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