(AP) — The federal government has agreed to pay up to $7.5 million to help repair taxiways and the main runway at Chadron Municipal Airport in northwest Nebraska.

The Panhandle Post website for Chadron radio station KQSK says (http://bit.ly/16QB3N0) the work is needed because concrete from a repaving project in 2000 has failed.

Chadron Public Works Director Milo Rust says the horizontal cracks were discovered last summer during a sealing project. He says the concrete failure has been blamed on an unexpected chemical reaction involving the silica sand used in the cement mix.

Rust says experts aren’t sure what caused the reaction. He says the concrete used in 2000 met specifications and passed required tests at the time.

He expects the project will begin next spring and could take a year.