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Technical Note 102
Selecting Testing Frequencies for Acceptance Sampling of Pavement Materials August 2013
Technical Note, Transport and Main Roads, August 2013
Copyright
http://creativecommons.org/licenses/by/3.0/au/
© State of Queensland (Department of Transport and Main Roads) 2013
Feedback: Please send your feedback regarding this document to: mr.techdocs@tmr.qld.gov.au
TN102 Selecting Testing Frequencies for Acceptance Sampling of Pavement Materials
1 Purpose
This Technical Note provides guidance for optimising acceptance sampling test frequencies for
pavement materials at all stages of Transport and Main Roads (TMR) projects (e.g. design,
construction). It applies to testing frequencies for acceptance sampling for quality assurance as part of
pavement materials’ supply and construction to Main Roads Technical Standards (MRTSs) and their
annexures.
2 Rationale
The Queensland Government’s vision is “to be more efficient, deliver better outcomes for the
community and achieve best value for money for the services we deliver”. Quality assurance of
pavement materials, during both supply and construction, is essential to delivering adequately
performing roads with minimised life cycle costs.
Acceptance sampling for materials supply and construction is part of this quality assurance. Through
EN10 Guideline to Quarry Assessment and Registration and EP108 Quarry Assessment and
Registration, TMR’s Quarry Assessment and Registration System (QARS) governs the registration
and acceptance of quarries supplying pavement materials to TMR projects. However the scope of
QARS does not assure ongoing production of compliant aggregate (nominated) products per:
“TMR registration does not guarantee any nominated product compliance with TMR technical
standards since this is influenced by many operational factors such as extraction and production
procedures and source material variability” (EN10, 2012, page 2).
Variability may occur in:
quarry source rock quality and selection
quarry production including manufacturing practices for equipment and production processes
including blasting, extraction, crushing, and mixing
stockpiling and transport
quarry quality control measures.
QARS assesses whether a quarry can produce complying material at a point in time, but does not
include ongoing monitoring to assure the compliance of material supplied to projects.
Into the future, TMR is moving toward rationalising testing across projects and prequalification
systems such as QARS, with a goal to reducing overall test frequencies while not compromising
quality. As a result, this Technical Note is expected to be interim and will be revised in accordance
with future changes.
3 Quality assurance functions and responsibilities
Quality assurance is defined as the systematic action necessary to give confidence of satisfactory
quality (Austroads, 2008C). Quality assurance activities for pavement materials supply and
construction within a road construction contract typically include three management functions:
quality control
acceptance
independent assurance.
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TN102 Selecting Testing Frequencies for Acceptance Sampling of Pavement Materials
For TMR contracts, responsibilities for these quality assurance functions are generally as follows:
1. Responsibility for quality control is assumed by the Contractor.
‘Quality control’ comprises the actions necessary to assess production and construction
processes, in order to control the level of quality being produced in the end product. The
Contractor’s quality control sampling and testing frequencies may be different to the
acceptance sampling / testing frequencies. “The responsibility for achieving quality lies with
the Contractor because the Contractor has control over the process” (Austroads, 2009).
2. Responsibility for acceptance is assumed by TMR (as the Principal).
‘Acceptance’ involves the systematic actions that provide confidence that a product
satisfactorily conforms with the contract requirements, and is free from defects that are at
unacceptable levels. For the purposes of quality assurance, "acceptance" is:
a formal procedure used to decide whether work should be accepted, rejected, or accepted at
a reduced payment (Freeman and Grogan, 1998).
the monitoring method used to determine whether or not a material or process is meeting
quality standards.
not a form of quality control and so is not a method to control or improve quality. Rather,
quality process controls are used to control and systematically improve quality (Montgomery,
1997).
3. Independent assurance is the management tool whereby a third party provides independent
assessment of the products and/or the reliability of the test results. Independent assurance is
typically separate to product acceptance, and may be applied to both quality control and
acceptance testing.
4 TMR approach to quality assurance
Quality assurance requirements for pavement materials and construction in TMR’s standard
documents include:
1. MRTS50 Specific Quality System Requirements which details the requirements of the Quality
System for the management of all aspects of the Contractor’s obligations including:
quality plan
construction procedures
identification and traceability
as applicable, reducing or increasing testing frequencies. For example, Clause 8.6 states: “for
an off-site continuing process (e.g. pavement material production) approval may be given by
the Administrator to move to a Reduced Testing Level based on testing undertaken outside
the Contract in accordance with the supplier's Quality System.”
auditing by the Administrator and/or the Principal
conformance and non-conformance
quality records.
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TN102 Selecting Testing Frequencies for Acceptance Sampling of Pavement Materials
2. MRTS01 Introduction to Technical Standards which defines:
additional Quality System requirements including conformance requirements, and
the method of calculating characteristic values and associated k-factors when these statistical
measures are used for compliance assessment.
3. TMR policies and systems for prequalification (eg QARS and the Asphalt Supplier Registration
System).
4. TMR policies for ensuring quality on a project level (eg Engineering Policy EP134 Product
Quality – Construction / Maintenance).
5. Conditions of contract including the defect liability and/or warranty provisions and the
Contractor’s quality control procedures accepted when forming the contract.
6. Conformance requirements for accepting pavement materials are stated within a specification/
technical standard. Where products are accepted at the ‘point of manufacture’ rather than at
the ‘point of use’, transport and handling processes between manufacture and use may also
be specified.
5 Acceptance procedures
5.1 Nominating acceptance procedures
Accepting a product can take one of the following three broad forms (Montgomery, 1997):
1. Accept with no inspection – generally used when there is no economic justification to look
for defective units or material.
2. 100 percent inspection – generally used where components or material are extremely critical
and passing any defective components or material would result in an unacceptably high failure
cost. The only way to determine lot properties with certainty is to test the entire lot
(100 percent inspection).
3. Acceptance sampling – uses a small number of random samples to draw conclusions about
a large amount of material (the “lot”). Since the entire lot is not inspected, these conclusions
are only estimates of actual lot properties and will therefore involve some amount of
uncertainty as to their accuracy. Acceptance sampling is generally used when there is some
economic justification to look for defective material and either:
some small finite percentage of defective material is acceptable, or
it is not economical or practical to use 100 percent inspection.
The benefits of using statistical techniques for acceptance include:
assuring unbiased quality information
informing towards effective and timely process control
providing objective evaluation of quality characteristics (including central tendency and
dispersion)
enabling acceptance decisions on a rational basis.
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TN102 Selecting Testing Frequencies for Acceptance Sampling of Pavement Materials
5.2 TMR approach to acceptance sampling
TMR accepts material and/or product characteristics. As part of its acceptance procedures, TMR
specifies sampling and testing plans in its contract documents, including:
quality characteristics, which are the properties to be measured, and which relate to pavement
performance
lot size, frequency and size of sampling, which are often nominated in annexures at pre-tender
stage
sampling and testing procedure.
TMR also specifies compliance limits which are based on:
acceptance/rejection limits
acceptance/ rejection methods which typically are based on either a pass/ fail criteria or
through statistical acceptance schemes, and
payment/adjustment schemes.
6 Selecting acceptance sampling test frequencies
Optimisation of acceptance sampling test frequencies for TMR projects should be based on the
following list of considerations, noting that the listed items may also assist Contractors and/or
independent assurers in determining optimum quality control and assurance test frequencies:
1. Larger sample sizes provide better estimates of the population quality, and hence reduce risk
of accepting unsatisfactory quality or rejecting satisfactory quality.
2. Some TMR specifications employ statistically-based acceptance sampling which utilise
acceptance constants (“k factors”) for which:
the associated operating characteristics for the “buyers” risk (percent probability of accepting
an unsatisfactory product) and the “sellers/producers” risk (percent probability of rejecting a
satisfactory product) are used, and
a 90/10 unknown variability acceptance sample plan (giving a 90% probability of accepting a
10% defective lot) as described in Auff (1986) is the basis, with adjustments for TMR
procurement methodologies.
3. The variability of the product needs to be considered, noting that more variability requires
more frequent sampling and testing. Conversely less variability may mean the required
sampling can be less frequent. Variability may be due to:
inherent variability of the material
fluctuations in the processing operations, noting that corrections made in a production process
necessitates more frequent sampling and testing in order to assure the required uniformity
variations in sampling methods and testing procedures.
4. Assurance provided by the scope and intensity of independent assurance which, in TMR
projects, may include:
independent (e.g. NATA) accreditation of testing facilities and testing officers
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TN102 Selecting Testing Frequencies for Acceptance Sampling of Pavement Materials
during production, programmed periodic duplicate/joint testing by an assessor independent to
the contract. (For example, during asphalt production, many US states adopt a joint testing
regime which is ten percent of the frequency of the acceptance sampling scheme)
auditing and surveillance of relevant activities including production, testing and
placement/construction.
5. The alignment between risk and the scope of the contract Administrator’s product quality
verification activities under EP134 may include:
verification testing, data communications and administration
inspection, particularly to identify instances of non-conformance and/or poor quality
assurance that the lot conformance data is representative of the material delivered to the
works
provisions to further review and/or test lots that yield borderline test results
protocols and contract outcomes associated with non-conformance, corrective action, dispute
of audit test results, defects and deficiencies.
6. The length and terms of warranty period and/or defect liability period where, for example, long
warranty periods may facilitate more final-state performance-based acceptance criteria and
less reliance on testing the properties of the constituent materials and acceptance at the time
of construction.
7. TMR Regional or project-specific systems and practices for assessing and/or monitoring
quality control for local material sources. For example, some Regions have historically
maintained programs of routine inspections and collation of test data for local quarries.
8. Industry guidelines for testing frequencies relating to quality control, for example the CCAA’s
(Cement Concrete and Aggregates Australia) documents Code of Practice – Testing
Frequencies for the Extractive Industry in Queensland (2005) and Guideline to Sampling for
the Extractive Industry (2006).
9. Interstate and international benchmarking, including that the nomination of test frequencies is
only one consideration in the complete and often complex procurement system/culture that
delivers quality assurance and fit-for-purpose product as part of a road construction contract.
10. Achieving an acceptable balance between sample size (accuracy) and inspection and testing
costs, considering that:
The cost of testing should be balanced against with the benefits of reduced risk of non-
conformance.
For a given sample size, reducing the risk of accepting poor material usually means increasing
the likelihood of rejecting good material and vice versa (Freeman and Grogan, 1998). To
simultaneously reduce both these risks, accurate estimates involve increasing the sample
size.
The criticality of the quality characteristic should be considered where, if a characteristic is
critical, the risk of accepting poor material should be small.
11. Whether the project is being supplied and/or delivered by a TMR prequalified Supplier and/or
Contractor.
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TN102 Selecting Testing Frequencies for Acceptance Sampling of Pavement Materials
12. Performance data and/or review data available from previous projects, and consistency and/or
rectification of ongoing practices that resulted in that performance.
13. A general principal of quality assurance that: “the relation between quality control testing and
acceptance testing is that the more testing done for the former, the less testing needed for the
latter” (Cho, Najafi, Kopac, 2011). The Contractor’s quality control management practices will
impact including:
Construction Procedures
Inspection and Test Plans that include acceptance criteria, timing, frequency, scope, test
methods, and analysis and application of testing (e.g. use of control charts and associated
interventions)
audit regimes
project personnel and supervision e.g. experience, expertise, availability and role.
14. When testing at pre-construction or construction stages, test methods do not exist that can
totally assure the pavement’s performance over its design life.
15. Most manufacturing and construction processes for pavement materials and pavements are
not fully mechanised, rely on process requirements, and thus trend toward being variable.
16. Pay schedules for some pavement materials and products are defined by relationships
between quality levels and payment levels.
17. Early in 2012, TMR, consultant designers and other stakeholders met in a forum to discuss
design documentation for natural disaster rectification works (i.e. Transport Network
Reconstruction Program (TNRP)) constructed under Performance Incentive Cost
Reimbursable (PICR) contracts. The purpose of the forum was to develop a standardised set
of annexures for pavement MRTSs to address, for many pavement materials sources,
significantly increased state-wide demand for pavement materials. Extracts from the standard
annexures resulting from this TNRP forum are included in this technical note.
7 References
Auff, A. A., 1986, The Selection of Statistical Compliance Schemes for Construction Quality Control.
Vermont, Vic.: Australian Road Research Board.
Austroads, 2008, Glossary of Austroads Terms, Austroads, Sydney, NSW.
Austroads, 2009, Guide to Pavement Technology: Part 8: Pavement Construction, Austroads, Sydney,
NSW.
Cho, C., Fazil, T. N. and Kopac, P. A., 2011, pp. 61-69, Transportation Research Record: Journal of
the Transportation Research Board, No. 2228, Transportation Research Board of the National
Academies, Washington, D. C.
Freeman, R. B., Grogan, W. P., May 1998, Statistical Acceptance Plan for Asphalt Pavement
Construction, US Army Corps of Engineers Waterways Experiment Station, Technical Report GL-98-7,
Vicksburg, Mississippi.
Montgomery, D.C., 1997, Introduction to Statistical Quality Control 3rd Edition, John Wiley and Sons,
New York, NY.
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