Within a single 24-hour period in October 2005, a fleet of 30 concrete trucks made 600 trips to pour of concrete, and thus create a 200-by-66-by-10-foot (61.0 m × 20.1 m × 3.0 m) concrete "mat". The mat serves as the base of the building, from which its spine rises. Those involved with the construction referred to the day as the "Big Pour". James McHugh Construction Co. was contracted for the concrete work on this job. They obtained the concrete from the Chicago Avenue and Halsted Street distribution site of Prairie Material Sales Inc of Bridgeview, Illinois, the former largest privately owned ready-mix concrete company in the United States. Prairie used a formula of concrete that had never been used in the construction business to meet a specification, which exceeded the standard for conventional concrete.