Old roads and concrete don’t have to take up space in landfills. They can become excellent substrates for raising oysters, according to a new study.

Morgan State University’s Patuxent Environmental and Aquatic Research lab conducted the three-part study with funding from the Maryland State Highway Administration.

While restoration groups have long used large pieces of concrete for reef balls and fishing habitat, it was unknown whether old road beds contained any contamination that would make them unsuitable for growing baby oysters.

Old roads and concrete are turned into recycled concrete aggregate, a crushed mixture of rock, cement and the chemicals that came into contact with the road.

The Morgan study showed that leachate from the aggregate remained well below regulatory levels. It did not raise the pH above the threshold for introduction into Maryland’s waters.

The second phase looked at whether the aggregate would harm other marine life. It found that the aggregate did not.

The third phase looked at whether the aggregate would disrupt harvest gear. That work found that it would for tongers.

Watermen suggested to researchers that the state not use the aggregate in areas set aside for tonging. Maryland regulates what kind of gear can be used on specific oyster bars, with some designated for either tongers, power-dredgers or divers. Watermen also suggested that the aggregate could be used with a veneer of oyster shells placed on top so they could work such a reef.

The work is important because Maryland is attempting to restore oysters, which are still at 1 percent of their historic population. Oysters are growing well in Maryland, both in aquaculture and in the wild fishery. But both fisheries suffer from a shortage of shell. Shell is the best substrate, but the scarcity has forced oyster habitat managers and oyster farmers to look at other alternatives.