Investigating the Consistency of Asphalt Density Measurement Methods Over a Wide Range of Air Voids

Abstract

The overall purpose of this paper is to identify the most reliable bulk mixture specific gravity (Gmb) measurement method for dense graded asphalt concrete that can be used for a wide range of air voids and specimen types. A secondary purpose is to identify ranges of conditions where less established Gmb measurement methods are suitable. A comprehensive literature review was performed to identify promising density test methods for further study. Findings from studies comparing AASHTO T166 (saturated surface dry method) and AASHTO T331 (Corelok method) were used to provide a succinct summary of the relative behaviors of the two methods at mix design, performance testing, and field construction air void levels. Density measurement was performed using four methods (AASHTO T166, T269, T331, and TP82) on dense graded mixture specimens. In total, approximately 2500 data points were used herein, with approximately 30 % of this total coming from literature review and 70 % coming from the authors of this paper. Review of literature along with the evidence presented in this paper indicates that T331 is the most reasonably accurate and versatile Gmb measurement method for a wide range of air voids all the way from mix design through performance testing to construction acceptance testing. T331 has also been recommended (or at least evaluated favorably) by several previous researchers over the last ten years. Based on the evidence presented in this paper, the provisional TP82 test method in its current form does not provide acceptable Gmb measurements relative to T166 or T331 over a wide range of air voids. The magnitude of the discrepancy begins to increase dramatically as air voids increase.

Vacuum Sealing–Based Volumetric Density Measurement Approach for Cold In-Place Recycling

“…Cross (8,9), who researched CIR, and NCHRP Synthesis 421 (21), on in-place recycling, expressed concerns that T 166 may not be suitable because of water absorption issues caused by typically high air voids in recycling mixtures. The CIR V a levels found in the literature are often higher than the 8% to 9% value mentioned by Howard and Doyle (7). The literature reports V a levels of 2% to 14% (17), 8.9% to 14.4% (18), 13.7% to 16.4% (20), 6% to 10% (11, 13), 9.7% to 14.2% (8), 8% to 17% (12), 9.2% to 17.9% ( 14), 5.8% to 10% ( 16), and 6.3% to 22.4% (6).…”

“…Figure 4a shows that, on average, T 269 air voids were 1.1% greater than those of T 331. Howard and Doyle found that V a(T269) minus V a(T331) ranged from 0.9% to 2.6% for air voids of 4% to 10% (7). CIR V a(T269) minus V a(T331) was on the lower end of this range despite air voids ranging from approximately 18% to 28%.…”

“…Approximately 2,500 data points coupled with an in-depth literature review of asphalt G mb measurement methods found that T 331 was evaluated favorably against T 166 and T 269 (7). For typical mixtures, the 2.0% water absorption limit for T 166 can easily be exceeded at air void (V a ) levels of 8% to 9%.…”

Density Observations from a Full-Scale, Untrafficked Test Section with Guidance for Dryback Methods

“…Multiple investigations have recently considered changes from SSD measurement to vacuum sealing methods (14)(15)(16). Howard and Doyle considered about 2,400 data points to conclude that AASHTO T 331 was the most accurate and versatile method to measure G mb over a wide range of mixtures (14).…”

“…Multiple investigations have recently considered changes from SSD measurement to vacuum sealing methods (14)(15)(16). Howard and Doyle considered about 2,400 data points to conclude that AASHTO T 331 was the most accurate and versatile method to measure G mb over a wide range of mixtures (14). Buchanan tested G mb on four mix types (open-graded friction course, stone mastic asphalt, coarse Superpave ® , and fine Superpave) with four density measurement protocols (i.e., SSD, dimensional, parafilm, and vacuum sealing) (15).…”