SS319-002020-02.docx
DOCX document 54 KB Posted
- Attached to
- Construction, University Drive Bike Lanes
- Solicitation number
- IFB-114424
- Issued by
- Fairfax County, Virginia
About this file
This document is a supplemental specification guideline issued by the Virginia Department of Transportation for Thin Hot Mix Asphalt Concrete Overlay (THMACO) work on state transportation projects. The specification establishes technical requirements for the production, placement, and acceptance of THMACO as part of road and bridge improvement initiatives. The work involves applying a thin asphalt overlay between 3/4-inch and 1-inch in compacted thickness at a minimum application rate of 80 pounds per square yard over existing pavement surfaces. Key requirements include surface preparation with cleaning and crack sealing, placement of a tack coat using either asphalt emulsion or hot-applied non-tracking materials, and delivery of material to the paver at 315°F ± 15°F. The specification mandates compaction using two steel double drum rollers weighing no less than 10 tons and requires the contractor to conduct gradation and asphalt binder content testing on one sample per 500 tons of production.
The specification details stringent material requirements including performance-graded asphalt PG 64V-28 binder, prohibition of recycled asphalt pavement (RAP), and specific aggregate gradation tolerances with defined production tolerances for each sieve size. Asphalt content shall range from 5.0 to 5.51 percent to achieve a minimum film thickness of 9 microns, with a production tolerance of ±0.2 percent. Antistripping additives are required and must produce a tensile strength ratio of at least 0.80 as determined through AASHTO T 283 testing. The contractor is responsible for all costs associated with materials, additives, labor, equipment, surface preparation, tack coat application, and warranty coverage, which extends for one year from final acceptance. The contractor must repair any delamination or flushing failures exceeding defined thresholds within 14 days of Department notification, with no additional compensation from the Department. Payment is calculated in tons at a contract unit price per ton for completed THMACO work.
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Guidelines: All projects.
SS319-002020-02 March 18, 2024
VIRGINIA DEPARTMENT OF TRANSPORTATION
2020 ROAD AND BRIDGE SUPPLEMENTAL SPECIFICATIONS
SECTION 319 – THIN HOT MIX ASPHALT CONCRETE OVERLAY
SECTION 319 – THIN HOT MIX ASPHALT CONCRETE OVERLAY of the Specifications is amended as follows:
319.01 – Description This work shall consist of the production and placement of a Thin Hot-Mix Asphalt Concrete Overlay (THMACO) according to the Plans, Specifications, and as directed by the Engineer.
319.02 – Materials
(a) Asphalt binder shall be a performance graded asphalt (PG) 64V-28 conforming to AASHTO M 332 and Section 210 or as designated by the Engineer
(b) RAP: Recycled asphalt pavement material will not be permitted.
(c) Coarse aggregate shall conform to Section 203 or as directed by the Engineer. Water Absorption when tested according to AASHTO T 85 shall be not exceed 2%. Material retained on the No. 4 sieve and larger sieves shall conform to the following when tested according to ASTM D4791:
| Flat & Elongated Ratio |
| Maximum Content |
| 3:1 |
| 25% |
| 5:1 |
| 10% |
(d) Fine aggregate shall conform to Section 202, except for grading, which shall be tested according to AASHTO TP 33 (Method A) with a value of at least 45% and a sand equivalent value of at least 50 when tested according to AASHTO T 176.
(e) Mineral filler shall conform to Section 201.
(f) Fiber additive when required shall be cellulose or mineral fiber approved by the Engineer based on supplier’s certification of properties and documentation of success in similar applications in hot mix asphalt.
(g) Antistripping additive shall be used and shall be hydrated lime, a chemical additive from the Department’s Approved List No. 7, or a combination of both. The approved chemical additive shall be added at a rate of not less than 0.30% by weight of the total asphalt content of the mixture. The mixture shall produce a tensile strength ratio (TSR) of at least 0.80 for the design and production tests. The TSR shall be determined according to AASHTO T 283, including a freeze-thaw cycle (4-inch specimens compacted with a Marshall Hammer or 3.5 by 6-inch specimens when compacted with a gyratory compactor), except that the 16-hour curing time requirement and the 72 to 96-hour storage period will not be enforced by the Department. Design tests shall use the same materials that are used in the production mix and shall be conducted in a laboratory approved by the Department.
When a chemical additive is used, it shall be added to the asphalt binder prior to the introduction of the asphalt binder into the mix. Any chemical additive or particular concentration of chemical additive found to be harmful to the asphalt concrete or that changes the original asphalt binder performance grade (PG) shall not be used.
(h) Hydrated lime shall conform to ASTM C977. Hydrated lime shall be added at a rate of at least 1% by weight of the total dry aggregate.
A separate bin or tank and feeder system shall be provided to store and accurately proportion the dry or slurried lime into the aggregate. The lime and aggregate shall be mixed by pugmill or other Department approved means to achieve a uniform lime coating of the aggregate before entering the drier. If lime is added in dry form, the aggregate shall contain at least 3% free moisture. The Department will not permit the stockpiling of lime treated aggregate.
The feeder system shall be controlled by a proportioning device, which shall be accurate to within 10 percent of the specified amount. The proportioning device shall have a convenient and accurate means of calibration. A flow indicator or sensor shall be provided with the proportioning device and interlocked with the plant controls, aggregate feed, or weigh system, such that production of the mixture shall be consistently maintained and, if there is a stoppage of the lime feed, interrupted.
The method of introducing and mixing the lime and aggregate shall be subject to approval by the Engineer before beginning production.
319.03 – MIX FORMULA
The Contractor shall submit for the Engineer’s approval, a job mix formula within the following design ranges of percent passing each sieve size as noted:
Sieve Size
| Percent By Weight Passing Square Mesh Sieves |
| Production Tolerance (Single Test) |
| 1/2 in |
| 100 |
| -2 |
| 3/8 in |
| 85-100 |
| ± 5 |
| No.4 |
| 25-40 |
| ± 4 |
| No.8 |
| 19-32 |
| ± 4 |
| No.16 |
| 15-23 |
| ± 3 |
| No. 30 |
| 10-18 |
| ± 3 |
| No.50 |
| 8-13 |
| ± 3 |
| No.100 |
| 6-10 |
| ± 2 |
| No. 200 |
| 4-7 |
| ± 1 |
Asphalt Content, %
Production Tolerance (Single Test)
| 5.0 – 5.51 |
| ±0.2 |
1Target asphalt content shall result in a minimum film thickness of 9 microns.
In addition to the job mix submittal, the Contractor shall submit ignition furnace calibration data according to VTM 102 and aggregate property test results prepared by an approved testing laboratory for the aggregate components or aggregate blend.
Job mixes outside the above design range will be considered by the Engineer based on mix performance documented by the supplier to eliminate or minimize flushing or visual deficiencies and may include changes to gradation, asphalt content or the use of fibers. The Engineer may require limited production of less than 300 tons for verification of an acceptable mix, before the Engineer’s approval of the job mix.
319.04 – SURFACE PREPARATION
Before beginning paving operations, the existing pavement surface shall be cleaned of all accumulated dust, mud, vegetation or other debris, which may affect the bond of the THMACO by the Contractor.
Pavement cracks or joints 1/4-inch or more in width shall be cleaned and filled with a sealant material conforming to Section 322.04. Quantities and payment will be according to Section 322.
Pavement markers, thermoplastic pavement marking and tape pavement markings shall be removed before beginning paving operations. Pavement irregularities greater than 1 inch in depth shall be filled with a material designated in the Contract or approved by the Engineer. Payment for the material will be according to Section 315.
Utility structures shall be protected and referenced before paving for location and adjustment (when necessary) after paving at no cost to the Department.
319.05 – Tack Coat Unless otherwise directed in the Contract, two options for placing the tack coat are available.
(a) Option 1: A tack coat of asphalt emulsion conforming to Section 210.04 (e) or other emulsion approved by the Engineer shall be applied before placement of the asphalt concrete. The tack coat shall be placed within 10 seconds prior to placing the THMACO unless otherwise directed by the Engineer. At no time should any part of the paving machine come into contact with the tack coat before the overlay is applied. The emulsion shall be uniformly applied with a paver spray bar, except hand spray equipment may be used in areas inaccessible to the paver spray bar as directed by the Engineer; inaccessible areas are exempt from the 10-second criterion. The asphalt emulsion shall be applied at a temperature recommended by the supplier at a starting rate of 0.20 gallons per square yard ±0.02 unless otherwise approved by the Engineer.
(b) Option 2: A Hot-Applied Non-Tracking tack coat conforming to Section 310 and listed on Approved List No. 50.1A shall be applied before placement of the THMACO. The tack coat shall be uniformly applied with a spray bar paver or a mechanical distributor, except hand spray equipment may be used in areas inaccessible. The tack coat shall be applied at a temperature recommended by the supplier at a residual rate of 0.12 gallons per square yard ±0.02 unless otherwise approved by the Engineer.
319.06 – Placement of Hot Mix Asphalt The horizontal alignment of the longitudinal joint in the THMACO shall align overtop the longitudinal joint in the existing pavement as follows:
- when placed over an existing asphalt pavement, the THMACO joint shall be within 1 inch of either side of the existing joint (2 inch allowable variation, total);
- when placed over an existing concrete pavement, the THMACO joint shall be within 1/4 inch of either side of the existing joint (1/2 inch allowable variation, total).
The application rate of the THMACO shall be a minimum of 80 pounds per square yard and shall have a thickness of between 3/4-inch and 1-inch compacted lift thickness.
THMACO shall be placed by a paver designed for the placement of thin lifts as designated in the Contract. The THMACOshall be delivered to the paver hopper at a temperature of 315°F ±15°F measured in the paver hopper. The paver shall be capable of placing the THMACO at a speed of 30 feet per minute. When the base temperature is 50°F or above, placement of the asphalt concrete wearing course will be permitted.
319.07 – Compaction Two steel double drum rollers weighing no less than 10 tons shall perform compaction of the THMACO. No less than two passes shall be completed before the surface temperature of the THMACO has reached 185°F.
319.08 – Acceptance The Contractor shall perform gradation and asphalt binder content tests on one sample taken in a random manner approved by the Engineer from each 500 tons of production. The material will be considered acceptable for gradation and asphalt binder content, if the results obtained are within the tolerance allowed from the job mix formula in the above table. Material represented by test results outside the tolerance may be removed and replaced with acceptable material by the Contractor at no additional cost to the Department at the discretion of the Engineer.
Should visual examination by the Engineer reveal that the material in any load, or portion of the paved roadway is contaminated, segregated, or flushed with asphaltbinder, that load, or portion of the paved roadway may be rejected without additional sampling of the material.
319.09 – Warranty The Contractor shall provide a one-year warranty from the date of final acceptance on all THMACO surfaces. The Department will periodically monitor the overlay surface installed throughout the warranty period for compliance and acceptability. The Contractor shall repair any area that fails before the end of the warranty period and shall do so within 14 days after Department notification unless otherwise directed by the Department. Failure of the THMACO surface is defined as either: the loss of adhesion of the material to the underlying layer resulting in a pothole greater than 1 square foot of area (delamination); or being flushedwith asphalt binder in greater than 1 square yard of area, either from within the mix or from the underlying tack (flushing). The Engineer shall notify the Contractor of the date for the warranty inspection at the end of the warranty period and the Contractor shall be present at the inspection.
319.10 – Measurement and Payment Thin hot mix asphalt concrete will be measured in tons and paid for at the contract unit price per ton, which shall include warranty, tack coat, surface preparation (except crack and joint sealing), all materials, additives, labor and equipment as described herein to install and complete the work.
Crack and joint sealing will be paid according to Section 322.
Payment will be made under:
| Pay Item |
| Pay Unit |
| Thin Hot Mix Asphalt Concrete |
| Ton |
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