Tampa’s Virage Bayshore Condominiums: A New Waterfront Landmark
In Tampa, Florida, a new 24-story luxury condominium tower joined the skyline in mid-2020. Its dramatic curved facades and floor-to-ceiling windows showcase panoramic bay and city views. The 71 residences, including 10 estate and penthouse units, all range in cost from $1 million to more than $5 million. The high-end, resort-style property is situated on Bayshore Boulevard, one of the longest contiguous waterfront sidewalks in North America. Given its Tampa location – coastal climate with potential exposure to hurricanes – a structural frame of concrete is an excellent choice.
Concrete strength levels have gradually increased over the last few decades; in 1992, the American Concrete Institute Committee on High-Strength Concrete (ACI 363) recognized 6000 psi as high strength but by 2001, had increased that to 8000 psi or greater. By the ACI definition, Virage’s structural system is built using high-strength concrete: the post-tensioned slabs are made with 8,000 psi concrete and the shear walls and columns are 10,000 psi. Except for the precast members, portland-limestone cement (PLC) and SCMs were used for most of the concrete mix designs.
Strength is an important consideration given to selecting concrete but not the only one. In a marine setting like coastal South Florida, durability for concrete to resist corrosion must be considered, too. PLC concrete has been shown to have similar resistance to chloride penetration as ordinary portland cement concrete and will protect embedded steel from corrosion equally well. This provides designers, builders, and owners the assurance that this property will be durable using typical maintenance procedures for reinforced concrete.
Using PLC mixes for the 18,701 cubic yards of concrete to construct the post-tensioned slabs, shear walls, and columns was an environmentally sound decision. The standard cement for this type of construction would normally have been an ASTM C150 Type I/II portland cement. To help convince contractors to use PLCs for the sustainable and performance aspects of the material, the ready-mix supplier provided mix design submittals. PLC is specified as an ASTM C595 Type IL cement; for this project, a PLC with nominal 10% limestone content was used, designated as Type IL(10). For the post-tensioned slabs, cement-only mixes were used. Post-tensioning on this project required that strength be a minimum of 3,000 psi in 24-36 hours; mix design submittals demonstrated 3,400 psi at 24 hours. For the shear walls and columns, the PLC was blended with 50% slag cement, meaning that the load-bearing members were made with concrete that had a cement clinker content of 40% compared to a historic portland cement-only mix, which reduces the CO2 of the PLC + SCM concrete by about 60%.