What is the significance of serviceability crack widths and how are they controlled in prestressed concrete bridge decks?

• A. Crack widths influence durability and corrosion risk; controlled by prestress levels, appropriate concrete cover, and proper loads distribution to limit tensile stresses.
• B. Crack widths influence durability but are never controlled.
• C. Crack widths are not related to corrosion.
• D. Prestress levels do not affect crack widths.

Answer: (A)

The key idea is that cracks in a prestressed concrete bridge deck, even when small, control how water and chlorides reach the steel and thus affect durability and corrosion risk. Prestress adds a compressive force to the section, which reduces the net tensile stress under service loads. When the tensile demand is kept low or offset by precompression, cracks form less and stay narrower, or may even remain closed, which slows the ingress of moisture and chlorides that drive corrosion.

Concrete cover acts as a barrier to moisture and aggressive ions, so the thicker the cover, the longer it takes for any potential crack to reach the steel and for corrosive agents to penetrate. Proper loads distribution helps avoid localized high tensile stresses that would open cracks wider than necessary, maintaining more uniformly small crack widths along the deck.

That combination—appropriate prestress levels to keep the section under low net tension, sufficient concrete cover to hinder ingress, and thoughtful load distribution to avoid concentration of tensile stresses—directly controls crack widths and, in turn, improves durability and reduces corrosion risk. This is why the statement is correct. The other options misstate the relationships by claiming cracks aren’t controlled, aren’t related to corrosion, or aren’t affected by prestress.