Semester

Spring

Date of Graduation

2012

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

John P. Zaniewski.

Abstract

A critical issue in determining theoretical maximum specific gravity (Gmm) for Hot Mix Asphalt (HMA) mixtures appears when the aggregates used have high absorption. This high absorption in aggregates, like air cooled iron blast furnace slag, can greatly affect the Gmm values of the sample, which in turn affects the contractor's ability to accurately evaluate the volumetric properties of the asphalt concrete. WV Paving, the largest asphalt paving contractor in West Virginia, uses slag aggregates in many of their mixes. There is concern that the dry-back procedure used to determine Gmm of these mixtures is not producing reliable results. Gmm results from lab prepared mixes were observed to be different from plant prepared mixes. This is of concern to both the contractor and the West Virginia Division of Highways as Gmm is an important parameter in both mix design and quality control. Two hypotheses for the issue were identified that may affect the measured properties of the plant produced mixes; residual moisture and a short conditioning time. To test the effects of residual moisture samples of slag aggregate were saturated with water for a period of time then heated allowing some of the water to evaporate and then mixed with other aggregates and binder. Samples were also produced and tested without having the two hour conditioning time required in the AASHTO procedures. Findings indicated that a third of the residual moisture samples were significantly different from the control values, with seventy percent of those samples containing high slag contents. The conditioning time results showed that the lack of a conditioning period was significantly different than the controlled two hour conditioning at a 95% confidence level.;A related issue is a vacuum method for measuring Gmm has been developed and is in use by some contractors. The experimental design for this research compared the results of the standard test method to the vacuum method. There is a small, but consistent difference between the standard and vacuum methods. Further research should be conducted to see if a short conditioning time should be required for HMA mixtures containing highly absorptive aggregates.

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