ITEM 308 – BITUMINOUS PLANT-MIX SURFACE COURSE, COLD-LAID

308.1 Description

This item shall consist of constructing Bituminous Plant-Mix Surface Course composed of aggregates, mineral filler and bituminous material mixed in a central plant, constructed and laid cold on the prepared base in accordance with this Specification and in conformity with the lines, grades and typical cross-section shown on the Plans.

308.2 Material Requirements

308.2.1 Composition and Quality of Asphalt Cold Mix (Job-Mix Formula)

The asphalt cold mix shall be composed of coarse mineral aggregates, fine mineral aggregates, mineral fillers and chemically bonding bitumen.

At least three weeks prior to production, 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 value for:

1. The percentage of coarse mineral aggregates passing each specified sieve size.

2. The percentage of fine mineral aggregates passing each specified sieve size.

3. The percentage of chemically bonding bitumen material to be added.

4. The temperature of the mixture delivered on the prepared base of the road.

5. The kind and percentage of chemical additive to be used.

6. The kind and percentage of mineral filler to be incorporated.

Stability Requirements:

The mixture shall conform to the following:

Test Property	Minimum	Maximum
Stability N at 22.20C	2224	-
Percent Stability Loss After Vacuum Saturation and Immersion	-	50
Aggregate Coating (Percent)	50	-

308.2.2 Bituminous Material

It shall be either Liquid Cut-back Asphalt or Emulsified Asphalt, whichever is called for in the Bill of Quantities. The type and grade of asphalt material will be specified by the Engineer and shall comply to the requirements of AASHTO Specification M82, M140 or M208 (ASTM Designation D 2397).

308.2.3 Coarse Aggregates

Coarse Aggregates shall conform to the applicable requirements of Item 703 or AASHTO M 79.

308.2.4 Fine Aggregates

Fine Aggregates shall conform to the applicable requirements of Item 703, AASHTO M 29 or ASTM D 1073.

308.2.5 Mineral Fillers

It shall conform to the requirements of Item 703A, Mineral Filler or ASTM D 242.

308.2.6 Proportioning of Mixture

The proportioning of Bituminous Material on the basis of total dry aggregate shall be from 4.5 to 7.0 mass percent when cut back asphalt is used and from 6.0 to 10.0 mass percent when emulsified asphalt is used. The exact percentage to be used shall be fixed by the Engineer in accordance with the job-mix formula and the other quality control requirements.

308.3 Construction Requirements

308.3.1 Weather Limitations

Cold Asphalt Plant Mix shall be placed only when the specified density can be obtained. The mixture shall not be placed on any wet surface or when weather condition will prevent its proper handling or finishing. Asphalt surface mixture shall not be placed when the surface temperature of the base course is below 10⁰C.

308.3.2 Preparing Area To Be Paved

1. The area to be paved shall be substantially true to line and grade. It shall have a firm and properly prepared surface before paving operations begin. All loose and foreign material shall be removed.

2. When the compacted subgrade on which the asphalt base is to be placed loosely bonded, it shall be primed with 0.5 to 1.40 liter/m² of the type and grade of asphalt priming material. The asphalt should be entirely absorbed by the base course and the prime should be fully set and cured before placing the surface.

3. Holes and depressions in existing surfaces shall be repaired by removing all loose and defective material to sound pavement and replacing with an approved asphalt-aggregate patching material. The patching mixture shall be compacted to produce a tight surface conforming to the adjacent pavement area.

4. Excess asphalt in patches and joints shall be removed only through methods approved by the engineer.

5. Immediately prior to application of the asphalt tack coat all loose and foreign material shall be removed by sweeping or by blowing, or both.

6. Surfaces of curbs, gutters, vertical faces of existing pavements, and all structures to be in actual contact with the asphalt-aggregate mixture shall be given a thin, even coating of asphalt material, type and grade. Care shall be taken to prevent spattering of the asphalt on surfaces that will not be in contact with the asphalt-aggregate mixture.

308.3.3 Preparing The Mixture

1. The asphalt shall be warmed, if necessary, at the paving plant to a temperature at which it can be applied uniformly to the aggregate.

2. When it is necessary to blend aggregates from one or more sources to produce the combined gradation, each source or size of aggregate shall stockpiled individually. Aggregate from the individual stockpiles shall fed through separate bins to cold elevator feeders. They shall not be blended in the stockpile.

3. Cold aggregates shall be fed carefully to the plant so that surpluses and shortages will not occur and cause breaks in the continuous operation.

4. Mixing time shall be the shortest time that will produce a satisfactory mixture.

308.3.4 Placing The Mix

The bituminous surface course mixture shall be placed with an asphalt paver to provide a nominal compacted thickness of the surface course. The minimum lift thickness shall be at least two times the maximum particle size. The maximum lift thickness shall be that which can be demonstrated to be laid in a single lift and compacted to a required uniform density and smoothness. Placing the mixture shall be a continuous operation. If any irregularities occur, they shall be corrected before final compaction of the mixture.

308.3.5 Compacting The Mixture

The mix shall be compacted immediately after placing. Initial rolling with a steel-wheeled tandem or three wheeled roller, vibratory roller, or a pneumatic-tired roller shall follow the paver as closely as possible. If needed, intermediate rolling with a pneumatic-tired roller shall be done immediately behind the initial rolling. An application of choke aggregate may be necessary to prevent mix pick-up by the pneumatic-tired roller. Final rolling shall eliminate marks from previous rolling. In areas too small for the roller a vibrating plate compactor or a hand-tamper shall be used to achieve thorough compaction.

308.3.6 Acceptance Requirement

Divide asphalt mixture production into lots, each lot equal to the mix produced during one day. Determine the target density for each lot by measuring the average density of six laboratory prepared specimens representing two randomly chosen subsamples from trucks delivering mixture to the jobsite. The target density should be reported as dry density.

Determine the compacted density in the field from five randomly located positions in each lot of the compacted mixture. The density of freshly compacted material can be determined using a properly calibrated nuclear density device or other procedure. Density determinations made after a period of curing may be determined on samples obtained from compacted material by a suitable core drilling technique. All compacted densities should be converted to dry densities. It is recommended that the average of five field density determinations made in each lot be equal to or greater than 97 percent of the average density of the six laboratory prepared specimens, and that no individual determination be lower than 95 percent.

The compacted base and surface shall have an average thicknesses no less than those specified on the plans. Any deficiency in thickness shall be made up with surface mixture when the surface course is placed.

The surface of the completed pavement will be checked longitudinally and transversely for smoothness with a 3 m straightedge. The surface shall not vary more than 5 mm in a 3 m parallel to the centerline and not more than 8 mm in 3 m at right angles to the centerline.

308.4 Construction Equipment

308.4.1 Equipment

The equipment shall include:

1. Asphalt mixing plants designed to produce a uniform mix within the job-mix tolerances.

2. Self-powered pavers that are capable of spreading the mix to the thickness and width specified, true to the line, grade and crown shown on the Plans.

3. Enough smooth metal-bedded haul trucks, with covers when required ensure orderly and continuous paving operations.

4. A pressure distributor that is capable of applying tack coat and prime material uniformly without atomization.

5. Steel-wheeled, pneumatic-tired, or vibratory rollers capacity of attaining the required density and smoothness.

6. A power broom or a power blower or both.

7. Hand tools necessary to complete the job.

Other equipment can be used in addition to the specified equipment when approved by the Engineer.

308.5 Sampling

Sampling of asphalt materials shall be in accordance with the latest revision of AASHTO Designation T40 (ASTM D140). Sampling of mineral aggregate shall be in accordance with the latest revision of AASHTO designation (ASTM D 75). Sampling of the asphalt mixture, as required by the Engineer, shall be in accordance with the latest revision of AASHTO 168 (ASTM D 979).

308.6 Testing

Methods of Testing shall be in accordance with the applicable AASHTO or ASTM Methods.

308.7 Method of Measurement

The bituminous mixture will be measured by square meter (m²). The quantity to be paid for shall be the number of square meters of the mixture placed and compacted in the accepted pavement. No deduction will be made for the weight of bituminous material in the mixture. Batch weights will not be permitted as a method of measurement.

308.8 Basis of Payment

The accepted quantity, measured as prescribed in Section 308.7, shall be paid for at the contract unit price for Bituminous Plant-Mix Surface Course, Cold-Laid, which price and payment shall be full compensation for furnishing all materials, handling, placing, rolling, compacting, labor, equipment, tools and incidentals necessary to complete this Item.

Payment will be made under:

Pay item No.	Description	Unit of Measurement
308	Bituminous Plant-Mix Surface Course, Cold-Laid	Square Meter