The replacement of Crossroads Plaza and ZCMI Center malls with City Creek Center isn't all out with the old, in with the new.

As The Church of Jesus Christ of Latter-day Saints' construction contractors tear down the downtown malls to make way for the 20-acre retail-office-residential complex, more than half of what comes down will be reused, either in City Creek or somewhere else.

"The idea is to divert away from the landfill as much as we possibly can, because the landfill is obviously a finite resource, and this effort is geared toward a more sustainable development," said Grant Thomas, director of construction services for Property Reserve Inc., the church's real-estate arm. "It takes more time and more care to do this, but it's the right thing to do."

The demolition work will knock down most of the buildings on the two blocks between South Temple and 100 South from West Temple to State Street — leaving more than 200,000 tons of concrete, marble, steel, drywall and other materials on each block.

About 55 percent of that material will find new life: Concrete, marble, stone and other masonry will be ground down and used as road base and fill material at other construction sites, and steel frames will be sold as scrap metal.

Only a handful of materials won't be reusable, including drywall and insulation.

The sorting process is mostly done by machine, and it depends on the building being demolished.

"It's really quite something to watch these operators," Thomas said. "The operators are pretty talented."

For some buildings, it's possible to tear down recyclable materials separately from non-recyclables, so the rubble ends up in already sorted piles. With other buildings, workers will have to manually sort through piles and pull out the recyclables.

The recycling will make the project costlier than if all rubble were hauled away to the dump, Thomas said. But officials have no estimates as to how much more it will cost "because we didn't really approach it from the other side."

The church always planned to recycle its waste, so that's how costs were predicted. A City Creek spokesman previously told the Deseret Morning News that the added cost for demolishing and recycling at the Inn at Temple Square was about 15 percent.

Some of the historic material pulled from the Crossroads and ZCMI blocks also will be reused.