ITEM 735 - POROUS ASPHALT MIXTURE

735.1 Description

This item shall consist of constructing a porous asphalt mix, an open or gap ·graded hot mix asphalt surface course laid on existing concrete or asphalt pavement as wearing course in accordance with this Specification and in conformity with lines, grades, thickness and typical cross-section shown on the Plans.

735.2 Classification

The porous asphalt mixture shall be classified according to the following types based on the grading used:

Type I - Open Graded

Type II - Gap Graded

735.3 Materials Requirements

735.3.1 Composition and Quality of Poro9s Asphalt Mixture

            The porous asphalt mixture is either: an open or gap graded bituminous asphalt mix composed of large proportion of coarse aggregate, fine aggregate, mineral filler and polymer modified bitumen as binder. The porous asphalt mixture shall allow the passage of water through it. It shall have the an air voids that is within the range when tested using ASTM D 3203:

            Type I – 18% - 25%

Type II – 15% - 25%

At least three weeks prior to the construction, the Contractor shall submit in writing a job mix formula for each mixture supported by laboratory test data along with samples and sources of the components and viscosity-temperature relationships information to the Engineer for testing and approval.

Each job-mix formula submitted shall propose definite single values for:

            1.         The percentage of aggregate passing each specified sieve size.

2.         The percentage of polymer modified bitumen to be added.

3.         The temperature of the mixture delivered on the road.

4.         The kind and percentage of additive to be used.

5.         The kind and percentage of mineral filler to be used.

After the job-mix is established, all mixture furnished for the project shall conform thereto within the following ranges of tolerances:

		Type I	Type II
Passing No.4 and larger sieves Passing No.8 to No.100 sieves (inclusive) Passing No.200 sieve Bituminous Material Temperature of Mixture	± ± ± ± ±	5 percent 4 percent 2 percent 0.4 percent 10°C percent	7 percent 4 percent 2 percent 0.4 percent 10°C percent

            Should a change in source of material be proposed or should a job­mix formula prove unsatisfactory, a new job-mix formula shall be submitted by the Contractor in writing and be approved by the .Engineer prior to production.

            Approval of a new job-mix formula may require laboratory testing and verification.

The porous asphalt mixture shall have a minimum compressive strength of 1.4 MPa.

The mixture shall also have an index of retained strength of not less than 70 when tested by AASHTO T 165. For aggregate having maximum sizes over 25 mm, AASHTO T 165 will be modified to use 150 mm x 150 mm cylindrical specimens. The 150 mm cylinders will be compacted by the procedures outlined in AASHTO T 167 modified to employ 1 O repetitions of a molding load of 9.6 MPa with no appreciable holding time after each application of the full load.

735.3.2 Polymer Modified Bitumen Properties

Polymer modified bitumen to be used in porous asphalt mixes shall be tested in accordance with AASHTO M 320.

In addition, polymer modified bitumen shall meet the following requirements.

	Test Method	Range
Penetration @ 25°C Softening Point, °C Flash Point, COC, °C Solubility in Trichloroethylene, % Ductility, cm	ASTM D 5 ASTM D 2398 ASTM D 92 ASTM D 2042 ASTM D 113	40-70 60 minimum 232 minimum 99.50 minimum 150 minimum

735.3.3 Aggregates

735.3.3.1 Coarse Aggregate

Coarse aggregate shall consist of crushed stone or crushed gravel or a combination of two. The maximum size of coarse aggregate used shall not exceed 19 mm and shall conform to the applicable requirements of Item 703, Aggregates.

735.3.3.2 Fine Aggregate

Fine aggregate shall conform to the applicable requirements of Item 703, Aggregates.

735.3.4 Mineral Filler

The mineral filler to be used shall be Portland cement and it shall conform to the requirements of Item 703 A, Mineral Filler.

735.3.5 Mixing Temperature

Aggregates shall be heated ·to 20° C above the recommended mixing temperature. Polymer modified bitumen should not be heated above 200° C. The ideal mixing temperature should be established prior to blending and may be determined by using a Bitumen Test Data Chart, plotting viscosity with respect to temperature. Mixing temperature must not exceed 180° C or that recommended by the polymer modified bitumen supplier.

735.3.6 Proportioning of Porous Asphalt Mixture.

The proportion of polymer modified bitumen shall be 4.0 to 5.5 percent for Type I and 4.5 to 6.5 percent by total dry aggregate weight for Type II. The exact percentage to be used shall be fixed by the Engineer in accordance with the job-mix formula and other quality control requirements.

Samples shall be taken from the hot bins in the asphalt plant. Sieve analysis shall be carried out on the samples and the proportioning of the mixture will be based on the results obtained.

735.3. 7 Storage

The storage silo shall be emptied prior to the production of asphalt concrete. The storage time should be kept minimum.

735.3.8 Recommended Mix Design of Porous Asphalt

The percent void content of porous asphalt mixture shall be designed by adjusting the ratio of fine and coarse aggregates. The following gradation is recommended to yield a higher percentage of voids, high stability and requirements necessary in the design of the mix. 

Sieve Sizes (mm)		Passing%
		Type I	Type II
¾ ½ 3/8 No. 4 No. 8 No. 16 No. 30 No. 50 No. 200	(19) (12.5) (9.5) (4.75) (2.36) (1.19) (0.63) (0.30) (0.075)	100 90 – 100 85 – 95 37 – 45 9 – 17 3 – 11 - - 1 – 4	100 88 – 98 34 – 48 17 – 24 12 – 20 6 – 12 3 – 9 - 2 – 7
Asphalt Content, o/o by weight of aggregate Air Voids, mass % Stability, lbs		4.0 - 5.5 18 - 25 1,500 minimum	5.0 - 6.0 15 - 25 1,500 minimum

735.3.9 Mix Design

Test specimens shall be made using methods described in ASTM D 1559 or equivalent. The specimens shall be compacted with 50 blows for Type I and 75 blows for Type 11 on each side of the specimen sample.

Perform the draindown test on the specimen samples at 15°C higher than ideal mixing temperature. Draindown results should not exceed 0.30 % by total mass of mix. Using the selected design gradation, prepare three (3) samples with binder contents at 0.50% increments.

Test air voids of the porous asphalt mix. Results for Type I and II should fall between18% to 25% and 15% to 25%, respectively.

Test stability, flow, specific gravity and durability.

735.3.10 Evaluation Procedure on the Design of Bitumen Content.

To determine the optimum asphalt content, the Cantabro test using the Los Angeles abrasion machine (ASTM C 131) on the samples must be conducted. The specimen samples shall be stored for at least 2 days at a temperature of not more than 25°C and tested within 7 days from manufacture of the sample. In this method, subject the specimen samples to 300 rotations in Los Angeles abrasion machine without the steel spheres at a rate of 30 to 33 revolutions per minute and a temperature of 25°C ± 1 °C. The abrasion, expressed as a loss in mass, is charted with respect to the binder content. The wear loss decreases when the binder content increases with the curve slope downward and becomes flat when a certain percentage of bitumen is reached, which corresponds to the minimum binder content needed to ensure adequate adhesion. The abrasion loss from the Cantabro test should not exceed 20% on the unaged specimens. The inflection point is the minimum asphalt content which the sample mixture can retain its shape under the condition after compaction. The optimum asphalt content is determined as the average of the two asphalt contents. Abrasion tests on aged (7 days @ 60°C) samples must also be conducted with abrasion loss not exceeding 30% on the aged specimens.

735.4 Construction Requirements

The construction requirements shall be in accordance whenever applicable with Item 307 Bituminous Plant - Mix Surface Course (General), subsection 307 .3, Construction Requirements.

735.4.1 Weather Limitations

Asphalt paving mix shall not be placed on any wet surface or when weather conditions will otherwise prevent its proper handling or finishing. It shall only be placed when the mix can be compacted to the specified density. No work shall commence when rain is imminent and all works should be suspended when it is raining and asphalt concrete delivered to the site shall be returned to the Contractor without compensation.

735.4.2 Construction Equipment

The Contractor shall provide a minimum of two (2) paving gangs for each Contract where necessary.

The Contractor shall have a minimum of two pavers, each with a capacity of not less than 40 tonnes per hour and are steel - wheeled rollers.

For the smooth operation of the works, the Contractor shall have an asphalt plant with a manufacturer quoted capacity of not less than 120 tonnes/hour for the purpose of this Contract. The Asphalt Concrete plant shall be equipped with a separate bitumen tank with capacity of not less than 20 tonnes for the purpose of storing the approved polymer modified bitumen.

Rolling should be carried out using a tandem, non-vibrating steel roller weighing not less than 6 tons. Pneumatic tired rollers should not be used at any time when compacting porous asphalt mixes.

735.4.3 Placement

Before commencing the paving work, it shall be the responsibility of the Contractor to check that all tools, equipment and machines necessary for the job are on the site and in proper working conditions. A competent paver operator shall be operating the paving machine throughout the duration of the works. All rollers to be used must be checked to ascertain that they contain water which are not muddy or in any way contaminated with chemicals.

A representative from the Contractor well versed in asphalt laying work must be on site and be present throughout the duration of the works to organize and supervise the works and to handle all contingencies which may arise.

The underlying, surface shall be clean before placing the mix. The approved tack coat of bitumen emulsion shall also be spray-applied at a rate of at least 0.54 liter per sq.m. to completely cover the surface where the Porous Asphalt Pavement is to be laid.

During the placement, the mix temperature shall not deviate from the mixing temperature by more than 10°C. The temperature shall be measured at a point 100mm within the load on the truck.

The asphalt paver hopper shall not left more than half empty unless new mix is immediately available to fill it up. In the event of break for rest or when the machine has remained idle for more than 15 minutes, the mix shall be fully discharged and joints constructed if no new mix is added.

As far as possible, the paving work shall cover the entire pavement width within one day.

735.4.4 Laying Temperature

The temperature of Plant mixtures in the spreader hopper shall be around 140°C at the time of spreading depending on the ambient temperature.

735.4.5 Compaction Temperature

Compacting should start at around 130°C. The surface shall be rolled when the mixture is in proper condition and when rolling does not cause undue displacement, cracking or shoving.

Firstly use a 3 - 4 metric ton static steel-wheeled rollers to compact the porous asphalt for 4 passes. Then followed by another 2 passes by using 6 - 8 metric tonnes steel wheeled rollers to finish off the compaction.

The compacted porous asphalt concrete shall be opened to traffic movement at ambient temperature.

735.4.6 Acceptance Procedures

Acceptance procedures for polymer modified bitumen shall conform to the applicable requirements of Item 702; Subsection 702.4 Acceptance Procedures for Bituminous Material.

735.5 Method of Measurement

The area to be paid for under this item shall be the number of square meters (m²) of porous asphalt pavement with polymer modified bitumen placed, compacted and accepted.

735.6 Basis of Payment

The accepted quantity, measured as prescribed in Section 735.5, shall be paid for at the contract unit price for Porous Asphalt Pavement with Polymer Modified Bitumen which price and payment shall be full compensation for furnishing all materials, handling, mixing, hauling, placing, rolling, compacting, labor, .equipment, tools and incidentals necessary to complete this item.

Payment will be made under:

Pay Item Number	Description	Unit of Measurement
735	Porous Asphalt Pavement with Polymer Modified Bitumen	Square Meter