Project architect Nina Maritz appointed Bührmann & Partners as the civil and structural engineer on the venture with the unusual instruction to design the building using alternative materials. “Our task as structural engineers was to assist with the design of the building using sustainable alternative materials. This meant that we had to retrain ourselves to think along unconventional lines since the project did not require us to conform to municipal regulations,” explains Rolf Trossbach, senior partner at Bührmann & Partners.

“The use of compressed soil-cement bricks was one of the most interesting materials that we used. These bricks were made on site using the Hydraform system; a patented machine rented from a local builder and stockpiled sand from Otjomuise a few kilometres away. The activity was quite labour intensive and required the bricks to be profiled, dry stacked and then plastered around window reveals and in corners,” notes Rolf.

Another interesting building material was the use of rammed earth. This entailed the use of steel shutters to compress earth into a solid block before sealing it with seal oil to preserve it. The relatively inexpensive sealant preserved the wall from further deterioration.

Structures were pre-tested by constructing sample walls in order to test whether or not the various components were durable for building purposes. These structures were designed and detailed with the help of AllyCAD. “I remember the first time that we were exposed to the program. We were given a three-month roads project and immediately realised that we needed the help of an extensive computer-aided draughting system in order to meet our deadline. This led us to acquire AllyCAD, which we used with great success. Since then we have used the product on all our projects as it cuts down on project time and helps us to produce a cost effective end result,” says Rolf.

Other innovative building materials that were used include the use of the local invader prosopis tree for shade and security screens in front of windows and extensions of overhangs and walkway shading. “A local company cut timber ‘droppers’ or ‘latte’ from the invader trees in the valley north of the industrial area. The trees were then debarked and treated on site by being soaked in a mixture of old motor oil.”

The “Spanish’ reed found in local riverbeds was another invader plant that was used. “The reeds were locally harvested by unskilled workers and were mainly used to provide ceiling walls and cladding for cupboard units. The ceilings were insulated by either using old feedbags filled with wool and lavender in order to prevent moth infestation, or by using waste polystyrene alternated with layers of flattened corrugated cardboard boxes,” explains Rolfe adding that the insulation had a minimum thickness of 60mm.

The self-made gabion wall was one of a kind. It was constructed using wire baskets made on site and concrete bricks and rubble from a demolition site. The same demolition site also provided the B-grade steel that was used for steel windows, columns and roof structures on the building.

The use of old car tyres provided a new alternative. The tyres were used to build the archive walls and were stacked on top of each other and rammed full of a soil-cement mixture. Although the use of cement was restricted, the team used small quantities as a binder in each tyre as the stockpile contained no clay. Tyre shops currently pay $7 to dispose of tyres, providing residents with a useful recycling option.

The first phase of the centre, consisting of the admin wing, was completed in April 2004, while the public wing has been completed in September 2004.

Civil Engineering
January 2005
pg 25