Replacement of the "popcorn" asphalt surface material, which crumbled prematurely on several state highways this January after a rapid series of freezes and thaws, is expected to be completed by winter at a total cost of $20 million, state highway officials estimate.
Charles R. Harrison, district engineer for Baltimore and Harford counties, said yesterday that the state has spent about $6 million since January to replace the eroded surfacing material on various roads, including stretches of Interstate 83, I-795 and the inner loop of the Baltimore Beltway. The money came from the state's snow removal account, which had a surplus because of mild weather.
Another $14 million is needed, according to figures released by the state Department of Transportation, to fix the remaining sections of road where the 3/4 -inch thick "popcorn" surface has crumbled or "raveled," as state highway engineers said.
About 90 percent of the $14 million will come from federal funds, with the rest paid by the state, state officials said.
The popcorn problems created shallow pools of fine gravel that rattled nerves and shattered windshields in some areas, particularly I-83 in northern Baltimore County.
The $14 million, the Department of Transportation says, would become available only if the legislature passes a series of increases in Motor Vehicle Administration fees during a special session tomorrow. If the money is approved, Department of Transportation officials said, repairs could be complete by November.
Popcorn mix, used widely in this country since the 1970s, is a porous material with a granular texture somewhat like the popular snack food. It is designed to drain water away from the road surface, reducing skids, tire noise and puddles that might splash on windshields.
All the state's interstate highways and roads with speed limits above 50 mph are covered with popcorn. But only about 250 lane-miles out of 15,000 lane-miles of state-maintained roads suffered a "major failure" of the popcorn mix, a Department of Transportation official said.
Mr. Harrison said the problem so far has been confined to roads where popcorn was applied between 1982 and 1988. The state's recipe for popcorn changed in both those years, leading to the suspicion that there may have been some flaw in the mixture of liquid asphalt and gravel or the type of gravel used in 1982.
But Dr. A. Haleem Tahir, director of materials and research for the state Department of Transportation, said engineers have not been able to pinpoint the problem and called talk of an improper mixture "speculative."
The mix now being applied to replace the eroded material, he said, is "latest state of the art." He noted that there is a new mixture developed in Europe that the state may apply on a section of roadway as an experiment. "That may help give it a slightly longer life," he said.
Mr. Harrison said the popcorn material is normally expected to last between eight and 10 years. On the affected stretches of road, he said, it has lasted only between five and six years.