The Redbrook Financial Center development in Owings Mills, Maryland included a 419,000 square foot parking structure with 4 elevated levels. The columns of the concrete structure were placed such that 60’ beam spans and 27’-long slab bays were required. Further, the slab dimensions were 7” thick on all levels. These dimensional constraints necessitated the use of cast-in-place post-tensioned construction.

To increase the durability of the structure and mitigate deflections of the beams and slab, fully encapsulated, bonded post-tensioned systems were utilized. The use of approximately 177,000 linear feet of VSL’s VSLAB+® bonded slab post-tensioning system in the slab sets the Redbrook garage apart from typical parking structures. In general, the use of a bonded post-tensioning system resulted in the reduction of slab mild steel for the project. Mild steel is even eliminated in certain areas of the slab. Because of this, the maintenance cost associated with corrosion control is reduced while the durability of the structure is significantly increased. Furthermore, the reduced mild steel allowed the concrete parking structure design to have no microsilica or calcium nitrate corrosion inhibitor in the mix.The VSLAB+® bonded slab post-tensioning system provided full encapsulation using HDPE flat duct and watertight duct to anchorage connections. The slab tendons were partially stressed the day after each concrete pour to prevent shrinkage cracking in the slab, while stressing to the full 66 kips per tendon was completed when concrete reached a compressive strength of 3,000 psi. Grout was mixed and placed using a high performance, low-bleed grout and colloidal mixer. Trumpets with bypass pipes connected anchorages with ducts across construction joints to create continuity in the tendon through concrete pours. This allowed the contractor to grout each slab tendon from only one location. Grout vents were placed at end anchorages and at beam high points to allow air to escape and ensure total grout encapsulation. With VSL serving as the designer and supplier of the post-tensioned floor levels, field issues were resolved quickly and efficiently. VSL provided site inspections for every concrete pour to ensure placement quality of the multistrand beam and slab tendons, as well as all structural-reinforcing bars for the post-tensioned decks. A solution minded, cooperative relationship fostered by VSL and Daniel G. Schuster, the concrete frame contractor, helped the project to be completed on time and on budget.

The garage now provides over 1,500 convenient parking spaces for the tenants of the Redbrook Financial Center.