What is the difference between concrete poured on-site and precast concrete?

The primary difference between concrete poured on-site and precast concrete lies in where the fabrication occurs and how it impacts the construction schedule.

• In situ (on-site) concrete: This method involves pouring liquid concrete into forms directly at the building site. Because concrete cures slowly and typically requires 28 days to reach its design strength, there is a significant time lag between pouring and when the structure can safely carry loads. This process often requires extensive on-site labor, such as the construction of handmade timber formwork.12
• Precast concrete: These structural members are manufactured in a central plant or factory under controlled conditions and then transported to the site for assembly. Because they are cured before arrival, precast components eliminate the waiting period associated with on-site pouring, which can help accelerate construction schedules and improve finish durability.21

While in situ concrete is commonly used for foundations and structural skeleton frames, precast concrete is utilized for various components, including slabs, beams, columns, and stairways. Precast elements are often pretensioned in the factory to increase their strength and allow for shallower structural members.21