Asphalt Rubber Mixture Design

1
Asphalt Rubber Mixture Design

• ADOTs AR-ACFC and ARAC

2
AR-ACFC

• Mix Design Considerations

3
AR-ACFC Purpose

• Final wearing surface
• Typically nominal 1/2 inch lift

4
AR-ACFC Aggregate

• Gradation
• Flakiness
• Sand Equivalent
• Crushed Faces
• Abrasion
• Percent Carbonates

5
AR-ACFC Gradation
6
AR-ACFC Mineral Admixture

• 1 Lime or Cement is mandatory

7
AR-ACFC Flakiness

• Maximum Flakiness 25
• To insure good particle shape, and minimize
  particle breakage.

8
AR-ACFC Sand Equivalent

• Minimum 55
• To insure that there are not excessive amounts of
  clay in the aggregate
• Done on washed aggregate

9
AR-ACFC Crushed Faces

• Minimum 95 Single Crushed Faces
• To insure good particle interlock and good
  frictional characteristics

10
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

11
AR-ACFC Percent Carbonates

• Maximum 30
• To minimize the amount of limestone which has a
  tendency to polish under traffic.

12
AR-ACFC Mix Design Steps

• Prepare Aggregate
• Determine aggregate specific gravities
• Determine maximum theoretical specific gravity
• Check draindown
• Determine mix density

13
AR-ACFC Design

• Determine aggregate specific gravities for fine
  and coarse mineral aggregate
• Calculate combined specific gravities (oven dry,
  saturated surface dry, apparent)

14
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.

15
AR-ACFC Design

• Calculate Binder content
• ((.38)(W) 8.6)(2.620/C) Binder content
• W water absorption
• Ccombined oven dry specific gravity

16
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.

17
AR-ACFC Design
1. Place Mix in a beaker
3. Empty beaker
2. Place beaker in oven for 1 hour
4. Determine mass loss
18
AR-ACFC Design

• Based on the results of the draindown test,
  adjust binder content if necessary

19
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

20
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

21
ARAC

• Mix Design Considerations

22
ARAC Purpose

• Highly flexible lift
• High quality structural lift
• Typically nominal 2 inch lift

23
ARAC Aggregate

• Gradation
• Sand Equivalent
• Crushed Faces
• Abrasion

24
ARAC Gradation
25
ARAC Mineral Admixture

• 1 Lime or Cement is mandatory

26
ARAC Sand Equivalent

• Minimum SE55
• To ensure that there are not excessive amounts of
  clay particles on the aggregate
• Done on washed aggregate

27
ARAC Crushed Faces

• Minimum 95 Single Crushed Faces
• To insure good particle interlock

28
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

29
ARAC Mix Design Steps

• Prepare Aggregate
• Determine aggregate specific gravities
• Determine maximum theoretical specific gravity
• Compact mix, determine optimum binder content
• Check mix volumterics

30
ARAC Design

• Determine aggregate specific gravities for fine
  and coarse mineral aggregate
• Calculate combined specific gravities (oven dry,
  saturated surface dry, apparent)

31
ARAC Design

• Determine the maximum theoretical specific
  gravity (Rice test)
• Done at 6.0 binder content and calculated to
  other binder contents as needed

32
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 325F

33
ARAC Design

• Check Volumetrics, select optimum binder content.
• Minimum VMA 19.0
• Effective Voids 4.0 - 6.0
• Maximum 1 binder absorption

34
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

35
ARAC Design

• If necessary, adjust gradation to improve VMA or
  voids. Repeat compaction process and remeasure
  maximum theoretical specific gravity.

36
ARAC Typical Design

• Typical binder content 6.5-8.5 depending on
  aggregate source and gradation

37

• Thank you