State departments of transportation (DOTs), as part of their routine practice, employ quality assurance (QA) procedures based on certifications, inspections, sampling, and testing in their acceptance process for highway pavement construction. The QA requirements are generally in accordance with the federal regulations for construction QA procedures (23 CFR, Part 637B) as well as the recommendations of the Federal Highway Administration (FHWA) and the American Association of State Highway and Transportation Officials (AASHTO) for QA programs. However, one thing generally absent from these programs or plans is the utilization of nondestructive testing (NDT) methods in the QA process.

Several studies in recent years have identified the potential advantages of incorporating NDT methods into the QA process for highway pavement construction. These NDT methods are considered to provide an “added value” in the QA process since they potentially allow for (1) quickly assessing product uniformity in real-time as construction progresses; (2) identifying potential defects during construction to allow for timely corrective actions; (3) more frequent inspecting, testing, and replicating without the damaging effects of coring and other destructive testing; and (4) minimizing testing and inspection costs, while improving construction quality. For example, for concrete, the NDT methods can evaluate concrete properties, uniformity, honeycombing, segregation, and cover depth as well as detect reinforcement and dowel bar location and characteristics. Similarly, for asphalt mixtures, the NDT methods can assess properties and conditions such as density, stiffness, thickness, and thermal uniformity. However, despite their high potential and usefulness, the transition of NDT methods from research and forensic investigation to DOTs’ QA process has been rather limited. This is because of the relative complexity of some NDT technologies, inadequate training of QA technicians and inspectors in their use, reluctance to adopt a new technology, and a lack of guidance on how to incorporate the NDT technologies into the overall QA program. 

Objective

The objective of this research is to develop a guidance manual to assist state DOTs in selecting and incorporating NDT methods into their QA programs for highway pavement construction.  

Research Plan

The research plan shall be executed in two phases and comprise, at a minimum, the following tasks:

 Phase I

Task 1. Perform a literature review and a scan of current and emerging NDT technologies and practices to provide an overview of potential NDT QA procedures for use in highway pavement construction applications.

Task 2. Recommend, with adequate justification, NDT methods identified as good candidates for inclusion in the quality control (QC) and acceptance testing program for highway pavement construction. 

Task 3. Provide a work plan aimed at developing guidance for incorporating NDT methods for various highway pavement construction applications into the state DOTs’ QA programs. These NDT methods should be suitable for inclusion at various stages in the QA process used by the contractors and/or in the acceptance process used by the state DOTs.

Task 4. Provide an outline of the guidance manual based on the findings and considerations from the above tasks. The guidance manual will be developed in Phase II of the project.

Task 5. Prepare an interim report detailing the outcomes of all of the above tasks.

Phase II

Task 6. Develop a guidance manual, providing an overview of the NDT methods applicable to highway pavement construction along with a brief description of their operating principles, detection/measurement capabilities, potential benefits, and limitations and drawbacks.  The objective of the manual is not to recommend any specific NDT method but rather illustrate the features and capabilities of various NDT methods and their applicability at various stages (for example, process control, QC, and acceptance) in the QA process for highway pavement construction. The guidance for state DOTs will include:

1.    Development and implementation of NDT-based QA procedures

2.    Assessing appropriate control and specification limits

3.    Technician training and certification

4.    Testing and analysis time

5.    Testing costs

6.    Setting up of pilot projects before full-scale implementation

7.    Lot and sublot size considerations

8.    Data management practices

9.    Independent assurance (IA) procedures

10. Dispute resolution process

11. Cost/benefits analysis assessment for different applications and project sizes/scopes.

Guidance on how to gain buy-in from state DOTs and construction industry should also be provided.  

Task 7. Upon approval of the draft guide by the NCHRP, prepare a final guide as an AASHTO recommended practice and develop a step-by-step plan for its implementation.

Task 8.  Prepare a final report that documents results, summarizes findings, draws conclusions, and makes recommendations.

Task 9. Conduct at least two webinars for state DOT, FHWA, and industry personnel and make a presentation before the relevant AASHTO committee.

Deliverables

Phase I

Phase I deliverables shall include, at a minimum:

1.    An interim report consisting of the following items:

2.   A critical literature review and a scan of state DOTs’ current practice to:

a.    Provide an overview of the current and emerging NDT QA procedures in use in highway pavement construction.

b.    Discuss current knowledge and practice of the NDT methods applicable to highway pavement construction.

c.     Identify NDT methods (including new and emerging) deemed suitable for inclusion in the state DOTs’ QA programs for highway pavement construction.

3   Recommendations for NDT technologies and methods for highway pavement construction QA programs for inclusion in the guidance manual.

4.  An outline of the guidance manual, to be developed in Phase II.

5.  A proposed work plan for Phase II.

Phase II

Phase II shall include, at a minimum, the following deliverables and activities:

1.    A final report that documents results, summarizes findings, draws conclusions, and makes recommendations.

2.    A guidance manual for state DOTs, based on the findings of Phase I work and developed as suggested in Task 6 of the research plan. The guide, intended to be an AASHTO recommended practice, will be prepared in an AASHTO manual format.

3.    A plan for implementing the final guide for adoption by state DOTs as an AASHTO recommended practice.

4.    Webinars for state DOT, FHWA, and industry personnel. Presentations at the AASHTO committees relevant to materials, pavements, and bridges.

5.     A draft TRNews article highlighting the products of this research and their implementation. 

Status: Project has been completed. The final report has been published.