Precast and prefabricated elements made of concrete (such as slabs, columns, beams, and walls) are part of a construction process called modular construction. This is a staged construction method based on the standardization of the parts that make up a building, whose modules are produced, transported, and assembled on assembly lines to form the building.
Over the past few decades, precast concrete and precast concrete elements have become increasingly common in the construction sector and are used in different projects and scales. Among their countless advantages, it is worth mentioning: reduced waste generation and less disruption to the site through leaner construction; speed of execution, since the production of parts is carried out simultaneously with other work on the site; efficiency, in the sense that it is possible to evaluate the performance of the parts and identify measures to improve the structural and economic capabilities; and finally, improved safety issues and a working environment with a reduced risk of accidents.
However, despite their growing popularity, precast concrete and precast concrete elements are still seen as the same, which ignores some basic differences between the two construction processes.
Precast concrete is produced by molding the material in molds that are usually reusable. For this purpose, the manufacturing is done in dedicated spaces on-site.
Prefabricated concrete elements, on the other hand, have a high degree of technical rigor and a more detailed quality, evaluating each stage of the manufacturing process, in addition to a catalogue through date registration, types of concrete and steel used, and signatures of the responsible person. According to Brazilian standards, prefabricated elements are "elements produced in factories or sites that also have adequate production resources and have personnel, laboratory organization, and other permanent quality control facilities, and are properly checked by the owner."
The main difference between prefabrication and precast is therefore that one is produced industrially, while the other can be produced in a specific location without the need for controls, such as laboratory tests. This difference is reflected in the way structures are applied, since prefabrication usually occurs in small and medium-sized buildings, such as single-family houses, while prefabrication is applied to large structures, such as factories, industries, and sheds. However, due to the high level of control over production, prefabrication tends to offer more guarantees in terms of safety, quality, and durability compared to on-site construction. Its application will depend on the type of project and other needs that must be met in terms of cost, construction time, and use.
To illustrate this, the Portuguese office SUMMARY recently designed a social housing building that used prefabricated elements, as the premise of the work was speed and economy.
Regarding prefabrication, it is worth mentioning the classic residential project of Paulo Mendes da Rocha, called Casa Gerassi, which represented an innovation in civil construction in the late 80s, using a system that was criticized at the time for its use in public and popular works. By prefabricating concrete and installing it dry on the construction site, the architect demonstrated that the rational use of materials can produce solutions that combine practicality and comfort in the same environment, in addition to saving time and costs.