Recommended Changes to the Precision Estimates of AASHTO T 313 (BBR)

Abstract

A comparison of precision estimates in the 2019 AASHTO T 313 (BBR) with those of 2012 indicates that the 2019 multilaboratory precision values are notably smaller than those of 2012. This decrease has a significant effect on the percentage disagreements between contractors’ test results and those of state departments of transportation (DOTs). A review of state DOT and contractors’ bending-beam rheometer (BBR) results indicated that 39% of contractors' data were in disagreement with the state DOT’s data, primarily because the allowable difference between the BBR results of two laboratories (d2s) is set too low. This could cause unnecessary additional costs of testing and delay in a project. Another shortcoming of the AASHTO T 313 precision statement is that the current precision values are for creep stiffness (S) and slope (m-value) at the PG+10°C test temperature only. With the increased applications of continuous low-temperature performance grade (LTPG) and delta Tc (ΔTc), asphalt binders are also required to be tested at the lower temperature of PG+4°C. Therefore, addition of precision values for the lower test temperature is necessary. This study aimed at reevaluating BBR precision properties at PG+10°C, preparing new sets of precision values for PG+4°C, and determining precision of LTPG and ΔTc. An interlaboratory study involving seven laboratories testing six binders was conducted. The new and improved sets of precision values at PG+4°C and PG+10°C have reduced disagreements between the BBR results of two laboratories to about 5%, which better represents the 95% reliability anticipated in the analysis of precision.

Keywords

infrastructure materials binders asphalt binder aging asphalt binder modifiers

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References

AASHTO T 313. Standard Method of Test for Determining the Flexural Creep Stiffness of Asphalt Binder Using the Bending Beam Rheometer (BBR). American Association of State Highway and Transportation Officials, Washington, D.C., 2019.

ASTM D6648. Standard Test Method for Determining the Flexural Creep Stiffness of Asphalt Binder Using the Bending Beam Rheometer (BBR). American Society for Testing and Materials, West Conshohocken, PA, 2016.

ASTM D4460. Standard Practice for Calculating Precision Limits Where Values Are Calculated from Other Test Methods. American Society for Testing and Materials, West Conshohocken, PA, 2022.

Holsinger

Fisher

Spellerberg

P. A.

Precision Estimates for AASHTO Test Method T308 and the Test Methods for Performance-Graded Asphalt Binder in AASHTO Specification M320, TRB’s National Cooperative Highway Research Program (NCHRP). Web Document 71, 2005. https://nap.nationalacademies.org/catalog/21969/precision-estimates-for-aashto-test-method-t308-and-the-test-methods-for-performance-graded-asphalt-binder-in-aashto-specification-m320.

AASHTO. Re:Source Proficiency Sample Program (PSP). http://www.aashtoresource.org/psp/overview.

ASTM E691. Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method. American Society for Testing and Materials, West Conshohocken, PA, 2021.

AASHTO T 240. Standard Method of Test for Effect of Heat and Air on a Moving Film of Asphalt Binder (Rolling Thin-Film Oven Test). American Association of State Highway and Transportation Officials, Washington, D.C., 2022.

AASHTO R 28. Standard Practice for Accelerated Aging of Asphalt Binder Using a Pressurized Aging Vessel (PAV). American Association of State Highway and Transportation Officials, Washington, D.C., 2022.

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ASTM D7643. Standard Practice for Determining the Continuous Grading Temperatures and Continuous Grades for PG Graded Asphalt Binders. American Society for Testing and Materials, West Conshohocken, PA, 2016.