Precast concrete offers a range of benefits when it comes to construction. It’s a durable, flexible solution for floors, walls and even roofs across a range of commercial, industrial and residential construction. Using precast concrete beams and panels saves construction time. They are also extremely flexible in terms of form, shape and aesthetic finishes. They are fire resistant and provide premium sound and temperature insulation.
However, building with precast concrete does have some challenges that are worth building in mind.
Precast concrete has two common production methods: tilt-up (poured on site) and precast (poured off site and transported to site).
Tilt-up concrete panels, beams and walls are poured on site and simply lifted into position. Tilt-up production overcomes a lot of transport and site access problems, since there is no need to move the finished panels long distances.
However, on-site tilt-up casting requires significant floor space to pour the panels. As a result, on-site space constraints may limit the size of the panels you can cast. Tilt-up casting can also slow the construction process, since walls and panels can only be cast once floor construction is complete.
Precasting, or offsite casting, is carried out in a controlled environment away from weather-related variables. As a result, it delivers higher levels of quality assurance and accuracy. It also generates less waste and reduces the amount of on-site materials and processes cluttering the worksite.
Precasting also makes it easier to incorporate more complex formwork, which can be difficult to achieve or incorporate onsite.
The obvious downside to precasting is the logistical complexity of transporting the finished panels to the worksite.
The choice between production methods is largely determined by site access, proximity to precasting facilities and design demands.
Regardless of which production method is best suited to your project, there are some factors that need to be considered.
Precast panels are not designed to be significantly altered after casting. That means that all formwork, structural inserts, lifting points, insulation, electrical and plumbing conduits, openings, flashing and pest and moisture barriers must be worked out in advance and incorporated into the casting.
Any errors or oversights in design can lead to significant wastage, time delays and cost overruns if panels need to be recast.
Specialist Erection Services
Unlike a number of other methods of construction, precast concrete erection requires specialist contractors, temporary bracing and specialised lifting equipment. Precast erection services also come with significant OH&S risks. Because of this, erection services can be expensive.
Specialist erection services and machinery are required regardless of whether you’re using tilt-up or precast production.
Transport and Site Access
These factors are less problematic for tilt-up production as all the casting is done onsite. However, for offsite casting, transport and site access are major considerations.
Site access for trucks, trailers and cranes should be carefully assessed before the casting choice is made. If site access is limited, then tilt-up production may be the only viable option.
The delivery route should also be thoroughly checked to ensure that the fully loaded trucks and cranes can complete delivery without running into obstacles like low bridges, overhead cables or transport weight restrictions.
Since the erection sequence will determine the order of transport, careful planning is required to ensure the correct panels are accessible in the correct order. Erection should also be planned to minimise crane positions to reduce costs and building time.
High Embodied Energy
The major downside to precast concrete is its high embodied energy. However, this can be offset by its extended life cycle (up to 100 years) and high potential for reuse and relocation. To optimise the life of the material, precast materials should be designed to be reused, extended or retrofitted to ensure that their initial embodied energy is amortised over their life span.