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Suggested Citation:"Chapter 4 - Conclusions." National Academies of Sciences, Engineering, and Medicine. 2017. Specifying and Measuring Asphalt Pavement Density to Ensure Pavement Performance. Washington, DC: The National Academies Press. doi: 10.17226/24870.
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Page 52

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52 The following conclusions are based on the work performed for this project: • QC/QA activities should be uniformly performed. This does not mean the same tests have to be performed—just that the tests should be uniformly performed regardless of the project. • Training for all personnel is a key need. With turnover in both agency and industry person- nel, it is an ongoing challenge to maintain high standards of performance but it is vital to the success of all asphalt projects, large or small. Verification that the training provided actually becomes best practices is important for both agency and contractor. • Frequency of testing is highly variable and should be standardized. Most agencies have guide- lines for testing frequency but there have been cases in which the guidelines were not followed for whatever reason. • With the well-established relationship between density and performance, density testing should be done for all paving projects. For maintenance projects, this requirement may be waived. • Both a minimum and a maximum density should be specified for projects that have density requirements. • Absorption evaluation of core samples should be standard for all testing on projects where core samples are taken. • Testing for Gmm should be performed during plant production of the mix. • Standard procedures for use of NDT gauges should be followed. For asphalt testing, standard- ization, correlation, and calibration are not always performed. These steps are critical in order to achieve realistic nuclear density testing results. • Adequate testing should be performed to properly evaluate all material placed. Testing helps assure the agency of the quality of the products and provides the contractor feedback on how to improve the production and placement process. • A vacuum drying procedure for all cores should be followed. Several procedures are available for drying of cores but the vacuum drying procedure has proven to be a quick and reliable protocol. • Roller management using IC should be used to ensure consistency of roller patterns. This technology is in its infancy but is expected to reap significant benefits for achieving density in asphalt pavements. • It is worthwhile to use a joint sealer for all longitudinal joints. In its report to FHWA, the Asphalt Institute proposed a variety of joint construction techniques. Some states have taken that advice one step further by requiring a joint sealer for all longitudinal joints, currently required only for interstate highways. C h a p t e r 4 Conclusions

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TRB's National Cooperative Highway Research Program (NCHRP) Research Report 856: Specifying and Measuring Asphalt Pavement Density to Ensure Pavement Performance examines the current state of knowledge and existing agency practices to measure and specify the in-place density of asphalt pavements. The report aims to guide agency decisions on selecting measurement methods and requirements for in-place density and identifies the specific knowledge gaps that need to be addressed to provide a complete basis for establishing more comprehensive density standards.

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