4-05  Permeable Asphalt Treated Base (PATB)
(December 12, 2025APWA GSP) 

Supplement Division 4 with the following:

4-05.1	Description
Permeable asphalt treated base (PATB) consists of a compacted course of base material which has been weatherproofed and stabilized by treatment with an asphalt binder.
This work consists of constructing one or more courses of PATB upon a prepared foundation or base in accordance with these Specifications and in conformity with the lines, grades, thicknesses, and typical cross-sections shown in the Plans or as established by the Engineer.

4-05.2	Materials
Materials shall meet the requirements of the following sections:

Asphalt	9-02.1
Anti-Stripping Additive	9-02.4

4-05.2(1)	Aggregates for PATB

4-05.2(1)A	General Requirements
Aggregates for PATB shall be manufactured from ledge rock, talus, or gravel, in accordance with the provisions of Section 3-01 that meet the following test requirements:

Los Angeles Wear, 500 Rev.		30% maximum
Degradation Factor	15 minimum

4-05.2(1)B	Grading
Aggregates for PATB shall meet one of the following requirements for grading:

Sieve Size	Percent Passing *	
	Grading 3/4  (1)	Grading 1-1/2  (2)	
1-1/2”		100	
1”		90 - 100	
¾” square	100	80 - 95	
½” square	90 – 100	35 - 65	
3/8” square	40 - 80	25 - 45	
U.S. No. 4	0 - 30	0 - 30	
U.S. No. 8	0 - 20	0 - 20	
U.S No. 16	0 - 10	0 - 10	
U.S. #200	0 - 4	0 - 4	
* All percentages are by weight.
(1) – Minimum asphalt binder content = 3.5%
(2) – Minimum asphalt binder content = 3.0%		

The aggregate shall consist of a combination of crushed and natural aggregates with a percent fracture greater than 75% on one face on the No. 4 sieve and above, in accordance with the field operating procedures for AASHTO T 335.

4-05.2(1)C	Test Requirements
When the aggregates are combined within the limits set forth in Section 9-03.6(2) and mixed in the laboratory with the designated grade of asphalt, the mixture shall meet the following test values:

Property/Test Method	Requirement	
% of Theoretical Maximum 
Specific Gravity (Gmm)	80 @ 75 gyrations (approximate = 20% void space)	
AASHTO T 283 – Standard Method of Test for Resistance of Compacted Asphalt Mixtures to Moisture-Induced Damage	

 TSR > 0.75	
ASTM D3625 – Standard Practice for Effect of Water on Asphalt-Coated Aggregate Using Boiling Water	Coating Area Greater than 95%	
Aggregate Sand Equivalent for PATB	Not less than 35	

4-05.2(2)	Paving Asphalt
The grade of paving asphalt binder shall be PG58V-22, or higher, unless otherwise specified by the Contract. 

The manufacture of PATB may include warm mix asphalt (WMA) processes in accordance with these Specifications. WMA processes include organic additives, chemical additives, and foaming that allow for lower mixing and placement temperatures without impacting the final PATB pavement properties.

4-05.3	Construction Requirements

4-05.3(1)	Asphalt Mixing Plant
Asphalt mixing plants for PATB shall meet the following requirements:

Heating
The plant shall be capable of heating the aggregates to the required temperature.

Proportioning
The mixing plant shall be capable of proportioning the aggregates to meet the Specifications, and the asphalt binder at the rate specified in the approved job mix formula (JMF). If the aggregates are supplied in two or more sizes, means shall be provided for proportioning or blending the different sizes of aggregates to produce material meeting the Specification requirements

Mixing
The mixer shall be capable of producing a uniform mixture of uniformly coated aggregates meeting the requirements of these Specifications.

4-05.3(2)	Preparation of Aggregates
Aggregates for PATB shall be stockpiled before use in accordance with the requirements of Section 3-02. The aggregates shall be heated in the Asphalt Mixing Plant in compliance with the JMF and related temperature viscosity curves for the asphalt binder grade specified.

4-05.3(3)	Mix Design
Binder content shall be between 3.0% and 4.5% by total weight of the mix and will be the highest percentage that passes void requirements test at Ndesign = 75 gyrations for specimens prepared via AASHTO T312. The binder content tolerance from the approved PATB mix design target shall be ± 0.3% during production/ placement of the PATB.  In no case shall the binder content for the chosen PATB grading (see Section 4-05.2(1)B Grading) fall below the specified minimum. The Contractor shall adjust the aggregate to meet the targeted void space specification.

Target void space shall be 20% per ASTM D3203 to determine binder content. Field placed density shall meet the requirements in section 4-05.3(8).

The Contractor shall include a mix design submittal documenting the PATB mix design test results presented alongside the mix design specification criteria included in this Specification, along with the submittal temperature-viscosity curves from the polymer-modified asphalt binder supplier showing the recommended mixing and compaction temperatures developed for dense graded HMA applications.

The Contractor shall determine anti-strip requirements for PATB and provide data for anti-strip dosage as part of the mix design approval process. The PATB mix shall be tested for its resistance to stripping by water in accordance with ASTM D3625. If the estimated coating area is not above 95 percent, a Qualified Products List (QPL) anti-stripping agent shall be added to the PATB to a level that achieves 95 percent plus asphalt binder retention using ASTM D3625.  The Contractor shall be responsible for conducting the anti-stripping evaluation and providing a report to the Engineer. A documented anti-strip evaluation of an existing dense graded hot mix asphalt (HMA) from the same aggregate source and binder supplier as the proposed PATB may be used to document acceptable anti-strip dosage rates in lieu of ASTM D3625 testing.

4-05.3(4)	Mixing
The PATB shall be mixed in accordance with the requirements of Section 5-04.3(6).

4-05.3(5)	Hauling Equipment
Hauling equipment for PATB shall conform to the requirements of Section 5-04.3(3)B.

4-05.3(6)	Spreading and Finishing
PATB shall be spread with a spreading machine equipped with a stationary, vibratory, or oscillating screed or cut-off device, subject to the approval of the Engineer. Approval of the equipment shall be based on a test section demonstrating that the finished product will meet all requirements of the Specifications. Automatic controls will not be required.

The internal temperature of the PATB mixture at the time final rolling and targeted consolidation is achieved shall be a minimum of 185°F.  Rollers shall only be operated in the static mode when the internal temperature of the PATB in less than 175°F.

Unless otherwise directed by the Engineer the nominal compacted depth for any layer of PATB must be less than 0.40 feet. A light tack coat (approximately 0.02 gallons/square yard residual asphalt) shall be applied between lifts of PATB. A tack coat shall also be applied between the PATB surface and the subsequent paving lifts when cleaning of the PATB surface is necessary.

Tack coat shall be uniformly applied to cover the existing porous pavement with a thin film of residual asphalt free of streaks and bare spots. A heavy application of tack coat shall be applied to all joints. The spreading equipment shall be equipped with a thermometer to indicate the temperature of the tack coat material.

Equipment shall not operate on tacked surfaces until the tack has broken and cured. If the Contractor’s operation damages the tack coat it shall be repaired prior to placement of the PATB.

Unless otherwise approved by the Engineer, the tack coat shall be CSS-1, or CSS-1h, emulsified asphalt. The CSS-1, or CSS-1h, emulsified asphalt may be diluted with water at a rate not to exceed one part water to one-part emulsified asphalt. The tack coat shall not exceed the maximum temperature recommended by the emulsified asphalt manufacturer.

4-05.3(7)A	Subgrade Protection Course
Unless otherwise specified by the Engineer, the Contractor shall place the PATB as a protection for the prepared foundation or base on all sections of individual Roadways which are to receive PATB as soon as 10,000 square yards of prepared foundation or base is completed. This requirement shall not be limited to contiguous areas on the project.

The surface of the prepared foundation or base protection layer when constructed on a grading project shall conform to grade and smoothness requirements that apply to the prepared foundation or base upon which it is placed.

4-05.3(7)B	  Finish Course
The final surface course of the PATB, excluding shoulders, shall not deviate at any point more than ⅜ inch from the bottom of a 10-foot straightedge laid in any direction on the surface on either side of the Roadway crown. Failure to meet this requirement shall necessitate sufficient surface correction to achieve the required tolerance, as approved by the Engineer, at no expense to the Contracting Agency.

When portland cement concrete pavement is placed on an asphalt base, the surface tolerance of the asphalt base shall be such that no elevation lies more than 0.05 feet below nor 0.00 feet above the plan grade minus the specified plan depth of portland cement concrete pavement. Prior to placing the portland cement concrete pavement, any such irregularities shall be brought to the required tolerance by grinding or other means approved by the Engineer, at no expense to the Contracting Agency.

4-05.3(8)	Density & Infiltration Testing for Acceptance
The PATB shall be consolidated to a firm and unyielding state. The Contractor will develop a roller pattern that will initially consolidate the pavement structure and then use static rolling only thereafter to prevent over compaction. The PATB shall be compacted to a density of 80%, or greater, than the maximum theoretical (Rice) density established for the mix by WSDOT FOP for AASHTO T209. In place Nuclear Density Gauge testing will be performed by the Contractor to monitor the consolidation effort and to avoid over compaction. The frequency of these tests shall be at the discretion of the Engineer. The use of equipment which results in damage to the materials, over consolidates the PATB or produces substandard workmanship shall not be permitted.

Pneumatic tire rollers shall not be used.

The Contractor shall conduct infiltration tests on the finished PATB per ASTM C1701 at locations chosen by the Engineer. Newly-placed PATB shall have a minimum infiltration rate of 150 inches/hour. Infiltration tests shall be completed every 150 linear feet of roadway and conducted in accordance with ASTM C1701. Target density may be adjusted and used for acceptance, at the discretion of the Engineer, if the PATB is consistently meeting the 150 inches/hour acceptance standard.

If the measured infiltration rate is less than 150 inches/hour, the Contractor shall conduct four additional tests as follows in line with the paver direction of travel. Two tests upstream and two tests downstream of the initial test location shall be taken at distances of 20 feet and 40 feet. Results of the additional tests will be averaged.  The Contractor shall conduct additional testing upstream and downstream to identify areas to be removed. If the average infiltration rate is less than required the Contractor shall remove and replace the failing PATB areas at the direction of the Engineer and at no cost to the Contracting Agency.

4-05.4	Measurement
PATB will be measured by the ton in accordance with Section 1-09.2, with no deductions being made for the weight of asphalt binder, anti-stripping additive, or any other component of the mixture.

4-05.5	Payment
Payment will be made for the following Bid item:

“Permeable asphalt treated base, PG ____”, per ton.
The unit contract price per ton for “Permeable asphalt treated base, PG ____” shall be full compensation for all costs, including anti-stripping additive, incurred to carry out the requirements of Section 4-05 except for those costs included in other items which are included in this Subsection and which are included in the Proposal.