ITEM 306 – BITUMINOUS ROAD MIX SURFACE COURSE

306.1 Description

This Item shall consist of constructing a bituminous road-mix surface course on a prepared base in accordance with these Specification and inconformity with the lines, grades and typical cross-sections shown on the Plans, or as established by the Engineer.

306.2 Material Requirements

306.2.1 Bituminous Material

The bituminous material shall be either Rapid Curing (RC) Cut-back, Medium Curing (MC) Cut-back or Emulsified Asphalt, whichever is called for in the Bill of Quantities. It shall conform to the requirements of Item 702, Bituminous Material. The type and grade will be specified in the Special Provisions.

306.2.2 Aggregate

The aggregate shall conform to applicable requirements of Item 703, Aggregates. It will be tested for acceptance immediately preceding addition of bituminous material to the mix. This Acceptance will be based on periodic samples from the windrowed materials after all aggregates have been blended for each layer.

The aggregate may be new or salvaged from the existing surface.

1. New Aggregate
   
   It shall conform to the applicable requirements of Item 703, Aggregates.


2. Salvaged Aggregate
   
   
   Where aggregate required for the road mix surface course is already in place, the Contractor shall not be responsible for its grading or quality except for removal of oversize pieces. In general, salvaged aggregate to be used for road mix surface course will consist of materials meeting the requirements given in Item 703, Aggregates, for new aggregate or may consist of selected granular material for other gradings. Any particles of salvaged aggregate appearing in the surface at the time of lay-down and finishing that will not pass 37.5mm sieve shall be removed by the Contractor as directed by the Engineer.

306.2.3 Proportioning of Mixture

The proportion 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.

During the mixing operation, one-half to one (0.5 to 1.0) mass percent of hydrated lime, dry aggregate basis, shall be added to the mixture. The lower percentage limit is applicable to aggregates which are predominantly calcareous.

306.3 Construction Requirements

306.3.1 Weather Limitations

The construction of road mix bituminous pavement shall be carried on only when the surface on which the material is to be placed is dry and when the weather is not foggy or rainy.

306.3.2 Construction Equipment

The equipment used by the Contractor shall include scarifying, mixing, spreading, finishing and compacting equipment; a bituminous distributor; and the equipment for heating bituminous material. The distributor shall be so designed, equipped, maintained and operated that bituminous material at even heat may be applied uniformly on variable widths of surface up to 4.5 m at readily determined and controlled rates from 0.2 to 10L/m2, with uniform pressure, and with an allowable variation from any specified rate not to exceed 0.1 L/m2. Distributor equipment shall include a tachometer pressure gauge, accurate volume measuring devices or a calibrated tank, and thermometer for measuring temperatures of tank contents. Distributors shall be equipped with a power unit for the pump, and full circulation spray bars adjustable laterally and vertically.

Travelling or stationary mixing plants or other equipment of proven performance may be used by the Contractor in lieu of the specified equipment, if approved by the Engineer.

Rollers shall be self-propelled steel-wheel tandem or 3-wheel rollers weighing not less than 8 tonnes each and pneumatic tire rollers having a total compacting width of not less than 1,520 mm and the gross mass adjustable within the range of 3,640 to 6,360 kilograms per meter of compaction width. The operating mass shall be directed. Tire pressure or contact pressure may be specified for pneumatic-tire rollers. All tires on pneumatic rollers shall be equally inflated, exerting equal unit pressure, with a means of varying the contact pressure to suit project conditions.

306.3.3 Preparation of Base

1. Case 1 (New Aggregate)
   
   When new aggregate is to be used for the road mix surface course, the existing base shall be scarified lightly and bladed to uniform grade and to the cross-section shown on the Plans and shall then be rolled or watered and rolled, as directed. If so ordered by the Engineer, depressions shall first be filled and weak portions of the base strengthened with new aggregate.


2.  Case 2 (Salvaged Aggregate)
   
   When material in the existing road surface is to be used for mixing, the surface shall be scarified lightly and bladed to uniform grade and to the cross-section shown on the Plans. The reshaped surface shall then be scarified again to the depth ordered by the Engineer and in such manner as to leave a foundation of undisturbed material parallel, both in profile and cross-section, to the proposed finished surface. The loosened materials shall be bladed aside into a windrow at the side of the road and the undisturbed material rolled or watered and rolled, as directed.
3. 
   

306.3.4 Placing Aggregates

New aggregates, where required, shall be uniformly spread on the prepared surface by the use of spreader boxes, or other approved mechanical spreading devices. When two or more sizes of aggregates are used, each size of aggregate shall be placed in the proper amount to provide for surfacing of the required width and thickness. The proper amounts of the separate sizes of aggregate for each course shall be blended and shaped into a windrow of uniform cross-section. At least one day shall be allowed for measuring, sampling and testing for approval of quantity and gradation before the windrowed material is spread for application of bituminous material.

If the surface moisture of the aggregate is more than 2 percent of the dry weight of the aggregate, except when the bituminous material is emulsified asphalt, the aggregate shall be turned by blades or disc harrows or otherwise aerated until the moisture content is reduced to 2 percent or less. The aggregate shall then be spread smoothly and uniformly over half the road or other convenient width of the surface ready for the application of bituminous material, except that when a traveling mixing plant is used, the aggregate shall be formed into a uniform cross-section.

In lieu of aerating and drying the aggregate, the Contractor may use an approved additive, except where emulsified asphalt is used, which shall be satisfactorily blended with the bituminous material. The additive shall permit suitable coating of the wet aggregate and shall prevent the bituminous coating from stripping in the presence of water.

306.3.5 Application of Bituminous Material

The bituminous material shall be uniformly distributed in successive application, in such amounts and at such intervals as directed. The mixing equipment shall follow immediately behind the distributor, after each application of bituminous material, to partially mix the aggregate and the bituminous material.

306.3.6 Mixing

After the last application of bituminous material and partial mixing, the entire mass of bituminous material and aggregate shall be windrowed on the road surface and then mixed, by blading the mixture from side to side of the road, or by manipulation producing equivalent results, until all aggregate particles are coated with bituminous material and the whole mass has a uniform color and the mixture is free from fat or lean spots, or balls of uncoated particles. During the mixing operations, care shall be taken to avoid cutting into the underlying course or contaminating the mixture with earth or other extraneous matter. When directed, the mixing process shall be confined to part of the width or area of the road so as to allow traffic to pass.

Should the mixture show an excess, deficiency or uneven distribution of bituminous material, the condition shall be corrected by the addition of aggregate or bituminous material as required and re-mixing. If the mixture contains excessive amounts of moisture or volatile matter, it shall be bladed, aerated or otherwise manipulated until the moisture and volatile content are satisfactory. The spreading of the mix shall not be done when the surface to be covered is in an unsatisfactory condition. At the end of each day’s work, or when the work is interrupted by weather conditions or otherwise, all loose materials shall be bladed into a windrow, whether mixing is completed or not, and shall be retained in windrow until operations are resumed.

When the mixing operations have been satisfactorily completed, the mixture shall be formed into a windrow of uniform cross-section.

If the Contractor elects to use traveling or stationary mixing plants in lieu of the specified equipment, the same requirements regarding residual moisture and evaporation of volatiles given above shall apply.

306.3.7 Spreading, Compacting and Finishing

The material shall be spread by a self-propelled pneumatic-tire blade grader or a mechanical spreader of approved type. In spreading from the windrow, care shall be taken to avoid cutting into the underlying base. After the material is spread, the surface shall be rolled. Rolling shall be parallel to the road center line and shall commence at the outer edges of the road, overlapping the shoulders and progressing towards the center, overlapping on successive passes by at least one-half the width of the roller, except that on superelevated curves, rolling shall progress from the lower to the upper edge.

Each pass shall terminate at least 910 mm in advance or to the rear of the end of the preceding pass. During compaction, the surface shall be dragged or bladed as necessary to fill ruts and to remove incipient corrugations or other irregularities. Rolling shall continue until the surfacing is of uniform texture and satisfactory compaction is obtained. Initial rolling shall be performed with a pneumatic-tire roller and final rolling with a 3-wheel or tandem type steel wheel roller. Rolling shall be discontinued whenever it begins to produce excessive pulverizing of the aggregate or displacement of the mixture.

When the compacted thickness of the road mix surface is to be more than 50 mm, the mixture shall be spread from the windrow and compacted in two layers, the first layer to be bladed and rolled before the second layer is spread.

While the surface is being compacted and finished, the Contractor shall trim the edges neatly to line.

306.3.8 Surface Requirements

Surface requirements shall be as specified in Subsection 307.3.11 except that the permissible surface variance will be 10 mm in 3 m.

306.4 Method of Measurement

Bituminous material and aggregate for Bituminous Road Mix Surface Course will be measured by the tonne (t). The quantity to be paid for shall be the number of tonnes of bituminous material and aggregate used and accepted in the completed work. The weight of all moisture in the aggregate will be deducted from the pay quantity.

Due to possible variations in the specific gravity of the aggregates, the tonnage used may vary from the proposed quantities. No adjustment in contract unit price will be made because of such variation.

306.5 Basis of Payment

The accepted quantities, measured as prescribed in Section 306.4 shall be paid for at the contract unit price for Bituminous Road Mix Surface Course, which price and payment shall be full compensation for furnishing 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
306 306 (1) 306 (2)	Bituminous Road Mix  Surface Course Aggregate for Bituminous  Road Mix Surface Course Bituminous Material for  Bituminous Road Mix  Surface Course	Tonne Tonne