Precast concrete casting
Limitations within the formwork
Reinforced concrete is a very durable structural material. It’s an inexpensive material that can take any shape. By stating this, it is understood that the limitations lies within the formwork. A visit to a precast concrete factory, provided a better understanding of why concrete is often used as a single surface decorative panel.
The horizontal cast
What makes concrete expensive is the formwork. Concrete itself is an inexpensive material. To save on formwork costs most concrete elements a casted vertically: this way the formwork has a smaller surface area, as one side can be left open as the casting-side. Also by casting on a horizontal surface, you have gravity working with you. It takes a lot less force to hold the formwork in place, when working on a horizontal single-surface mould.
While saving on the cost of the formwork, this horizontal casting method limits the possibilities of a more amorphous shaped concrete elements. Because of gravity acting upon concrete in its liquid form, horizontally casted concrete elements will always have one flat horizontal ‘casting-side’ surface. This limits the elements to be single-surface elements, with a clear front and back.
The horizontal cast:
+ Less formwork surface, saves on cost
+ Easier to hold the formwork in place
– Limitations in shape
– The casting surface dictates a clear front and backside
– The horizontal casting, restricts the shape of the concrete element to have one flat side.
When looking closer into the precast concrete production, it became clear that such a thing as standard elements rarely exists. In theory the same formwork could be used to create hundreds of concrete elements. The production of standard elements are taking place, but in a much more limited numbers than you would expect. The truth is that most concrete elements are somewhat customized. Even though the elements might look similar, small changes like a duct or a vent requires the formwork to be modified. When most concrete elements are custom-made, you can wonder why concrete in architecture commonly are associated with repetitiveness.
Seeing that the formwork is the expensive part of the concrete casting process an ideal mould would be reusable and flexible. A flexible mould would be able to adapt various shapes and smaller changes. The same formwork could be used without having to construct a new mould for every cast. This would create savings on production costs and on the CO2 emissions related to the formwork construction.
An expensive customized precast element at Hansons Precast Factory
The standard horizontal formwork.
Customization in the form of polystyrene inserts in ‘standard’ horizontal mould