STANDARD SPECIFICATION

ITEM 310 - BITUMINOUS SURFACE COURSE-HOT LAID

DESCRIPTION

This item shall consist of constructing a bituminous concrete surface source composed of aggregates, mineral filler, and bituminous material mixed at a central plant, constructed and laid hot on the prepared base in accordance with this specification and conformity with lines, grades, thickness and typical cross-section shown on the plans.

MATERIAL REQUIREMENTSBituminous Material

It shall be either medium curing Cutback asphalt or Asphalt Cement, whichever is called in the Bill of quantities. It shall conform to the requirements of Item 702, Bituminous Materials.

The penetration grade, type and grade of bituminous material shall be specified in the Special provision.

Aggregates

Aggregates shall conform to the requirements of Item 307, Bituminous Plant-Mix Surface Course, General.

Mineral Filler and Hydrated Lime It shall conform to the requirements of Item 307

PROPORTIONING OF MIXTURES:

1. The proportion of bituminous material on the basis of total dry aggregates, shall be from 5.0 to 8.0 mass percent.

2. The exact percentage to be used shall be fixed by the engineer in accordance with the job-mix formula and other quality control requirements.

3. During the mixing operation, one-half to one mass percent of hydrated lime, dry aggregates basis, shall be added to the mixture.4. The lower percentage limit is applicable to aggregates which are predominantly calcareous.

COMPOSITION OF BITUMINOUS MIX

Aggregates account for 92% to 95% of the weight of the mixture, while asphalt accounts for 5% to 8% of the weight of the mix. The exact percentage to be used is established by the job-mix formula.

BITUMINOUS MATERIAL

There are two types of bitumen that are commonly used in bituminous concrete surface course:

Tar is a viscous liquid obtained from the distillation of coal or wood.Petroleum asphalts are products of the distillation of crude oil. There are three major petroleum asphalt products:

Asphalt Cements are produced in various penetration grade, the most common being penetration grade 200/300, 120/150, 85/100, 60/70 and 40/50.Liquid Asphalts are asphalts mixed with solvent to reduce their viscosity and make them easier to at ordinary temperature. The solvents are gasoline for rapid curing type; kerosene for medium curing type; and diesel fuel for slow curing type cutback asphalt.

Asphalt emulsions are mixtures of asphalt cement and water with emulsifying agent. Emulsified asphalts are either cationic emulsion which work better with wet aggregates and in cold weather, and anionic emulsion which adhere better to aggregate which have positive charges.

Blown Asphalt manufactured thru oxidation process.

PENETRATION GRADE OF ASPHALT

The service performance of an asphalt pavement is greatly influenced by the grade and quantity of asphalt it contains.

The grade of asphalt cement normally used ranges from 60/70 to 200/300 penetration.

ESTABLISHING THE JOB-MIX FORMULA:

The producer of the asphalt mix or the contractor shall submit the job mix formula in writing at least three weeks prior to production for the approval of the Project/Material Engineers.

The formula contains provision on grading of aggregates, percentage and type of asphalt, temperature of aggregates and asphalt, and temperature or mixture upon delivery or at time of compaction.

The job-mix formula is the primary quality control mechanism for the production of asphalt mixture, which shall conform with the following ranges of tolerances:

Passing no. 4 and larger sieves + or -7%Passing no. 8 to no.100 sieves + or -4%Passing no. 200 sieves+ or -2%Bituminous Material + or -4%Temperature of mixtures+ or -10C

The mixture shall have a minimum dry compressive strength of 1.4 MPa (200psi).

The mixture shall have a mass percent air voids with the range of 3 to 5.

The mixture shall have an Index of Retained Strength (IRS) of no less than 70%.

CONSTRUCTION REQUIREMENTS (PLACING AND COMPACTION)

The mixture shall be placed at a temperature not less than 107 degrees centigrade as measured in the truck just prior to dumping into the spreader.When tar is used, the mixture shall be placed at between 66 and 107 degrees centigrade.Compaction should be done while the mixture is still hot and workable in order to attain the required density.A trial section is done to determine the number of roller passes that would attain the required density.The initial or breakdown compaction is done by a pneumatic-tired roller ( not less than 10 tons) while final compaction and smoothing is done by a tandem smoothed-wheeled roller (not less than 10 tons). The speed of a roller shall not exceed 5 km per hour.

Rolling shall begin at the sides and proceeds longitudinally parallel toward the road centerline, each trip overlapping one-half the rollers width, gradually progressing to the crown of the road.After final rolling, the degree of compaction should be checked. The compacted pavement shall have a density equal to or greater than 97% of the laboratory compacted density.No traffic shall be permitted on the finished pavement until it has cooled to atmospheric temperature.The construction requirements shall be in accordance, whenever applicable, with Item 307, section 307.3.

SAMPLE/TESTING & ACCEPTANCE OF FURNISHED PAVEMENT(Per D.O. 181, Series of 2001)

The contractor shall cut full depth samples as directed from the finished pavement, for testing. Samples shall be neatly cut by saw or core drill.Each sample shall be at least 150mm x 150mm or 100mm diameter full depth.At least one, but not more than three samples, shall be taken for each full days operation.If no core samples were taken during the days operation, core samples shall be taken from the completed pavement for every 100 L.M. per lane.The contractor shall supply and furnish new material to backfill voids left by the samples taken.

The samples obtained will be used to measure the thickness of the pavement. The same samples will be used to test the density of the compacted pavement by AASHTO T-166.The compacted pavement shall have a density equal to or greater than 97 mass percent of the density of a laboratory specimen. The asphalt pavement represented by the cores shall not be accepted if the deficiency in density is more than 2%.The compacted pavement shall have a thickness tolerance of negative (-) 5mm. Thickness in excess of the specified thickness shall not be considered in the payment of asphalt pavement.The asphalt pavement represented by the cores shall not be accepted if the deficiency in the average thickness is more than 5mm.

SURFACE TOLERANCE

The surface tolerance will be checked by the use of a 3-m straight edge, which will be applied at right angles, as well as parallel to the centerline of the roadbed.The variation of the surface from the testing edge of the strength-edge between contacts with the surface shall not exceed 6mm.

METHOD OF MEASUREMENT (D.O.181, Series of 2001)

The area to be paid for under this item shall be the number of square meters of asphalt pavement placed compacted and accepted based on the thickness and densities of the cores taken in accordance with subsection 307.10 ( Acceptance, Sampling and Testing ).

BASIS OF PAYMENT

The accepted quantity, measured as prescribed in section 310.4, shall be paid for at the contract unit price for Bituminous Concrete Surface Course, Hot-Laid, which price & 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 this Item in square meter.

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