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

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 % (general range %) 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

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 % 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 % depending on aggregate source and gradation

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