Category: Green Design
The San Francisco International Airport, owner of this green concrete project, set out to demonstrate its leadership in sustainable building by achieving LEED credits for its new parking structure through the use of concrete made with supplemental cementitious materials, specifically slag cement. While the specs originally called for fly ash, Graniterock suggested slag would work better because of its efficient set time. Engineers specified an aggressive higher-than-normal early strength, which is not feasible with fly ash without increasing the sack content. In addition, slag cement helped combat a corrosive soil environment.
The owner’s goal was to reach gold level LEED accreditation for construction of the new parking garage. Reaching that level of green building accreditation required 45 percent supplemental cementitious materials in grade beams and pile caps, and 30 percent slag in all other concrete mixes. To meet the airport’s January 2019 completion goal, the decks required high early strength concrete. The SCM requirement and high early strength were made possible by utilizing slag cement. Slag cement helped bridged the gap in requirements from the owner and engineer. An additional benefit of use was impressive later day strengths.
If slag cement had not been used, the project would have compromised its reduction of CO2, mix performance, and project schedule. Slag cement helped accomplish all the project’s green building goals and provided a significant cost savings for the airport.
This is a structure that will be heavily used by SFO travelers for many decades. Due to the collaboration between the project’s diversified teams to use a less permeable material, the parking garage may last longer than originally anticipated, adding to slag cements impact on the project’s environmental sustainability.
Project Team: SIFA, Nibbi Brothers General Contractors, Kwan Henmi/FMG Joint Venture, Buehler Engineering Inc. Graniterock, Lehigh Southwest Cement Company