Chicago's Soldier Field received a face-lift that will add at least 50 more years to the stadium's life, thanks to the strength and weathering properties of latex-modified concrete used for the renovation. In addition to numerous improvements in the overall layout of the stadium, the plan involved refurbishing the old concrete tread-and-riser system by placing latex-modified concrete over the original structure to form a new base for seating. Latex-modified concrete would be cast directly on the original horizontal tread to a thickness of 3 inches, and 6 inches against the vertical riser surface, forming a 6-inch-wide beam.
Latex-modified concrete is a mixture of non-air-entraining Portland cement, aggregate, water and a styrene-butadiene polymeric emulsion. The emulsion bonds chemically to the aggregate, remains in the voids as they form and thus relieves internal microstresses and retards the formation or enlargement of cracks; this increases overall strength and blocks penetration of moisture or corrosive chemicals. This was the first project on which latex-modified concrete had been used to bolster a tiered structure.
As the first step, all supporting columns were inspected and, where necessary, repaired to assure proper support for the new structure. The underside of all old concrete was chipped and shotcreted to stem further deterioration and to provide added strength. Top surfaces were also chipped to clean away loose and delaminated material. Before pouring the new concrete, the old was sandblasted to expose a clean top surface and eliminate any contaminants that might interfere with proper bonding between the two materials. The night before the pour, reinforcement was installed and forms for each tier were set in place. In the morning, the old concrete was thoroughly wetted before casting so that moisture would not be pulled from newly poured concrete during the first 24 hours of curing.