When is post-tensioning typically performed on a concrete structure?

When is post-tensioning typically performed on a concrete structure?

• A. After the concrete has hardened
• B. Before pouring the concrete
• C. During mixing of the concrete
• D. During curing

Answer: (A)

Post-tensioning introduces compressive forces into concrete after it has gained sufficient strength to carry those loads. The tendons run through ducts in the concrete, are anchored at the ends, and are stretched with hydraulic jacks to compress the concrete. The concrete must be hard enough to transfer and resist the tendon forces; doing this too early—while the concrete is still plastic or still curing—would cause cracking or failure and the system wouldn’t anchor properly. That’s why the normal practice is to tension after the concrete has hardened and reached the required strength. (For contrast, pre-tensioning involves tensioning the tendons before pouring the concrete.)

Post-tensioning introduces compressive forces into concrete after it has gained sufficient strength to carry those loads. The tendons run through ducts in the concrete, are anchored at the ends, and are stretched with hydraulic jacks to compress the concrete. The concrete must be hard enough to transfer and resist the tendon forces; doing this too early—while the concrete is still plastic or still curing—would cause cracking or failure and the system wouldn’t anchor properly. That’s why the normal practice is to tension after the concrete has hardened and reached the required strength. (For contrast, pre-tensioning involves tensioning the tendons before pouring the concrete.)