What Is the Difference Between Precast and Prefabricated Concrete Structures?

The precast and prefabricated elements made of concrete (such as slabs, pillars, beams and walls) are part of the constructive process known as modular construction. A construction methodology carried out in stages, based on the standardization of the parts that make up the building, with its modules produced on an assembly line, transported and assembled to shape the architecture.

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Precast and prefabricated concrete structures are increasingly present in the field of construction, applied in different programs and scales over the last decades. Among its innumerable advantages, it is worth mentioning: the reduction in waste generation, reducing disturbances in the site with a leaner construction; speed in execution, since the production of the parts occurs concurrently with other works on the site; efficiency, in the sense that it is possible to evaluate the parts’ performance and identify measures that increase structural and economic capacity; and, finally, the improvement in safety issues, with a work environment that reduces the risk of accidents.

However, despite their growing popularity, precast and prefabricated structures are still treated as synonyms, which ignore some basic differences between the two construction processes.

Precast concrete is produced by molding this material in an often reusable mold. Manufacturing is done on-site in a dedicated space for this purpose.

Prefabricated concrete structures, on the other hand, have a high technical rigor and more detailed quality that evaluates each phase of the manufacturing process, in addition to going through catalogs such as date registration, type of concrete and steel used and signature of those responsible. According to Brazilian standards, prefabricated structures are “elements produced in a plant or site similarly adequate in resources for production and that have the personnel, laboratory organization and other permanent facilities for quality control, duly inspected by the owner's inspection.”

Therefore, the main difference between prefabricated and precast structures is that one is industrially made while the other can be produced in specific locations and does not require control, such as laboratory tests. This difference reflects in how structures are applied since precast elements are often present in small and medium-scale buildings, such as single-family homes, and prefabricated elements are applied in large-scale structures, such as factories, industries and sheds. However, due to the high production control, the prefabricated tends to offer more guarantees concerning safety, quality and durability compared to the precast. Its application will depend on the type of project and other needs that must be met in terms of costs, construction time and use.

To illustrate, the Portuguese office SUMMARY recently designed a building for social housing using prefabricated structural elements since the premises of the work were speed and economy. Regarding precast structures, it is worth mentioning the classic residential project by Paulo Mendes da Rocha known as Casa Gerassi, which in the late 80s represented innovation in civil construction using a system that was stigmatized for its use in public and popular works at the time. With the precast concrete elements mounted dry on the construction site, the architect demonstrated that the rational use of materials can generate solutions that combine practicality and comfort in the same environment, besides saving time and costs.