On the banks of the Chicago River, construction of the Trump International Hotel & Tower is in its early stages with the recent completion of its mat-slab. Designed and engineered by Skidmore, Owings, and Merrill (SOM), the multi-use building will be structurally reinforced concrete, standing 1160 feet tall with 2.6 million square feet of floor space.
The foundation includes concrete caissons 6 to 12 feet into bedrock (which can be as much as 100 feet below grade), caisson caps and grade beams to support building columns, and a mat-slab supporting the core walls.
The construction of the 10-foot-thick, 200x60-foot mat-slab represents state-of-the-art self consolidating concrete (SCC) technology and the largest U.S. SCC application to date. SOM specified that the 4700 cubic yards of SCC should meet the following requirements:
- 10,000 psi minimum compressive strength at 56 days
- 6000 ksi static modulus of elasticity at 56 days
- 80° F (26.7° C) maximum concrete temperature delivered to the site
- 170° F (76.7° C) maximum in-place core temperatures
- 40° F maximum temperature differentials between the top of the slab and its midpoint.
The ready-mix producer for the project, Prairie Materials Group, Bridgeview, Ill., supplied the concrete. Mike Pistilli, technical director, and Gary Hall, senior concrete technician, developed the SCC mix. The CTL Group, Skokie, provided modulus of elasticity testing during the mix development phase, and Degussa Admixtures, Cleveland, supplied the admixtures and backup support. Here are the mix ingredients:
- A very low amount of type-II portland cement
- Grade 120 slag cement
- Class-C fly ash
- Polycarboxylate high-range water reducer
- Type D water-reducing chemical retarder
- VMA (viscosity modifying admixture)
- ½-inch and ¾-inch crushed dolomite stone and natural sand
- A water-cement (w/c) ratio between 0.26 and 0.28
Though there was considerable excitement about casting the mat slab, the actual placement was very routine—just what everyone hoped for. Placing the concrete started at noon on September 30, 2005, and ended 23 hours later using three Telebelt conveyors. A majority of the loads were tested on-site. The measured spread of the concrete was 26 to 28 inches, which corresponded to a point-of-placement flow of approximately 40 feet. The maximum core temperature of the mat-slab didn't exceed 155° F (68° C) and the maximum temperature differential between the middle of the slab and its top surface never exceeded 28° F. At 56 days the average compressive strength of the concrete was 14,400 psi and the static modulus of elasticity was 6850 ksi.
Construction of Chicago's Trump is scheduled to conclude in 2009.