(Image Credit: Portland Cement Association)
Florida’s unique environmental challenges, including its vulnerability to hurricanes, rising sea levels and extreme weather, highlight the need for sustainable and resilient building designs. As coastal urbanization grows and climate concerns escalate, there’s increasing pressure on architects and developers to implement materials and methods that ensure long-term durability while reducing environmental impact.
Concrete, especially when specified with lower-carbon cement such as portland-limestone cement (PLC) in the mixture, has emerged as a leading solution for sustainable construction. PLC (Type IL) is engineered with a higher limestone content and gives specifiers, architects, engineers, producers and designers a greener way to execute any structure, paving or geotech project—with the same strength and durability as traditional portland cement.
Concrete structures, known for their strength and durability, are particularly well-suited to regions where resilient design is a must, such as in Florida’s coastal climate. However, incorporating PLC into the concrete mixture significantly improves the sustainability of these projects. By using PLC, construction projects can reduce the carbon footprint by up to 10 percent while maintaining the structural integrity needed for hurricane-resistant buildings.
Recent coastal luxury developments in Florida, such as The Heron at Water Street and Virage Bayshore—both in Tampa—exemplify how innovative design combined with PLC-based concrete mixtures can offer both aesthetic appeal and structural resilience. These projects demonstrate that low-carbon concrete not only meets the rigorous demands of high-performance buildings but also aligns with broader sustainability goals, making it a forward-thinking solution for Florida’s evolving architectural landscape.
Striking Design with Sustainable Concrete Solutions
The Heron at Water Street, a luxury condominium building, is the first residential property to open at Water Street Tampa, a $3.5 billion mixed-use development from the owner of Tampa Bay’s NHL Lightning team and an investment group led by Bill Gates. It has 420 apartment homes.
The Heron at Water Street’s innovative concrete columns are key to the building’s dramatic appearance. (Image Credit: Portland Cement Association)
This high-profile project, with such discerning backers, necessitated eye-catching design. Architects chose innovative structural and architectural components for The Heron, such as the three-legged column at one of the building’s corners. They specified exposed architectural concrete finishes for some structural members to add to the building’s dramatic appearance. And though the effect is minor, PLCs can have a slightly lighter color than ordinary portland cement, imbuing the concrete with a slightly lighter color, too, which can be appealing to some design teams.
This building, which sits at the entrance to the Tampa Riverwalk, is both to see and be seen. It offers a prime vantage point and is, itself, visually striking. The waterfront location offers desirable water or downtown views, made even more accessible by the floor-to-ceiling windows and spacious balconies that encourage outdoor living and entertaining. Common element green roof gardens and rooftop pools enhance the livability of city life. It’s part of Water Street Tampa, a mixed-use neighborhood on 56 acres of waterfront property that promotes itself as walkable, sustainable and connected. PLC concrete fits perfectly with these design goals by offering similar performance as ordinary portland cement concrete with increased sustainability.
To help convince contractors to use PLCs, the ready-mix supplier provided mix design submittals. For the 49,410 cubic yards of concrete used to construct The Heron, most of the mixes were made using PLC and supplemental cementitious materials (SCMs). Cement-only mixes were used for precast members and most decks, which were post-tensioned.
High-Strength, Sustainable Concrete Solution for Tampa’s Coastal Luxury Tower
The Virage Bayshore, a 24-story luxury condominium tower, joined the Tampa skyline in mid-2020. Its dramatic curved facades and floor-to-ceiling windows showcase panoramic bay and city views for 71 residences, including 10 estate and penthouse units. 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 during the last few decades. In 1992, the American Concrete Institute Committee on High-Strength Concrete (ACI 363) recognized 6,000 psi as high strength. By 2001, the committee increased that to 8,000 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, 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 such as coastal South Florida, durability for concrete to resist corrosion must be considered. 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-percent 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-percent slag cement, meaning that the load-bearing members were made with concrete that had a cement clinker content of 40 percent compared to a historic portland cement-only mix, which reduces the CO2 of the PLC and SCM concrete by approximately 60 percent.
How to Specify PLC
PLC can be a direct replacement for portland cement (PC), so it only requires one change to project specifications: Refer to ASTM C595 Type IL instead of (or in addition to) ASTM C150 Type I portland cement.
• DOT Construction using AASHTO Specifications: For some state DOT construction, specifications developed by the American Association of State Highway Transportation Officials (AASHTO) are used instead of ASTM. AASHTO M 85 is the specification for portland cements; AASHTO M 240 is the specification for blended cements. The technical provisions of AASHTO M 85 and M 240 are the same as those of ASTM C150 and C595, respectively, so switching to PLC requires reference to an M 240 Type IL cement instead of (or in addition to) M 85 Type I. Just as with C150/C595, similar special cement types are available.
• American Institute of Architects (AIA) MasterSpec: AIA MasterSpec includes PLC as an option under the Blended Hydraulic Cement entry. MasterSpec Section 03 30 00 on Cast-in-Place Concrete includes the following options in Section 2.5D on Cementitious Materials: Portland Cement: ASTM C150/C150M, [Type I] [Type II] [Type I/II] [Type III] [Type V], [gray] [white] Blended Hydraulic Cement: ASTM C595/C595M, [Type IS, portland blastfurnace slag] [Type IP, portland-pozzolan] [Type IL, portlandlimestone] [Type IT, ternary blended] cement.
• Federal Aviation Administration (FAA) Specification:For airport construction, PLC is permitted under FAA Advisory Circular AC 150/5370-10H, Standard Specifications for Construction of Airports. Item P-501, Cement Concrete Pavements, as modified by FAA Engineering Brief #106, includes the following text with the option to use Type IL cements: 501-2.2 Cement. Cement: [ASTM C150, Types I, II, or V; ASTM C595, Types IS, IP, IL, or IT; ASTM C1157 Types GU, HS, MS, MH, or LH]. The Engineer should retain all cements appropriate for use on the project. Note: ASTM C1157 cements are typically only used for repair projects. Other cements may be specified with the concurrence of the FAA. AC 150/5370-H also permits Type IL cement in sections P-153, Controlled Low-Strength Material (CLSM); P-207, In-place, Full-Depth Reclamation (FDR) Recycled Asphalt Aggregate Base Course; P-220, Cement Treated Soil Base Course; P-307, Cement Treated Permeable Base Course (CTPB); and P-610, Concrete for Miscellaneous Structures.
If special properties such as moderate sulfate resistance are required, a qualifier is added to the IL designation. The table below shows a comparison of PC vs. PLC to meet special properties for cements specified by either ASTM C150 or C595, or their counterparts from AASHTO, M 85 or M 240.
It’s recommended that trial batching be performed to confirm expected fresh and hardened performance, just as if a new source of portland cement was being used. Because PLCs are typically optimized to provide the same type of performance in concrete, mix designs may remain unchanged or it may require minor adjustments, such as dialing in admixture dosages or modifying aggregate content.
The Future of Cement
The increasing adoption of lower-carbon cements, such as PLC, demonstrates a crucial advancement in sustainable construction, and PLC is only the beginning. The U.S. cement industry is committed to creating new cements using existing and even alternative materials to reduce emissions. By reducing a project’s carbon footprint and maintaining structural integrity, lower-carbon cements are paving the way for a more-sustainable future in Florida and beyond.
Ashley Kizzire is the senior director of marketing and communications for the Portland Cement Association; email: akizzire@cement.org
About Ashley Kizzire
Ashley Kizzire is the senior director of marketing and communications for the Portland Cement Association; email: akizzire@cement.org
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