InstroTek Industry News

Committee Recommends Changes to AASHTO T-166

Under the direction of the Federal Highway Administration (FHWA) Asphalt Mix and Construction Expert Task Group, a subcommittee was charged to review current specific gravity measurement methods for aggregates and asphalt mixtures. Based on the review, which included current precision estimates, recent research studies and information provided by state agencies and equipment suppliers, the committee recommended the following revisions to AASHTO T 166 (bulk specific gravity of compacted specimens):

» Delete references to AASHTO T 275 (paraffin coating method) and replace with AASHTO T 331 (vacuum sealing method).

» Replace the current 2.0 percent water absorption limit for AASHTO T 166 specimens with a limit of 1.0 percent.

» Replace the incomplete precision statement contained in the current method (Section 13) with the precision estimates recommended by NCHRP 9-26.

As a result of the proposed revisions, AASHTO T 166 will essentially be limited for use with fine-graded mixtures, while AASHTO T331 will be used for coarse-graded and stone matrix asphalt (SMA) mixtures. This will significantly affect mix design and quality assurance testing for coarse-graded and SMA mixtures, as summarized below:

» AASHTO T331 results in higher air voids and VMA for coarse-graded and SMA mixtures--approximately 0.5 and 0.9 percent, respectively, at normal mix design compactive efforts, based on available data. To provide performance equivalent to or better than currently used mix designs, agencies should consider increasing VMA criteria by 0.5 percent for both coarse-graded SuperPave and SMA mixtures.

» AASHTO T331 also yields higher in-place air voids for coarse-graded and SMA mixtures--approximately 1.0 and 1.7 percent, respectively, based on available data. This change would require contractors to improve their compaction processes in order to meet existing in-place density requirements. Alternatively, agencies could adjust in-place density specifications consistent with the proposed measurement method so that density can be achieved with current compaction practices.

Spring 2010 NCAT Asphalt Technology News; v22, #1

ASTMs D6752 and D6857

Two New CoreLok ASTM standards, D6752 and D6857, are now in publication phase. Contact ASTM for copies of these standards.
ASTM D6752- "Standard Test Method for Bulk Specific Gravity and Density of Compacted Bituminous Mixtures Using Automatic Vacuum Sealing Method"
ASTM D6857- " Standard Test Method for Maximum Specific Gravity and Density of Bituminous Paving Mixtures Using Automatic Paving Mixtures"

CoreLok is now specified under Indiana Specification, Section 401 "Quality Control/Quality Assurance, QC/QA, Hot Mix Asphalt, HMA, Pavement", 2003.

University of Oklahoma at Norman has just completed a research study for Oklahoma DOT. The work is titled "An Alternate Method for the Determination of Asphalt Content". This method uses the bulk and apparent gravity results of combined aggregates, only possible with CoreLok, and maximum specific gravity of the mixture to determine the %AC. This method is environmentally friendly and requires much less testing time than the existing methods. The results reported in this research are accurate and repeatable. Please contact Dr. Zaman at University of Oklahoma or Mr. Ken Hobson at Oklahoma DOT for more information regarding this exciting new test method.

CoreLok is now successfully used for bulk gravity determination of Automobile brake components and in the mining industry for gravity determination of precious materials.