Concrete Strength and Curing time

Tilt-up panels should only be lifted when the concrete has cured long enough for the panel to be safely lifted and the 2.5 factor of safety can be maintained on the lifting inserts. The minimum concrete strength at which this can be achieved, for most proprietary brand lifting inserts is 25 MPa. Some inserts may require a higher strength than 25 MPa. Tilt-up panels are usually cast in stacks so the panels cannot be lifted until the last panel to be cast, on top of the stack, has reached adequate strength.

The panel erector should provide written documentation to verify the concrete has reached the minimum acceptable strength. There should be a sampling and concrete testing procedure in place to verify concrete meets its design specification. Guidance on sampling and testing systems for concrete is provided in AS 1379 - Specification and supply of concrete.

Documentation verifying the following should be available on site:

• concrete specification of concrete supplied on site for use in panels
• minimum final concrete strength (i.e. 28 day strength) of concrete delivered to site
• minimum concrete strength to be achieved prior to lifting of panels (information for the inserts should be available that specifies the minimum concrete strength required for using the insert)
• results of a sampling program that demonstrates the concrete is of an appropriate strength, and
• casting dates for each panel and earliest date when the panel can be lifted (each panel should be numbered, and written records maintained).