I am a slow and recent convert to concrete. Although I have built with brick, mud, stone and cement my material of choice has always been wood. However, I realised concrete would be an important ingredient in our project at 43 Stockdale Street because of it’s size and the fact that much of it is underground. Concrete is the building material of this age because of its versatility and durability. However, as with all materials there are environmental and social consequences, some welcome and some harmful. We recognised this conundrum and used concrete in new and innovative ways in our efforts to achieve material and energy efficiencies.
Concrete provides good fire protection and acoustic separation so is excellent for multi-unit buildings. However, it is heavy and embodies a lot of energy. We chose to use Hebel Panel, a light aerated concrete walling system that reduces both the mass and the embodied energy. This enabled us to achieve the energy efficiencies, and fire and sound protection without using foam board with the health hazards of toluene and styrene gasses.
Concrete has a high compressive strength but a low tensile strength, a characteristic that poses a challenge in pouring slabs with significant spans. This was our situation in our basement and we resolved it by using Corcon, a local Canberra invention. Corcon not only provides greater tensile strength and longer spans because of its rib and dome structure, but also reduces the mass of concrete by 30% and uses recycled formwork. In fact, the formwork on our job had already been used for some 17 other major works of construction.
Concrete is surprisingly ancient having been used in a similar form to contemporary concrete by the Romans almost 2500 years ago. In fact because of its durability many of these ancient structures still survive. In using concrete the challenge for an artist is to allow a material to speak in a way that compliments other materials as well. This has always been a problem with concrete as it will often hide or overwhelm other materials, such as in many of the Brutalist buildings from about 50 years ago. On this project we took the novel approach of asking the trades to throw their tools into the slab and then polishing back the concrete to create a collage. This has had the effect of humanising the material, softening our foyer entrance and contributing to the story of our project.