Walking on broken glass is something usually reserved for those with great mental concentration, but it could become commonplace in Iowa. The Iowa Department of Transportation is experimenting with an asphalt mix that substitutes crushed recycled glass in the place of sand. D-O-T engineer Mike Heitzman says they’re using the “glasphalt” mix to pave recreational trails in Ames, Des Moines and Cedar Falls.He says the glass is finely ground and walkers and bike riders probably won’t even notice it. Heitzman says there’s not enough recycled glass available for large highway paving projects, but he says it fits nicely with small batches of paving mix used for trails. He says they don’t know yet how much more, or less, the use of recycled glass will add to the cost of paving the trails.Heitzman says they use recycled glass from drink bottles, fluorescent lights and from windows.