Good Quality Control/Quality Assurance practices are essential to obtain a satisfactory product. Quality Control (QC) normally refers to those tests necessary to control a product and to determine the quality of the product being produced. Quality control testing is usually conducted by the supplier of the product – i.e. the contractor. Quality assurance (QA) refers to those tests and actions necessary to make a decision about the acceptance of the product and to ensure that the product being evaluated is indeed what the owner specified. The QA tests are usually conducted by the contractor.
In this module we will review the types of specifications, provide a short overview of process control, discuss where the sampling is accomplished and provide an introduction to acceptance procedures.
There are three fundamental questions that are a key to determining the quality of a product from an owner's perspective. These are: 1. What do we want? This question relates to the performance characteristics of HMA mixtures. 2. How do we order it? This question relates to selecting the critical or most important HMA mixture properties that affect performance characteristics and preparing specifications that use these properties and parameters. 3. How do we know we got what we ordered? This question relates to how the owner accepts the HMA mixture and includes both acceptance testing and inspection.
How do we order what we want? How one measures or defines the quality of an HMA mixture is usually dictated by the specifications (i.e., conformance to specifications). There are different types of specifications. These are: 1. Proprietary Product 2. Method 3. End Result 4. Performance Based 5. Warranty The Method and End Result type of specifications are the two that are most commonly used for HMA paving mixtures. The use of warranty specifications is growing throughout the United States.
The proprietary specification can be thought of like purchasing an automobile. You decide you want a Ford with a specific body type, a specific size of engine, etc. In other words – the only thing you accept is that specific item. It is generally not used in the Hot Mix Asphalt industry because it restricts competition.
Historically, method specifications have been the type most commonly used for HMA construction and some State highway agencies still use this type of specification. For this specification, maximum control is held by the specifying agency.
The disadvantages of a method specification is: 1. Contractors may not be allowed to use the most economical or “innovative” procedures to produce the product sought. 2. They are inspector intensive. 3. If the quality is measured and found to be less than desirable, the contractor has no legal responsibility to improve it. 4. The quality attained is difficult to relate to the performance of the finished product.
End result specifications are now being used by a number of State highway agencies and are increasing in popularity. In fact, end result specifications (or a form of end result) are rapidly becoming the most popular type of specification. For this specification, the specifying agency only sets the limits for the contractor. End result specifications are also referred to as performance specifications.
One approach that can often lead to problems is to combine a method specification with end-result testing. This is potentially a very controversial specification. If the contractor is directed as to what equipment to use and how to use it, and an end-result specification is also imposed on the product, arguments frequently result. Combining stipulated methods with required end results may render the specification legally indefensible.
The next step in the evolution of specifications was a more rational form of end-result specification in which, among other requirements, specification acceptance limits are derived using mathematical concepts proven valid in writing defense specifications. These mathematical concepts are proven and have been used in some states for almost 30 years. Additionally this concept can tie the materials properties to the specification and thus can tie the specification to the performance of the pavement.
Statistics is the science that deals with the treatment and analysis of numerical data. This course will hopefully provide the ability to use or apply simple statistics for analyzing test results for determining the quality of HMA mixtures and/or compliance to specifications. It is simply a mathematical process or tool for helping to make informed decisions. The level of statistical knowledge necessary for using a Quality Assurance (QA) specification is very basic; it is no more difficult than calculating most test results.
In order to be effective, QA must include the functions of process control, acceptance and independent assurance. All three of these QA functions provide measurement data on the quality of the materials or construction under consideration. Measurement is an important component of the continuous management functions in a total quality management (TQM) system. The value of measurement results depends entirely on how well conceived and executed is the measurement in the first place. Since the specifications stipulate the procedures to be followed and the tests to be run, well thought out, rationally developed specifications are important ingredients for quality improvement. The relationship among process control, acceptance and independent assurance varies from agency to agency, primarily depending on their experience in QA specifications. The one constant that must be present is the necessity for clearly stating which party is responsible for each function.
The process control function, often referred to as QUALITY CONTROL (QC), has become recognized as an important part of QA. Quality cannot be tested or inspected into a product after-the-fact. It must be present in the product from step-one. In virtually every instance, process control is best performed by the contractor or producer, or that party to the contract who has control over the product at its initial stage.
ACCEPTANCE. The acceptance function can be varied and may consist of acceptance testing, monitor testing, or process control monitoring. However, one essential ingredient is inspection. The need for an inspection activity is as important in a QA specification as it is in other types. This acceptance function is generally performed by the owner. However, some agencies have experimented with basing acceptance decisions on tests conducted by the contractor.
Independent Assurance (IA) is a management tool that requires a third party, not directly responsible for process control or acceptance, to provide an independent assessment of the product. The purpose of the IA program is to make independent checks on the reliability of the results obtained in acceptance sampling and testing and not for directly determining the quality and acceptability of the materials and workmanship. The tests are performed by the owner's personnel not normally responsible for process control or acceptance. For the IA program to be effective, inspectors who witness test procedures or obtain IA samples should make a strong effort to maintain good rapport with inspectors responsible for acceptance. A reasonable philosophy might be expressed by the following: it is not the purpose of IA to find things being performed incorrectly, but rather to verify that procedures are proper. However, for the IA program to be effective, all variations from specified procedures and significant differences between acceptance tests and IA tests must be reported. IA inspectors must be knowledgeable regarding all sampling and testing procedures so that they can recommend correction to procedures before leaving the project.
If you do not get what you ordered – if it is a car or TV you return it. But, if it is a pavement and it meets most of the requirements and will function your options may be different. Also it may have qualities that you want, such as improved smoothness, that are beyond the contract requirements. So you can penalize the contractor for not providing what you want; or, you can give him a bonus for providing something above and beyond. Or if it is very bad – you can reject it. But, the rejection option is seldomly used. What you do depends on how the item being out of tolerance affects the performance of the HMA pavement. For example if the pavement is too thin – the life of the pavement can be adversely affected. This slide shows a listing of the properties that are usually evaluated when considering performance.
Since about 1998 the industry has seen the rise of the use of warranties for pavement construction. They are being promoted by the more “progressive contractors”. The perception is that this will allow the HMA contractor to control his own destiny.
The idea of warranties has meet some resistance in the field. But, there are some advantages to this type of spec.
There are two types of warranties in use. The materials and workmanship warranties are being used for projects with a short duration. The performance warranties are being used for a longer duration.
There are some concerns about the use of warranty specifications. The biggest is that the small contractor that cannot afford to take the perceived risks associated with the use of a warranty specification will be unable to bid and will thus be driven out of the contracting business. The result would be less competitive bidding for the specifying agencies.
There are five different classifications of sampling types which define where the samples are taken. They include: 1. Judgment Sampling - The location of samples for this type of sampling is based upon the judgment of the technician or inspector. The sample is supposed to be selected to represent the overall quality or condition of the mixture being sampled. However, individual bias is almost always present and there is always a chance of both a conscious and an unconscious bias. 2. Quota Sampling - Sampling during strategic time frames or every time a procedure, equipment or source is changed in the construction process. This requires highly trained and experienced technicians or inspectors. 3. Systematic Sampling - The sampling of materials at uniform time, distance or production intervals. 4. Stratified Sampling - The sampling of materials that includes two or more independent parts (or specimens) of a given quantity of material. When a material is categorized by lots, the lots are divided into multiple parts based on a reasonable breaking point. 5. Random Sampling - This sampling involves the selection of samples so that each increment or specimen comprising the sample has the same chance of being chosen from the lot.
This slide shows the various locations for sampling aggregates. The location chosen depends on the use of the data. If you are doing quality control testing – you may sample the flowing aggregate steam or the conveyor belt – if you are doing acceptance testing you may sample the stockpiles, the transportation units or the roadway.
What you will learn….• Types of specifications• An introduction to process control• Sampling• An introduction to acceptanceConstruction QC/QA Background 2
Fundamental Questions Related to a Specification• What do you want?• How do you order it?• How do we know we get what we ordered?Construction QC/QA Background 3
What do we want - what do we specifyStrength Volumetric PropertiesDurability GradationDensity Asphalt contentSmoothness ThicknessConstruction QC/QA Background 4
How do we order it - types of specifications How do we order what we want? Proprietary product Method or recipe End result Quality Assurance WarrantyConstruction QC/QA Background 5
Proprietary Product Specification• Brand or manufacturer or equal• Relies on past performance• Relies on the integrity of the producer• Generally not used in the HMA industryConstruction QC/QA Background 6
Method Specification• Procedural• Prescription• Materials and workmanship - descriptive• Detailed description of the materials and methods used to prepare the product• Maximum control by specifying agencyConstruction QC/QA Background 7
Method Specification disadvantages• Does not allow for innovation• Inspector intensive• Contractor - no legal responsibility• Quality Performance ?Construction QC/QA Background 8
End-result specification• Minimum requirements for the in-place materials• Does not specify construction methods• Component materials specifications may or may not be included SPECIFYING AGENCY SETS THE LIMITS FOR THE CONTRACTORConstruction QC/QA Background 9
Disadvantages• Spec limits based on subjective judgement• Target + what• Often n = 1• Who has responsibility for process control?Construction QC/QA Background 10
Method Specification + End result Testing = DANGERConstruction QC/QA Background 11
Quality Assurance Specifications• A form of end- result specificationMaterials properties Specification PerformanceConstruction QC/QA Background 12
Advantages of QA specification• Can be performance related• Pay factors can be related to performance• Less inspector intensive• Responsibility for process control and acceptance is separated and clearly definedConstruction QC/QA Background 13
Statistics IS A TOOL USED IN QA SPECIFICATIONSConstruction QC/QA Background 14
INDEPENDENT SUPPLIERLABORATORY PROCESS CONTROL HIGHWAY CONTRACTOR AGENCYConstruction QC/QA Background 16
Acceptance function• Acceptance testing• Monitor testing• Process control monitoring• INSPECTION• Performed by the owner or his representativeConstruction QC/QA Background 17
Independent assurance• Provides for an independent third party assessment of the reliability of the results obtained for acceptance• Must be performed by personnel NOT directly responsible for process control or acceptance sampling and testingConstruction QC/QA Background 18
What Do We Do If We Don’t Get What We Ordered?Mix Properties/Characteristics: Decisions:• Density Mixture• Strength • Incentives Performance• Durability • Penalties• Smoothness • Reject• Thickness• Etc. Construction QC/QA Background 19
To be considered in establishing a sampling and testing program• Frequency of tests• Location of samples• Size of samplesConstruction QC/QA Background 20
Warranties to the rescue?Construction QC/QA Background 21
Perceived Advantages• Decreased construction oversight• Improved quality• Lower maintenance and life cycle cost• Innovation in materials, testing, and constructionConstruction QC/QA Background 22
Types of warranties• Materials and workmanship – the contractor is responsible for correcting defects in work elements within the contractors control for the warranty period• Performance – The contractor assumes full responsibility for pavement performance during the warranty period.Construction QC/QA Background 23
Perceived Disadvantages• Large contractors emerge• Surety issues• Uncertainty and risk may drive cost up – contractor involvement in design process• Definition of performanceConstruction QC/QA Background 24
Reasons for sampling materials• Certification or source approval• Process/quality control• Acceptance• Independent verification samplesConstruction QC/QA Background 25