to incorporate a third dimension to the triangular forms of the façade . In the end , the most suitable material to achieve this 3 dimensionality was raw concrete , allowing the triangular shapes to transition from 2 dimensional patterns in the curtain walls , to 3 dimensional extrusions within the concrete . The raw concrete juxtaposed with the smooth curtain wall would create a harmonious balance in the design .
The 3 dimensional triangular pattern was a construction feat in itself , constructed by creating 35mm deep recesses within the concrete . The function of the triangular windows is to allow natural light to filter into the internal office space situated behind the concrete feature walls .
Challenges Creating the recessed lines which define the triangular geometry meant that once the shutters were removed there was a risk that the concrete could break out , leaving the face of the walls with ragged edges that would require patching .
Patching of the concrete is a process the entire team wanted to avoid at all costs as the beauty of off-shutter concrete lies in the seamless and sculptural appearance as well as its unique texture . A sample panel was constructed beforehand , allowing the architects and contractors to explore different methods and materials to achieve the desired finish . These methods include :
• The use of fibre reinforced concrete
• The use of self compacting concrete
• The use of premixed concrete with a smaller aggregate . Another challenge was that the structural engineer required the concrete feature walls to form part of the structural framework of the building . This required portions of the feature wall to be cast simultaneously with the main frame of the building . To deliver the required structural integrity , the construction of the concrete was done as follows :
The down stand portion of the feature walls were cast simultaneously with the first floor slab . Construction with regular premixed concrete as opposed to self compacting concrete was used , as a continuously cast concrete structure was required by the structural engineer . Due to the added cost of self compacting concrete , it could not be used for the casting of the floor slabs . The second cast of the feature wall ( first floor to second floor level ) was completed using self compacting concrete . On the top portion of the feature wall , a polystyrene pocket on floor slab level served as a permanent shutter for the concrete of the second floor slab .
The second floor slab was cast using regular premixed concrete , with splicing of reinforcing done above the floor slab level . This procedure was repeated for the second , third and fourth floor pours ( to the underside of the roof slab )
As with the bottom portion of the wall , the uppermost portion of the wall also required one continuous pour for the structural integrity of the roof slab upstand . This upper portion was again cast using regular premixed concrete due to cost constraints .
The construction joints in the concrete walls were required at very specific heights so as not to impact on the contractor ’ s programme . Numerous consultations between architect , contractor , structural engineer and concrete specialists were held , resulting in a design solution that had no impact whatsoever on the programme of the building .
Two sets of shutters were used for the construction of the three feature walls . A single set of shutters was used for both the eastern and western façade ’ s feature walls . The eastern and western feature walls were phased by levels , i . e . once the first down stand was complete on both the eastern and western façades , the first wall cast on the western wall ’ s shuttering was used on the eastern wall ’ s first cast , and so the process continued . The walls are , therefore , a mirror image of the other .
The second set of shutters was used for the construction of the fire escape stairwell on the southern façade . The utilisation of the same shutter for the construction of the two walls meant a cost saving of 40 % on the shuttering .
The contractor approached Lafarge Readymix Gauteng and , in the end , it was decided to use Lafarge ’ s Agilia Vertical self compacting concrete solution . Of the total volume of 11,500m 2 of concrete used , 360m 2 was Agilia Vertical .
What makes this methodology so unique is the fact the building ’ s entire façade grid was set out using the same grid of the concrete feature walls . One would imagine that , due to time and cost restraints , the triangular grid of the feature walls would only be an external surface treatment . However , upon entering the interior of the building , it becomes apparent that the internal faces of the feature walls are , in fact , a continuation of the triangular grid . It is evident that
168 Podium at Menlyn