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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

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© State of Queensland (Department of Transport and Main Roads) 2013

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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.

Technical Note,Transport and Main Roads, August 2013 1


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.



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.



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



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.



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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