Precast concrete has helped lend an air of timelessness and minimalism to Norval Foundation, a modern pavilion for art set against the dramatic Constantiaberg Mountain and vineyard landscape in the Steenberg area of Cape Town.
The building is an expression of concrete, glass, steel and timber with concrete being the primary element in both the finish and structure. Exuding honesty and rawness through these selected materials, Norval Foundation chose precast readymix concrete to both control the quality and texture of the concrete as well as to speed up the build time. The concrete frame also gives the building large spans which are void of internal column support, to maximise gallery space.
Designed by dhk Architects and constructed by contractors WBHO with concrete from AfriSam, the building hosts gallery spaces comprising a large environmentally-controlled special exhibitions space, and a series of nine gallery spaces. This culminates in a triple-volume sculpture gallery, a dramatic setting for large-scale pieces with Table Mountain as a backdrop. All the gallery spaces are column-free, giving optimal flexibility when displaying art; the displays can be treated as separate experiences or as a sequential journey.
Technical specifications for the gallery spaces required an environment that could carefully control light, temperature, humidity and acoustics, while also preventing fire. To create the minimal spaces required for the display of art, all the services are concealed in the wall and ceiling cavities to create a seamless appearance.
The primary internal and external finish is a combination of polished concrete, smooth class one precast concrete panels and textured precast concrete panels. Externally, the precast concrete is finished with a chamfered tartan grid, which draws the eye upwards and lengthways to emphasise the scale of the building. A Teflon mould was developed to create a horizontal textured pattern on the precast panels. This mould can also be used as a repair tool should any of the panels be damaged.
WBHO set up a manufacturing site for the three-tonne concrete panels, where casting, mixing and stacking took place before they were transported to the construction site. Twenty casting platforms were put in place to sustain a manufacturing programme that produced a total of 501 panels, at a rate of 23 panels a week. This precast option allowed WBHO to manufacture the precast panels off site while in-situ concrete work was progressing on site.
To accommodate the many different precast items to be manufactured, 76 types of moulds were created. These included window sills, flat external panels, external corner panels, patterned panels and capping panels. In addition to finding a suitable under-roof site to manufacture the panels, the contractor also had to secure enough ground space to stack and lay down 800 m2 of completed panels.
A total of 7,500 m3 of readymix concrete was used for the Norval Foundation building. While most of the concrete comprised standard mixes, the precast panels used a special mix with 9 mm aggregate for a prescribed 30 MPa full strength within three days. The water-cement ratio of 0,44 was also critical, with the required slump of between 110 mm and 120 mm. The correct amount of crusher dust in the mix and correct stone aggregate were crucial to achieve the off-shutter finish. For consistency in the colour of the concrete, all raw materials had to be stockpiled ready for use, with fly-ash and slag stored separately.
The advantages of designing Norval Foundation with a precast concrete façade were many, including the flexibility of shape and form, and the variety of surface finishes which could be achieved. In terms of physical properties, concrete offered durability and low maintenance while providing good insulation against sound and resistance to fire. The precast option – in addition to speeding up the building programme – also allowed high levels of quality control and consistency in the finish; there was also no need for façade scaffolding.
The precast panels went through a rigorous design process of testing and sampling in order to achieve the desired finish. To ensure that the precast concrete method was optimally applied, it was important that the right material was chosen for the patterned moulds, and that the correct stripping oil was used. The substantial weight of each panel was a challenge in terms of moving and placing, requiring the use of special lifting equipment. Panels would need to be cleaned of oil stains to ensure a consistent finish, and the edges of the patterned panels also sometimes needed to be repaired.
The building is situated in an elevated position, shielding a wetland and creating a private space for a The Sculpture Garden. This wetland is one of the last known breeding sites of the Western Leopard Toad, an endangered species that is endemic to the area. The linear circulation spine of the building is positioned between a busy road and the wetland, with the galleries and public spaces facing the natural landscape and capturing framed views of the wetland, vineyards and mountains beyond. The triple-volume atrium creates a deliberate visual connection between these zones – one urban and the other natural – and provides a physical transition between these contrasting environments.
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