W912DW20R0019 Attachment I - Combined UFCs.pdf

Inspector’s Manual for HMA/PCC Construction TSC-1, Jan 2013 Page i

Contents

CHAPTER 1 INTRODUCTION

1-1 OVERVIEW

1-2 PURPOSE

1-3 FORMAT

1-4 ACKNOWLEDGEMENTS

CHAPTER 2 GENERAL REQUIREMENTS

2-1 LABORATORY COMPLIANCE

2-1.1 Introduction

2-1.2 Accrediting Agencies

2-1.3 USACE Validation

2-1.4 Compliance Checklist

2-2 SUBMITTALS

2-2.1 Introduction

2-2.2 Procedures

CHAPTER 3 HOT MIX ASPHALT

3-1 SUBMITTALS

3-1.1 Introduction

3-1.2 Procedures

3-1.3 Requirements

3-2 MATERIALS AND MIX DESIGN

3-2.1 Introduction

3-2.2 Aggregates

3-2.3 Asphalt Binder

3-2.4 Mix Design

3-2.5 Mix Design Checklist

3-3 PLANT PRODUCTION

3-3.1 Introduction

3-3.2 Stockpile Operations

3-3.3 Stockpile Checklist

3-3.4 Hot Mix Asphalt Plants

3-3.5 Asphalt Plant Checklist

3-4 TRANSPORTATION

3-4.1 Trucking Checklist

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3-5 SURFACE PREPARATION

3-5.1 Introduction

3-5.2 Milling and Grinding

3-5.3 Crack Sealing

3-5.4 Repair of Local Damaged Areas

3-5.5 Application of Tack Coat

3-5.6 Application of Prime Coat

3-5.7 Surface Preparation Checklist

3-6 PLACEMENT

3-6.1 Introduction

3-6.2 Transfer from Truck to Paver

3-6.3 Laydown Operation

3-6.4 HMA Placement Checklist

3-7 COMPACTION

3-7.1 Introduction

3-7.2 Compaction Equipment and Procedures

3-7.3 Transverse Joints

3-7.4 Longitudinal Joints

3-7.5 Density Measurement

3-7.6 Factors that affect compaction

3-7.7 Compaction Checklist

3-8 QC/QA TESTING AND ANALYSIS

3-8.1 Introduction

3-8.2 Quality Control

3-8.3 Control Charts

3-8.4 Aggregate Gradation

3-8.5 Asphalt Content

3-8.6 Air Voids

3-8.7 Voids in Mineral Aggregate

3-8.8 Marshall Stability and Flow

3-8.9 In-place Density (Mat)

3-8.10 In-place Density (Joint)

3-8.11 Smoothness

3-8.12 Grade

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3-8.13 QC/QA Checklist

3-9 PERFORMANCE PROBLEMS

3-9.1 Introduction

3-9.2 Rutting

3-9.3 Bleeding

3-9.4 Surface distortion

3-9.5 Cracking

3-9.6 Raveling

3-9.7 Moisture Damage

3-9.8 Block Cracking

3-9.9 Bibliography

CHAPTER 4 PORTLAND CEMENT CONCRETE

4-1 SUBMITTALS

4-1.1 Requirements

4-2 LABORATORY COMPLIANCE

4-2.1 Accreditation and Certification

4-2.2 USACE Validation

4-2.3 Compliance Checklist

4-3 MATERIALS

4-3.1 Introduction

4-3.2 Cementitious Materials

4-3.3 Aggregates

4-3.4 Chemical Admixtures

4-3.5 Water

4-3.6 Other Materials

4-3.7 Compliance Checklist

4-4. MIX PROPORTIONING

4-4.1 Introduction

4-4.2 Design Criteria

4-4.3 Aggregate Blending

4-4.4 Trial Batches

4-4.5 Compliance Checklist

4-5 PLANT PRODUCTION AND CALIBRATION

4-5.1 Introduction

4-5.2 Batch Plant Components

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4-5.3 Uniformity Test

4-5.4 Compliance Checklist

4-6 TRUCK MIXERS

4-6.1 Introduction

4-6.2 Transit Truck Mixers

4-6.3 Transit Mixer Modes

4-6.4 Truck Mixer Components

4-6.5 Uniformity Test

4-6.6 Volumetric Mixers

4-6.7 Compliance Checklist

4-7 SURFACE PREPARATION AND DEMOLITION

4-7.1 Surface Preparation

4-7.2 Checklist for Surface Preparation

4-7.3 Demolition

4-7.4 Checklist for Demolition

4-8 PLACEMENT OF REINFORCEMENT/ LOAD-TRANSFER:

4-8.1 Introduction

4-8.2 Slipform Construction

4-8.3 Reinforcement Checklist

4-8.4 Placement of Dowels

4-8.5 Dowel Checklist

4-8.6 Dowel Spacing

4-8.7 Dowel Placement Checklist

4-8.8 Dowelled Contraction Joints

4-8.9 Contraction Joint Dowel Checklist

4-8.10 Doweled Construction Joints

4-8.11 Dowels in Construction Joint Checklist

4-8.12 Alignment of Dowels

4-8.13 Dowel Alignment Checklist

4-8.14 Placement of Tie Bars

4-8.15 Tiebar Checklist

4-9 TRANSPORTING CONCRETE

4-9.1 Introduction

4-9.2 Haul Distance

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4-9.3 Equipment

4-9.4 Transportation Checklist

4-10 DISTRIBUTION AND PLACEMENT OF CONCRETE

4-10.1 Introduction

4-10.2 Placement and Distribution Checklist

4-11 SLIPFORM PAVING

4-11.1 Introduction

4-11.2 Equipment

4-11.3 Execution

4-11.4 Common Problems

4-11.5 Compliance Checklist

4-12 FIXED FORM PAVING

4-12.1 Introduction

4-12.2 Form Requirements

4-12.3 Paver Types

4-12.4 Accessories

4-12.5 Execution

4-12.6 Common Problems

4-12.7 Compliance Checklist

4-13 CONSOLIDATION

4-13.1 Introduction

4-13.2 Vibrators

4-13.3 Execution

4-13.4 Common Problems

4-13.5 Compliance Checklist

4-14 FINISHING, TEXTURING AND EDGING

4-14.1 Introduction

4-14.2 Finishing

4-13.3 Texturing

4-13.4 Edging

4-14.5 Common Problems

4-14.6 Compliance Checklist

4-15 CURING AND PAVEMENT PROTECTION

4-15.1 Introduction

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4-15.2 Curing

4-15.3 Checklist for Curing

4-15.4 Protection

4-15.5 Protection Checklist

4-15.6 Hot Weather Protection

4-15.7 Checklist for Hot Weather Concrete

4-15.8 Cold Weather Protection

4-15.9 Checklist for Cold Weather Placement

4-16 GRADE AND SMOOTHNESS

4-16.1 Introduction

4-16.2 Grade

4-16.3 Smoothness

4-16.4 Diamond Grinding

4-16.5 Compliance Checklist

4-17 CONSTRUCTION AND CONTRACTION JOINTS

4-17.1 Introduction

4-17.2 Construction Joints

4-17.3 Joint Plans

4-17.4 Joint Alignment

4-17.5 Partial Panels

4-17.6 Drainage Structures and Embedments

4-17.7 Joint Check List

4-18 JOINT SAWING AND SEALING

4-18.1 Introduction

4-18.2 Saw Cut - Joint Layout

4-18.3 Timing for Sawing

4-18.4 Depth of Sawcut

4-18.5 Sawing Equipment

4-18.6 Temporary Sealing and Curing

4-18.7 Random Cracking

4-18.8 Factors Affecting Timing of Sawing

4-18.9 Check List for Sawing

4-18.10 Joint Reservoir Sawing

4-18.11 Preparation for Sealant

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4-18.12 Checklist for Joint Reservoir Sawing and Sealing

4-19 QC/QA TESTING AND PAY ADJUSTMENTS

4-19.1 Introduction

4-19.2 Contractor Quality Control (CQC)

4-19.3 Quality Assurance (QA) and Pay Adjustment

4-19.4 Compliance Checklist

4-20 IDENTIFICATION AND CAUSE OF HARDENED PCC DISTRESS

4-20.1 Introduction

4-20.2 Plastic Shrinkage Cracks

4-20.3 Spalling

4-20.4 Weak Surfaces

4-20.5 Slab Removal and Replacement

4-20.6 Compliance Checklist

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CHAPTER 1 INTRODUCTION

1-1 OVERVIEW.

This Pavement Inspection Manual is written to provide supplemental information, and help provide specific training for pavement construction inspectors. It primarily addresses Department of Defense airfields but also applies to hot mix asphalt and Portland cement concrete pavement construction on non-airfield areas such as roads. This manual provides guidance on all aspects of pavement construction and provides supplementary information to the other referenced technical publications. It is not intended to take the place of the contract specifications but should be used along with specifications to help ensure that a high quality pavement is constructed.

Airfield pavements are constructed by the same contractors that construct roads and highways. The airfield pavements often require higher quality materials than highways and it is important to ensure that the contractor produces a mix that meets the airfield specification requirements. Since most of the work performed by most contractors is on highways they may not be familiar with the UFGS specification requirements and this will require close inspection at the start-up of work. Airfield pavements are unique. In comparison to highways they are exposed to higher tire pressures, higher wheel loads, and blast and heat from jet engines. Any spalling, raveling, or other deterioration can lead to particles of pavement becoming dislodged resulting in foreign object debris (FOD). This FOD can become ingested into a jet engine resulting in costly damage and potentially loss of life.

The objective in constructing any pavement is to satisfy the design criteria and provide quality for maximum serviceable life with minimum maintenance. This objective may be achieved only through detailed attention to each step in the construction of a pavement. Inspectors play a key role in obtaining pavement quality and without their full commitment to the project, performance is likely compromised. They have to read and understand the contract specifications, observe and evaluate the contractors work, and take appropriate action on any contractor deficiencies. This includes the review of initial submittals through participation in the final acceptance. It involves the quality of materials and construction as well as workmanship.

The control of the quality and the production is the responsibility of the contractor and the assurance of the quality is the responsibility of the inspector and owner.

Many times one inspector is burdened with the responsibility for multiple contracts, which may be under construction at the same time. Sufficient qualified and experienced inspectors have to be provided to insure quality. Inspectors have to be thoroughly familiar with all provisions of the contract documents, including submittals. They have a difficult role because they are sometimes put into the position of justifying contract requirements, especially when they affect

Inspector’s Manual for HMA/PCC Construction TSC-1, Jan 2013 Page 2 schedules and unanticipated contractor costs. This manual should provide the inspectors with the background for many of the specification requirements and help ensure improved performance and a more satisfied customer.

1-2 PURPOSE.

The purpose of this manual is to provide guidance to the inspector, Quality Assurance (QA), and Quality Control (QC) representatives on construction oversight of hot mix asphalt (HMA) and Portland cement concrete (PCC) airfield pavements. This manual is not a contract document and does not take the place of the project specifications but is to be used as a companion document. The manual identifies a number of areas where problems often occur and it helps to clarify some of the specification requirements that may be a little more difficult to understand.

1-3 FORMAT.

The format of this manual follows the anticipated sequence of construction activity: materials and mix design, mix production, transporting mix, placing mix, QC/QA, and discussion of potential performance problems. A separate chapter is devoted to concrete and asphalt with each chapter being divided into each of these specific topic areas. Inspector’s checklist items are provided in colored text boxes. More detail concerning the checklist items is provided in the body of each chapter. Notes and “rules of thumb” are provided in yellow text boxes and inspector’s checklist items are provided in green text boxes.

The specification requirements are addressed in UFGS 321311, “Concrete Pavement for Airfields and Other Heavy-Duty Pavements More Than 10,000 Cubic Yards” and in UFGS 321215, “Hot Mix Asphalt for Airfields.”

1-4 ACKNOWLEDGEMENTS.

This manual is based on the “PCC Airfield Pavement Workshop” presentation developed by the U.S. Army Engineers, Transportation Systems Mandatory Center of Expertise (TSC) and the “HMA Airfield Pavement Workshop” presentation developed by the U. S. Army Engineer Research and Development Center (ERDC). Thanks to Terry Sherman and Gene Gutierrez for the use of their PCC photographs and for their guidance and insight and to Ray Brown for the use of his HMA photos. Thanks also to Richard Donovan and Jack Scott for their photos and authoring portions of this document.

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CHAPTER 2 GENERAL REQUIREMENTS

2-1 LABORATORY COMPLIANCE.

2-1.1 Introduction.

Contractor Quality Control (CQC) and Government Quality Assurance (GQA) begin with assuring that commercial or contractor-operated laboratories and staff are qualified to provide test results in accordance with the standards referenced in the specifications. For concrete and concrete aggregate testing and evaluation, laboratory compliance with ASTM C 1077, “Standard Practice for Laboratories Testing Concrete and Concrete Aggregates for Use in Construction and Criteria for Laboratory Evaluation” is required. For hot mix asphalt materials and mixtures compliance with ASTM D 3666, “Minimum Requirements for Agencies Testing and Inspecting Bituminous Paving Materials” is required.

2-1.2 Accrediting Agencies.

Independent third-party agencies provide the basic laboratory and staff inspection services. These inspections are broadened into a laboratory accreditation by including a review of the laboratory’s organization, human resources, facilities, equipment, reports and records, and quality control system.

Independent third-party accrediting agencies include:

• NVLAP, National Institute of Standards and Technology (http://ts.nist.gov/standards/accreditation/index.cfm)

• A2LA, American Association for Laboratory Accreditation (http://www.a2la.org/)

• CMEC, Construction Materials Engineering Council (http://www.cmec.org/)

• AASHTO, American Association of State Highway and Transportation Officials (http://www.amrl.net/Portal/AMRLLogin.aspx)

• ERDC-MTC, U.S. Army Engineers Research and Development Center, Materials Testing Center (http://gsl.erdc.usace.army.mil/SL/MTC/)

Upon accreditation by any of these agencies, the laboratory is issued a certificate which lists the laboratory’s name and address and the individual ASTM or AASHTO methods for which the laboratory is accredited.

This information can be double-checked by reviewing the accredited laboratories category on the accrediting agency’s website. An example of a print out from the ERDC MTC website is presented in Figure 2.1.

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Figure 2.1 Validation Printout from ERDC-MTC Website

Concrete technicians are certified by local chapters of the American Concrete Institute (ACI) located at http://www.concrete.org/certification/cert prog.asp. The following grades of technician certification are required:

• Concrete Transportation Inspector - personnel responsible for inspection of concrete paving operations

• Concrete Flatwork Technician/Finisher - lead foreman or journeyman of the concrete placing, finishing and curing crews

• Concrete Field Testing Technician, Grade I - field testing technicians

• Concrete Strength Testing Technician or Laboratory Testing

Technician, Grade I or II - laboratory testing technicians.

There is no national certification program for those involved with hot mix asphalt testing and inspection. Within DOTs, individuals are certified at the state or regional level in some regions. Certification categories generally include three areas: materials technician, mix designer, and roadway inspector. Those

Laboratory Name

Street Address City, State, Zip Code Telephone Number

Expiration Date: January 27, 2009

Aggregate: ASTM C40 C117 C127 C128 C136 C29 C88 C123 C131 C142 C535 C566 C702 C1252 C1260 D75

D2419 D4791 D5821 CRD-C104 CRD-C119 CRD-C130

Bituminous: ASTM D70 D2170 D2171 D2726 D3203 D3666 D4867 D5444 D6307 D6925 D6926 D6927

Concrete: ASTM C31 C39 C138 C143 C172 C173 C231 C1064 C42 C78 C157 C174 C192 C511 C617 C1077 C1231

Soils: ASTM D421 D422 D698 D1140 D1557 D2166 D2216 D2434 D2435 D2487 D2488 D2922 D3017 D3740 D4253 D4254 D4318 D4643 D5084

Masonry: ASTM C140 C1093

AASHTO Accredited

Methods Inspected

NOTE: The accreditation is for the listed laboratory only and does not cover branch offices, field laboratories, portable laboratories, or other locations.

Separate inspections are required for these subsidiaries.

Not all the specified tests may be listed for a given laboratory. Typical omissions include ASTM C 78, C 1260 and C 1567. Additional inspections or an additional accredited laboratory will be required to perform any missing test methods.

Inspector’s Manual for HMA/PCC Construction TSC-1, Jan 2013 Page 5 working on airfield pavements should, as a minimum, be certified within the local state DOT. A national certification program, is needed but has not yet been established.

2-1.3 USACE Validation.

For projects managed by the U.S. Army Corps of Engineers (USACE), validation of the laboratory is required. This validation is performed by ERDC-MTC. The validation process ranges from a desk audit of the accrediting agency’s documentation for an accredited laboratory to a full scope inspection/accreditation for an unaccredited laboratory. This validation is performed at the Contractor’s expense and should be performed prior to initiating any asphalt or concrete materials sampling or testing.

2-1.4 Compliance Checklist.

2-2 SUBMITTALS.

2-2.1 Introduction.

The submittal process is the Contractor’s method for documenting his materials, methods, and quality control processes to produce concrete pavement in accordance with the specification requirements.

All submittals for a definable feature of work shall be submitted and approved before the preparatory meeting is scheduled for that feature. The Contracting Officer may request submittals in addition to those specified when deemed necessary to adequately describe the work covered in the respective sections.

2-2.2 Procedures.

• Submittal includes:

• Laboratory accreditation certificate

• ACI concrete technician certificates

• Local DOT certification for those dealing with HMA

• The accredited laboratory actually does the work, it’s not subcontracted out

• Accreditation should not expire for the duration of the laboratory work

• All the specified test methods have been inspected

• ERDC-MTC validation has been conducted (for USACE managed projects)

• All certifications are current and the appropriate level of expertise

• Use the agency websites to check and resolve discrepancies

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The contact submittal procedures are contained in UFGS 013300, “Submittal Procedures.” The following items highlight the requirements.

2-2.2.1 Contractor Submittals:

• Units of weights and measures used on all submittals are to be the same as those used in the contract drawings.

• Each submittal is to be complete and in sufficient detail to allow ready determination of compliance with contract requirements.

• Contractor's Quality Control (CQC) System Manager and the Designer of Record, if applicable, to check and approve all items prior to submittal and stamp, sign, and date indicating action taken.

• Proposed deviations from the contract requirements are to be clearly identified.

• Submittals requiring Government approval are to be scheduled and made prior to the acquisition of the material or equipment covered in the submittal.

2-2.2.2 Government Review:

Government approval is required for submittals with a "G" designation; submittals not having a "G" designation are for information only. Government approval is required for extensions of design, critical materials, deviations, equipment whose compatibility with the entire system must be checked, and other items as designated by the Contracting Officer.

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CHAPTER 3 HOT MIX ASPHALT

3-1 SUBMITTALS.

3-1.1 Introduction.

The submittal process is the Contractor’s method for documenting materials, mix design, equipment, construction methods, and quality control processes to produce hot mix asphalt in accordance with the specification requirements. All submittals for a definable feature of work shall be submitted and approved before the preparatory meeting is scheduled for that feature. The Contracting Officer may request submittals in addition to those specified when deemed necessary to adequately describe the work covered in the respective sections.

3-1.2 Procedures.

The contact submittal procedures are contained in UFGS 01 33 00, “Submittal Procedures.” The following items highlight the requirements, as applicable to hot mix asphalt (HMA) airfield pavement construction.

3-1.2.1 Contractor Submittals. Units of weights and measures used on all submittals are to be the same as those used in the contract drawings. Each submittal is to be complete and in sufficient detail to allow ready determination of compliance with contract requirements. Contractor's Quality Control (CQC) System Manager and the Designer of Record, if applicable, are to check and approve all items prior to submittal and stamp, sign, and date indicating action taken. Proposed deviations from the contract requirements are to be clearly identified. Submittals requiring Government approval are to be scheduled and made prior to the acquisition of the material or equipment covered in the submittal.

Government approval is required for submittals with a "G" designation; submittals not having a "G" designation are for information only. Government approval is required for extensions of design, critical materials, deviations, equipment whose compatibility with the entire system must be checked, and other items as designated by the Contracting Officer. All submittals in the project specifications are classified as “G.”

3-1.3 Requirements.

The submittal requirements are provided in the project specifications. Some of the more important items to look for are discussed below.

3-1.3.1 Placement Plan. The contractor is required by the specifications to provide a placement plan. This placement plan should provide information including proposed schedule of work, planned lane width, sequence of paving, Inspector’s Manual for HMA/PCC Construction TSC-1, Jan 2013 Page 8 and method for handling longitudinal joints. When changes in the plan are expected a revised plan should be submitted to the government.

3-1.3.2 Mix Design. The items required to be provided in the mix design are clearly identified in the specifications. Some important items that are often overlooked in the mix design include identifying the amount of natural sand used in the mixture, the laboratory compactive effort during mix design, and the grade of asphalt cement.

Mix designs that were developed several months or in some cases several years prior to the project are sometimes submitted for approval. Aggregate sources and asphalt cements may change with time so an old mix design may not still be accurate. Hence, the specifications require that the mix design shall not be over 6 months old and this requirement should be enforced. If an old mix design is desired for use, the contractor must verify that it is still accurate.

3-1.3.3 Contractor Quality Control Plan. The CQC program does not automatically ensure that satisfactory construction quality is obtained. QA has to make sure that CQC takes the initiative to identify any material or construction issues and to take steps to correct the problems. In many cases the CQC will only be as strict on the contractor as QA requires, hence, if QA does not closely oversee CQC then CQC will not closely control the contractor.

The first step to ensuring that the CQC program is effective is the development of an acceptable QC plan. The QC plan should clearly lay out the steps that QC is going to take to ensure that a quality product is produced. The plan should provide detail on types of inspections to be made, tests to be conducted, where samples will be taken, number of tests to be conducted, and proposed action to be taken if inspections or test results are not satisfactory.

3-1.3.4 Submit Samples of Aggregates and Asphalt Cement. The primary purpose of these samples is to allow the QA to validate the mix design if desired.

Most of the time the mix design can be evaluated based on the information provided but there might be cases where one or more of the tests may need to be verified. The aggregates should be inspected to determine if natural sand is being used and to observe the overall quality of all aggregate.

Look for good angularity in the aggregate and make sure that there is no contamination such as clay balls and organics. Angularity is typically a potential problem with naturally occurring gravels and sands (however the amount of sand to be used in the mix is controlled so rounded natural sand is allowed). Naturally occurring gravels must be properly crushed to be acceptable for HMA. If there are any concerns about the mix design, the mix design should be validated by QA or, if necessary, the contractor should provide additional test results and/or explanations concerning the design.

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3-1.3.5 QC Test Results. The contractor must provide a QC plan to indicate the testing and inspection plan and this has to be approved by the government. As the tests are conducted and inspections are made during the construction process, a report of the results should be prepared and provided to the government for review and concurrence. These test results and inspection observations should be made available to the government within a short period of time after the work is completed. The contractor should indicate in the CQC plan when the reports will be made available to the government. Generally test and inspection results are made available to the government by the end of the day following the day that work was completed (24 hours).

3-1.3.6 Asphalt Cement Certification. The contractor should provide the government with a certificate, for each truckload of asphalt cement, from the material supplier showing the asphalt cement test results and showing that the asphalt cement being used meets the specification requirements. A certificate should be provided for the original asphalt cement used in the mix design and for all additional asphalt cement delivered to the contractor. The government does not normally conduct these tests as part of QA but, if needed, samples can be taken and sent to a commercial laboratory for testing.

Also it is good to keep samples of the asphalt cement in a closed container so that the asphalt cement can be tested later if a problem occurs. It is recommended that these samples be kept for at least one year after the entire project is completed.

3-1.3.7 Laboratory Certification. When working on a military airfield project, the laboratory (QC and/or QA) to be used on the project must be inspected and validated by the Materials Testing Center of the Engineer Research and Development Center, Corps of Engineers before work begins. This certification will take a little time so QC and QA, if applicable, should contact the Center early to allow enough time to certify the laboratory before work begins.

3-2 MATERIALS AND MIX DESIGN

3-2.1 Introduction.

The quality of the materials used to produce an asphalt mixture is very important to ensure good performance of the constructed product. Without high quality materials, the performance of the project will likely not be satisfactory even if good mix design and construction methods are used. After it has been determined that acceptable materials are available, a mix design is developed to determine the optimum asphalt cement and aggregate proportions. Generally the mix is designed by selecting the proportions of aggregates to provide a gradation meeting the specification requirements and then determining the asphalt content to provide 4% air voids in the mixture.

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Even though the mix design is typically performed by the contractor, it is important that QA ensure that the completed design is acceptable prior to beginning construction of the project. It is also important that the design, as specified in the specifications, be a recent design since materials, such as aggregates and asphalt binder, change with time. A design that was conducted 2 or 3 years ago may not be representative of the materials currently available.

A government representative should ensure that the materials and mix design meet the specification requirements. This will involve reviewing the finished design and may involve observing some of the lab testing during conduct of the design.

The overall management of the construction project is the responsibility of the government and this requires that proactive steps be taken to ensure that the overall quality is satisfactory. It is not good enough to simply rely on CQD to ensure that the construction quality is acceptable. This is a recipe for disaster.

The information provided in this section provides guidance to the inspector that should enhance his/her ability to evaluate the quality of materials and mix design.

This discussion will include aggregates, asphalt cement, and mix design.

3-2.2 Aggregates.

Prior to testing the aggregates, representative samples of each aggregate source to be used must be taken. There are two types of samples that can be obtained:

representative and random. A representative sample is taken in such a way that the sample is representative of the entire stockpile of material being evaluated.

A random sample is taken by obtaining a sample in a random location or at a random point in time. This random sample will likely not be representative of the entire quantity of material being sampled but it should represent the material in the localized area where the sample is taken.

Taking a number of random samples and then combining them will provide a representative sample of the material being evaluated. Representative samples are generally taken for materials evaluation and mixture design prior to start of mixture production. Random samples are typically utilized during quality control operations during the construction process. For example, a sample of asphalt mixture for gradation testing is normally taken at a random point in time during the production of the mixture.

It is important that QA observe the condition of the stockpiles that are going to be used on the project. QA has to be at least knowledgeable enough about the construction operation to ask questions of the QC people that will help assure that sufficient control measures are in place to provide a quality product at the conclusion of the project. A good time to observe the stockpiling operation is when aggregate samples (ASTM D75) are being taken for mix design.

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It is important to look at stockpiling methods to ensure that excessive segregation is not occurring. It is also important to look at the stockpiles to ensure that they don’t contain any organic materials, clay balls, or any other type of contamination which may affect the quality of the stockpiles. Visually inspecting aggregate samples in the laboratory or in the office does not provide a good evaluation of the overall quality of the aggregate. Visually inspecting the stockpiles does provide a good picture of the quality as far as clay balls, organic material, etc.

This will be discussed in more detail in the section on asphalt plants.

In areas where natural gravels are used it is important to ensure that the gravel is properly crushed before use in asphalt mixtures (Figure 3-1). Rounded particles do not provide sufficient shear strength and often result in the mixture rutting when exposed to traffic. The fractured face count, which is specified in the specifications, is used to determine if a coarse aggregate is properly crushed.

Figure 3-1 shows crushed gravel on the left side and rounded, uncrushed, gravel on the right side.

It is also important to ensure that too much natural sand is not used in the mix.

For airfields the amount of natural sand is limited to 15 percent maximum according to the specifications. Natural sands tend to be rounded which can result in a mixture stability problem. Also the asphalt often does not bond very well to sand particles primarily due to the smooth sides and/or high silica content resulting in eventual stripping within the mixture as well as other performance problems.

Figure 3-1 Rounded Gravel on the Right and Crushed Gravel on the Left

After the aggregate samples are obtained, the materials are brought back to the laboratory for testing. The specifications identify the tests that have to be

Inspector’s Manual for HMA/PCC Construction TSC-1, Jan 2013 Page 12 conducted and provide the requirements that the aggregates must meet. If in doubt about the quality of the material being proposed for use, past performance is often a very good indicator. Since the state Departments of Transportation (DOTs) do a lot of HMA work and are typically very familiar with specific aggregates throughout their state, they should be contacted if in doubt about the aggregate quality or the history of performance for a particular aggregate type.

They will likely have a good understanding of the history of past performance with each aggregate available within the state.

The inspector cannot oversee all of the sampling and testing involved with the mix design but enough oversight needs to occur to provide some level of understanding of what materials are being used and the overall quality of these materials. The best way to obtain some indication of the quality of the materials and the way the materials are being handled is to visit the plant where the materials will be produced.

It is difficult to obtain truly representative samples from stockpiles of aggregate.

The easiest place to take a sample is near the bottom of the stockpile but this usually contains a coarser gradation since the coarse material tends to roll down the side of a stockpile when stockpiles are being built or material is being added to a stockpile.

A typical stockpile is shown in Figure 3-2. When taking a representative sample (ASTM D75) of the stockpile, several small random samples should be taken at various points around the stockpile but about ½ of the way up the side of the stockpile. It is also important that the surface material be removed when taking a sample of a stockpile and the material sampled is taken from underneath the outer material that is removed.

Some stockpiles are significantly high so one must be careful when working around a stockpile, otherwise, an injury may occur due to the side of the stockpile giving way. If the stockpile is too high it may be necessary to remove samples with a loader or some other device to ensure safety to those involved in taking the samples. A representative sample can then be taken from the bucket load of material taken from a random location.

When utilizing a loader to retrieve samples, it is recommended that the bucket be at least six inches above the bottom of the pile to avoid both contaminants and coarser particles. It is good practice to have the loader go through the face of the material and then turn the sample over on the ground. Once the sample is on the ground, the top should be scalped to sample from the “heart” of the material.

Some of the laboratories conducting QC testing for the contractor are not very well qualified and some oversight is needed to ensure that proper sampling and testing techniques are used. When the contractor and QC know that there will be

Inspector’s Manual for HMA/PCC Construction TSC-1, Jan 2013 Page 13 oversight, they will generally make an effort to ensure that qualified people perform the work and that all appropriate test procedures are followed. The lack of good oversight only encourages some laboratories to use some of their less experienced people on the project often resulting in loss in test quality and lack of good inspection of the constructed product.

The problems that are most commonly observed with aggregate properties, tests, and inspections include:

• Too much material passing the No. 200 sieve,

• Inadequately crushed coarse aggregate (this only occurs with naturally occurring gravel aggregates),

• Too much natural sand, and

• contamination with clay balls and organics

Figure 3-2 Typical Aggregate Stockpile

The high amount of material passing the No. 200 sieve typically occurs with crushed stone. Some crushed stone is softer than others and it is this softer stone that generates high dust content during the crushing operation. There are a number of ways this high percentage of No. 200 material can be reduced. It can sometimes be reduced by adjusting the percentages of each stockpile being used, wasting some of the dust caught in the dust collector, washing the fine aggregate stockpile, or obtaining a new source of aggregate.

Inadequately crushed coarse aggregate may occur when gravel materials are used but should not be a problem when crushed stone is used. When the gravel does not meet the fractured face requirements, this is caused by inadequate set

Inspector’s Manual for HMA/PCC Construction TSC-1, Jan 2013 Page 14 up at the crushing operation. In general to produce crushed gravel with up to ½ inch maximum aggregate size requires that the minus ½ inch material must be removed from the uncrushed gravel stockpile before crushing. So if the quarry does not first waste this material, adequately crushed material will not be produced.

Too much natural sand can occur anywhere that natural sand is available. It is typically cheaper than other aggregate materials so using the sand can result in somewhat lower material costs. Some amount of natural sand is not detrimental to the mixture quality but it must be ensured that the amount used does not exceed the specification requirements of fifteen percent. Once the sand is mixed with the other aggregates and asphalt, there is no way to determine the amount of natural sand in the mixture. The only way to measure the amount of natural sand in a mixture is to measure it from the rate of feed of the sand compared to other materials during mixture production.

There are lots of examples where stockpiles contain clayballs and organic material. The most likely source of these problems is the natural sand stockpile but it can occur in all aggregates. When a stockpile has organics or clayballs, it should not be allowed to be used in the HMA production. It is unlikely that this problem will be noticed when materials are sampled and submitted to the government for review. Generally, the only way to see this problem during the production process is to closely observe the aggregate stockpiles at the HMA plant.

3-2.3 Asphalt Binder.

The grade of asphalt binder to be used will be specified in the specifications.

The testing, to confirm that the asphalt cement supplied to the project meets the specification requirements, is typically performed by the refinery and/or asphalt supplier and a certificate of tests is provided, with each tanker of material

Checklists for aggregates during mix design

1. Ensure that percentage passing the No. 200 sieve is not too high

2. Ensure that aggregate is adequately crushed

3. Make sure that the amount of natural sand used in the mixture does not exceed the specification limit

4. Observe stockpiles, in addition to testing, to ensure that no organic material or clayballs are in stockpile

5. All specification requirements for the aggregate should be met.

Inspector’s Manual for HMA/PCC Construction TSC-1, Jan 2013 Page 15 delivered to the plant, showing the test results for the asphalt cement. Unless there is a potential problem or concern, additional testing of the binder is not typically performed by the government. Certainly if there is reason to believe that government testing should be performed then this should be accomplished but otherwise this is not normally performed.

The most common procedure that is used is to take 1 gallon samples of the asphalt binder during binder delivery and to store these samples for future testing if necessary. If there is no performance problem after a predetermined amount of time, typically 1 year after completion of construction, then the samples can be disposed.

The asphalt binder grading system that is normally used is the performance grading (PG) system. With this system the grade of asphalt binder is specified based on the upper and lower temperatures that are expected at the location the pavement is being constructed.

The most common grade is PG 64-22. This PG grade is designed to ensure that the asphalt binder is stiff enough to perform satisfactorily up to a high pavement temperature of 64 degrees Celsius (C) and flexible enough to perform satisfactorily down to a low pavement temperature of -22 degrees C. If the pavement is built in an area with a climate that experiences hotter temperatures then the high end grade of the asphalt binder will have to be increased above the 64 degrees C. If the pavement is built in a colder climate then the low end grade of the asphalt binder may have to be decreased below -22 degrees C.

The designer will often bump the grade of asphalt binder when paving taxiways, runways, etc. where there will be slow moving traffic. In other words the high temperature PG grade may be increased to a 76 from a 64, for example, to provide a factor of safety against rutting. This higher grade asphalt binder will likely be more expensive but it will be more resistant to rutting.

Adding the high temperature and low temperature numbers together will help determine if the asphalt binder is modified (polymer or some other modifier). If the sum of the high and low temperature numbers exceeds 90 then the asphalt binder is likely modified. If the sum is approximately 90 or less then the asphalt binder is likely not modified. For example, a PG 64-22 adds up to 86, hence, this asphalt binder is probably not modified. However, a PG 76-22 adds up to 98 and this asphalt binder is almost certainly modified. Generally a modified asphalt binder will cost significantly more than a non-modified asphalt binder.

It is not uncommon for a contractor to have more than one asphalt binder storage tank. These extra tanks are needed since many state DOTs typically use at least 2 grades of asphalt binder for a given climatic area. One grade is used for normal construction and another grade is used for high volume roads such as

Inspector’s Manual for HMA/PCC Construction TSC-1, Jan 2013 Page 16 interstate highways. It is important to ensure that the correct grade of asphalt binder is actually being added to the mixture being produced.

Even though the correct grade of asphalt binder is added to the mix during production, the grade can be altered by the amount of heat that is applied to the mixture. The specifications set an upper limit of approximately 350 degrees Fahrenheit (F) for the asphalt mixture. When the mix is heated to approximately 350 degrees F or higher, damage will likely occur to the asphalt binder. This high heat will remove some of the lighter portions of the asphalt binder and some oxidation will occur during the mixing process.

After the asphalt binder (which is in thin films coating aggregate particles) is exposed to high heat, it will stiffen and become more brittle and will have more cracking potential at low temperatures. Hence, care is needed during plant production to ensure that excessive damage to the asphalt binder does not occur. It is important that QC make temperature measurements throughout the day to ensure that mixture temperatures are maintained within a desirable range (high enough for the mix to be workable and compactable but low enough so that the asphalt cement is not damaged).

3-2.4 Mix Design.

After the asphalt binder and the aggregate have been shown to meet the specification requirements, a mix design can be performed. There is no need to begin the design before it is known that the asphalt binder and the aggregate are satisfactory. Retests on both the aggregates and liquid asphalts may be an option when either material fails to meet design requirements.

There are two methods that are generally used to design asphalt mixtures. The most common method for airfields is the Marshall method, however, the most common method for highways is the Superpave mix design method. The biggest difference between these two methods is the procedure used to compact samples in the laboratory. The Marshall method uses a hammer (Figure 3-3) while the Superpave method uses a gyratory compactor (Figure 3-4).

The first step in the mix design process is to perform aggregate gradation tests on all aggregates to be used and then to determine the percentage of each aggregate to use in the mixture to provide a blend of aggregates that meets the specification requirements. This is typically a trial and error procedure that can quickly determine the percentage of each aggregate. Washed gradations (ASTM C117) should always be used during the mix design process.

Inspector’s Manual for HMA/PCC Construction TSC-1, Jan 2013 Page 17

Figure 3-3 Manual Marshall Hammer

Figure 3-4 Superpave Gyratory Compactor

Inspector’s Manual for HMA/PCC Construction TSC-1, Jan 2013 Page 18

After the desired percentage of each aggregate is determined, a number of samples are prepared using these percentages and placed in an oven to heat and dry the aggregate. Typically, after storing the samples overnight at the desired mixing temperature, various percentages of asphalt binder are added to the aggregate blends. Most often, three replicate samples will be prepared at each asphalt binder content and the samples compacted. The samples should be compacted with 75 blows per face with a Marshall hammer when designing mixtures for an airfield or with 75 gyrations with a gyratory compactor if Superpave is specified for design.

The Marshall hammer should be the manual type (Figure 3-3). Research has shown that the mechanical and manual hammers provide different results when used for compaction. Typically the mechanical hammer will provide a slightly lower density than the manual hammer. This lower density will require that more asphalt binder be added to the aggregate to provide the proper air void content after compaction. It is important that the compaction pedestal be placed on and anchored to a solid foundation prior to being used for compacting samples.

Generally, a concrete slab is used as the foundation.

There have been many instances where the quality control personnel on a project used a mechanical hammer even though the manual hammer is specified in the specifications. A mechanical hammer can be used but it must first be calibrated to determine the number of blows needed to provide a density similar to that with the manual hammer. This calibration needs to be performed using the mixture being used for the project since the mixture properties will affect the correlation between the two hammers. When a mechanical hammer is used for compaction, a copy of the calibration should be provided to the government.

After the samples are compacted the mixture properties have to be determined.

Properties that are used to evaluate the quality of asphalt mixture include:

• Unit weight

• Air voids

• Voids in mineral aggregate (VMA)

• Voids filled with asphalt

• Stability

• Flow

The mix design should show plots of the mixture properties versus asphalt content. Typical plots are shown in Figure 3-5. The design is usually conducted to provide 4 percent air voids in the laboratory compacted samples.

Inspector’s Manual for HMA/PCC Construction TSC-1, Jan 2013 Page 20

The mixture properties have typical relationships when plotted vs. asphalt content. There is always variability in measured mixture properties so the trend might not be obvious in some cases. As the asphalt content increases the density increases to a point and then begins to decrease. With some aggregates the density continues to increase slightly with increasing asphalt content within the range of asphalt contents normally used. This is not a problem.

As the asphalt content increases, the stability increases to a point and then begins to decrease with increasing asphalt content. The stability curve looks similar to the unit weight curve but generally it will peak at slightly lower asphalt content.

As the asphalt content increases, the air voids decrease. The rate of decrease reduces as the asphalt content continues to increase.

As the asphalt content increases, the flow value increases. The rate of increase is higher as the asphalt content continues to increase. The flow test results are sometimes unreasonably high when using modified binders. This is a problem with the test and does not indicate a mix that will perform poorly. For this reason, the flow requirements are generally waived when modified asphalts are used.

As the asphalt content increases, the VMA decreases to a point and then begins to increase again. Generally the bottom of the VMA plot is very near the optimum asphalt content. The VMA in the mix has to be above some minimum number so that a reasonable amount of asphalt binder can be added to the mixture.

The VMA is a measure of the voids in between the aggregate particles and if the VMA is too low then there is not sufficient room for the asphalt binder. The VMA is primarily controlled by the gradation and particle shape of the aggregate and is most sensitive to the percentage of material passing the No. 200 sieve. As this percent passing the No. 200 sieve increases, the VMA decreases.

After the mix design is completed tests are conducted to measure the moisture susceptibility of the mixture (ASTM D 4867). If the mixture is susceptible to moisture, the asphalt may strip off of the aggregate during the life of the pavement resulting in loss of asphalt binder from the mixture and thus loss of cohesion. This testing involves preparing samples to simulate the expected density in the field. One half of the samples will be conditioned in water and the other half will not be conditioned. If the conditioned samples lose too much tensile strength then the mixture fails the test and some adjustments must be made such as adding an anti-strip agent to the mixture.

Sufficient data must be provided to allow for a good evaluation of the mix design.

The government representative should have a good understanding of all aspects

Inspector’s Manual for HMA/PCC Construction TSC-1, Jan 2013 Page 21 of mix design to be able to identify any deficiencies in the design. Some of the data that should be included in the mix design report are provided below:

• Aggregate properties o LA abrasion o Specific gravity and absorption o Flat and elongated count o Fractured face count o Fine aggregate angularity o Sand equivalency o Soundness o Gradation

• Percent passing each sieve size for each aggregate used and for the blended aggregate

• Percent of natural sand in the mixture

• Plot showing gradation and specification limits

• Optimum asphalt content

• Table showing volumetric and specific gravity properties of asphalt mixture

• Material proportions

• Grade of asphalt cement

•…