Concrete Waterproofing Alternatives
EXISTING CONSTRUCTION CASE STUDY 2
Project: Providence Regional Medical Center
Location: Everett, Washington
General Contractors: Hoffman Construction
Masonry Contractors: Fairweather Masonry of Seattle
The Challenge: The existing concrete block foundation wall at this busy medical center was leaking badly. Because of the proximity of the adjacent building, it was impossible to excavate on the exterior and install positive-side drainage.
The Solution: A negative-side waterproofing system was chosen by Hoffman Construction, which was the general contractor for the construction. Working with masonry contractor Fairweather Masonry of Seattle, which had erected the foundation system, the two determined together the best path forward. Because of the variable nature of the block density and the extensive amount of water seepage, a system consisting of one coat of crystalline slurry mixture concentrate and a second finish coat was selected. A manufacturer’s representative was on-site to assist with the initial phases of the application.
Results: The water leakage has stopped, and the facility is able to function smoothly again.
EXISTING CONSTRUCTION CASE STUDY 3
Project: H. B. Allen Centre at Oxford University’s Keble College
Location: Oxford, England
The Project: Keble College, opened in 1870, is the first Oxford College of the modern era. It was founded in memory of John Keble (1792–1866), well known for his best-selling Christian verse and a key member of the so-called ‘Oxford’ movement. Located just 300 meters north of the existing college, The H. B. Allen Graduate Centre is described as one of the most exciting and significant building expansion projects in Oxford. The centre hosts top-quality accommodations, a lecture theatre seating up to 120 people, seminar rooms, and a large exhibition/performance space. Facilities will be available throughout the year and help supplement the offering of the main college site during vacation.
The Challenge: Part of the expanded centre includes retaining an existing building that dates to the 1800s and is a listed historical building. The basement of the expansion covers the entire footprint of the site and extends under a new connected building and new gardens as well as under the retained building. The design was complex because of differing levels and uses in the updated facility. To allow for differential settlement, a movement joint was required, which further complicated the design. Due to the nature of the structure, its contents, and the high level of the water table, the water-penetration risk was determined to be high in accordance with local standards.
The Solution: Crystalline waterproofing technology was introduced to the project architect during the design stage. After review of a number of different options and input of the entire design team, a two-system approach was decided upon using crystalline waterproofing in conjunction with a bentonite system to meet all of the design requirements. Drawings were produced accordingly and issues resolved as part of an in-depth process prior to work commencing work on-site. Crystalline admixture was used on the capping beam, basement slab, basement walls, elevator pits, and attenuation tank. Crystalline coating was applied to all joint surfaces, including a movement joint to allow for a differential in settlement between elements of the structure above. The application coat was also used where numerous ducts were cast in place and needed sealing as part of the complete package. Local manufacturing representatives were very involved in the development of the waterproofing strategy for the entire basement structure.
The Results: Crystalline technology allowed for a primary solution throughout the basement to waterproof the entire substructure against the ever present ground water.
Special Building Conditions
In addition to conventional concrete walls, floor slabs, and other structures, crystalline technology has been found to be particularly useful in building conditions that are more specialized or require more detailed attention. This can include the type of conditions described as follows.
Elevator Pits
Out of necessity, elevator pits are often the lowest points of excavation in a building. That means they breach the waterproofing continuity of the surrounding slab and need to be waterproofed in their own right. Exacerbating the issue is that the shape and geometry of typical elevator pits have more joints and variations, all of which usually offer more opportunities for water leakage. That can be a serious problem since equipment and/or materials in the pit need protection from water for smooth operation and long-term durability.
A common practice in elevator pits is to install a sump with a pump in the hope that any water that does find its way in will end up there and be pumped out. Of course, that does not help in a power outage, and even a sump with a cover will allow moisture to permeate up into the pit. A better solution is to use crystalline concrete in the elevator pit to assure a continuous waterproof enclosure. That way, water and moisture never get into the pit to begin with, equipment is protected, and it does not matter if the power is on or not to keep things dry.
Cisterns/Water Storage
A number of buildings may require bulk-water storage either to store water for fire protection or collect and store “grey water” for reuse in the interest of water conservation. An underground storage tank can be installed for this purpose, but sometimes it is more economical and space efficient to locate such a tank in the lowest level of a building and make it out of concrete. Waterproofing is clearly an important requirement in this case, and given all of the characteristics already described, crystalline concrete is an ideal solution for this circumstance. In fact, it has been used quite successfully not only for storing water in buildings but also all manner of infrastructure and water-processing and storage facilities.
Shotcrete Construction
Shotcrete is a technique where concrete is spray applied under pressure onto a substrate with reinforcing in place or another surface. It is most commonly used in heavy construction projects such as tunnels, highways, etc. but has also been used for foundations where lot-line restrictions do not allow excavation or access on both sides for formwork. Waterproofing such an installation is also problematic since adding membranes can be difficult or complicated. Instead, adding crystalline admixture to the shotcrete mix has been shown to be a very cost-effective and reliable way to provide waterproofing.
ELEVATOR PITS CASE STUDY
Project: The Willis Building
Location: London
Architect: Foster + Partners
The Project: This 28-story skyscraper, opposite Lloyd’s in the heart of London’s financial mile, is the new headquarters of the global insurance broker, Willis Group Holdings. Designed by world-renowned architects Foster + Partners, it was the fourth-tallest building in the city at the time of construction. Its progressive environmental strategy surpasses statutory carbon-reduction targets and meets the highest standards for sustainability. More than 15,000 cubic meters of concrete were used in its construction.
The Challenge: The project is significant in both urban and environmental terms. Most of the material from demolition of the previous building was recycled and crushed for use in the 38-meter-deep foundations. This meant that the waterproofing of the foundation and the elevator pits needed to be carefully considered.
The Solution: Crystalline concrete admixture was used to waterproof and protect the below-grade slab and elevator pits. Crystalline waterproofing coatings were then installed in all floor-to-wall joints and at the elevator pits in both a dry and slurry formulation to keep water from leaking at these common seepage areas.
The Results: The building won the 2007 New City Architecture Award for its unique architectural form and contribution to the streetscape and skyscape of London.
