HD25 - Feasibility of Using Recycled Glass in Asphalt
Executive Summary: This report was written by Charles S. Hughes, Senior Research Scientist of the Virginia Transportation Research Council, in response to House Joint Resolution No. 301 which "requests the Virginia Department of Transportation to conduct a study of the feasibility of using recycled glass as supplemental aggregate in asphalt." A literature review is included which documents experimental uses of waste glass from the 1970s to the present. The literature indicates that adhesion between the asphalt and glass has been a problem and that for the glass to be used effectively it must be crushed so that it will pass a 3/8 inch sieve. Early results of the recent use of recycled glass in New York City indicate that glass percentages of 15 percent or less can perform satisfactorily. The study reported here was a laboratory study comparing mixes using 5 and 15 percent glass with a control mix that contained no glass. The study shows that mix properties do change with increased percentages of glass, but not adversely. This means that if glass is going to be used in an asphalt mix, the percent of glass should not exceed 15 percent, and the percent chosen must be included in the mix design process so that the mix properties can be determined. The propensity of moisture damage to occur is still a concern, although this type of failure was not found to be critical in the laboratory study. A cost analysis indicates that the cost of the recycled glass can vary considerably depending on crushing and haul cost. At the present time, unless some economic incentive can be provided for the use of waste glass, it probably cannot compete with the cost of sand. If waste glass is to be used in asphalt mixes, consistency of supply is another factor that must be addressed. However, the use of recycled glass in both highway embankments and in unbound aggregate base materials would be preferable to its use in asphalt because of the propensity of the asphalt coating to be separated from the glass in the presence of moisture. The consistency of supply is not as critical if glass is used in embankments, and the potential for moisture damage to occur at the asphalt/glass interface would be removed if glass is used in unbound aggregate layers. |
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