By late March 2004, most of the roof decking had been waterproofed and crews began placing a 6-inch gravel bed on top of the waterproofing membrane in preparation for a 6-inch topping slab. Formwork for the lower level floor slab in the southwest end of the side was progressing rapidly and was in place below the Great Hall south skylight. Work continued on the slab on grade throughout the site and for the Library of Congress pedestrian tunnel. Demolition work continued in the East Front to clear the way for the transition zone between the CVC and the Capitol, and two large columns supporting the East Front Steps were removed. In addition, portions of the floor slabs in the East Front had been demolished to clear the way for elevators, stairs and air shafts. Work on the truck tunnel continued and close to 60 percent of the concrete had been placed by this time.