California Asphalt Rubber Case Studies – Reduced

Thickness

Jack Van Kirk

Basic Resources

Presentation Outline

• What is Asphalt Rubber• Where has it been used successfully• Caltrans reduced thickness design

guidelines and supporting research• Cost-effective strategies• Advantages of asphalt rubber

Definition of Asphalt Rubber

• Uses a minimum of 20 +/- 2 % crumb rubber

• Uses 2mm size crumb rubber• Reacts/interacts crumb rubber for a

minimum of 45 min. at elevated temperatures

• Modifies original properties of asphalt cement

Crumb Rubber Modifier

Ground tire rubber is received in 2,000 pound “Supersacks”.

Current Use Asphalt Rubber Strategies

• Asphalt Rubber Hot Mix (ARHM)

• Asphalt Rubber Chip Seal

• Asphalt Rubber Cape Seal

• Multi-Layer Systems

Where have Asphalt Rubber strategies been used successfully?

Caltrans Reduced Thickness Design Guideline

• Caltrans developed the guidelines

in 1992

• Based on laboratory and long-term field data (two decades)

• Supported by research efforts

Design of Asphalt Rubber Pavements

• Uses a deflection based design method

• Up to 50 % reduction in thickness compared to conventional AC design thickness

• Over 1000 reduced thickness projects

  

Structural EquivalenciesThickness (mm) 

DGAC ARHM-GGARHM-GG

on a SAMI

45

30 --

60

30 --

75

45

30

90 45

45

Ravendale Project• First project to use reduced thickness

Asphalt Rubber pavements when compared to the conventional AC design thickness

• Different thickness test sections of Asphalt Rubber and conventional AC mixes were placed for comparison

75mm 45mm 45mm 45mm 75mm 45,60,75,150mm

45mm AR over SAMI 16 yrs old

45mm AR over SAMI 16 yrs old

75mm AR over SAMI 16 yrs old

75mm AR over SAMI 16 yrs old

Council On Scientific and Industrial Research (CSIR)

• Caltrans conducted a research project with CSIR, UCB, and Dynatest Consulting to verify the reduced thickness theory for Asphalt Rubber pavements

• The research used accelerated pavement testing (APT) using the heavy vehicle simulator (HVS)

• The research included laboratory testing to support the field testing

Original condition of pavement in South Africa

75 mm Conv. AC 38 mm ARHM25 mm ARHM

 

 

Repetitions 

Wheel LoadAC Overlay

Section (75mm)

ARHM-GG Section (38mm)

ARHM-GG Section (25mm)

0-100,000 40kN Fine cracks at 100,000

__ __

100,000 to 175,000

40kN Block cracks at 175,000

__ __

Wheel load Changed to 80 kN

175,000 to 200,000

80kN Completely cracked

__ Fine cracks

200,000 to 237,000

80kN Test stopped __ Completely cracked

Surface Temperature Reduced to –5 C

237,000 to 250,000

80kN Test stopped 1/2 of section cracked

Test stopped

Performance

Supporting Research• UAF (Raad) - Conducted laboratory beam

fatigue testing of ARHM-GG and conventional DGAC and concluded that ARHM-GG had significant improvement in fatigue properties

• OSU (Hicks) and UNR (Epps) - Conducted life cycle cost analysis and concluded that Asphalt Rubber was more cost-effective when compared to conventional AC pavement maintenance and rehabilitation strategies

Asphalt Rubber 3-Layer Systems

• Asphalt Rubber binder used in hot mix and chip seals can be used in different thin layer systems

• These systems can save hundreds of thousands of dollars when compared to full reconstruction using conventional strategies

Asphalt Rubber SAMI• Caltrans conducted field trials using

Asphalt Rubber stress absorbing membrane interlayers (SAMI)

• In 1991 Caltrans concluded that SAMI’s in AC overlays of AC pavements with aggregate base are equivalent to approximately 52mm of AC in retarding initial cracking

Randolph AvenueCosta Mesa, CA

37mm ARHM-GGARCS

25mm AC

10 years old

Philadelphia StreetWhittier, CA

37mm ARHM-GGARCS

25mm AC

10 years old

Los Angeles, CA

Thin Asphalt Rubber Overlays

25mm ARHM-GG1 year old

5 years old

10 years old

Advantages of Asphalt Rubber Binder

• Significantly higher binder contents - 20 % higher in dense graded mixes - 40 - 50 % higher in gap graded mixes - 50 - 60 % higher in open graded mixes• Thicker film thickness• Reduced oxidation• Increased durability• Increased resistance to reflective cracking

Advantages of Asphalt Rubber Pavement Strategies

• More abrasion resistant• Reduced oxidation• Increased fatigue resistance• Can reduce thickness• Reduced construction time/Increased safety• Savings in energy and natural resources• Lower maintenance cost

Why choose Asphalt Rubber strategies?

• Has a long term performance history (over 30 years)

• Over 1000 successful reduced thickness projects

• Proven alternative to costly reconstruction• Established life cycle cost-effectiveness

Asphalt Rubber = Performance

Thank you!