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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.
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Caltrans HMA Type C
CalAPA Fall Conference24 October 2013
Skip BrownAsphalt Consulting Services
Sacramento, CA
Presentation Overview
What? Why? Where? How? Local Successes
Caltrans HMA Type C – What’s in a name? AKA
…
High Stability
IntersectionDesert
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
What?
Type Chigher stability than conventional Type A
3 Mix choices: 1-inch, ¾-inch, ½ -inch
Mix choice CRITICAL as it determines minimum lift thickness
What?
Modified Compaction with CA Kneading Compactor150 tamps at 230ºF500 additional tamps at 140ºF
Stability Initial – ≥ 37Modified – ≥ 35
What? Type A vs Type C(½-inch Mix)
Sieve Size Type A Type C
¾-inch 100 100
½-inch 95-99 90-98
⅜-inch 75-95 64-86
No. 4 55-66 42-57
No. 8 38-49 29-39
No. 30 15-27 13-19
No. 200 2-8 3-7
What? Type A vs Type C
Mix Design Data - Example
Property Type A Type C Spec
OBC (% dwa) 5.5 4.9
Air Void Content (%)
4.0 4.0 4.0
Initial Stability 37 39≥37≥37
Modified Stability 41 ≥35
VFA (%) 72 6865 – 7560 – 70
Note – Caltrans recommends selecting binder content at 5% air voids for Central Valley and Desert.
Bradshaw Rd off-ramp Highway 50 (WB)¾-inch, Type A, AR-80008-years after placement
More than 1-inch of rutting!
Why?
Where? Intersections Bus Stops Toll Facilities Haul Roads Landfills Airports High Traffic Roadways
Ticket Booths Ready-Mix
Plants HMA Plants Quarries Recycle Yards
Slow moving or Standing Loads
How? – Mix Design Mix Designation
1-inch ¾-inch ½-inch
Aggregate Crushed Particles
Aggregate Size Type A Type C
Coarse(2 Fractured Faces)
≥ 75% ≥ 95%
Fine(1 Fractured Face)
≥ 70% ≥ 90%
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
Impact of Aggregate Sizeon Lift Thickness
½-inch Type CTolerance
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
Nominal Maximum Aggregate Size (NMAS)
(one size larger than the first sieve to retain more than 10%)
1001009072654836221594
100998972654836221594
¾-inch
½-inch
⅜-inch
No. 4
No. 8
No. 30
No. 200
⅜-inchmix
½-inchmix
What? Type A vs Type C(½-inch Mix)
Sieve Size Type A Type C
¾-inch 100 100
½-inch 95-99 90-98
⅜-inch 75-95 64-86
No. 4 55-66 42-57
No. 8 38-49 29-39
No. 30 15-27 13-19
No. 200 2-8 3-7
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 machineMTVRaking
Improper handling and/or placement can cause segregation resulting in raveling.
Paver with Slides inserted over Wings
The WRONG way
The RIGHT way
Effective Way to “Pinch” and Roll a Cold Joint
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 )
Watt Ave & Folsom Blvd
Traffic – Very Heavy w/ High Truck Volume
Teichert Mix Design - ½-inch Type C
Watt Ave ½-inch Type C
Watt Ave Number 2 Lane½-inch Type C Mix
After 4 Years
< ¼-inch rutting
No rutting in any other lanes!
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
QUESTIONS?
Your 1-stop shopping resource
www.calapa.net
