Asphalt Rubber Mixture Design
ADOT’s AR-ACFC and ARAC
AR-ACFC
Mix Design Considerations
AR-ACFC: Purpose
• Final wearing surface
• Typically nominal 1/2 inch lift
AR-ACFC: Aggregate
• Gradation
• Flakiness
• Sand Equivalent
• Crushed Faces
• Abrasion
• Percent Carbonates
AR-ACFC: Gradation
Sieve Size Percent PassingWithout admixture
3/8” 100
#4 30-45
#8 4-8
#200 0-2.5
AR-ACFC: Mineral Admixture
1% Lime or Cement is mandatory
AR-ACFC: Flakiness
• Maximum Flakiness = 25
• To insure good particle shape, and minimize particle breakage.
AR-ACFC: Sand Equivalent
• Minimum 55
• To insure that there are not excessive amounts of clay in the aggregate
• Done on washed aggregate
AR-ACFC: Crushed Faces
• Minimum 95% Single Crushed Faces
• To insure good particle interlock and good frictional characteristics
AR-ACFC: Abrasion
• Maximum at 100 rev. 9 at 500 rev. 40
• To insure that the aggregate will hold up to the wear and tear of traffic
AR-ACFC: Percent Carbonates
• Maximum 30%
• To minimize the amount of limestone which has a tendency to polish under traffic.
AR-ACFC: Mix Design Steps
• Prepare Aggregate
• Determine aggregate specific gravities
• Determine maximum theoretical specific gravity
• Check draindown
• Determine mix density
AR-ACFC: Design
• Determine aggregate specific gravities for fine and coarse mineral aggregate
• Calculate combined specific gravities (oven dry, saturated surface dry, apparent)
AR-ACFC: Design
• Determine the maximum theoretical specific gravity (Rice test)
• Done at 3.5 to 4.0% binder content
• Determine the amount of asphalt absorption.
AR-ACFC: Design
• Calculate Binder content:
((.38)(W) + 8.6)(2.620/C)= Binder content
W=% water absorption
C=combined oven dry specific gravity
AR-ACFC: Design
• Check Draindown using the Schellenberg test
This test is performed in the laboratory in order to determine whether or not an
unacceptable amount of binder drains down from the mix.
AR-ACFC: Design
1. Place Mix in a beaker
2. Place beaker in oven for 1 hour
3. Empty beaker
4. Determine % mass loss
AR-ACFC: Design
Based on the results of the draindown test, adjust binder content if necessary
AR-ACFC: Design
• Determine mix density– Compact in Forney (4” diameter, 200 psi)
– Determine density by volumetrics
• Information used for determining spread, may also calculate voids for information only
AR-ACFC: Typical Design
• Typically 2 stockpiles: 95% intermediates, 5% fines
• Typical binder content 9.2-9.3% (general range 8.7-9.7%)
• Over PCC add 1% to design binder content
ARAC
Mix Design Considerations
ARAC: Purpose
• Highly flexible lift
• High quality structural lift
• Typically nominal 2 inch lift
ARAC: Aggregate
• Gradation
• Sand Equivalent
• Crushed Faces
• Abrasion
ARAC: Gradation
Sieve Size Percent PassingWithout admixture
¾” 100½” 80-1003/8” 65-80#4 28-42#8 14-22
#200 0-2.5
ARAC: Mineral Admixture
1% Lime or Cement is mandatory
ARAC: Sand Equivalent
• Minimum SE=55
• To ensure that there are not excessive amounts of clay particles on the aggregate
• Done on washed aggregate
ARAC: Crushed Faces
• Minimum 95% Single Crushed Faces
• To insure good particle interlock
ARAC: Abrasion
• Maximum at 100 rev. 9 at 500 rev. 40
• To insure that the aggregate will hold up to the wear and tear of traffic
ARAC: Mix Design Steps
• Prepare Aggregate
• Determine aggregate specific gravities
• Determine maximum theoretical specific gravity
• Compact mix, determine optimum binder content
• Check mix volumterics
ARAC: Design
• Determine aggregate specific gravities for fine and coarse mineral aggregate
• Calculate combined specific gravities (oven dry, saturated surface dry, apparent)
ARAC: Design
• Determine the maximum theoretical specific gravity (Rice test)
• Done at 6.0% binder content and calculated to other binder contents as needed
ARAC: Design
• Compact with Marshall hammer at three binder contents
• Typically 6.5, 7.5, 8.5 or 6.0, 7.0, 8.0 depending on aggregate source
• Mix/Compact at 325°F
ARAC: Design
• Check Volumetrics, select optimum binder content.
• Minimum VMA 19.0%
• Effective Voids 4.0 - 6.0%
• Maximum 1% binder absorption
ARAC: Design
• Watch to make sure that the VMA is not being created by the binder
• Typically when VMA is being created by the binder, voids will drop
• VMA/Voids are very interrelated for this mix type
ARAC: Design
If necessary, adjust gradation to improve VMA or voids. Repeat compaction process
and remeasure maximum theoretical specific gravity.
ARAC: Typical Design
Typical binder content 6.5-8.5% depending on aggregate source and gradation
Thank you
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