Presentation by Skip Brown of Asphalt Consulting Services on "Intersection Mix" aka "Type-C or High-Stability Mix delivered at the CalAPA Fall Asphalt Pavement Conference Oct. 24, 2013 in Sacramento, Calif.

1. Caltrans HMA Type C
CalAPA Fall Conference
24 October 2013
Skip Brown
Asphalt Consulting Services
Sacramento, CA

2. Presentation Overview
What?
 Why?
 Where?
 How?
 Local Successes


3. Caltrans HMA Type C –
What’s in a name? AKA …
 High
Stability
 Intersection
 Desert

4. What?
Type A … on steroids
 Rut resistant mix made with similar
components as Type A, BUT with
minor changes in the aggregate
structure and stiffer binder


5. What?

Type C
 higher stability than conventional Type A
 3 Mix choices: 1-inch, ¾-inch, ½ -inch
 Mix choice CRITICAL as it determines
minimum lift thickness

6. What?

Modified Compaction with CA
Kneading Compactor
 150 tamps at 230ºF
 500 additional tamps at 140ºF
 Stability
 Initial – ≥ 37
 Modified – ≥ 35

7. What? Type A vs Type C
(½-inch Mix)
Sieve Size
Type A
Type C
¾-inch
½-inch
100
95-99
100
90-98
⅜-inch
No. 4
No. 8
No. 30
No. 200
75-95
55-66
38-49
15-27
2-8
64-86
42-57
29-39
13-19
3-7

8. What? Type A vs Type C

9. Mix Design Data - Example
Property
Type A
Type C
OBC (% dwa)
5.5
4.9
Air Void Content (%)
4.0
4.0
4.0
39
≥37
≥37
41
≥35
68
65 – 75
60 – 70
Initial Stability
37
Modified Stability
VFA (%)
72
Spec
Note – Caltrans recommends
selecting binder content at 5% air voids
for Central Valley and Desert.

10. Why?
Bradshaw Rd off-ramp
Highway 50 (WB)
¾-inch, Type A, AR-8000
8-years after placement
More than 1-inch of rutting!

11. Where?







Intersections
 Ticket Booths
Bus Stops
 Ready-Mix Plants
Toll Facilities
 HMA Plants
Haul Roads
 Quarries
Landfills
 Recycle Yards
Airports
High Traffic Roadways
Slow moving or Standing Loads

12. How? – Mix Design

Mix Designation
1-inch
 ¾-inch
 ½-inch


Aggregate Crushed Particles
Aggregate Size
Coarse
(2 Fractured Faces)
Fine
(1 Fractured Face)
Type A
Type C
≥ 75%
≥ 95%
≥ 70%
≥ 90%

13. How? Mix Design

Binder
Recommend “harder” binder, ie, Grade “bump”
 Central Valley – PG 70-10 (rather PG 64-10)


Binder Content
5% air voids or 4% air voids?
 Caltrans recommendation

5% for Valley and Desert
 4% for Coast and Mountain


14. Impact of Aggregate Size
on Lift Thickness
½-inch
Type C
Tolerance
TV ±
¾-inch
100
─
½-inch
90-98
6
⅜-inch
64-86
6
No. 4
42-57
7
No. 8
29-39
5
No. 30
13-19
4
No. 200
3-7
2

15. Nominal Maximum Aggregate Size (NMAS)
(one size larger than the first sieve to retain more than 10%)
⅜-inch
mix
100
100
90
72
65
48
36
22
15
¾-inch
½-inch
⅜-inch
No. 4
No. 8
No. 30
No. 200
100
99
89
72
65
48
36
22
15
½-inch
mix

16. What? Type A vs Type C
(½-inch Mix)
Sieve Size
Type A
Type C
¾-inch
½-inch
100
95-99
100
90-98
⅜-inch
No. 4
No. 8
No. 30
No. 200
75-95
55-66
38-49
15-27
2-8
64-86
42-57
29-39
13-19
3-7

17. Construction Considerations

Ratio of Lift Thickness (LT) to NMAS



Maintain LT/NMAS of 4:1
Segregation ** – doesn’t like to be
“handled”
Compaction – It’s difficult to compact!
Need high amplitude, low roller speed to
achieve density.
**
Pick-up machine
MTV
Raking

18. Improper handling and/or placement can cause
segregation resulting in raveling.

19. Paver with Slides inserted over Wings

20. The WRONG way
The RIGHT way

21. Effective Way to “Pinch”
and Roll a Cold Joint

22. Local Successes



Highway 50 Ramps
I-80 at Yolo Causeway
Local Agencies
Sac County (Watt Ave)
 Roseville (Sierra College Blvd)
 Elk Grove (Bradshaw Rd)
 West Sac (I-80 Off Ramp to West El Camino )


23. Watt Ave & Folsom Blvd


Traffic – Very Heavy w/ High Truck Volume
Teichert Mix Design - ½-inch Type C

24. Watt Ave ½-inch Type C

25. Watt Ave Number 2 Lane
½-inch Type C Mix
After 4 Years
< ¼-inch rutting
No rutting in any other lanes!

26. Review - HMA Type C









AKA High Stability, Intersection, Desert
Rut Resistant Mix
Slow Moving & Standing Loads
3 Choices: 1-inch, ¾-inch, ½ -inch**
Coarser Aggregate Gradation & Stiffer Binder
OBC at 5% Air Voids**
Maintain LT/NMAS of 4:1
High Amplitude, Low Roller Speed
Local Success!
** Skip’s Recommendations

27. QUESTIONS?

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