Which statement about long-term deformation is most accurate?

• A. Creep causes no deflection; shrinkage doesn't affect cracks.
• B. Creep reduces deflections.
• C. Shrinkage increases stiffness as time passes.
• D. Creep increases deflections under sustained loads and shrinkage induces cracking, widening cracks, reducing stiffness and durability.

Answer: (D)

Long-term deformation in concrete involves time-dependent creep under sustained load and drying shrinkage from moisture loss. Creep causes continued deformation even when the applied load is constant, so deflections grow with time. Shrinkage reduces volume as moisture leaves the concrete; when movement is restrained, this creates tensile stresses that lead to cracking. Those cracks can widen under sustained loads and environmental changes, which lowers the member’s stiffness and overall durability. So the statement that combines both effects—creep increasing deflections over time and shrinkage causing cracking, widening cracks, and reducing stiffness and durability—best reflects how long-term deformation behaves in structural concrete. The other options contradict observed behavior, such as creep producing no deflection, or shrinkage increasing stiffness.