Member Company: Lehigh Hanson
Selected Award Categories: Green Design
This landmark project in Santa Clara, CA is 500,000 sq. ft. in size and has two levels of subterranean parking for 1500 vehicles and two levels of office space above ground. This unique triangular-shaped building, designed with a major focus on the seismic concerns for this Northern California geographical region, required just over 50,000 CY of structural concrete. Approximately 32,000 CY utilized 50% supplemental cementitious materials (SCMs) -- with at least half of this consisting of ground, granulated blast furnace slag. The NVIDIA building is supported by a foundation that ranges from 2.5 to 3 feet in thickness and 40-foot-long steel braces that make up the buckling-restraining braces – a design approach that assists in resisting lateral forces during earthquakes, and steel cores encased in concrete. The top-level parking and the office-level slabs were post-tensioned decks that consisted of high early strength concrete and over five miles of cables.
Approximately 65% of the concrete placed on this project consisted of slag as a cement replacement, at a 25 – 30% replacement rate. With this 50,000 CY landmark project in the heart of Silicon Valley pursuing the Gold Leadership in Energy and Environmental Design (LEED) certification rating level it was critical to utilize this slag cement in all areas that allowed for it. The ground, granulated blast furnace slag is a by-product of the steel manufacturing process and contributes specifically to the recycled materials category for LEED credits.
Additionally, when considering the green aspect of this building and the efforts related to the sustainability initiative, the use of slag mixes (when compared to the alternate mixes made up of cement and 15% fly ash), with all other variables remaining constant, resulted in an approximate savings of 6.7 million pounds of carbon emissions. Subsequently, the ozone depletion potential of this mix shall be considered less when compared to the alternate mix.
The use of slag was also significant when selecting the mix for the large foundation. The foundation was up to three feet in thickness due to the multiple pours -- totaling approximately 25,000 CY. The ground, granulated blast furnace slag assists in limiting the rise in temperature in large concrete pours due to the hydration process -- considered gradual when compared to the traditional Portland cement. In addition, the selected mix specified with 25% slag, resulted in an 8-degree Fahrenheit reduction in the expected temperature rise (based on the most widely used and accepted formulas and calculations), when compared to a traditional cement/15% fly ash mix.
The use of ground, granulated blast furnace slag on this project contributed to the overall project goals and ambitions of the owner to apply for a LEED Gold rating, as measured by the US Green Building Council. The overall impact on the environment can be measured by the impressive reduction in CO2 emissions, which saved approximately 6.7 million pounds. The recycled materials characteristics of slag contributed specifically to the recycled materials content category as outlined in the LEED documents.
Not only was slag used to achieve the project’s aggressive green goals, but it was chosen to deliver the highest level of performance. Slag was utilized in all the mixes that were selected for the high strength columns and the shearwalls for the subterranean parking structure. These elements provided the support for the massive above-ground steel framing, and therefore, strength optimization was critical. The slag used also contributed to the overall improved job performance as it related to the pumpability and finishability of these walls/columns.
From its unique triangular shaped corporate building with state-of-the-art sustainability features, to its aggressive reuse of materials and its attention to energy use and much more, this project is clearly one of the Silicon Valley’s premier projects and will be recognized for its attention to excellence. Central Concrete’s mixes, many of which utilized slag and other cement replacement materials, were engineered to achieve optimal performance, while significantly reducing the carbon footprint. These solutions were recognized for their key contribution to best-in-class constructability and meeting green and sustainability requirements - a recognition that goes above and beyond the quantifiable numbers, which is undoubtedly considered a success.
The key component to this building’s development was safety. Due to its location in the heart of the San Francisco Bay Area, a major concern was making sure the building could withstand earthquakes. Earthquake resilience was the driving force behind the design approach based on an impressive foundation and buckling-restraining braces. The mat slab was the thickest in the areas that were to support the large atrium, which was made up entirely of glass. The use of slag cement, while perhaps not required based on the engineering design for this particular steel braced framing on the above ground portions, undoubtedly brings additional inherit strength and durability aspects to the final structure.
Project Team: (Owner: NVIDIA Corporation) (Architect: Gensler) (Engineer: Nishkian Menninger) (General Contractor: Devcon Construction) (Concrete Contractor: Conco) (Concrete: Central Concrete Supply Co.) (Slag Cement: Lehigh Heidelberg Cement Group)
Photos courtesy of Central Concrete. Photographer: David Sievert AIRPHOTO DESIGNS.