Overview of laydown considerations of Rubberized Hot Mix Asphalt. Delivered at the California Asphalt Pavement Association "Where the Rubber Meets the Road" asphalt rubber educational workshop April 18, 2023 in Sacramento.

1. Overview of Asphalt Rubber
Mixture Production and Laydown
Presented to:
CalAPA Asphalt Rubber Workshop,
Sacramento, CA
By:
Pascal Mascarenhas
CRM Co, LLC
(626) 705-6611
pascal@crmrubber.com
April 18, 2023

2. Presentation Outline
I. Engineering Properties of Rubber Modified Asphalt
A. Benefits of Ground Tire Rubber (GTR) in Asphalt Binders
B. Benefits of GTR on Performance of Rubber Modified Asphalt Pavements
C. Physical & Chemical Specification Requirements for GTR in Asphalt
Pavements
II. Summary

3. From Scrap Tires to Rubber Modified
Asphalt Pavements

4. How does it work?
22,937,600 rubber particles per ton of mix enhances
performance of asphalt

5. Conventional vs. Rubber Modified
Asphalt Mixes
• Conventional Asphalt Mix:
• 5.5% Liquid Bitumen Asphalt
• 94.5% Aggregate
• Asphalt Rubber Mix:
• 6% Liquid Bitumen Asphalt
• 1.5% GTR
• 92.5% Aggregate

6. Conventional vs. Rubber Modified
Asphalt Surfaces

7. Benefits of Asphalt Rubber Binders
• Rubber modified asphalt binders are temperature resilient:
▪ In cold temperature, less thermal cracking
▪ In high temperature, less deformation
▪ Resulting in longer life of pavements & lower maintenance costs
over time
Asphalt Rubber Pavements in low and high temperature climates

8. GTR increases the Asphalt Binder Film Thickness on
the Aggregate
Why Asphalt Rubber Mixes are More
Durable

9. Cracking
I-10 West of Phoenix
Dense Graded
8 year period
Cracked Condition
I-10 West of Phoenix
Asphalt Rubber Gap Graded
8 year period
No cracks

10. Rutting

11. • Increased Durability
• Increased Fatigue Life
• Reduces Permanent
Deformation (Rutting)
Benefits of GTR on Performance of
Asphalt Rubber Pavements

12. • Asphalt rubber binder is less temperature sensitive,
therefore making the asphalt rubber pavement less
temperature sensitive
• It allows use of larger size aggregate and more
stones in aggregate structure
• It allows more binder in the mix without bleeding or
flushing
Differences Between Asphalt Rubber vs.
Conventional Pavements

13. • Any of the mix design methods can be used for
RHMA.
• Arizona primarily uses the Marshall Mix design
method. Typically, the volumetrics are determined
using a 75 blow Marshall mix design.
• Caltrans used the Hveem method until equipment
availability and inconsistency is testing became an
issue.
• Caltrans currently uses the Superpave gyratory
method.
Mix Designs for RHMA

14. • Caltrans requires a minimum of 7.5% ARB TWM.
• The number of gyrations is between 50 to 150
gyrations.
• The compactor ram pressure is to be between 600
to 850 kilopascals
• The hold time is a maximum of 90 minutes.
Mix Designs for RHMA

15. Use with Rubber
Open Graded Gap Graded Dense Graded
Aggregate Gradation Comparison

16. AR Open Graded (ARFC) and Gap Graded (ARAC)
Gradation
Asphalt Rubber
Gap Graded Mix
7.3 % Asphalt
Air Voids 5.2 %
20.2 % VMA
Asphalt Rubber
Open Graded Mix
9.2 % Asphalt Rubber
Air Voids 20.2 %
VMA 32.5 %

17. Sieve Size Scrap Tire CRM
Passing ( % )
High Natural CRM
Passing ( % )
No. 8 100 100
No. 10 98 – 100 100
No. 16 45 – 75 95 – 100
No. 30 2 – 20 35 – 85
No. 50 0 – 6 10 – 30
No. 100 0 – 2 0 – 4
No. 200 __ 0 – 1
Typical GTR Gradation Specification for
Asphalt Rubber Modifiers

18. • GTR increases elastic properties of asphalt binder and reduces its plastic
property.
• The use of GTR in asphalt pavements reduces temperature susceptibility of
pavements under cold and hot environmental conditions.
• It is important to follow chemical and physical specification requirements in
order for GTR to be compatible with aggregate and asphalt rubber binders.
• Highway Agency concerns have been addressed by the FHWA Report to
Congress stating that asphalt rubber does not increase threat to human or
environmental health, it can be recycled and performs as good as
conventional asphalt pavements.
• California DOT has been using rubber modified asphalt and has approx.
25,000 miles in service. They have found that asphalt rubber is more cost
effective than conventional asphalt.
Summary

19. Pascal Mascarenhas
CRM Co, LLC
(626) 705-6611
pascal@crmrubber.com
THANK YOU
www.CRMRUBBER.COM