variety of roadway and
  traffic conditions is needed

25
Wrap Up

• Rubberized Asphalt Pavement is proven to be
  superior to Conventional Asphalt Concrete
  Pavement in service life, durability and
  maintenance.

26
Wrap Up

• Rubberized Asphalt Pavement may be a more
  viable solution for sound mitigation where a well
  funded pavement management system is in place.
• Scheduled pavement overlay within 10 years

27
Wrap Up

• The use of Rubberized Asphalt Pavement for
  sound mitigation is promising.
• The potential benefits will be better
  understood through continual monitoring.

28
Thank You

• Related reports are available at the Catalina
  Engineering websitehttp//www.catalinaengineerin
  g.com
• Continuing Research on the Sound Reduction
  Benefits of Rubberized Asphalt Pavement in
  Southern Arizona, December 2002.
• Rubberized Asphalt Concrete State of the
  Practice, November 2001.