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Las Vegas CityCenter: No Gambling with Water

April 23, 2012 In the News

Las Vegas is a city that needs no introduction. One can reference the city and it almost immediatly conjures up notions of elaborate architechture, an unrestrained lifestyle, and opulence all around. However, deep below the glitz and bright lights of vegas is a shallow aquifer that threatens below-grade concrete construction.

Unknown to most of the 30 million tourists that frequent Las Vegas each year, the famous strip sits atop a shallow aquifer generated by excess runoff. In other words. Las Vegas is a natural oasis, which is what attracted people to the area originally. Merely 15.2 HI (50 ft) below the sandy desert, one can find groundwater trapped by impermeable clay and a sedimentary hardpan. This aquifer is insignificant to most ofthe city’s visitors, yet for developers who operate the high·stakes real estate environment, these implications are serious and can turn their investments into risky wagers.

The gamble
CityCenterCityCenter is the largest privately licenced construction project in United States history. This urban community has more than 917,466 m3 (1.2 million cy) of concrete, which is equivalent to approximately 120,000 typical concrete-mixing trucks—enough to build a 1.2-m (4-ft) sidewalk from Las Vegas to New York City and back. When owners and developers of the new Las Vegas CityCenter were planning construction, they knew waterproofing concrete would be the underlining threat. With 78.000 tons of steel in the CityCenter— enough to build 10 Eiffel Towers—the waterproofing needs were clear.

The grandiose site spans more than 27 ha (67 acres) on the Strip. between the Bellagio and Monte Carlo resorts. lt integrates five separate buildings, a sprawling landscape, and even its own lire station. The showpiece of this new complex is the 61-story Aria Hotel and Casino, which on its own has 168,202 m·‘ (220,000 cy) of concrete. Also joining the project are the Mandarin Oriental Hotel, Vdara Hotel and Spa. the Harmon Hotel, and Veer Towers. These buildings encircle The Crystals, an ultra high-end retail and entertainment district. In total, the project’s price tag was approximately $8.5 billion. The risk At street level, CityCenter is a collection of buildings. However, the entire development is interlinked by a sophisticated valet tunnel running below ground, dangerously close to the aquifer. There were several other building elements that posed additional waterproofing risks. ln the main building alone, some 72 elevator pits were constructed to service the buildings, all of which run below grade. Swimming pools are generously placed throughout ground level, overtop parking lots. Water features throughout the complex provide relief from the 38-C (l(l()·F) summer months and add to the extravagant setting.

CityCenter, Las-VegasWith over 4000 guest rooms, 16 restaurants, and a 14,000~m2 (150,000-sf) casino, the Aria Hotel could not risk any potential threats to its operations, It is also the permanent home to Cirque du Soleil’s acrobatic theater troupe, which included an 1800-seat theater with water features on stage—an integral part ofthe show. Even more impressive, the water tank holding the water for the performance is located deep in the ground, into the middle ofthe active aquifer under the strip.

There were several elements vulnerable to water damage, and the most accomplished team would be needed to bring the project to life. CityCenter was a collaborative project by eight internationally acclaimed architectural firms, including:
• Pelli Clarke Pelli;
• Kohn Pedersen Fox;
• Helmut Iahn;
• RV Architecture LLC led by Rafael Vinoly;
• Foster + Partners;
• Studio Daniel Libeskind;
• Rockwell Group; and
• Gensler.

The lead Firm, Gensler, was chosen as the executive architect overseeing the project, managing seven architects, three architects of record, 90 interior designers. and hundreds ofconsultants.

The solution
A proprietary technology was chosen to waterproof the valet tunnel, 72 elevator pits in the main tower. elevator pits in all the other buildings, all of the other critical below-grade structures and areas, swimming pools, and the water tank supporting the Cirque du Soleil show.

The material used for waterproofing turns the concrete itselfinto the water barrier. When combined with water, its chemicals react to form millions of needle—like crystals within the concrete. These crystals grow and till the capillary pores and micro—cracks in the concrete, blocking water passage.

By waterproofing from the inside out, integral crystalline waterproofing products have several major advantages over surface-applied products. They are invulnerable to damage in that they cannot be scraped, punctured, or torn. There are also no workmanship issues to be concerned with because membrane installation is not required. Of course, by eliminating the installation process, the general contractor also removes an entire trade from the jobsite along with the scheduling and access requirements.

Additionally, because time is not wasted on surface preparation and membrane installation, backfilling and other crucial construction processes can proceed without delay. Given the timeframe for this massive development—from concept to completion in five years—time savings were important.

A key advantage of using the waterproohng materials is if minor cracks form in the concrete at any point in the future, and water enters the crack, the chemicals reactivate to form new additional crystals to block the water. The resulting superior long-term reliability means integral crystalline waterproofing systems can save significant worryand an enormous amount of money as compared to surface·applied systems.

Although surface-applied membranes have been the industry norm. integral crystal-forming waterproofing systems are being considered and selected more often. Advancements in this technology make it a highly versatile and sophisticated method for waterproofing. lt provides a cost-effective way to seamlessly and reliably waterproof concrete——creating permanent and durable structures.

Bright green lights
Las Vegas is well-known for its bright lights, but CityCenter developers had green in mind and, from the onset. the team was committed to environmental sustainability. The project aimed to achieve Leadership in Energy and Environmental Design (LEED) Gold certification from the U.S. Green Building Council (USGBC), and it succeeded. CityCenter is the lirst for any hotel, retail district, or residential development in Las Vegas to attain this level of LEED.

CityCenter saves nearly 189 million L (50 million gal) of water annually, which is equivalent to the amount used by 380 residential homes each year. Considering Las Vegas is a desert, it is apparent the developers had put thought into many variables, exceeding the typical considerations. The sustainability initiatives continue long after the community opened its doors. For example, CityCenter is the first in Las Vegas to participate in a cork recycling program, where the wine corks collected from its I6 restaurants are recycled into footwear through the reCORK program.2

City Center, Las Vegas Among their sustainability certifications is one for materials selection. When the designers chose their materials, they carefully selected the products to fit their predetermined criterion. They preferred products made from recycled materials or ones that would be receptive to recycling in the future after the lifespan of it deteriorated. The admixture helped them achieve this as it extends the concrete structure`s life, reduces jobsite waste through use of pulpable bags, and enables future recycling of concrete materials.

The crystalline waterproofing contains no volatile organic compounds (VOCs), is non-toxic and safe for contact with potable water, and does not adversely affect the concrete. Centuries later, if the CityCenter planned on rebuilding a portion ofthe community, the concrete could be broken down and reused for the new structure, whereas a building that would have used traditional membranes would have tarnished the concrete. To further increase the stakes, the manufacturer was challenged to waterproofthe tank supporting the water features ofthe Cirque du Soleil performance. Not only was the tank nestled in the path of the aquifer, but it also sat directly above a hotbed of electricity—the control center that would house all ofthe electronics that governed the show. Leaking of any kind, whether by product malfunction or natural cracking and settling, would be disastrous. The same admixture was used to waterproofthe tank, keeping the water for the show securely inside and contaminants from the aquifer out.

Conclusion
With five buildings going up at different rates, all with a common foundation and a need to interface these elements with the existing Las Vegas structures, the pr0ject’s waterproofing needs were both numerous and challenging.

The CityCenter has since opened its doors successfully and has received a flood of accolades for architectural, sustainable, and building excellence. The skyline ofthe Las Vegas Strip is forever being moved and reconstructed, but fortunately, the aquifer will stay in place. lS.2 m below ground and remains one of the city’s mysteries. DS

By Alexandra Emlyn, LEED AP

Notes
 1 See www2.citycenter.com/press_pdf/Tishman%20 Construction%20-%20CityCenter%20Press%20 Release.pdf. 
2  Visit recork.org for more information.

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