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Suggested Citation:"Summary ." 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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Suggested Citation:"Summary ." 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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1 S u m m a r y The in-place density of asphalt mixtures is the single most important property of the asphalt mixture in the pavement. The relationship between in-place density and the perfor- mance of the mixture has been studied for decades. The process of achieving in-place density involves creating the proper mix design, under- standing aggregate and asphalt binder properties, understanding paver and roller operations, and adjusting the process to account for environmental conditions. Many details are involved in the process. Significant changes have occurred since the implementation of Superpave for materials and mix design but there is not a standard on how agencies measure and establish specifica- tion criteria for in-place pavement density. The objective of this study was to collect specific information on the current state-of-the- knowledge of in-place density of asphalt concrete pavements and pavement performance as well as the current practices agencies follow to measure and specify in-place density of asphalt mixtures. As would be expected, the state-of-the-art and the state-of-practice do not directly cor- relate to one another. Based on the results of this project, areas in which improvements in the state-of-the-practice should be considered are the following: • Quality control and acceptance activities should be consistently performed for projects. The testing may not be the same for both activities but should be consistent. • Training for all personnel is a key need. With the turnover in both agency and con- tractor personnel, the need for training is constant. In addition, it is imperative that managers for both agency and contractors enforce the best practices that are empha- sized in training sessions. • Frequency of testing is highly variable and should be standardized within specific classes of project. • With the well-established relationship between density and performance, density testing should be done for all projects, regardless of size. Engineering judgment must be used for patching or maintenance jobs. • Both a minimum and maximum percent density should be specified. • Absorption evaluation of core samples should be standard for all testing if cores are obtained from the project. This does not apply to open graded mixtures. • Testing for maximum theoretical specific gravity (Gmm) should be performed during mix design and plant production of the mix. The Gmm produced from a plant-produced mix- ture should be used for determining percent density. • Established standard procedures for use of non-destructive testing gauges should be followed. Specifying and Measuring Asphalt Pavement Density to Ensure Pavement Performance

2 Specifying and measuring asphalt Pavement Density to Ensure Pavement Performance • Adequate testing should be performed to properly evaluate all material placed. Test fre- quencies should take into account observed variations in the product to ensure a robust testing plan. This will vary by project type, size, and state specifications. • A vacuum drying procedure for all cores should be followed. Studies have shown this to be a quick, repeatable procedure. • Roller management using intelligent compaction should be used to ensure consistency of roller patterns. • Joint sealers should be required for all longitudinal joints.

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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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