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Pavements 2025

Construction Quality Control and Quality Assurance

POSTER RECEPTION (View list of posters here)

Development of Precision Estimates for AASHTO T 84 Using Fine Aggregate

Tuesday, June 10, 2025
4:45 PM – 6:00 PM MT
Abstract: In California and other parts of the world, aggregates comprise the greatest component of any pavement. The use of quality aggregates in California is essential in building durable and long-lasting pavements. The California Department of Transportation (Caltrans) has established rigorous specifications and test methods to ensure that aggregates used in pavement construction meet the required standards. One of the tests required by Caltrans at Job Mix Formula (JMF), JMF verification, Production Start-Up Evaluation (PSUE), and renewal during road construction is AASHTO T 84, Standard Method of Test for Specific Gravity and Absorption of Fine Aggregate, which is an important element for the determination of volumetric properties of hot mix asphalt (HMA). AASHTO T 84 is a standard test method used to determine fine aggregate's specific gravity and absorption. An interlaboratory study (ILS) was conducted by Caltrans in 2022 in conjunction with the Reference Sample Program (RSP) to determine variability of AASHTO T 84 for California aggregates. Eighty-three Caltrans-accredited laboratories participated in this study. Two replicate samples for each participating laboratory were used. This study was conducted to provide an estimate of precision for the AASHTO T 84 test procedure in all three specific gravity conditions (i.e., bulk (dry), bulk (SSD - saturated surface-dry), and apparent) and absorption. In the test method, the mass of a fine aggregate sample is determined in three separate conditions: Oven-dry, SSD, and submerged in water. These three masses are then used to calculate bulk (dry) specific gravity, bulk (SSD) specific gravity, apparent specific gravity, and absorption. Data from the participating laboratories were evaluated in accordance with ASTM C802 and ASTM C670. This study showed that the allowable difference (d2s) for properly conducted tests on the same material under the three conditions (bulk (dry), bulk (SSD), and apparent specific gravity) was lower than the precision estimates in AASHTO T 84 test method. However, the d2s determined in this study for absorption was higher than the precision estimate in AASHTO T 84 test method.

Learning Objectives:

Attendees can expect to learn the following from this session:
  • Upon completion, participant will be able to define the variability limits for AASHTO T 84 for California aggregates.
  • Upon completion, participant will be able to describe the difference in variability limits for AASHTO T 84 between California aggregates and AASHTO standard.
  • Upon completion, participant will be able to conduct similar studies for local aggregates in their State.