There are two main construction methods when it comes to building with precast concrete: tilt-up and precasting. Both have their pros and cons and may be more or less suited to different projects and worksites. There are a number of factors to consider when designing and building with precast concrete and that includes the casting method. The choice of casting method will be determined by a range of factors including site access, proximity to local precasting facilities, required finishes and design demands.
So let’s have a look at tilt-up construction, what it is and its benefits.
What is Tilt-up Construction?
Tilt-up construction is also known as on-site construction. It involves casting the concrete panels on the worksite, rather than manufacturing them at a precasting facility and transporting them to the worksite.
The concrete panels are poured on-site on existing concrete floors or on flat surfaces near their erection point. Once the casting surface or floor slab has cured, forms are built on top. Dimensional lumber, a high quality plywood or fibreboard that has at least one smooth face is typically used, although aluminum or steel forms are also common. The concrete mixture is poured into these forms and allowed to cure.
Slabs can be poured one on top of the other in a process known as stack casting, or poured as individual slabs.
When stack casting, bond breaker compounds are used to ensure the slabs can be separated after curing. However, if the bond breaker isn’t properly applied then there can be problems separating the slabs. This can lead to significant material wastage and construction delays.
Once the panels are cast, they are lifted into place and secured.
Tilt-up construction is the favoured construction process for worksites with limited site access, since truck access isn’t required for panel transport or for remote worksites.
Benefits of Tilt-up Construction
The primary benefit of tilt-up construction is the elimination of transport requirements. Since the panels are cast on-site, there is no need to transport panels from the casting facility to the worksite. This eliminates size limitations imposed by transport constraints and can be helpful for worksites where access is problematic. It also eliminates the considerable cost, time and logistical complexities associated with transporting precast concrete panels. As a result, tilt-up construction can be the most cost-effective casting method when working with concrete.
Tilt-up construction is also a good option for remote worksites. If the worksite is a long way from concrete casting facilities, then concrete panel transportation can be incredibly costly and time consuming. Casting the panels on-site will be a much more practical solution for remote worksites.
Some Downsides to Tilt-up Construction
One of the main downsides of tilt-up construction is the space requirements. You need ample flat floor space on the worksite to pour the concrete panels. If you’re on a worksite where space is at a premium, then tilt-up construction may not be a practical option. Additionally, any concrete floors must be fully cured before they can be used to cast panels. And then that floor space cannot be used while the panels are being cured. This can make large areas of floor space unusable during the curing process, which can be time consuming and impractical.
To cut back on on-site curing times, stronger mixes are sometimes used, which means a higher proportion of cement, resulting in a higher embodied energy for each panel.
Limits to existing floor space can also mean that you can’t pour the panels to the correct size. This can mean that additional joints may be required to properly bring the panels to the correct size.
Casting on-site also means you have less control over the site conditions, which can affect curing time and the quality of the final pour. This makes quality assurance much more difficult than precasting in a controlled production facility.
Tilt-up construction also requires significant organisation and collaboration on the building site. The building’s design and construction process must be worked out prior to the first pour and factored into the design of each panel. Any mistakes can result in a panel that isn’t usable.
While there are some significant downsides to the tilt-up construction process, if properly planned it can save time and money and reduce the logistical complexities associated with transportation.