Construction World June 2019

COVER STORY

CONCRETE CAPTURES FORM AND FUNCTION IN NATURAL CAPE ART SPACE

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.

T he 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. Mixing and casting 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 m 2 of completed panels. A total of 7 500 m 3 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,

20

CONSTRUCTION WORLD JUNE 2019