Glass and roads CAN mix — if the price is right

Note: Devin Rigby, D4's District Engineer for decades, was a resident engineer in District 6 on the Interstate 15B project in Idaho Falls in the early '90s. The project was one of a few in Idaho that used crushed glass in the granular borrow below the processed or engineered material. Idaho lawmakers convinced the department to purchase a bunch of the glass, and ITD then experimented with it in projects – the aforementioned I-15 job, the Clear Lakes Grade in District 4, and around 1998, a job on ID-75 between Hailey and Ketchum.

"The glass had no negative impact, but was significantly more expensive than just digging granular material/pit run out of the ground," Rigby said.

The decision was made to use the glass because there were stockpiles of glass at waste-processing plants with no buyers, so legislators got involved and the department bought it and placed it.

"From a materials perspective, glass is essentially quartz rock and incorporating it into pit run with sand and round rock did not cause a problem in the granular borrow at all. Although 500 tons sounds big, with respect to the granular borrow on each of these projects, it was less than 1%," Rigby added.

Here's that original story. Please keep in mind that any pricing information was current...25 years ago:

Road to conservation paved with...glass?

What do glass and paper have in common besides the ability to be recycled? They also can all be reused in and along Idaho's roads.

When crews reconstruct Clear Lakes Grade in Twin Falls, 500 tons of crushed glass will be deposited in the road's base. Five hundred tons already were used in the reconstruction of Interstate 15's Business Route from Riviera to Jameston Road south of Idaho Falls.

Don't worry about glass shards lying on the road. Glass crushed to three-eights of an inch is safe enough to handle with bare hands.

Though using crushed glass instead of sand and other aggregate in roadways keeps the glass from taking up space in landfills, it's expensive in Idaho, about $40 per ton compared with $2 per ton of fill dirt, according to lTD Materials Engineer Everett Kidner. Glass accumulates faster in urban areas like New York, so costs are lower. There, crushed glass is frequently used in pavement and costs about $8 per ton, the same as sand.

But because of Idaho's relatively rural population and the distances between glass sources and construction sites, crushed glass in Idaho costs more.

Aside from cost, there are some physical problems with using glass in roadways, according to Kidner. While using glass as material in a highway's base should not create a problem, Kidner said, glass is not very good for incorporation into pavement. Asphalt doesn't adhere well to glass, so it is likely to break down and need repair more quickly than a roadway without glass.

According to Kidner, 15,000 tons of aggregate with a 2-percent glass blend would require 300 tons of glass. On a 28-foot-wide road, for example, this could be used in one mile of roadway base about a foot deep. lTD constructs and repairs many miles of road every year that could use glass, according to Kidner.

But old glass has another use at lTD.

Each year in Idaho, about 1.6 million pounds of recycled glass is used as reflective material in paint stripes on the pavement.

"The glass is made into small beads," Maintenance Engineer Clayton Sullivan said, "and added to the paint and on top of the paint to provide reflectiveness at night."

Even if recycling was no consideration, Sullivan said, lTD would still use the glass beads in the paint because they are the best reflective material available.

Availability of glass in highway construction is a problem in Idaho. Availability of newspapers is not. Idaho's recyclers estimate that 50,000 tons of newspaper are generated in the state each year. lTD uses about 50 tons of paper mulch each year in seeding slopes around the state, compared to about 680 tons of straw or hay mulch used for the same purpose.

Pulp from recycled paper is mixed into a slurry that is sprayed onto barren slopes, said District 4 Environmental Planner Bob Humphrey.

"When this slurry hardens, it keeps the seeds in contact with the soil to promote growth and is designed to keep the seeds from being carried away by erosion," he said.

Paper mulch is not used as much as straw and hay because it may blow away if it's in a windy area or does not receive about 12 inches of annual rain fall. Hay or straw mulch is used on slopes where equipment can mechanically punch it into the ground. The paper-mulch spray is usually used on steep slopes.

Plastic is another substance that could be used by lTD, if reprocessed plastic was available at economical prices. Plastic grocery sacks and clear packing strips can be used in asphalt mix.

"Using plastics in asphalt creates a stiff plant mix that could be used on city streets," Kidner said. "I think it would make a good product, but the demand just isn't there."

There have been no projects in Idaho using recycled plastic in highways because of the differences in plastic quality and the distance it would have to be transported to get here. There are no plastic-processing plants in Idaho.

Published 03-08-19