1. Transitioning to IRI for Pavement Smoothness
2018 Quality Paving Conference
January 3rd -4th, Little Rock
By Chris Abadie
Pine Bluff Sand and Gravel Company

2. 2017 Asphalt Paving Alliance: Facts about Smooth Pavements

3. Building Smooth Pavements-Design
Provide sufficient Yield: Length(ft) x Width(ft) x Thickness(ft) x unit weight(lbs/cu. ft.) of in-place Asphalt Mixture/2000 lb/ton = ______est. Tons of mix for project.
Design Sufficient Thickness to allow optimum smoothness:
Is plan thickness a minimum thickness?
- If underlaying surface is irregular, to achieve minimum thickness over the high spot, low spots must be paved with excess thickness.
So typically, plan thickness is average thickness to avoid overruns on the job
Design Multiple lift projects (or methods of surface preparation such as milling) to enable highest level of as-built smoothness.

4. Design considerations cont’d
Rule of thumb – 50% reduction in IRI possible for every 2” lift.
- 20 year old pavement good base , spec mil ½” and overlay 2”.
- 20 year old pavement with 1” rut ,if structure is sound, mil 2” and inlay 2”.
When existing conditions exceed 250 iri; Consider what is an achievable ride quality vs. $$$ available for multiple lift overlay??
Strive to balance improvement of ride quality vs. total miles to be covered with existing budgets.
Maybe include a % improvement requirement in lieu of 75 IRI when only one lift can be afforded and initial IRI is “high” and service level of road is relatively low.

5. 1” /mile PI = 25”/mile IRI 3”/mile PI = 75”/Mile IRI.
Constructing smooth roads QC –rule of thumb
1” /mile PI = 25”/mile IRI 3”/mile PI = 75”/Mile IRI.

6. Construction Tips from Mike Davis
 Know your paver
 Keep a consistent head of material on the paver screed.
 Keep stops to a minimum
 If you must stop; keep stops less than 10 minutes
Restart very slowly, increasing speed in small increments over 5 minutes to desired paving speed.
 Plan enough trucks to do the job, too many is better than not enough!
 For construction joints, know the matching thickness of existing pavement, determine shim height based on densification of ¼” per inch of pavement, or based on history with paver.

7. Construction Tips for smooth paving, con’t
Rollers can cause bumps:
Don’t get too close to paver if mix is too hot, evidenced by shoving.
Make sure Roller stops at an angle.
If the roller stops straight, it is almost impossible to roll it smooth.

8. On grinding Demand a smooth ride from grinding subcontractor
Strive for no must grinds in final lift.
Grind the bumps before you place the top lift.
Diamond grind the surface as a last resort-- Once you grind the surface, the public will see it forever.
Diamond Grinding to improve the pavement surface should be the exception, not the rule

9. Advice from Asphalt paving/milling expert: David Madden of Minden LA.
Achieving smoothness with milling machine:
“Use Dual skis , left and right.”
“Do not set milling machine nor paver to Match Joint” , this just magnifies the bumps.
“ Consider using quadruple wrapped milling drums”
“Change teeth after every project.”
“Keep rotomill at 75 ft/min. speed or less”
“Milling or Paving faster does not equal smoother pavements” .
Paving
“A Good paver speed is 40ft/min.”, this depends on rollers ability to keep up.

10. David Madden Tips on Paving, Con’t
Measuring Smoothness in QC- Seat of the pants is a good first indicator.
“Use IRI for final pay, use profilograph settings to locate bumps (localized roughness), check grinding with 10ft. Straight edge 1/4” in 10 ft”.
To physically locate a bump after electronic detection,
a. Start 10’ before dmi location of bump,
b. with a 10 ft straight edge drag to find bump
c. continue to drag the straight edge up to 40 ft. after the station.
d. if no bump is found, move on.

11. Historical Measure of Smoothness
Rod and Level
10 ft. Straight edge
Profile Index (PI), 25 ft. Walk behind California style profilograph
International Roughness Index (IRI); Quarter car and half car.
Walking Profiler
AUTOMATION HAS ENABLED REAL TIME IRI MEASURE.

12. ARDOT’s Current Ride Smoothness SP (PWL with Ride Smoothness)
ASTM E ft. California walk behind profiler, Profile Index, Inches / mile
ASTM E automated profiler; laser measure simulating 25 ft. profile index.
Measure center of lane with 25 ft. lead in required.
Measure each “day” of construction
Definition of “Wearing Surface Bump” = 1/8” in 10 ft.
Maximum measure = 5”/mile travel lane; 8”/mile Ramps.
Minimum areas of removal defined as 50 linear ft, full width.
Blanking band = 0.1”

13. ARDOT’s Current Ride Smoothness SP (PWL and Ride Smoothness)
Picture taken from ASTM 1274

14. ARDOT’s current ride smoothness SP (PWL with ride smoothness)
+3% price adjustment if 1” per mile or less.
+2% ; 1” – 2”per mile
+1%; 2”-3” per mile
100% pay ; 3”-4” per mile
-1%; 4”-5” per mile
-2%; 5”-6” per mile
- 3%; >6” per mile
Note: Blanking band = 0.1”

15. ARDOT – New Ride Smoothness SP (for Jobs without PWL)
Run Daily setup routine
Measure smoothness with inertial profiler in presence of engineer
Insure a clean surface
Run in direction of traffic
Apply incentive to final surface only
Measure left and right wheelpath
For every 0.1 mile, Report Average of L and R wheelpath.
When 5% tolerance between wheelpaths is maintained. (If not in 5%, no incentive)
Combine short segments within adjacent 0.1 mile segment before measure.
Provide electronic “.ERD” and “.ADF” files named using specified naming convention
“YYMMDD-J-T-N-D-L-W-S”

16. Inertial Profilers, High and Low Speed

17. (Cont’d)-ARDOT’s Proposed New Ride Smoothness SP (for jobs without PWL)—applies to every 0.1 mile
0% adjustment for IRI measures of inches per mile
1% adjustment for IRI measures of inches per mile
2% adjustment for IRI measures of inches per mile
3% adjustment for IRI measures less than 45 inches per mile.
Final spec is pending review and final action by the Departments Specifications Committee.

18. Training and Implementation
In development
University of Arkansas Center for Training Transportation Professionals will provide individual and equipment certification program.
ARDOT goal is to require certification of all individuals and equipment used for smoothness measurements (both PCCP and ACHM).

19. REMEMBER BUILD IT SMOOTH on a good foundation, and
Why Specify IRI ? Safety!! IRI measure with an inertial profiler is fast and repeatable.
REMEMBER BUILD IT SMOOTH on a good foundation, and
IT WILL STAY SMOOTH
Smooth roads forever!!!