the minimum criteria required for Quality Assurance (subpart B) on all federal-aid projects on the National Highway System. It is important to note this new regulation was restricted to a subset of projects on the NHS, but many states chose to apply this approach to most or all projects. The purpose for this regulation was to ensure that the materials and workmanship performed on a project met the minimum criteria set forth in a contract or specifications where Federal Highway Administration (FHWA) funded via reimbursement to the DOT. Today, VDOT follows a robust program to verify and validate contractor test results in the lab and in the field. Statistical comparisons are made on individual test results as well as lots of material. For compaction/density in the field, a combination of processes is followed to verify results. Like anything, the approach used by VDOT has evolved—but can it improve? FUTURE APPROACH So, what must change—or stay firm—when implementing a new approach? With the development of technology and changes in the workforce, we should debate new approaches to acceptance; but we must first agree what non-negotiables qualities should be monitored and measured, and if those qualities apply to every project or only the applicable metrics. Meanwhile, quality materials and workmanship in the final product must not be jeopardized. While there may be debate on the metrics, five non-negotiables rise to the top: mix quality, mat compaction, surface uniformity, layer bonding, and pavement smoothness. Other than a non-subjective approach to determine surface uniformity, the other four qualities are part of VDOTs acceptance and payment process. So, what is the difference? Simple. How the process is administered, and the technology utilized. START RIGHT, STAY RIGHT Before the first ton of mix is shipped to the project, it must be produced. Prior to production, the mix must be designed, validated, and confirmed. This is nothing new. The tests used to approve mixes, however, have changed from the Marshall Era to SUPERPAVE to BMD. During production, the amount of testing by the contractor and the independent validation/verification testing by VDOT should follow a risk-based approach. All mixes in all situations should not have the same level of sampling and testing. Subdivision streets and high-volume interstates do not carry the same level of risk, so the sampling frequency and testing regimen should be different. This will allow VDOT and the contractor to focus on those mixes being supplied to high-priority routes (i.e., interstates, high-volume primary routes, and high-volume secondary routes) and adjust the limited resources accordingly. (Note: in 2024, VDOT’s specifications on testing asphalt surface mixes will vary during production. An important first step in a future approach.) TAKING IT TO THE STREET Arguably, the biggest adjustment to a future acceptance approach will be in the field. What will be the role of the inspector, and what technology(s) will be employed to ensure quality installation and workmanship? In nearly every instance, the compaction or in-place density of the asphalt material is deemed the most important quality metric. At this point, destructive and non- destructive testing protocols are followed to determine the acceptance of a lot and sublot of material. While a stratified random approach is used to select the testing locations, the amount of area tested is very small. Further evaluation and piloting of equipment to cover a larger area of the mat is the next step. Instead of a straight average for density, other statistical measures such as cumulative distribution or percentage of the mat meeting or exceeding a minimum density may be more appropriate. However, it is important to note with density and other field quality metrics, this will not be a one-size-fits-all-projects approach either. The ability to meet density uniformity will be different on a maintenance overlay project as opposed to new construction. While density has been long regarded as the “king” of quality parameters, the bonding between layers cannot be overlooked. A thick asphalt pavement in which the surface △ continued from page 13 RETHINKING REALITY 14 FALL/WINTER 2023
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