Examples of vertical casting systems
In the initial stage of my research I would like start out by exploring already operating methods of vertical casting systems. By taking a closer look at casting systems that are already fully functional, I hope to gain a better understanding of problems and potentials related to the vertical casting technique.
Rammed earth, Pise systems
Having a close contact within the rammed earth industry, it seemed obvious to have a closer look at the pise system. Also when working with tectonic and architectural integrity the rammed earth can be a particular good example of technique, material and construction all working together. In a pise structure both material and technique contributes to the final appearance.
Understanding rammed earth production
To gain a better understanding of the pise formwork, I first went to visit a building site of a rammed earth house. My next step was to produce a smaller rammed earth wall myself. Building a rammed earth wall involves compressing a damp mixture of earth that has suitable proportions of sand, gravel and clay into an externally supported frame, creating a solid wall of earth. Often cement is mixed in with the soil mixture to increase the structure’s load bearing capacity. A temporary frame of prefabricated formwork is first built, usually out of varnished wood or plywood, to act as a mould for the desired shape and dimensions of each wall section. The frames must be sturdy and well braced, and the two opposing wall faces clamped together, to prevent bulging or deformation from the high compression forces involved. Damp material is poured in to a depth of 10 – 25 cm and compressed to around 50% of its original height. The compression of material is done iteratively in batches, to gradually build up the wall to the required height dictated by the top of the frame. Once the wall is complete, it is strong enough that the frames can be immediately removed. The walls are best constructed in warm weather so that they can dry and harden. Walls take some time to dry out completely, and may take up to two years to completely cure. Compression strength increases with increased curing time.
Rammed earth shares many of the same properties as concrete:
– Reinforcement: Like concrete, rammed earth can only take pressure forces and need reinforcement to withstand tension. Rammed earth uses re-bar, wood or bamboo reinforcement.
– Low cost material, but labor-intensive production: Soil is a widely available, low cost and sustainable resource. Like concrete the cost of material is low, but constructing rammed earth structures are a very labor-intensive process mainly because of the tamping.
– Formwork has to be able to hold in enormous forces: On site there was actually surprisingly minimal support structure to hold the formwork in place. Being a vertical casting system I was of the perception that it would take a lot more effort to withstand the forces from the tamping. Some of the key features were that the formwork was interlocking and bolted together from the inside