WASHINGTON (Reuters) - Builder Tutor Perini Corp has won a $9.6 million contract to repair earthquake damage to the Washington Monument, the National Park Service said on Wednesday.

The award of the contract to Perini Management Services Inc, a Tutor Perini unit, allows repair work on the Washington landmark to begin, the agency said in a statement.

Repairs are expected to take 12 to 18 months to complete. Scaffolding will sheathe the 555-foot-high (169.2-meter-high) structure during the work.

The marble and granite monument to George Washington, the first U.S. president, was widely damaged by a 5.8 magnitude earthquake on August 23, 2011.

The structure sustained cracks and loosened pieces of stone and lost mortar when it was shaken. The monument has been closed since the quake.

Repairs have been completed on the monument's elevator, which was severely damaged, the statement said.

Congress has appropriated $7.5 million for the work. The amount was matched by David Rubenstein, the billionaire co-founder of Washington's Carlyle Group, a private equity firm.

The rest of the $15 million will go toward a completed damage assessment, construction management, a contingency fund and overhead, among other things, the statement said.

(Reporting by Ian Simpson; Editing by Cynthia Osterman)