Determining Air Void Content of Compacted Hot-Mix Asphalt Mixtures

Abstract

A project to develop a new method or adapt a current method with wide applicability for determining bulk specific gravity of compacted hot-mix asphalt (HMA) mixtures ( Gmb) is described. A more reliable Gmb would result in more reliable HMA volumetric properties, specifically, percent air voids. Consequently, pavement distress types such as rutting, bleeding, stripping, and age hardening (whose occurrence is related to percent air voids, among other factors) could be avoided more often. The project goal was accomplished in three steps. In Step 1, a literature review and survey of state departments of transportation revealed 13 existing Gmb determination techniques. In Step 2, a feasibility study of the seven methods selected was conducted to evaluate cost, logistical factors, and preliminary repeatability. In the final step, 50 compacted HMA samples and four aluminum cylinders were used to evaluate the precision and accuracy of the four methods selected. The dimensional analysis (AASHTO T269) and the parafilm (ASTM D1188) methods were found to form upper bounds for true sample air voids, whereas the saturated surface-dry method (AASHTO T166) was found to form a lower bound for true air voids. Although the true air voids can never be determined, for 90% of Tennessee Department of Transportation sample groups tested, the InstroTek Corelok method yielded results in this range between the upper and lower bounds for accurate air void results. In the precision and accuracy evaluation, all four methods were found to be capable of producing high-precision results.

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

“…Hubbard and Field (5) evaluated voids in mineral aggregate in 1926, and in-place density was measured for both the WASHO (6) and AASHO (7) road tests in the 1950s and 1960s with the use of square specimens from pavement sections. A more recent survey indicated that most state departments of transportation (DOTs) continue to measure bulk mixture specific gravity, or G mb (8). pavement density measurement.…”

Bulk Specific Gravity Measurements of 25.0-mm and 37.5-mm Coarse-Graded Superpave Mixes

“…During construction, the property of bulk specific gravity is used in most measures of quality control and quality assurance (QC/QA). Problems with HMA mixture density have been linked to pavement distresses such as rutting, stripping, bleeding, cracking, age hardening, and excessive permeability (1,2). Thus, errors in this measurement have real consequences for both contractor pay and pavement quality.…”

“…A study conducted in Tennessee focused on four test methods-SSD, CoreLok, height-diameter, and parafilm (2). In this study, the precision and accuracy of the chosen methods were measured by performing seven replicate tests by each method on a set of 50 widely varied HMA samples and three replicate tests on a set of four aluminum samples.…”

Technological and Economic Design of Asphalt Mixture Composition Based on Optimization Methods

“…However, the actual variability in air void content in the field tends to be greater than that because of compaction variability and temperature segregation (Chang et al 2002). Air voids play an important role in influencing the performance of asphalt mixtures (Mohammad et al 2004;Dubois et al 2010;Crouch et al 2002). Seo et al (2007) presents an experimental study on developing air void models for dynamic modulus and predicting the performance of the asphalt concrete mixture.…”