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2013WinShotcreteEMag

2012 Outstanding Architecture Project VanDusen Botanical Gardens By Gary Hawkins tthat was unforeseen at the design stage. The insulation to attain higher thermal resistance.”2The solution to the thermal issue was to userammed earth should be coupled with thermalorrent Shotcrete Structures was approachedby the project team with a particular problem original design called for a rammed-earth wall for an internal rigid insulation to increase the R-value. all the structural/architectural walls in this project. However, with the combination of these two key One of the issues that surfaced with rammed earth issues (structural and thermal resistance), it in this application was the inability to provide became apparent to the design team that alternates enough strength for the structure’s required bearing had to be explored. loads and seismic specifications. “The New Mexico Structural architecturally finished concrete was building code defines qualified rammed earth as soil the only answer. However, due to the unique design consolidated to full compaction that attains 300 psi of the building with varying geometry from the (2 MPa) compressive strength and has a modulus curved walls that oscillated up and down, and the of rupture equal to at least 50 psi (0.34 MPa).1 This free-formed configuration of the living roof, as is a much lower strength than the 1450 to 5800 psi well as new requirements to have sandblasted (10 to 40 MPa) compression strength range reach- concrete walls, a conventional cast-in-place formed able by concrete.”2 concrete wall would have been very difficult and Another concern that arose was the thermal costly. Even with exposed concrete walls, the performance of a rammed-earth wall that is thermal resistance issue required insulation to be exposed both on the exterior of the building and sandwiched in the wall itself. This may have been the inside of the building. Frost-resistant walls easy for a flat, straight wall on a tilt-up building, made of steel studs with insulation were not part but would have been extremely challenging in a of the desired finished look. “The thermal resis- cast-in-place wall with this unusual geometry. tance of rammed earth alone is not great enough The management team from Ledcor Construc- to retain heat in a cold climate building. Obtaining tion, in conjunction with Whitewater Concrete, a meager R-20 would require an 11.5 ft (3.5 m) approached our management team for some wall thickness. Cold climate design dictates that alternative solutions using structural shotcrete Fig. 1: VanDusen Botanical Gardens (Photo Credit: Nic Lehoux; Courtesy: Perkins+Will Canada) 36 Shotcrete • Winter 2013


2013WinShotcreteEMag
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