Before lifting, what minimum compressive and flexural strengths should tilt-up concrete panels achieve?

• A. 2500 PSI compressive and 500 PSI flexural.
• B. 3000 PSI compressive and 600 PSI flexural.
• C. 2000 PSI compressive and 400 PSI flexural.
• D. 3500 PSI compressive and 700 PSI flexural.

Answer: (A)

Before lifting tilt-up panels, they must have enough strength to safely take the stresses of lifting and handling. Two measures are used: compressive strength and flexural (bend) strength. The panel needs a minimum compressive strength of 2,500 psi so it won’t crush under its own weight and around lift inserts, and a minimum flexural strength of 500 psi (modulus of rupture) so it can resist bending and cracking when the hoist applies load at the lifting points. Concrete is strong in compression but weak in tension, and lifting creates bending that induces tensile stresses near the anchors; meeting these minimum values helps prevent cracking or failure during lift. Higher values aren’t required for the minimum lift criteria, so the 2,500 psi and 500 psi combination represents the standard minimum.