SHANGHAI, April 14 -- The technology behind microwave ovens will be used to save time on road repairs, infrastructure maintenance managers said yesterday.

Managers said workers recently used microwave heat to melt a two-square-meter piece of damaged asphalt on the Yangpu Road Bridge. Constructors were then able to lay down a new piece of asphalt.

"The new technology will shrink construction time and keep traffic disruption to a minimum," Yan Jiting, an official from the Shanghai Pujiang Bridge and Tunnel Management Company, said yesterday.

He said the company has imported a new road maintenance vehicle that sends out microwaves. The two-man vehicle takes just 20 minutes to repair a patch of asphalt.

Road repairs normally involve a crew of five workers with picks and drills to remove the old surface and then lay down new asphalt. The work can last more than an hour.

Yan said the technology is likely to be expanded to tunnel repair.

The city wants to resurface or repair nearly one-fifth of its roads ahead of the World Expo 2010 Shanghai.

Most of the target roads are arteries and key venues within the Outer Ring Road, particularly around the 5.28-square-kilometer Expo site between Lupu and Nanpu bridges.

Officials with the Shanghai Engineering Administrative Bureau said some of the city's roads were not built with "proper material."

Some road surfaces have become uneven, a situation not helped by the growing number of vehicles on city streets.

The Outer Ring Road Tunnel went into use in 2003 but underwent major repairs just three years later because of the worsening state of its asphalt.