1 Scope
NOTE This specification covers the materials, mix design, execution, and quality control for hot-mix asphalt (HMA) flexible pavement constructed on a prepared aggregate base course. (1.1)
NOTE This standard addresses the HMA mixture types and the role of each course in the section, aggregate gradation and nominal maximum aggregate size, the performance-graded binder grade and its climate dependence, the mix design method and volumetric acceptance, prime and tack coats, reclaimed asphalt pavement content, field quality control for density and thickness and smoothness, and the execution of subgrade and base verification, prime and tack application, placement temperature, lift thickness, compaction, and joint construction. (1.2)
NOTE Asphalt pavement is a layered, flexible system in which each course carries load by flexing slightly and distributing wheel loads downward over an increasing area, so that the stress reaching the subgrade is a small fraction of the contact stress at the tire, and the system performs only as well as its weakest layer. (1.3)
NOTE A surface course placed over a deficient base, or a properly designed mix compacted to inadequate density, fails prematurely regardless of how good the other elements are, and the cost of correcting an asphalt defect after the pavement is opened to traffic vastly exceeds the cost of placing it correctly the first time. (1.4)
NOTE Predecessor work — the aggregate base course on which this pavement is placed — is covered by
Aggregate Base Course, and the subgrade beneath the base is covered by
Earthwork.
(1.5) 1.6The Contractor placing asphalt shall not place asphalt over an aggregate base that has not been accepted.
1.7All work under this specification shall conform to the pavement section, course thicknesses, limits, grades, and drainage shown on the contract drawings and to the recommendations of the geotechnical report.
1.8Where this standard and the geotechnical or pavement-design report conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
1.9The pavement section thicknesses shown on the drawings are design-specific and are not subject to reduction, and the Contractor shall not thin a course to compensate for a high base or to economize on material.
2 Referenced Standards
2.1Materials, mix design, testing, and execution shall comply with the latest adopted edition of the following standards.
| Standard |
Title |
| AASHTO M 323 |
Standard Specification for Superpave Volumetric Mix Design |
| AASHTO R 35 |
Standard Practice for Superpave Volumetric Design for Asphalt Mixtures |
| AASHTO M 320 |
Standard Specification for Performance-Graded Asphalt Binder |
| AASHTO M 332 |
Standard Specification for Performance-Graded Asphalt Binder Using Multiple Stress Creep Recovery (MSCR) Test |
| AASHTO T 350 |
Standard Method of Test for Multiple Stress Creep Recovery (MSCR) Test of Asphalt Binder Using a Dynamic Shear Rheometer (DSR) |
| AASHTO T 209 |
Standard Method of Test for Theoretical Maximum Specific Gravity (Gmm) and Density of Asphalt Mixtures |
| AASHTO T 166 |
Standard Method of Test for Bulk Specific Gravity (Gmb) of Compacted Asphalt Mixtures Using Saturated Surface-Dry Specimens |
| ASTM D6373 |
Standard Specification for Performance-Graded Asphalt Binder |
| ASTM D2041/D2041M |
Standard Test Method for Theoretical Maximum Specific Gravity and Density of Asphalt Mixtures |
| ASTM D6307 |
Standard Test Method for Asphalt Content of Asphalt Mixture by Ignition Method |
| ASTM D2950/D2950M |
Standard Test Method for Density of Asphalt Mixtures in Place by Nuclear Methods |
| ASTM D6926 |
Standard Practice for Preparation of Asphalt Mixture Specimens Using Marshall Apparatus |
| ASTM D6927 |
Standard Test Method for Marshall Stability and Flow of Asphalt Mixtures |
| ASTM D946/D946M |
Standard Specification for Penetration-Graded Asphalt Binder for Use in Pavement Construction (legacy) |
| ASTM D2995 |
Standard Practice for Estimating Application Rate and Residual Application Rate of Bituminous Distributors |
| ASTM D6690 |
Standard Specification for Joint and Crack Sealants, Hot Applied, for Concrete and Asphalt Pavements |
| ASTM D5821 |
Standard Test Method for Determining the Percentage of Fractured Particles in Coarse Aggregate |
| ASTM C131/C131M |
Standard Test Method for Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine |
| ASTM C88/C88M |
Standard Test Method for Soundness of Aggregates by Use of Sodium Sulfate or Magnesium Sulfate |
| Asphalt Institute MS-2 |
Asphalt Mix Design Methods |
| Asphalt Institute MS-19 |
Basic Asphalt Emulsion Manual |
2.2Where project documents, adopted codes, and referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
NOTE Mixtures shall be designed and accepted under the Superpave volumetric framework (AASHTO M 323 / R 35) or the Marshall method (ASTM D6926 / D6927) as specified herein, and shall not be accepted under the withdrawn ASTM D3515. (2.3)
NOTE Performance-graded (PG) binder per AASHTO M 320 or M 332 is the default, and penetration-graded binder (ASTM D946) is a legacy grading system retained only where a local authority still specifies it. (2.4)
3 Submittals
3.1 Action Submittals
3.1.1The Contractor shall submit the following for the Engineer of Record's review before delivering any asphalt mixture to the site:
- Job-mix formula (JMF) for each mixture and course, prepared under the specified mix design method, showing the design aggregate gradation against the control points for the specified nominal maximum aggregate size, the design binder content, and the volumetric properties at the design number of gyrations or Marshall blows (air voids, voids in the mineral aggregate, voids filled with asphalt, and dust-to-binder ratio)
- Performance-graded asphalt binder certification (certificate of analysis) for the specified PG grade, traceable to the supply terminal lot, confirming compliance with AASHTO M 320 or M 332
- Aggregate gradation analysis for each aggregate stockpile feeding each mixture, and the combined gradation of the JMF
- Aggregate quality test results: Los Angeles abrasion (ASTM C131/C131M), sulfate soundness (ASTM C88/C88M), and percentage of fractured faces (ASTM D5821) for the coarse aggregate
- Reclaimed asphalt pavement (RAP) characterization where RAP is proposed: source, gradation of the extracted aggregate, recovered binder content, and the resulting blended binder grade
- Prime coat and tack coat material product data and the proposed application rates
- Mix design verification or prior approval letter from the producing plant's certified laboratory, or from the state DOT where the plant holds a current approved-mix listing that matches the specified mixture
☐ Job-mix formula (JMF) for each course
☐ PG binder certificate of analysis
☐ Aggregate gradation analysis (each stockpile + combined)
☐ Aggregate quality (L.A. abrasion, soundness, fractured faces)
☐ RAP characterization (where RAP is used)
☐ Prime and tack coat product data and application rates
☐ Plant mix design verification / DOT approved-mix listing
3.1.2The Contractor shall submit the action submittal items listed above for the Engineer of Record's review before delivering any asphalt mixture to the site.
3.1.3Paving shall not begin until the submittals are reviewed and returned.
3.1.4Submittal review does not relieve the Contractor of responsibility for compliance with the contract documents.
3.2 Closeout Submittals
3.2.1Prior to substantial completion the Contractor shall provide the following:
- Field and plant test reports for asphalt content, gradation, volumetrics, in-place density, and core thickness, indexed to lot, course, and location, and signed by the testing technician
- Daily placement records showing tonnage placed by course, ambient and mix temperatures, and the areas paved each day
- As-built record of finished pavement surface elevations and course thicknesses sufficient to confirm conformance with the drawings and with the thickness and smoothness tolerances of this specification
- Material certifications for the binder and aggregate sources delivered, including any source changes during construction
- Manufacturer's and Contractor's warranty documentation as required by this specification
☐ Field and plant test reports (asphalt content, gradation, volumetrics, density, core thickness)
☐ Daily placement records (tonnage by course, temperatures, areas paved)
☐ As-built record of surface elevations and course thicknesses
☐ Material certifications (binder and aggregate sources, including source changes)
☐ Manufacturer's and Contractor's warranty documentation
3.2.2Prior to substantial completion the Contractor shall provide the closeout submittal items listed above.
4 Quality Assurance
4.1 Asphalt Producer Qualifications
○ Current state DOT plant certification with matching approved-mix listing
○ Plant quality-control program submitted and approved by Engineer of Record
○ Per local Authority Having Jurisdiction certification program
4.1.1The asphalt mixture shall be produced by a plant with a current quality-control program and, where the Authority Having Jurisdiction maintains a producer-certification program, a current certification.
4.1.2The plant shall be capable of producing the specified mixture at the specified rate, maintaining mix temperature within the limits specified herein during loading and haul, and providing certified plant test data for each lot.
4.1.3Where the plant does not hold a current state DOT certification and an approved-mix listing matching the specified mixture, the Contractor shall submit the plant's quality-control plan and recent production test history for the Engineer of Record's review.
4.2 Mix Design Approval
NOTE Approval confirms that the gradation falls within the control points for the specified nominal maximum aggregate size, that the design binder content produces the specified air void content at the design compactive effort, and that the volumetric properties meet the requirements of the specified mix design method. (4.2.1)
4.2.2Each job-mix formula shall be approved by the Engineer of Record before production begins.
4.2.3A JMF that was approved on a prior project may be reused only if the aggregate sources, the binder grade, and the RAP content are unchanged.
4.2.4Any change in aggregate source or RAP fraction requires a new or revised JMF and re-approval.
NOTE The volumetrics shift with aggregate shape, absorption, and the stiffness contributed by recovered RAP binder, which is why a source or RAP change requires re-approval. (4.2.5)
4.3 Independent Testing Agency
○ Owner-retained testing agency (independent of Contractor)
○ Contractor-retained agency with Owner approval — non-structural areas only
4.3.1Acceptance testing for in-place density, thickness, and mixture properties shall be performed by a qualified independent testing agency retained by the Owner.
4.3.2Testing for acceptance shall not be performed by the Contractor or by an agency under the Contractor's direction, because the testing entity must be independent of the party whose work it accepts.
4.3.3The testing agency shall be experienced in HMA testing, equipped with calibrated nuclear density gauges and a coring rig, and capable of providing results within the reporting times required by this specification.
4.4 Pre-Construction Conference
4.4.1Before paving begins the Contractor shall participate in a pre-construction conference attended by the Contractor's paving superintendent, the asphalt producer's representative, the testing agency, and the Engineer of Record.
4.4.2The conference shall review the approved job-mix formulas, the pavement section and course sequence, the prime and tack coat materials and rates, the placement temperature and weather limits, the lift thickness and compaction requirements, the density and smoothness acceptance criteria, the joint construction details, the procedure for handling failing density and thickness results, and the lines of communication for field decisions.
5 Environmental and Service Conditions
5.1 Minimum Surface and Air Temperature for Placement
40°F surface, rising — surface and intermediate courses ≥ 1-1/2 in. lift
50°F surface, rising — thin surface course < 1-1/2 in. lift
60°F surface, rising — thin lifts and cold/windy conditions
Per producer recommendation for the specified mix and lift
NOTE Hot-mix asphalt loses heat to the surface it is placed on and to the air, and compaction must be completed before the mat cools below the temperature at which the binder is workable, so the minimum placement temperature depends on the compacted lift thickness because thicker lifts retain heat longer and tolerate cooler conditions. (5.1.1)
5.1.2The surface on which asphalt is placed shall be dry.
5.1.3HMA shall not be placed on a wet, frozen, or frost-covered base, because trapped moisture flashes to steam under the hot mat and disrupts the bond and a frozen base thaws beneath the new pavement to create a low-density layer that propagates as a settlement defect.
5.1.4The Contractor shall measure surface temperature, not just air temperature, before placement.
5.2 Seasonal Paving Window
○ Standard season — placement when surface temperature and weather limits are met
○ Surface course deferred to favorable weather; base/intermediate placed in shoulder season
○ No paving during the locally defined winter shutdown period
NOTE The surface course is the most sensitive to cold-weather placement because it is the thinnest course and cools fastest. (5.2.1)
5.2.2Where the schedule forces base and intermediate courses to be placed in marginal weather, the Engineer of Record may permit deferral of the surface course to a period of favorable weather, with the intermediate course serving as a temporary wearing surface.
5.2.3Deferral of the surface course shall be documented so that the surface course obligation is not lost at closeout.
5.3 Wind and Rain
5.3.1Paving shall be suspended at the onset of rain and shall not resume until the base surface is dry.
5.3.2Mix in transit or in the paver hopper at the time rain begins shall be evaluated for temperature loss, and mix that has cooled below the minimum compaction temperature shall be wasted rather than placed.
5.3.3High wind accelerates surface cooling and shall be treated as a reduction in the available compaction window, narrowing the conditions under which thin lifts can be placed.
6 HMA Mixture Types and Courses
6.1 Course Function in the Pavement Section
NOTE A flexible pavement section is built from the base up, and each course has a distinct function that drives its mixture design. (6.1.1)
○ Surface (wearing) course
○ Intermediate (binder) course
○ Asphalt base course
NOTE The asphalt base course (where used) is the lowest asphalt-bound layer, placed directly on the aggregate base, and carries the largest structural contribution per inch of any asphalt course using the largest nominal maximum aggregate size. (6.1.2)
NOTE The intermediate (binder) course bridges between the base and the surface, providing structural depth, leveling out irregularities in the layer beneath it, and establishing the plane on which the surface course is placed. (6.1.3)
NOTE The surface (wearing) course is the layer exposed to traffic and weather, uses the smallest nominal maximum aggregate size to provide a dense, tight, smooth, durable, skid-resistant surface, and is designed for durability and impermeability as much as for structural contribution. (6.1.4)
NOTE A typical commercial parking lot uses a single surface course over an intermediate course, and a heavy-duty truck or drive lane adds an asphalt base course or increases the intermediate-course thickness. (6.1.6)
7 Aggregate Gradation and Nominal Maximum Aggregate Size
7.1 Nominal Maximum Aggregate Size
9.5 mm — surface course, thin lifts and tight texture
12.5 mm — surface or intermediate course (most common)
19 mm — intermediate or base course
25 mm — asphalt base course, heavy-duty sections
NOTE The nominal maximum aggregate size (NMAS) is the controlling gradation parameter for an HMA mixture, with a smaller NMAS producing a finer, denser, lower-permeability surface and a larger NMAS producing a coarser, stiffer, more economical mix suited to lower courses. (7.1.1)
7.1.2The NMAS shall be matched to the course and to the compacted lift thickness.
7.1.3The compacted lift thickness shall be at least three times the NMAS for fine-graded mixes and at least four times the NMAS for coarse-graded mixes, so that the largest particles can reorient under the roller rather than locking and fracturing.
7.2 Gradation Control Points
7.2.1The combined aggregate gradation shall fall within the control points of AASHTO M 323 for the specified nominal maximum aggregate size, and shall avoid the restricted zone guidance such that the mixture is a well-graded, dense mixture rather than a tender, fine-sand-prone gradation.
7.2.2The job-mix formula gradation, once approved, becomes the target, and production gradation shall track the JMF within the production tolerances rather than wandering anywhere within the broad control-point band.
NOTE A gradation that drifts within the band from truck to truck produces a mat with variable density, variable permeability, and variable durability even though every individual sample is within specification. (7.2.3)
7.3 Aggregate Quality
○ 85 percent with two or more fractured faces (light/medium traffic)
○ 95 percent with two or more fractured faces (heavy traffic, drive lanes)
○ Per pavement design ESAL category
NOTE Angular crushed faces interlock under load and resist rutting, while rounded, uncrushed gravel particles roll past one another and the mix shoves and ruts under traffic. (7.3.1)
7.3.2Coarse aggregate shall be crushed, angular, and durable.
7.3.3The aggregate shall resist mechanical breakdown during mixing, placement, and compaction, as measured by Los Angeles abrasion (ASTM C131/C131M).
7.3.4The aggregate shall resist weathering breakdown over the pavement service life, as measured by sulfate soundness (ASTM C88/C88M).
8.1 PG Binder Grade Selection
PG 58-28 (cold climate, standard traffic)
PG 64-22 (temperate climate, standard traffic — most common)
PG 64-28 (temperate climate, improved low-temperature performance)
PG 70-22 (warm climate or elevated traffic — polymer-modified)
PG 76-22 (heavy/slow traffic, intersections — polymer-modified)
Per project location climate map and traffic
NOTE The performance-graded (PG) binder is designated PG XX-YY, where the first number is the upper pavement temperature the binder must resist without rutting and the second is the lower temperature it must resist without thermal cracking. (8.1.1)
NOTE Specifying a binder grade that does not match the climate is a common and consequential error, because too soft a high grade rutts in summer and too stiff a low grade cracks in winter. (8.1.2)
8.1.3The binder grade shall be selected for the project climate, with the high-temperature grade keyed to the seven-day average maximum pavement temperature and the low-temperature grade keyed to the minimum pavement temperature, both adjusted for the desired reliability.
8.1.4The local climate-appropriate base grade shall be confirmed against the project location using the Asphalt Institute and state DOT binder maps, because PG 64-22 is the most common temperate-US grade but is not universal.
8.2 Traffic Grade Bumping and MSCR Designation
○ AASHTO M 320 — PG grade, traffic addressed by grade bumping
○ AASHTO M 332 — PG grade with MSCR traffic designation (S/H/V/E)
○ Per local Authority Having Jurisdiction adopted system
S — Standard traffic (< 0.3 million ESALs, fast moving)
H — Heavy traffic (3 to 10 million ESALs or slow)
V — Very heavy traffic (10 to 30 million ESALs or standing)
E — Extremely heavy traffic (> 30 million ESALs or standing)
Not applicable — M 320 grade-bumping system used
8.2.1Where traffic is heavy, slow, or standing — truck drive lanes, loading docks, bus stops, and intersection approaches — the binder high-temperature grade should be increased ("bumped") one or two grades above the climate base grade to resist rutting under the longer load duration.
NOTE Under the MSCR specification (AASHTO M 332), traffic is addressed by a grade letter (S, H, V, or E for standard, heavy, very heavy, or extremely heavy loading) appended to the base PG grade and verified by the non-recoverable creep compliance (Jnr) from the MSCR test (AASHTO T 350), rather than by bumping the high-temperature number. (8.2.2)
8.2.3Either the M 320 grade-bumping system or the M 332 MSCR designation is acceptable where it is the locally adopted convention.
9 Mix Design and Volumetrics
9.1 Mix Design Method
○ Superpave volumetric (AASHTO M 323 / R 35) — default
○ Marshall method (ASTM D6926 / D6927) — where locally adopted
NOTE The Superpave volumetric method (AASHTO M 323 with AASHTO R 35) is the default mix design method, compacting trial specimens in a gyratory compactor to a number of gyrations selected for the design traffic level and accepting the mixture on its volumetric properties at that compactive effort rather than on a stability load. (9.1.1)
NOTE The Marshall method (ASTM D6926 for specimen preparation and ASTM D6927 for stability and flow) is a legacy method that compacts specimens with a drop hammer at 35, 50, or 75 blows per face and accepts the mix on stability, flow, and air voids. (9.1.2)
9.1.3The Marshall method shall be used only where it is the locally adopted method or where the project is too small to justify a gyratory design.
9.2 Design Compactive Effort
50 gyrations — low traffic (< 0.3 million ESALs)
65 gyrations — medium traffic (0.3 to 3 million ESALs)
75 gyrations — medium-high traffic (3 to 10 million ESALs)
100 gyrations — high traffic (10 to 30 million ESALs)
Per pavement design ESAL category
○ 35 blows per face — light traffic, parking stalls
○ 50 blows per face — medium traffic
○ 75 blows per face — heavy traffic, drive lanes
○ Not applicable — Superpave method used
9.2.1The design number of gyrations (Ndesign) for a Superpave mix shall be selected for the design traffic expressed in equivalent single-axle loads (ESALs) over the design life.
NOTE Selecting too high a gyration count for a low-traffic lot produces a dry, low-binder mix that is brittle and prone to raveling and cracking, and selecting too low a count for a heavy-traffic drive produces a rich mix that ruts. (9.2.2)
9.3 Design Air Void Content
NOTE The design air void content is the volumetric target that governs binder content, because the binder content is selected to produce the design air voids at the design compactive effort. (9.3.1)
NOTE Four percent air voids is the long-standing Superpave design target and is appropriate for the great majority of mixtures. (9.3.2)
NOTE Too few design air voids produces a rich mix that bleeds and ruts, and too many produces a dry, permeable mix that ages quickly, ravels, and admits water into the section. (9.3.3)
9.4 Voids in the Mineral Aggregate and Dust-to-Binder Ratio
9.4.1The voids in the mineral aggregate (VMA) shall meet the minimum for the nominal maximum aggregate size, because VMA is the space available to hold both the design air voids and enough binder for durability.
9.4.2The dust-to-binder ratio (the ratio of material passing the No. 200 sieve to the effective binder content) shall fall within the specified range.
NOTE Excess dust stiffens the mix and reduces its fatigue resistance, while too little dust produces a tender mix. (9.4.3)
9.4.4The VMA and dust-to-binder ratio are part of mix design approval and shall be verified in production.
10 Reclaimed Asphalt Pavement (RAP)
0 percent — virgin mix only (surface course, premium applications)
15 percent — surface course, no binder grade adjustment required
25 percent — intermediate and base courses
30 percent — base course with softened virgin binder grade
Per approved JMF and local Authority Having Jurisdiction limit
NOTE Reclaimed asphalt pavement (RAP) is milled or crushed existing asphalt that is processed and incorporated into new HMA, recovering both the aggregate and the aged binder, which reduces material cost and conserves resources but introduces oxidized, stiff recovered binder. (10.1)
10.2The allowable RAP content shall be limited based on the course, the traffic, and whether the binder grade is adjusted for the RAP contribution.
10.3Where the RAP content exceeds the fraction at which no binder adjustment is required (commonly about 15 to 20 percent of total binder), the virgin binder grade shall be softened one grade on the low-temperature side, or the blended binder grade shall be verified by testing the recovered-plus-virgin blend, so that the in-place mixture meets the specified PG grade.
10.4RAP shall be of consistent, characterized source.
10.5Commingled or unknown-source RAP shall not be used in surface courses.
11 Prime Coat
NOTE A prime coat is a low-viscosity asphalt material applied to an untreated aggregate base to penetrate and bind the surface of the base, promote adhesion between the base and the first asphalt course, and limit moisture intrusion before paving. (11.1)
○ Required — penetrating prime on untreated aggregate base
○ Not required — dense-graded base too tight to accept prime; use tack coat
○ Per geotechnical engineer / local practice
Emulsified asphalt prime (per Asphalt Institute MS-19)
Cutback asphalt prime (where permitted by air-quality regulations)
Per local Authority Having Jurisdiction
0.150.4
Default: 0.25 gal/sq yd
NOTE On a tight, dense, well-compacted dense-graded aggregate base, a true penetrating prime often cannot penetrate, so a prime coat may be omitted in favor of a tack coat, and the need for a prime coat depends on the base type and local practice. (11.2)
12 Tack Coat
NOTE A tack coat is a thin application of diluted asphalt emulsion applied between asphalt courses (and between asphalt and any abutting existing pavement or vertical face) to bond the lifts into a monolithic section. (12.1)
Asphalt emulsion, slow-setting (SS-1, SS-1h) diluted
Asphalt emulsion, rapid-setting (CRS / RS) for cooler conditions
Trackless / non-tracking tack emulsion
Per Asphalt Institute MS-19 and local practice
0.020.1
Default: 0.05 gal/sq yd
NOTE The bond between lifts is essential to flexible-pavement performance, because an unbonded interface allows the courses to slip independently, concentrating stress and producing slippage cracking, debonding, and premature surface failure. (12.2)
NOTE Tack coat is one of the lowest-cost and most frequently shortchanged elements of asphalt paving, and too little, applied unevenly, or contaminated by tracking, the bond fails. (12.3)
NOTE The application rate is expressed as residual (undiluted) asphalt per square yard, and the as-sprayed rate of diluted emulsion is higher in proportion to the dilution. (12.4)
NOTE New, clean asphalt surfaces require a lower tack rate, and milled, oxidized, or dusty surfaces require a higher rate. (12.5)
12.6The tack coat shall be allowed to break (the emulsion color shall turn from brown to black) before the overlying course is placed, so that the water has left the emulsion and the residual asphalt is in place to bond.
12.7The distributor application rate shall be verified per ASTM D2995.
12.8Tracking of tack coat by construction traffic onto adjacent surfaces and out of the paving area shall be controlled, because tracked-away tack leaves bare spots that do not bond.
13 Field Quality Control and Testing
13.1 In-Place Density
9197
92939495
Default: 92 percent of theoretical maximum specific gravity (Gmm)
○ Cores tested per AASHTO T 166 (Gmb) — reference / dispute method
○ Nuclear gauge per ASTM D2950/D2950M, correlated to cores
○ Both — nuclear for production, cores for verification
NOTE In-place density is the most important single acceptance parameter for asphalt pavement, because the long-term durability of an otherwise sound mix is governed almost entirely by how well it is compacted. (13.1.1)
NOTE Under-compacted asphalt has high in-place air voids, and those interconnected voids admit water and air, the binder oxidizes and embrittles, and the pavement ravels and cracks years before its design life. (13.1.2)
13.1.3Density shall be specified and accepted as a percentage of the theoretical maximum specific gravity (Gmm, the "Rice" value) of the mixture, determined per AASHTO T 209 or ASTM D2041.
13.1.4In-place density shall be a minimum of 92 percent of theoretical maximum specific gravity (Gmm) — equivalently, a maximum of 8 percent in-place air voids — for surface and intermediate courses, unless the pavement design or local DOT specification requires a higher value.
NOTE A density above approximately 97 percent of Gmm (below about 3 percent in-place voids) is undesirable because it leaves insufficient void space and the mix becomes prone to flushing and rutting, so the acceptance range has both a floor and a practical ceiling. (13.1.5)
13.1.6The nuclear gauge (ASTM D2950/D2950M) is the standard production method, but it shall be correlated to pavement cores tested for bulk specific gravity (Gmb) per AASHTO T 166 at the start of production and periodically thereafter.
13.1.7Where nuclear and core results disagree, the core result governs.
13.2 Joint Density
NOTE The longitudinal joint between adjacent paver passes and the transverse joint between a day's work and the next are the most common locations of low density and the first places a pavement fails. (13.2.1)
13.2.2The joint shall be compacted to a density not more than 2 percent below the specified mat density.
NOTE Confined (hot) longitudinal joints, made by paving the adjacent lane while the first is still hot or by overlapping a hot lane against a freshly placed one, achieve better density than cold joints made against a cooled, cut edge. (13.2.3)
13.3 Course Thickness
○ Minus 0, plus 1/4 in. from design compacted thickness (surface course)
○ Plus or minus 1/4 in. from design compacted thickness (intermediate/base)
○ Per pavement section detail
13.3.1Each course shall be placed to the compacted thickness shown on the pavement section.
13.3.2Thickness shall be verified by cores or by survey of top-of-course elevations against the accepted surface beneath.
NOTE Deficient thickness reduces the structural capacity of the section in direct proportion and is not correctable except by removal and replacement or by an additional overlay. (13.3.3)
13.3.4The Contractor shall not place a deficient lift in the expectation of making up thickness in the next course.
13.4 Surface Smoothness
○ Maximum deviation 1/4 in. in 10 ft (surface course)
○ Maximum deviation 3/8 in. in 10 ft (intermediate course)
○ Per project specification
NOTE Beyond ride quality, smoothness governs drainage, because a wavy surface ponds water and standing water on asphalt accelerates stripping of the binder from the aggregate and creates a hydroplaning and icing hazard. (13.4.1)
13.4.2The finished surface shall be smooth and true to grade and cross slope, checked with a 10-foot straightedge laid in any direction.
13.5 Asphalt Content and Volumetrics in Production
○ Ignition method (ASTM D6307)
○ Solvent extraction
○ Plant automated batch records with periodic ignition verification
13.5.2The theoretical maximum specific gravity (Gmm) shall be determined per AASHTO T 209 / ASTM D2041 on production samples to establish the density reference and to confirm that the in-place air voids fall in the acceptable range.
13.5.3Production binder content, gradation, and volumetrics shall track the approved JMF within the production tolerances, and drift beyond tolerance is cause to suspend production and recover the mix to target.
13.6 Testing Frequency
13.6.1Minimum acceptance-testing frequencies, in the absence of a more stringent project or DOT requirement, shall be as listed below.
- One in-place density lot per day's production per course, with cores or nuclear readings at the frequency required to characterize the lot (commonly one test per 250 tons or one per defined sublot)
- One asphalt content and gradation test per 500 to 750 tons of mixture produced, or one per day per mixture, whichever is more frequent
- One theoretical maximum specific gravity (Gmm) determination per day per mixture, and whenever the JMF or source changes
- Core thickness verification at the locations and frequency directed by the Engineer of Record, with a minimum of one core per defined paving area per course
- Smoothness checked over the full paved area
1 lot per day per course
1 test per 250 tons (or defined sublot)
1 test per 500 tons
Per local Authority Having Jurisdiction / DOT
13.6.2Minimum acceptance-testing frequencies, in the absence of a more stringent project or DOT requirement, shall be as listed above for density, asphalt content and gradation, theoretical maximum specific gravity, core thickness, and smoothness.
13.7 Failing Tests
13.7.1When an acceptance test fails — low density, deficient thickness, out-of-tolerance binder content, or excessive surface deviation — the Contractor shall stop placing additional pavement in the affected area, determine the cause, and remediate before proceeding.
13.7.2Low-density mat that has cooled shall be removed and replaced, because the binder is no longer workable and rolling a cold mat only crushes aggregate at the surface.
13.7.3Deficient thickness shall be corrected by removal and replacement or by an approved overlay.
13.7.4The Contractor shall not conceal failing results, and a pattern of unreported failures discovered at closeout requires coring, density verification, and removal and replacement at the Contractor's expense.
14 Installation and Execution
14.1 Verification of Subgrade and Base
14.1.1The Contractor shall verify that the aggregate base course has been placed, compacted, proof-rolled, and accepted in accordance with Aggregate Base Course, and that the subgrade beneath it was prepared in accordance with Earthwork, before placing any asphalt. 14.1.2The base surface shall be at the correct elevation and cross slope within the surface tolerances of the base course specification, shall be clean and free of loose material and standing water, and shall be dry and unfrozen.
NOTE Defects in the base telegraph directly into the asphalt, and the Contractor placing asphalt accepts the base condition by paving over it. (14.1.3)
14.1.4The Contractor shall report any deficiency in the base rather than paving over it.
14.2 Prime and Tack Application
14.2.1Where a prime coat is required, it shall be applied to the accepted base at the specified rate and allowed to cure and penetrate before the first asphalt course is placed.
14.2.2Tack coat shall be applied uniformly to the underlying asphalt course (and to any vertical faces, abutting existing pavement, curbs, gutters, and structures the new asphalt will contact) at the specified residual rate, and shall be allowed to break before the overlying course is placed.
14.2.3The tacked surface shall be protected from contamination and tracking until the overlying mat covers it.
14.2.4Curbs, gutters, manhole frames, and structures within the paving area shall be protected from overspray.
14.3 Placement Temperature
250°F — minimum for unmodified binder, thick lift, warm conditions
275°F — typical minimum for unmodified PG binder
290°F — minimum for polymer-modified binder
Per producer recommendation for the specified mix
14.3.1The mixture shall arrive at the paver, and shall be placed, within the temperature range established by the producer for the specified binder grade and mix, typically in the range of about 275°F to 325°F at placement for unmodified PG binders and higher for polymer-modified binders.
14.3.2Mix delivered below the minimum placement temperature shall be rejected, because cold mix cannot be compacted to density and tears and segregates under the screed.
14.3.3Hauling units shall be insulated and tarped to retain heat, and the haul shall be scheduled so that mix is not held so long that it cools or the binder ages.
14.4 Lift Thickness
1-1/2 in. — 9.5 mm surface mix
2 in. — 12.5 mm surface/intermediate mix
3 in. — 19 mm intermediate/base mix
4 in. — 25 mm base mix
Per pavement section detail
14.4.1Each course shall be placed in a compacted lift thickness appropriate to its nominal maximum aggregate size, with the compacted lift at least three to four times the NMAS so that the aggregate can reorient under the roller.
NOTE Thicker lifts retain heat and compact more readily but are limited by the paver and screed capability and by the course thickness shown on the drawings, while thinner lifts cool fast and are difficult to compact in cold or windy conditions. (14.4.2)
14.4.3Where the total course thickness exceeds the maximum single-lift thickness, the course shall be placed in multiple lifts, each compacted before the next is placed, with a tack coat between lifts.
14.5 Compaction
☐ Vibratory steel-wheel roller (breakdown)
☐ Pneumatic-tired roller (intermediate, kneading)
☐ Static steel-wheel roller (finish)
☐ Per test-strip-established rolling pattern
NOTE Breakdown rolling immediately behind the paver achieves most of the density, intermediate rolling follows, and finish rolling removes roller marks. (14.5.1)
14.5.2Compaction shall begin as soon as the mat will support the roller without excessive displacement and shall be completed before the mat cools below the lower compaction temperature limit.
14.5.3The roller pattern (number of passes, vibration on or off, sequence) shall be established by a test strip at the start of paving and adjusted to achieve the specified density consistently.
14.5.4The Contractor shall not over-roll a cooling mat, which crushes surface aggregate and decompacts the mat, nor allow the mat to cool before the specified density is reached.
14.6 Joint Construction
○ Confined (hot) joint — adjacent lane paved while first is hot (preferred)
○ Cold joint — vertical face tacked before adjacent lane is placed
○ Notched-wedge joint
○ Hot-applied joint sealant per ASTM D6690
○ None — confined hot joints, no sealant required
○ Per project specification
14.6.1Longitudinal joints (between adjacent paver passes) and transverse joints (between a day's work and the next) shall be constructed to achieve density and a tight, durable bond.
14.6.2Longitudinal joints shall be offset between courses so that the joints in successive lifts do not stack vertically, and shall be located on lane lines or pavement-marking lines as indicated on the striping plan rather than in a wheel path. 14.6.3Transverse joints shall be formed by a transverse bulkhead or by sawcutting and removing the tapered cold end of the previous day's mat to expose a full-depth vertical face, which is then tacked before paving resumes.
14.6.4Where a joint sealant is specified at the asphalt-to-concrete interface (against curbs, gutters, structures, or adjacent rigid pavement) or at constructed cracks, the sealant shall be a hot-applied joint and crack sealant conforming to ASTM D6690 of the type matching the project's service temperature range.
NOTE On well-constructed confined hot longitudinal joints in a new asphalt lot, a separate sealant is generally not required. (14.6.5)
15 Delivery, Storage, and Handling
NOTE Asphalt mixture is a perishable, time-and-temperature-sensitive product. (15.1)
○ Approved non-petroleum release agent
○ Soap/water solution
○ Diesel or solvent — PROHIBITED
15.2Asphalt mixture shall be delivered in clean hauling units, insulated and covered to retain heat, and shall be discharged into the paver before it cools below the minimum placement temperature or the binder ages from prolonged holding.
15.3Loads that have crusted, segregated, or cooled below the minimum temperature shall be rejected.
15.4The bed of each hauling unit shall be coated with an approved non-petroleum release agent.
15.5Diesel fuel and other solvents shall not be used as a release agent, because they dissolve the binder and contaminate the mix.
15.6Bulk asphalt binder at the plant shall be stored at the producer's recommended temperature, because overheating or prolonged storage ages the binder and shifts its grade.
15.7Emulsion for prime and tack coats shall be stored above its minimum storage temperature to prevent the emulsion from breaking in storage, and shall be circulated or agitated per the manufacturer's instructions so that it does not separate.
15.8Aggregate stockpiles at the plant shall be managed to prevent segregation, cross-contamination between stockpiles, and excessive moisture, because wet aggregate requires additional burner energy to dry and ages the binder during mixing.
16 Warranty
1 year from substantial completion
2 years from substantial completion
16.1The Contractor shall warrant the asphalt paving, including achievement of the specified mixture properties, in-place density, course thickness, smoothness, and joint construction, for the project warranty period beginning at substantial completion.
16.2Warranty obligations include correction of raveling, rutting, shoving, slippage cracking, premature fatigue cracking, debonding between lifts, and surface drainage defects (birdbaths) attributable to non-conforming materials or workmanship.
16.3The warranty does not relieve the Contractor of liability for concealed non-conforming work discovered after the warranty period expires.
16.4Distress that develops after the warranty period and is traceable to inadequate compaction, deficient thickness, out-of-tolerance mixture, omitted or deficient tack coat, or undocumented failing tests may constitute a latent defect extending the Contractor's responsibility beyond the warranty term.
16.5Normal weathering, oxidation, and routine maintenance such as crack sealing and seal coating are Owner maintenance obligations and are not warranty items.