Durability and Sustainability: PLC Helps Rebuild New St. Pete Pier
St. Pete Pier is a landmark recreational attraction extending into Tampa Bay from downtown St. Petersburg, Florida. It serves as an anchor for a 26-acre waterfront park, which has been named one of the top tourist attractions in the country. When it came time to replace the previous pier, design architect ROGERS PARTNERS Architects+Urban Designers and executive architect ASD/SKY Architects created a new $92 million St. Pete Pier with restaurants, interactive areas, a local artisan/vendor marketplace, a fishing deck, and public art.
Similar to a bridge in many respects, the pier is a robust structure. It is supported on 425 piles with a 148,000-sq-ft concrete deck over water. Each pile measures 24 in. by 24 in. by 75 ft in length. There are also drilled-shaft foundations that range in size from 36 to 66 in. in diameter and 30 to 40 ft deep.
Marine exposures are aggressive to reinforced concrete because chlorides corrode steel. This is true not just for the submerged portions of the structure, but also for the above-water components, as marine air carries salt. Encasing metal reinforcement in concrete protects it from salt and corrosion, and reducing concrete permeability improves protection for the steel. Tactics for reducing permeability include using supplementary cementitious materials (SCMs) like fly ash and slag cement, reducing the water-cementitious materials ratio (w/cm), and increasing the concrete strength. These techniques all improve corrosion resistance and are equally applicable to portland-limestone cement concrete (PLC) mixes as they are to traditional portland cement mixes. For the St. Pete Pier, high-strength concrete (12,000 psi) was used. Although precast elements were made with traditional portland cement concrete, most of the 12,000 cubic yards of concrete for the pier project were formulated with PLCs and SCMs. To help convince the contractor, Skanska, that PLC mixes would meet the performance requirements for this project while also offering sustainability benefits through a reduced carbon footprint, the ready mix concrete supplier provided mix submittals.