How we do it
Below you can view the step by step process of tilt-up construction
Tilt-up construction is a proven construction method where concrete wall panels (specifically designed for the application) are cast on-site and ‘tilted’ into position using cranes. This results in a faster construction process than other methods, such as a precast panel systems and conventional brick and blockwork.
It should be noted, that Tilt-up construction is a fully engineered system that adheres to all engineering codes and standards and are inspected and signed off by professional structural engineers.
Pouring the floor slabs
(Permanent or Temporary)
Concrete floor slabs are used for the casting of Tilt-up panels. These could be either the permanent slabs (interior or exterior slabs) or temporary sacrificial beds that are removed after the panels have been placed in position. The permanent floor slab thicknesses will be determined by the civil and structural engineer depending on the ground conditions on site.
Traditionally only 50mm thick slabs are required for temporary sacrificial slabs. Specific site conditions (size of building, permanent floor, or sloped floors) will dictate the casting on temporary or permanent floor slabs or if both will be used as casting surface.
Creating the walls
Once the floor slabs have been floated a curing compound is applied (or floor slabs can be cured conventionally) and the process of forming the panels can commence. The crews set out the perimeter of the panels as well as marking out all the openings within the panel, such as windows, doors, lifting insert possitions and steel embeds on the concrete floors all as per the agreed layout plan. The sides (thickness of the panels) are created with either dimensional timber; shutter board or by means of patented shutters that are joined together in the exact shape and size required.
Formwork is also used to create openings for doorways, window openings and any other penetration that is required through the panel. Once all the formwork is completed the concrete surface is sprayed with a release agent that will prevent the newly cast concrete element from sticking to the surface bed.
Following these first two steps, workers place and fix the reinforcing bars into the form, all as per the engineers’ design and bending schedules issued. Lifting inserts (for lifting the panels) and steel embeds (connections to the footing and the roof system or to each other) are then placed inside the steel reinforcing that is already installed in the panel and fixed to the steel.
Pouring the concrete
Prior to casting the panels, the floor slabs beneath the formwork is cleaned from any debris or standing water. Workers then cast concrete into the forms to create the panels. Once the panels are cast, the team proceeds to powerfloat the panels to achieve the desired finish. Where panels are stacked on top of each other the top finish becomes the exterior finish for the next panel.
Insulated concrete panels
When Insulated Tilt-up panels are manufactured the same process is followed as per the conventional Tilt-up panels. The process of casting the panels however, differs slightly as the process starts with the casting of an additional 50mm solid reinforced protective layer. While the concrete is still workable insulation (XPS) is placed on top of the wet concrete. Specially designed connectors are installed through the XPS into the wet concrete below.
These connectors will ultimately connect the structural and non structural elements with the insulation “sandwitched” in between. These connectors are specially designed to not only enable the structural connection, but also not allow thermal transfer between the two elements. By forming large concrete panels on site with insulation that does not hold water (XPS), the result is true edge-to-edge insulation, offering greater design versatility, energy efficiency and fire resistance.
Lifting the panels
This is the step that Tilt-up construction got its name from! Once the concrete panels have solidified and the forms have been removed, the crew connects the first panel to a crane with cables that hook into the inserts. Before lifting, pipe braces for the propping of the panel after it is in place, are connected to the Tilt-up panel, as such will be lifted with the panels. The crane lifts, or “tilts up,” the panel from the slab into a vertical position above the footings.
The position of the lifting inserts (as advised/designed by the structural engineer) ensures that panels hang horisontally on the gear despite openings, windows and doors often set assemtrically within the panel. The position of the lifting inserts is also designed to allow the panel to “tilt” when the panel is lifted to hang approximately 5 degrees out of plumb. This allows for the easy placing of panels. Once placed the props that were lifted with the panels are secured to either the floor slabs or to temporary “Deadman” anchors until the roof structure is complered.
Integrating the panels into the structure
Once the panels are lifted into their final position, the process of installing the structural steel roof trusses can begin. Steel brackets are welded to steel inserts cast in place in the panels to allow the bolting of steel trusses to panels. These steel plates are also used to connect the panels to each other at truss height. Once steel trusses are connected to panels the panel to foundations connections are made.
There are different ways to connect these and the engineer will advise the most suitable method to be used. Once panels are connected to the foundations, non-shrink grout is poured below the panels to create a continuous bearing between the panels and the foundations. Props are kept in place until the steel trusses are installed and panels are connected to foundations.
Finishing
During the last step of the process, the building begins to look like a finished product. Exterior wall finishes, like painting, metal cladding, sandblasting or specialised finishes can take place. The joints are also caulked to prevent water penetration. Interior finishing of the panels largely depend on the requirements of the client and could vary between leaving the raw concrete as a finish or as specialised as applying food grade epoxy. Floor to panel openings are closed and sealed as per the project specifications. The small indents left by exposing the lifting inserts can either be closed by means of steel plates or by caulking these closed with grout.