The Richard O. Jacobson Building, Rochester, MN, is a state-of-the-art cancer treatment center consisting of two floors cast-in-place below grade and three floors above that are structural steel with composite decks. The building is designed for an additional 16 stories in the future. Of the approximately 32,000 yd3 (24,500 m3) of concrete, 50% is being used for radiation shielding around four treatment gantries and fixed beam room. The treatment equipment weighs approximately 120 tons (109 tonnes) and is supported from both the walls and the floors of the mass concrete with embedded steel plates cast into the concrete for equipment support. Some of the steel plates were 4 in. (100 mm) thick, 4 ft (1.2 m) wide, 7 ft (2.1 m) long, and weighed 4574 lb (2070 kg).
Slag cement was used at 40% in combination with 30% Class C fly ash and portland cement in mass concrete placement mixture designs. The specified compressive strength was 5000 psi (35 MPa) at 28 days. The mixture controlled thermal stress and met concrete density requirements for radiation shielding. The largest mass concrete placement consisted of 5280 yd3 (4030 m3) of concrete. Much of the concrete was placed during the summer months in temperatures up to 90°F (32°C). This added to the need to control the setting time of the concrete to reduce shrinkage and cracking.
Project credits: Mayo Clinic, Owner; AECOM, Architect and Engineer; Gilbane Knutson, Contractor; Knutson Construction Services Rochester, Inc., Concrete Contractor; Rochester Ready Mix, Concrete; and Lafarge North America, Slag Cement.