F - UFC 3-250-03 Standard Practice for Flexible Pave.pdf

UFC 3-250-03

30 May 2018

UNIFIED FACILITIES CRITERIA (UFC)

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED

O&M MANUAL:

STANDARD PRACTICE

FOR FLEXIBLE PAVEMENTS

UNIFIED FACILITIES CRITERIA (UFC)

O&M MANUAL: STANDARD PRACTICE FOR FLEXIBLE PAVEMENTS

Any copyrighted material included in this UFC is identified at its point of use. Use of the copyrighted material apart from this UFC must have the permission of the copyright holder.

Use of the name or mark of any specific manufacturer, commercial product, commodity, or service in this UFC does not imply endorsement by the Department of Defense.

U.S. ARMY CORPS OF ENGINEERS (Preparing Activity)

NAVAL FACILITIES ENGINEERING COMMAND

AIR FORCE CIVIL ENGINEER CENTER

Record of Changes (changes are indicated by \1\ ... /1/)

Change No. Date Location

This UFC supersedes UFC 3-250-03, dated 15 May 2001, Air Force ETL 01-7, dated 5 June 2017, and Air Force ETL 01-9, dated 17 July 2001.

FOREWORD

The Unified Facilities Criteria (UFC) system is prescribed by MIL-STD 3007 and provides planning, design, construction, sustainment, restoration, and modernization criteria, and applies to the Military Departments, the Defense Agencies, and the DoD Field Activities in accordance with USD(AT&L) Memorandum dated 29 May 2002. UFC is used for all DoD projects and work for other customers where appropriate. All construction outside of the United States is also governed by Status of Forces Agreements (SOFA), Host Nation Funded Construction Agreements (HNFA), and in some instances, Bilateral Infrastructure Agreements (BIA).

Therefore, the acquisition team must ensure compliance with the more stringent of the UFC, the SOFA, the HNFA, and the BIA, as applicable.

UFC are living documents and is periodically reviewed, updated, and made available to users as part of the Services’ responsibility for providing technical criteria for military construction.

Headquarters, U.S. Army Corps of Engineers (HQUSACE), Naval Facilities Engineering Command (NAVFAC), and Air Force Civil Engineer Center (AFCEC) are responsible for administration of the UFC system. Defense agencies should contact the preparing service for document interpretation and improvements. Technical content of UFC is the responsibility of the cognizant DoD working group. Recommended changes with supporting rationale should be sent to the respective service proponent office by the following electronic form: Criteria Change Request (CCR). The form is also accessible from the Internet sites listed below.

UFC are effective upon issuance and are distributed only in electronic media from the following source:

• Whole Building Design Guide web site http://dod.wbdg.org/.

Refer to UFC 1-200-01, DoD Building Code (General Building Requirements), for implementation of new issuances on projects.

AUTHORIZED BY:

LARRY D. McCALLISTER, PhD, PE, PMP, SES

Chief, Engineering and Construction Directorate of Civil Works U.S. Army Corps of Engineers

JOSEPH E. GOTT, P.E.

Chief Engineer Naval Facilities Engineering Command

EDWIN H. OSHIBA, SES, DAF MICHAEL McANDREW Director Air Force Civil Engineer Center

Deputy Assistant Secretary of Defense (Facilities Investment and Management) Office of the Assistant Secretary of Defense (Energy, Installations, and Environment)

UNIFIED FACILITIES CRITERIA (UFC)

REVISION SUMMARY SHEET

Document: UFC 3-250-03, O&M Manual: Standard Practice For Flexible Pavements

Superseding: UFC 3-250-03, Standard Practice Manual for Flexible Pavements, 15 May 2001; AF ETL 01-7, Large Aggregate Asphalt Mixtures, 5 Jun 2017; and AF ETL 01-9, Procedures to Retard Reflective Cracking, 17 Jun 2001.

Description: This UFC provides guidance for the preparation of drawings and specifications for road and airfield flexible pavements using asphalt cement materials. It also provides useful information for design engineers, laboratory personnel, and project managers concerning mix design, materials, production, and placement of the various asphalt mixtures.

Reasons for Document: This UFC provides engineers with current changes in technology to outline materials, equipment, techniques, and cautions required to produce a cost-effective and durable flexible asphalt pavement. Additionally, a number of editorial changes were needed to improve readability. Figures and tables were also improved.

Impact: Cost impact is negligible; improved guidance results in improved performance and reduced life cycle cost.

Unification Issues: None i

TABLE OF CONTENTS

CHAPTER 1 INTRODUCTION

1-1 PURPOSE

1-2 SCOPE

1-3 REFERENCES

1-4 UNITS OF MEASURE

1-5 SPECIAL TERMS

1-6 BACKGROUND

1-7 SAFETY CONSIDERATIONS

CHAPTER 2 HOT-MIX ASPHALT

2-1 INTRODUCTION

2-1.1 Advantages

2-1.2 Gradations and Layer Thickness

2-1.3 Uses

2-2 EQUIPMENT

2-2.1 Plant Equipment

2-2.1.1 Batch Plant

2-2.1.2 Drum Mix Plant

2-2.1.3 Asphalt Mixture Storage Silo

2-2.2 Placement Equipment

2-2.2.1 Asphalt Spreader (Paver)

2-2.2.2 Material Transfer Vehicle

2-2.2.3 Joint Heaters

2-2.2.4 Asphalt Distributor

2-2.2.5 Rollers

2-3 MATERIALS

2-3.1 Asphalt Materials

2-3.1.2 Performance Graded (PG) Asphalt Cements

2-3.1.3 Classification Method for PG Graded Asphalt Cements

2-3.1.4 Asphalt Cement Selection by Temperature Region

2-3.2 Aggregates

2-3.2.1 Sieve Analysis

2-3.2.2 Specific Gravity

2-3.2.3 Abrasion and Impact Resistance of Coarse Aggregate

2-3.2.4 Soundness Test

2-3.2.5 Percent Crushed Pieces

2-3.2.6 Particle Shape

2-3.2.7 Clay Lumps and Friable Particles ii

2-3.2.8 Sand Equivalent

2-3.2.9 Natural Sand Content

2-3.2.10 Fine Aggregate Angularity

2-3.2.11 Voids in Mineral Aggregate (VMA)

2-3.3 Mineral Fillers

2-3.3.1 Addition of Mineral Filler

2-3.4 Antistrip Agents

2-3.4.1 Recommended Antistrip Agent

2-3.5 Antifoam Agents

2-4 DENSE-GRADED HMA

2-4.1.1 Aggregate Considerations

2-4.2 Marshall Mix Design

2-4.2.1 Contractor-provided Job Mix Formula (JMF)

2-4.2.2 Procedure

2-4.2.3 Preparation of Test Specimens

2-4.2.4 Asphalt Contents for Specimens

2-4.2.5 Selection of Design Compaction Method

2-4.2.6 Tabulation of Data

2-4.2.7 Relationship of Test Properties to Asphalt Cement Content

2-4.2.8 Requirement for Additional Test Specimens

2-4.2.9 Importance of Asphalt Content

2-4.2.10 Determination Optimum Asphalt Content & Acceptability of Mix. .. 38

2-4.2.11 Dust/Asphalt Ratio

2-4.2.12 Moisture Susceptibility

2-4.2.13 Superpave Mix Design

2-4.3 Mixture Control

2-4.3.1 JMF Production at Asphalt Plant

2-4.3.2 Asphalt Plant Laboratory Burden

2-4.3.3 Mix Adjustments

2-4.3.4 Production & Laydown Quality Control & Quality Assurance

2-4.4 Significance of Changes in Mixture Properties

2-4.4.1 Hot-bin Gradations

2-4.4.2 Construction Control

2-4.4.3 Pavement Sampling

2-4.4.4 Testing Pavement Samples

2-4.4.5 Density Data

2-4.4.6 Pavement Imperfections and Probable Causes

2-5 POROUS FRICTION COURSE

iii

2-5.1 Materials

2-5.1.1 Aggregates

2-5.1.2 Asphalt Cement

2-5.2 Mixture Design

2-5.2.1 Proportioning of Aggregates

2-5.2.2 Fiber Stabilizers

2-5.2.3 Asphalt Content

2-5.2.4 Kc Factor

2-5.2.5 Mixing Temperature

2-5.3 Plant Control

2-5.3.1 Plant Laboratory

2-5.3.2 Sieve Analysis

2-5.3.3 Asphalt Content Tests

2-5.3.4 Mix Proportions

2-5.3.5 Controlling Plant Production

2-5.4 Construction

2-5.4.1 Pavement Control

2-5.4.2 Pavement Sampling

2-5.4.3 Storage Silos

2-5.4.4 Pavement Operations under Normal Conditions

2-6 STONE MATRIX ASPHALT

2-6.1 Materials

2-6.1.1 Aggregates

2-6.1.2 Filler

2-6.1.3 Stabilizer

2-6.1.4 Asphalt

2-6.2 Mixture Design

2-6.2.1 SMA Draindown Test

2-6.2.2 JMF Requirements

2-6.3 Mixing Plants

2-6.3.1 Batch Plants

2-6.3.2 Drum-Mix Plants

2-6.3.3 Mixing Time

2-6.3.4 Storage

2-6.4 Test Section

2-6.5 Placement

2-6.5.1 Equipment

2-6.5.2 Surface Preparation iv

2-6.5.3 Paving

2-6.5.4 Compaction

2-7 WARM-MIX ASPHALT

CHAPTER 3 SPRAY APPLICATIONS

3-1 INTRODUCTION

3-2 PRIME COAT

3-2.1 Materials

3-2.1.1 Asphalt

3-2.1.2 Prime Coats

3-2.2 Application Rate

3-2.3 Placement

3-2.4 Control

3-3 TACK COAT

3-3.1 Materials

3-3.2 Application Rate

3-3.3 Placement

3-3.4 Control

3-4 FOG SEALS

3-4.1 Materials

3-4.2 Application Rate

3-4.3 Placement

3-5 REJUVENATION

3-5.1 Testing

3-5.2 Materials

3-5.3 Application Rate

3-5.4 Placement

3-5.5 Control

3-5.6 Skid Resistance

CHAPTER 4 SEAL COATS

4-1 INTRODUCTION

4-2 SINGLE AND DOUBLE BITUMINOUS SURFACE TREATMENTS

4-2.1 Materials

4-2.1.1 Binder

4-2.1.2 Aggregates

4-2.2 Design

4-2.3 Construction

4-2.3.1 Equipment

4-2.3.2 Surface Preparation v

4-2.3.3 Application

4-2.3.4 Control

4-3 SLURRY SEAL

4-3.1 Equipment

4-3.2 Material Requirements

4-3.2.1 Emulsion

4-3.2.2 Aggregate

4-3.2.3 Mineral Filler

4-3.2.4 Water

4-3.3 Design

4-3.4 Factors Affecting Design

4-3.5 Surface Preparation

4-3.6 Application

4-3.6.1 Joints

4-3.6.2 Hand Application

4-3.7 Curing

4-3.8 Rolling

4-4 FUEL-RESISTANT SEALER

4-4.1 Areas of Application

4-4.2 Considerations for Use

4-4.3 Material Requirements

4-4.3.1 Coal-tar Emulsion

4-4.3.2 Aggregates

4-4.3.3 Water

4-4.3.4 Additives

4-4.4 Design

4-4.4.1 Application Rate

4-4.4.2 Requirements

4-4.5 Equipment

4-4.6 Surface Preparation

4-4.7 Application

4-4.8 Curing

4-5 MICRO-SURFACING

4-5.1 Equipment

4-5.2 Material Requirements

4-5.2.1 Emulsion

4-5.2.2 Additives

4-5.2.3 Aggregates vi

4-5.2.4 Water

4-5.3 Design

4-5.3.1 Mix Characteristics

4-5.3.2 Determination of Optimum Asphalt Content

4-5.4 Surface Preparation

4-5.5 Application

CHAPTER 5 ASPHALT STABILIZATION

5-1 INTRODUCTION

5-2 MATERIALS

5-2.1 Soil/Aggregate

5-2.2 Asphalt

5-3 COMPOSITION AND MIXTURE

5-4 CONSTRUCTION

5-5 DRAINAGE LAYERS

5-5.1 Design

5-5.2 Construction

CHAPTER 6 MISCELLANEOUS MIXTURES

6-1 RECYCLED ASPHALT MIXTURES

6-2 SAND-ASPHALT MIXTURES

6-2.1 Advantages and Disadvantages

6-2.2 Uses

6-3 SHEET ASPHALT

6-4 ROCK ASPHALT

6-4.1 Advantages and Disadvantages

6-4.2 Uses

6-5 COLD-MIX ASPHALT

6-5.1 Design

6-5.1.1 Preliminary Work

6-5.1.2 Materials

6-5.1.3 Design

6-5.2 Plant Mix

6-5.2.1 Plant Operation

6-5.2.2 Plant Laboratory

6-5.2.3 Adjusting Mix Proportions

6-5.2.4 Preparation of Construction Specifications

6-5.3 Road Mix

6-5.3.1 Advantages and Disadvantages

6-5.3.2 Uses vii

CHAPTER 7 RESIN MODIFIED PAVEMENT (RMP)

7-1. overview

7-2 MATERIALS

7-2.1 Open-Graded Asphalt Mixture

7-2.1.1 Aggregates

7-2.1.2 Asphalt Cement

7-2.2 Cement Slurry Grout

7-2.2.1 Aggregate

7-2.2.2 Filler

7-2.2.3 Cement

7-2.2.4 Cross Polymer Resin Additive

7-3 MIXTURE DESIGN

7-3.1 Open-Graded Asphalt Mixture

7-3.2 Cement Grout

7-4 EQUIPMENT

7-4.1 Rollers

7-4.2 Hand Tools

7-5 PLACEMENT

7-5.1 Open-Graded Asphalt Mixture

7-5.2 Cement Slurry Grout

7-5.2.1 Mixing and Transport

7-5.2.2 Placement

7-5.2.3 Covering Pavement Surface

APPENDIX A REFERENCES

APPENDIX B BEST PRACTICES

APPENDIX C GLOSSARY

FIGURES

Figure 2-1 Batch Plant (Courtesy of National Asphalt Pavement Association

(NAPA))

Figure 2-2 Drum Mix Plant (Courtesy of NAPA) Figure 2-3 Minimum Anticipated Pavement Temperature as a Function of DFI Figure 2-4 Gradation Curves for Stockpile Samples Figure 2-5 Gradation Curves for Bin Samples Figure 2-6(a-f) Asphalt Paving Mix Design for Typical Mix Figure 2-7 Mat Density Control Chart Figure 2.8 Types of HMA Deficiencies and Probable Causes Figure 2-9 Types of HMA Pavement Imperfections and Probable Causes Figure 4-1 Classification of Mix Systems by Cohesion Test Curves viii

Figure 4-2 Mineral Filler Content Optimization “Benedict Curve” Figure 4-3 Determination of Optimum Asphalt Content

TABLES

Table 2-1 Aggregate Gradations for HMA Pavements Table 2-2 Specification References for Asphalt Materials Table 2-3 Asphalt Binder Base Grade Selection Criteria Based on Pavement

Temperature Index* Table 2-4 Example PTI Data Table 2-5 Asphalt Cement Selection Criteria Based on Design Air-freezing

Index* Table 2-6 Computation of Properties of Asphalt Mixtures

Table 2-7 Minimum Percent Voids in Mineral Aggregate (VMA) Table 2-8 Design Criteria Table 2-9 Determination of Optimum Asphalt Content1 Table 2-10 Evaluation for Acceptability of Design Mix Table 2-11 Lot Density as a Percent of Laboratory Density Table 2-12 Aggregate Gradation for PFCs Table 2-13 SMA Gradation Guideline (after NAPA 1999*) Table 2-14 Recommended SMA Coarse and Fine Aggregate Properties

(after NAPA 1999) Table 2-15 Properties of Cellulose Fibers (after NAPA 1999) Table 2-16 Properties of Mineral Fibers1 (after NAPA 1999) Table 2-17. SMA Mix Design Requirements (after NAPA 1995) Table 3-1 Prime Coat Materials Table 3-2 Tack Coat Materials and Spray Application Temperatures Table 4-1 Surface Treatment Asphalt Materials Table 4-2 Gradations for SBST Table 4-3 Gradations for DBST Table 4-4 Slurry Seal Aggregate Gradations Table 4-5 FRS Minimum Application Rates and Corresponding Aggregate

Gradations Table 4-6 Physical Properties of Sealer Mixtures Table 4-7 Gradation Types for Micro-Surfacing Table 6-1 Typical1 Aggregate Gradations for Plant-Mix Cold-Laid Asphalt

Mixtures Table 6-2 Selection of Asphalt Type and Grade Table 6-3 Selection of Optimum Asphalt Content Table 6-4 Mixing Temperatures for Asphalt Materials Table 7-1 Aggregate Physical Properties Table 7-2 Gradation Limits for Open-Graded Asphalt Mixture Table 7-3 Aggregate Gradation for Slurry Grout Table 7-4 Resin Modified Cement Slurry Grout Mixture Proportions Table 7-5 Slurry Grout Viscosity…………………………………………………...114 ix

Table B-1 Factors Used in Calculating Surface Area of Slurry Seal Aggregate

Table B-2 Surface Area Calculation Table B-3 Kerosene Absorption Calculation Table B-4 Product and Vendor Information ……………………………………...128 x

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CHAPTER 1 INTRODUCTION

1-1 PURPOSE.

This UFC provides guidance for the preparation of drawings and specifications for road and airfield flexible pavements using asphalt cement materials. The term “asphalt” is used herein instead of bitumen or bituminous (a generic term for both asphalt and tar materials) because asphalt is the material typically used in pavement construction. In the past, tar or coal tar was used only in instances where fuel resistance was required.

Due to problems with emissions, tar is no longer used in flexible pavement construction except occasionally as a sealer. This UFC also provides useful information for design engineers, laboratory personnel, and project managers concerning mix design, materials, production, and placement of the various asphalt mixtures.

1-2 SCOPE.

This UFC prescribes materials, mix design procedures, and construction practices for flexible pavements.

1-3 REFERENCES.

Appendix A contains a list of references cited within this UFC.

1-4 UNITS OF MEASURE.

The primary system of measurement used in this UFC is the International System of Units (SI). In some cases, inch-pound (IP) measurements are the governing critical values because of applicable codes, accepted standards, industry practices, or other considerations where the IP measurements govern. The IP value is shown in parentheses following a comparable SI value.

1-5 SPECIAL TERMS.

Special terms used in this UFC are explained in Appendix C.

1-6 BACKGROUND.

Asphalt mixtures (hot-, cold-, and warm-mix asphalt and other asphalt surfaces) provide a resilient, relatively waterproof, load-distributing medium that protects the base course and underlying pavement structure from the harmful effects of water and abrasion from traffic. Asphalt pavements wear, weather, and deteriorate from aging; therefore, maintenance of these pavements extends pavement life. The flexibility of asphalt mixtures allows a pavement structure to adjust slightly to consolidation of underlying layers or deflection due to load without affecting pavement performance. Flexible pavements also allow stage construction and use a range of construction materials, often leading to substantial savings through the use of locally available materials.

Additional pavement courses are placed on existing pavements to provide additional structural strength as total loads increase or as traffic intensity increases. Design and construct the economical pavement that satisfy the objective of long pavement life.

1-7 SAFETY CONSIDERATIONS.

Department of Defense’s (DoD) objective is to construct pavements that provides traffic safety. A non-skid surface is essential, and grade control is required to provide rapid removal of surface water to minimize the potential for hydroplaning. All pavement surfaces normally exhibit a sufficiently coarse texture to provide skid resistance. Avoid aggregate types known to have a history of polishing because they are probably the greatest cause of low skid resistance, prevalent in surface treatments and seal coats.

Avoid aggregates having friable particles, as these tend to break down and form foreign object debris (FOD). Construction techniques are important for surface treatments and seal coats to ensure good bond between the asphalt and aggregate, providing aggregate retention. Pavement surfacing such as sealers that do not include aggregate are not applied in areas of high-speed traffic.

CHAPTER 2 HOT-MIX ASPHALT

2-1 INTRODUCTION.

Hot-mix asphalt (HMA) is often used for high-performance pavements. Select the degree of performance required based on traffic conditions and the availability of materials. HMA mixtures consist of mineral aggregate and asphalt cement. These HMA mixtures are meet the design requirements for airfield pavements, roads and streets, and storage areas. In general, from 4 to 6.5 percent asphalt cement content is required for asphalt base, intermediate courses, and surface courses and 5 to 7 percent asphalt cement content for porous friction course (PFC) and stone matrix asphalt (SMA);

however, determine the optimum asphalt content according to mix design procedures.

The term “hot-mix asphalt” refers to any hot asphalt mixture produced in a hot-mix plant;

however, unless referred to directly by a specific name, it refers to dense-graded HMA with aggregate gradations shown in Table 2-1. Much of the information discussed in this section is found in report AATP 05-01 developed by Auburn University.

2-1.1 Advantages.

The hot-mix method of preparing paving mixtures provides for thorough coating of the aggregates with a uniform film of asphalt cement and accurate control of aggregate sizes and quantity of asphalt cement. Hot-mix pavements require no curing period after being laid and are used as soon as the pavement has cooled. Roll the paving mixture to compact the mix while it is sufficiently hot because rolling is ineffective after the mixture has cooled, making the mix design density unachievable. Hot-mix asphalt pavements are constructed rapidly minimizing the probability of damage to the HMA due to weather conditions that occur immediately after construction is completed. Immediately after adequate rolling and a cooling period, the pavement has a high degree of stability from the interlocking of the coarse and fine aggregate and adhesion of the asphalt cement, as well as a high resistance to moisture penetration and frost damage.

2-1.2 Gradations and Layer Thickness.

Selection of a gradation from Table 2-1 is based on the layer thickness of the HMA to be placed and the need to limit aggregate segregation. Segregation occurs more quickly in mixes with coarser aggregates; therefore, do not use aggregate gradation No. 1 on the surface. Ensure the layer thickness for gradation No.1 is at least 57 millimeters (2.25 inches), the layer thickness for gradation No. 2 is at least 37.5 millimeters (1.5 inches), and the layer thickness for gradation No. 3 is at least 28.5 millimeters (1.1 inches). Use 25-millimeter- (1 inch) thick layers of HMA only in unusual situations, such as level courses, since these thin layers tend to cool quickly and are difficult to place and compact properly. The preferred thickness of the surface layer for an airfield pavement is 51 millimeters (2 inches). Design and/or construct underlying layers with a thickness no greater than 76 millimeters (3 inches). The thickness of underlying layers is determined by the total designed thickness of the asphalt mixture. Surface layers for airfields are not less than 37.5 millimeters (1.5 inches) thick.

Table 2-1 Aggregate Gradations for HMA Pavements

Sieve Size, mm

Gradation 1 19 mm Nominal Max Agg Size by Mass

Gradation 2

12.5 mm Nominal

Max Agg Size by Mass

Gradation 3

9.5 mm Nominal

Max Agg Size by Mass

25.0 100 – –

19.0 90-100 100 –

12.5 68–88 90-100 100

9.5 60–82 69–89 90-100

4.75 45–67 53–73 58–78

2.36 32–54 38–60 40–60

1.18 22–44 26–48 28–48

0.60 15–35 18–38 18–38

0.30 9–25 11–27 11–27

0.15 6–18 6–18 6–18

0.075 3–6 3–6 3–6

Sieve Size, inch

Gradation 1 3/4 inch Nominal

Max Agg Size by Mass

Gradation 2 1/2 inch Nominal

Max Agg Size by Mass

Gradation 3 3/8 inch Nominal

Max Agg Size by Mass

1 100 – –

3/4 90-100 100 – 1/2 68–88 90-100 100

3/8 60–82 69–89 90-100

No. 4 45–67 53–73 58–78 No. 8 32–54 38–60 40–60

No. 16 22–44 26–48 28–48 No. 30 15–35 18–38 18–38

No. 50 9–25 11–27 11–27

No. 100 6–18 6–18 6–18 No. 200 3–6 3–6 3–6

When a leveling course is applied, ensure layers are at least 37.5 millimeters (1.5 inches) thick except in areas where it is tapered to tie into the underlying layer. Ensure areas of leveling course that require tapering (it’s better not to use tapering techniques) of the mix are at least 19 millimeters (0.75 inch) thick in the thinnest part of the taper to allow sufficient thickness for minimal compaction. Before overlaying, mill the asphalt surface to a grade resulting in no need for a leveling course. This allows each layer to be placed at a constant thickness throughout which is preferred.

Mixes with maximum aggregate size tend to have lower optimum asphalt content so these mixes are potentially a little cheaper for the contractor to produce but these mixes are more difficult to handle and compact and tend to segregate during handling. Use gradation 2 for all surface course mixtures for airfields unless the thickness is less than

37.5 millimeters (1.5 inches); in this case, use gradation 3. Provide good justification to use asphalt layer thicknesses less than 37.5 millimeters (1.5 inches). Use gradation 2 for intermediate layers as well unless the layer thickness exceeds 57 millimeters (2.25 inches); then gradation 1 is allowed to be used. Use gradation 3 for shoulders and for any layer that is constructed less than 37.5 millimeters (1.5 inches) thick.

2-1.3 Uses.

If properly designed, HMA paving mixtures are used for an asphalt base course, intermediate course, surface course, porous friction or stone matrix asphalt course.

Wheel loads, wheel spacing, tire pressures, intensity of traffic, and subgrade strength (California Bearing Ratio (CBR)) dictate the thickness of the pavement (UFC 3-260-02).

For airfield pavement applications, HMA is used for intermediate and surface courses on types A, B, C, and D traffic areas, blast areas, and any other areas (including non-traffic) where their use is economical. The four types of airfield traffic areas (A, B, C, and D) and their relationship to other methods of traffic area nomenclature are described in UFC 3-260-02. HMA is often used on any road or street, classification A through F. PFCs have been used in the past to prevent hydroplaning but have not been used in recent years on airfields primarily due to potential for raveling of the surface resulting in FOD. Gain approval from the Pavements Discipline Working Group (DWG) or their designated representative before using a PFC on an airfield. Grooving is used on runways in place of PFCs to facilitate removal of the water from the pavement surface. SMA is used in applications requiring a rut- and abrasion-resistant surfacing.

SMA mixtures are more expensive than HMA, so they are not used. Areas subjected to fuel spills require an application of a fuel-resistant sealer to protect the HMA pavement or the use of a fuel resistant binder. When possible, investigate the use of a rigid pavement for areas with expected fuel spillage.

HMA is used for new construction and for rehabilitating existing pavements. For new construction it is important to ensure that the existing subgrade meets the strength requirements used for design. It is also essential that the quality of materials in the subbase and base courses meet the design requirements. Ensure a condition survey of existing pavements is made in order to develop a design for existing pavement repairs.

During construction, it is essential that the design for materials and thicknesses be followed. Immediately address any construction issues prior to placement of material to avoid ultimately having to remove and replace such.

2-2 EQUIPMENT.

2-2.1 Plant Equipment.

The purpose of an asphalt plant is to produce the mixture using mix design proportions of aggregate materials and asphalt cement and mix the materials so that all aggregates are thoroughly coated and the mixture is uniform throughout. HMA is produced in both batch and drum mix asphalt plants. Drum mix plants are common in the U.S. Either type of asphalt plant is used to produce high quality HMA. Initiate asphalt mixture quality control at the aggregate stockpiles. Manage each aggregate stockpile to prevent segregation or mixing with adjacent stockpiles or contamination from other materials including underlying material.

2-2.1.1 Batch Plant.

The components of a batch plant are illustrated in Figure 2-1. Cold feed hoppers have individual feeders for each of the aggregates used in the mixture. Set feeders so that the desired percentage of each aggregate as specified in the job mix formula is fed into the plant. Rate of feed is controlled by the gate opening, belt speed, or other methods, depending on the type of cold feed. If aggregate feeders are not set as specified in the job mix formula, the following problems occur:

a. One of the aggregate hot bins overflows with material while another hot bin runs low on material.

b. The gradation of the aggregate in the mix being produced does not meet the design gradation.

c. The amount of natural sand varies from the design proportion and exceeds the amount allowed in the specifications.

Figure 2-1 Batch Plant

(Courtesy of National Asphalt Pavement Association (NAPA))

A-Storage Silo B-Reclaimed Asphalt

Pavement (RAP) Feeder

C-Baghouse D-Binder Storage E-Cold Feed Hoppers F-Cold Elevator G-Dryer H-Plant Scales I-Control House J-Hot Elevator K-Silo Truck Scales L-Pug Mill M-Mix to Silo N-Hot Bins

2-2.1.1.1 Cold Feed Bins.

Before the start of a project, calibrate the cold feed bins so that each bin feeds the desired rate of material. The cold feed calibration involves feeding one aggregate at a time onto a belt that is common to all aggregates. Determine the speed of this belt prior to calibration of the feeders. One way to do this is to divide the belt length by the time required for one revolution. After the material is fed onto the belt, completely remove and weigh the material over a given length (for example; 2 meters (6.5 feet)). To convert the weight of the sample taken to kilograms per hour (pounds per hour) and later to metric tons (tons) per hour, use the following relationship:

3600 WS

R

L

Where:

R = rate of feed, kilograms per hour (pounds per hour) W = weight of sample, kilograms (pounds) S = speed of belt, meters per second (feet per second) L = length of belt sampled, meters (feet)

Feed each aggregate at four to five different feeder settings and determine the rate of feed for each setting. Develop a plot of this data showing the relationship between the rate of feed (kilograms or metric tons (pounds or tons) per hour) and the feeder setting (gate opening, feeder belt speed, or other method for setting the aggregate feeder) for each aggregate. Use these plots to set each cold feed bin to feed at the desired rate.

2-2.1.1.2 Dryer.

After the aggregate cold feed bins have been properly set, the aggregate feeders are set to provide the desired percentages, and the aggregate is fed up the cold elevator and through the dryer. The dryer removes the moisture from the aggregate down to less than 0.5% and heats the aggregate to the desired temperature for mixing and handling.

2-2.1.1.3 Dust Collector.

A dust collector collects the dust created in the dryer and at other plant locations and adds all or any portion of it back into the mix at the hot elevator. Ensure the plant has the capability to remove any desired portion of the collected dust or to return it back to the mixture.

2-2.1.1.4 Screens.

The aggregate exits the dryer and is carried, along with the returned dust, up the hot elevator, over the screening deck, and into the hot bins. Screen sizes are selected such that the oversize material is rejected and the remaining aggregates are separated into various sizes. Ideally, select the screen sizes so that the amount of material going into each hot bin is proportional to the relative volume of that hot bin. For example, suppose that hot bin No. 1 has a volume of 3 cubic meters (4 cubic yards), hot bin No. 2 has a volume of 1.5 cubic meters (2 cubic yards), and hot bin No. 3 has a volume of 1.5 cubic meters (2 cubic yards). Select screens so that 50 percent of the material goes into bin No. 1, 25 percent into bin No. 2, and 25 percent into bin No. 3. This is not done for each mix since it takes effort to change the screens and asphalt batch plants produce a range of mixes during a normal workday.

2-2.1.1.5 Hot Bins.

Determine the percentage of each hot bin to be used in the mixture. Take samples of each hot bin and the gradation for each sample determined. Select the percentage of each bin so that the gradation of the combined materials from the hot bins is equal to the gradation of the job-mix formula (JMF). Variations occur in the combined hot bin gradation and that sent through the drier due to possible aggregate degradation or loss of fines in the dust collection system; however, ensure the gradation of the blended aggregate is equal to that originally developed in the mix design.

2-2.1.1.6 Mixer.

After the cold feed and hot bins are properly set, the combined aggregate from the hot bins is mixed with the approved mix design amount of asphalt binder. Select the mixing time, 5 seconds for dry mixing and 25 to 40 seconds for wet mixing, so that all aggregate particles are coated. Ensure the plant produces a uniform asphalt mixture having approved mix design aggregate gradation, asphalt content, and temperature.

The batch plant weighs in approved mix design percentage of the various nominal size aggregates stored in the hot bins and asphalt binder to produce a batch of material that is then mixed in a pugmill.

2-2.1.1.7 Storage Silo.

A storage silo is not required in a batch plant but almost all asphalt plants have one or more storage silos to temporarily store material during production. Ensure the storage silo in a batch plant meets the same requirements as that for a drum mix plant discussed below.

2-2.1.2 Drum Mix Plant.

The drum mix plant is illustrated in Figure 2-2. The drum mix plant is generally produces HMA at a higher production rate compared to a batch plant. When a drum mix plant is used, the gradation is completely controlled at the cold feed bins since no additional screening of the mixture occurs. The asphalt cement is either added to the aggregate while inside the drum or added to the aggregate immediately after passing through the drum. This plant type is used to readily produce HMA containing reclaimed asphalt pavement as well as HMA containing no reclaimed asphalt pavement.

Figure 2-2 Drum Mix Plant

(Courtesy of NAPA)

2-2.1.2.1 Cold Feed Bin

The cold feed bins in a drum mix plant are set up much the same way as for the batch plant, but the drum mix plant has a weight sensor on the aggregate feed belt that weighs the aggregate on the run prior to being fed into the dryer. Adjust this aggregate weight based on moisture content since there is moisture in the aggregate that is removed during the drying process. The asphalt pump adds binder based on the belt-measured weight of aggregate which is more asphalt binder than desired unless the aggregate weight is corrected based on the measure moisture content.

2-2.1.2.2 Dryer.

For the drum mix plant, the burner for the dryer is normally located on the high side (parallel flow) or the low side (counter flow) of the drum. In the parallel flow dryer, the aggregate enters the dryer on the high end of the drum and helps to shield the asphalt binder being added inside the drum from direct contact with the flame. The asphalt cement is added to the dryer at the midpoint to two-thirds the length to prevent close contact with the flame, which causes over-heating and damage to the asphalt binder. A counter-flow drum mix plant has the burner on the low end of the drum and is more energy efficient than a conventional drum mixer and produces less emissions during plant operations. With a counter flow plant, various techniques are used to protect the asphalt from the flame as it passes through the plant. Examples of techniques used include double barrels (where the aggregate is heated in the inner drum and the asphalt cement is added in the outside drum), coaters (where the asphalt cement is added to

A-Storage Silo B-RAP Feeder C-Binder Storage D-Baghouse E-Control House F-Cold Feed Hopper G-Cold Elevator H-Dryer and Mixer I- Truck Scales

I the aggregate after it passes through the dryer), and heat shields (shield the asphalt cement from the flame).

2-2.1.2.3 Dust Collector.

The dust collector in a drum mix plant operates similar to that in a batch plant.

2-2.1.3 Asphalt Mixture Storage Silo.

Asphalt storage silos are used to store HMA mixture before loading it onto trucks.

Ensure the storage silo volume is maintained for the drum mix plants continuous flow production. The silos allow plants to run continuously even when there is a temporary shortage of trucks. Material is stored in silos for short periods of time, but if stored too long, the material cools excessively or oxidizes excessively, causing the asphalt binder to become hard and brittle. The asphalt binder has the potential to drain from the aggregate during long-term storage. This draindown is more likely to occur with mixes having high coarse aggregate content such as open-graded friction course and stone matrix asphalt. Hence for these mixture types storing the mixture in the silo for more than 30 minutes is not allowed.

Meet the stored mixture specification requirements when sampled and tested after storage. As a general rule, HMA dense-graded mixtures are not stored more than 3 hours in a non-insulated storage silo or for more than 8 hours in an insulated storage silo. If segregation of aggregate or draindown of asphalt binder occurs in the silo, disallow use of the silo or make changes in the equipment or process to prevent segregation and draindown.

2-2.2 Placement Equipment.

2-2.2.1 Asphalt Spreader (Paver).

2-2.2.1.1 Types of Spreaders.

An asphalt spreader is used to place mixture types, such as hot mix, cold mix, and base course material. Spreaders currently in use operate on either tracks or rubber tires, and have a vibrating screed to strike off and smooth the paving mixture. Spreaders use a tamping bar in conjunction with the screed, or an oscillating screed with a vibrating compactor, and others use a vibrating screed for both strike-off and initial compaction.

Conventional paving machines are place HMA, provided these machines are maintained in good mechanical condition, kept adjusted, and operated by experienced personnel. Poor pavement surfaces result if the screed plates are worn or rusty or if the tamping bars (when used) are worn or not properly adjusted.

2-2.2.1.2 Automatic Grade Control.

Ensure asphalt spreaders have a means of automatically controlling the grade. In many cases the grade of the base course or underlying layers is controlled and the desired thickness of asphalt mixture is placed resulting in the desired grade on the surface.

When directly controlling grade of an asphalt layer, grade control is used on both sides of the paver for the first pass. For additional passes, the existing edge is matched on one side of the paver while grade control is used on the opposite side of the paver. For roads, slope control in the paver is often used to control the desired grade. In this case one side of the paver matches the existing pavement and the opposite side is controlled by setting the screed of the paver to provide the desired slope. Controlling the grade by utilizing the transverse slope with the paving machine is not acceptable when multiple lanes are to be placed since the error using the transverse slope approach increases as the number of lanes placed is increased. Methods of grade control that have been used include stringline, laser, and Global Positioning System (GPS)/automation. The asphalt mixture is placed to a desired grade with the asphalt paver but after compaction the mix rolls down 20 to 25 percent of the loose thickness. Hence, if 63.5 millimeters (2.5 inches) of loose mix is placed, this results in 51 millimeters (2.0 inches) of mix after compaction. This results in the initial placement of the asphalt mixture being 13 millimeters (0.5 inch) higher than the desired grade after compaction.

2-2.2.2 Material Transfer Vehicle.

Segregation and lack of smoothness are problems that occur on many paving projects.

The use of a material transfer vehicle (MTV) has been shown to minimize segregation and improve pavement smoothness. The MTV is used to transfer the HMA paving mixture from the transport truck to the hopper of the paver. These devices hold a substantial amount of paving mixture, allowing more freedom in mixture transport, and they remix the paving mixture to help reduce segregation that often occurs during placement. In addition to helping prevent segregation, the MTV improves pavement smoothness by allowing a paver to operate continuously (less stopping and starting) without having to be concerned with trucking operations. MTVs receive mixtures directly into a hopper from dump trucks. State’s Department of Transportation (DOT) require that an MTV be used on critical projects, such as interstate highways, so MTVs are readily available. All MTVs are not the same. MTVs work better for reducing segregation and improving performance. As a minimum, specify an MTV that has an articulating arm and one that is self-propelled and operated independently from the paver. Ensure the MTV has remixing capability to minimize segregation. There are many machines that simply transfer the mix from the truck to the paver. Many of these do not remix the asphalt mixture. One method of remixing is to have an auger inside the MTV that has auger blades at varying spacing (closer together near the end and further apart near the middle of the auger where the material is fed to the paver) which results in mixing of the materials as they are being fed to the paver.

2-2.2.3 Joint Heaters.

Joint-heating devices that are attached to asphalt spreaders have been used on a number of HMA construction projects. The joint heaters are used to heat the edge of an adjacent pavement lane during placement so that a hot joint is obtained. The hot joint allows for higher compaction. Experience with joint heaters has shown that there is a danger of overheating the existing asphalt mixture. Accordingly, do not use joint heaters on airfields.

2-2.2.4 Asphalt Distributor.

Asphalt distributors are used to apply asphalt material evenly over a pavement surface.

Clean the openings of all nozzles of any blockages. Ensure nozzles are the same size and turned at the same angle with reference to the spray bar to produce a uniform fan of bituminous material. The height of the spray bar above the surface being sprayed is important for uniform application. When the bar is too high or too low, a difference in application rate across the spray bar occurs, causing streaking. Adjust the height of the spray bar so that a double or triple overlap of the spray fan is obtained. The Asphalt Institute's Manual Series No. 19 (MS-19) offers guidance for calibrating and checking application equipment. American Society for Testing and Materials (ASTM) Standard D2995 (ASTM D2995) details a method for the determination of the application rate of asphalt (bituminous) distributors. Fully calibrate a distributor before being allowed to be used on a project.

2-2.2.5 Rollers.

A number of roller types are used for paving operations. Rollers used to compact asphalt mixtures are static steel-wheel, vibratory steel-wheel, and rubber-tired rollers.

Occasionally rollers have a steel drum on one end of the roller and rubber tires on the other end of the roller. These types of rollers are not allowed for use on HMA because the rubber tires tend to pick up the asphalt mixture resulting in damage to the HMA surface.

2-2.2.5.1 Static Steel-Wheel Rollers.

Static steel-wheel rollers are available in two-wheel (tandem) and three-wheel (tricycle) versions. These two wheel tandem rollers are used for finish rolling but have been used for breakdown rolling as well. Static steel-wheel rollers leave a smooth finish on the pavement surface, but excessive rolling with steel wheel rollers results in lateral movement of the mixture as it’s being rolled, causing surface cracking and a general loss in density. Equip these rollers with a system for watering the drums and ensure they have scrapers to remove any material that sticks to the drums. The three-wheel rollers, tricycle rollers, are not used as often, partially due to their tendency to push and shove the asphalt mixture, which results in surface problems.

2-2.2.5.2 Vibratory Steel-Wheel Rollers.

Vibratory steel-wheel rollers are commonly used for breakdown and intermediate rolling of HMA mixtures. They consist of dual-drum vibration, single-drum vibration and single-drum static, or single-drum vibration and rubber tires on the rear axle; however, use of rubber tires on the vibratory steel wheel rollers for asphalt is not normally recommended due to the potential for pickup of the HMA. These vibratory steel wheel rollers are used for breakdown, intermediate, and finish rolling. Breakdown rolling is performed in either static or vibratory mode, although almost everyone now uses a vibratory roller for breakdown rolling. Intermediate rolling is almost always performed in the vibratory mode, while finish rolling is performed in the static mode. Limited data that indicates that excessive rolling with a vibratory roller results in bleeding of the asphalt surface resulting in excessive loss of friction. Therefore, limit the maximum number of passes to three in the vibratory mode. Ensure the vibratory roller has a watering system along with scrapers on the steel drums. Although the vibratory roller is used for intermediate rolling, it does not replace a rubber-tired roller.

2-2.2.5.3 Rubber-Tire Rollers.

Rubber-tired rollers are used commonly for intermediate rolling of HMA mixtures. They are also used as breakdown rollers when mixtures are excessively tender. Whether used as breakdown or intermediate rollers, these rollers provide for an increase in compaction and produce a watertight surface. Ensure a rubber-tired roller consisting of nine tires, four on one end of the roller and five on the end of the roller and with a minimum total mass load of 18,180 kilograms (40,000 pounds) or 2,020 kilograms (4,440 pounds) per tire and a minimum tire inflation pressure of 620 kilopascals (90 pounds per square inch (psi)), is available for construction of heavy-duty pavements on roads or airfields. Ensure the rubber-tired roller has a watering system for the tires and has scrapers and pads in good shape to prevent accumulation of materials on tires.

Commercially available products are available that when applied to the rubber tires keep the HMA mixture from sticking to tires. An effective method for preventing pickup is to get the tires hot and keep them hot. In cold climates or in windy conditions, apply skirts to protect the tires from excessive cooling caused by wind. While roller types are not in the specifications, it is recommended that a rubber-tired roller be included in the train of rollers for compaction of all heavy-duty HMA pavements, and these rubber tire rollers have tires containing the minimum pressures and weights as described above.

The rated weight for a rubber tire roller is the loaded weight for the roller. If the roller is not filled with ballast (sand and water), the weight is less than the rated weight. If the actual weight of the roller is needed, weigh it. Rubber tire rollers always yield the best results for longitudinal cold joints and transvers transition joints between asphalt and concrete vs. vibratory or non-vibratory steel rollers.

2-2.2.5.4 Operation of Rollers.

Operate rollers at or below a rate of 4.8 to 8 kilometers per hour (3 to 5 miles per hour) (fast walking speed). Ensure starts and stops are gradual to avoid damaging the freshly laid mixture. Quick turns or any turns that cause cracking on freshly laid mixture is not allowed.

2-3 MATERIALS.

2-3.1 Asphalt Materials.

Asphalt materials used in hot-mix paving operations include the products conforming to the specifications listed in Table 2-2. Asphalt cements for use in pavement design and construction are graded or classified in one of two ways. They are graded on the basis of penetration (ASTM D946) or by the performance grading system (ASTM D6373).

Currently, in the continental United States (CONUS) and many other countries, the performance grading system is used; however, in many countries, penetration grades of asphalt are obtained more easily. If performance graded asphalt is available, specify it for any airfield project. In general, use the softest grade of asphalt cement consistent with traffic and climate. Base selecting a grade of asphalt cement on several considerations, such as climate, traffic conditions, economics of asphalt availability, and previous regional experiences. Traffic conditions and economic considerations vary from project to project, but environmental conditions and regional experiences are normally similar. For example, in warm and hot regions, primarily select a grade of asphalt cement to ensure that the mix is stable during the summer months, and in cold regions, primarily select a grade of asphalt cement to ensure that the mix is not prone to cracking during winter months. These requirements are discussed in the following subparagraphs.

Table 2-2 Specification References for Asphalt Materials

Bitumen Type Specification

Asphalt cement (performance-graded asphalt binder) ASTM D6373

Asphalt cement (penetration-graded) ASTM D946

Cutback asphalt (slow-curing type) ASTM D2026

Cutback asphalt (medium-curing type) ASTM D2027

Cutback asphalt (rapid-curing type) ASTM D2028

Asphalt, emulsified (anionic) ASTM D977

Asphalt, emulsified (cationic) ASTM D2397

2-3.1.2 Performance Graded (PG) Asphalt Cements.

The performance grading system (ASTM D6373) classifies asphalt binders using performance-related properties according to the upper and lower temperatures that are expected during the life of the pavement. American Association of State Highway and Transportation Officials (AASHTO) R29 provides information for grading or verifying the performance grade of asphalt cement. PG asphalts have replaced penetration- and viscosity-graded asphalts in the United States. Unlike the viscosity and penetration grading systems, the performance grading system is used to classify unmodified as well as polymer modified asphalt binders.

2-3.1.3 Classification Method for PG Graded Asphalt Cements.

Specify PG graded asphalt binders wherever available. Consider the same PG binder grade as that used by the state highway department in the specific geographic area as the base grade for the project (e.g., the PG grade specified in that specific location for dense-graded mixes on highways with design equivalent single axle loads (ESAL) less than 10 million). The exception is that grades with low temperature requirements higher than PG XX-22 are not to be used (e.g., PG XX-16 or PG XX-10), unless the engineer or the local DOT has had successful experience with these grades.

Rutting is not a problem on airport runways but there have been issues on taxiways where the traffic is slower moving. At airfields with a history of stacking on ends of runways and taxiway areas, rutting has occurred due to the slow speed of loading on the pavement. If there has been rutting on the project or if stacking occurs regularly during the design life of the project, then apply the following grade "bumping" for the top 125 millimeters (5 inches) of paving in the end of runway and taxiway areas: for aircraft tire pressure between 0.7 and 1.4 megapascals (100 and 200 psi), increase the high temperature grade by one grade; for aircraft tire pressure greater than 1.4 megapascals (200 psi), increase the high temperature grade by two grades. For those projects used by aircraft and missions intended to primarily support air operations on ships, a high temperature increase of two grades is required for all HMA projects.

PG grades are provided in 6 degree increments, for example PG 64-22, PG 70-22, PG 76-22 on the high temperature side and PG 64-22, PG 64-28 on the low temperature side. However, many state DOTs, in the southern climates, have selected a mid-range grade on the high end, PG 67-22, as the primary grade of asphalt binder to use. When in these states specify the mid-range grade, PG 67-22, unless the high temperature grade needs to be bumped to be more resistant to rutting.

Polymer-modified asphalt (PMA) has been shown to perform well for improving the resistance to rutting. Using PMA results in a bumped grade of asphalt binder. When bumping the high temperature grade, ensure the low temperature grade remains the same as that for the base grade asphalt. A rule of thumb is that any asphalt binder, having the sum of the high and low temperature grades exceeding 90, is likely to contain a polymer. For example a PG 64-22 has a sum of 86 and this is likely not modified; however, a PG 76-22 has a sum of 98 and this asphalt binder is almost certainly modified. Changing from a PG 64-22 to a PG 76-22 provide much improved resistance to rutting but substantially increase the cost of the asphalt mixture (by 15%, but this varies considerably).

2-3.1.3.1 Polymer Modification of Asphalts.

Many polymers greatly improve the stiffness and flow…