A few hundred or thousand tons of unsalable colored glass can be a big headache for local recycling facilities but small potatoes to highway agencies, as a recent demonstration showed. The demonstration project showed two low-tech methods for using glass: as fill around culverts and in cold-mix asphalt.

To fill around a culvert, Columbia County [Wisconsin] crews took green glass from the recycling facility and crushed it roughly by running over it with a roller. They bladed a mix of about five percent glass with material excavated from the culvert trench. Returning the fill around the culvert, they compacted it normally, leaving a top layer without glass. State specs permit up to five percent glass in base course material that will be covered by pavement.

Glass has been part of the aggregate in cold mix asphalt for four years in Green County. It is crushed to a grade of less than 3/8 inch and mixed with conventional aggregate, up to 10 percent of the total mix design weight. The cold mix, which is covered with a seal coat, is used to resurface county roads.

"To date we've done around nine miles with the material," says Dallas Cecil, Green County Highway Commissioner. "You can see the glass as it's laid behind the paver, but we've seen no serious raveling." There is little cost to the County in using glass with otherwise has no market.