How does increasing concrete cover affect durability and crack width in prestressed decks?

• A. Increasing concrete cover reduces crack widths and enhances durability with no downsides.
• B. Increasing concrete cover has no effect on durability or crack width.
• C. Increasing concrete cover improves corrosion protection and reduces crack widths, but adds weight and can affect constructability.
• D. Increasing cover reduces the need for reinforcement.

Answer: (C)

Increasing the concrete cover acts as a thicker protective shield around the prestressing tendons, which directly improves durability and helps control crack width. A larger cover lengthens the diffusion path for aggressive agents like chlorides and carbon dioxide, slowing their reach to the steel and making corrosion less likely. It also enhances the concrete’s ability to keep cracks within a smaller width because the extra concrete surrounding the tendons provides more confinement and a stronger passive state, helping maintain structural integrity as cracks form.

At the same time, more cover adds weight to the section and can complicate construction: it requires more concrete volume, heavier elements, and potentially more complex formwork and curing logistics. These trade-offs mean that while durability and crack control improve, there are practical limits and added costs.

So the best description is that greater cover improves corrosion protection and reduces crack widths, but increases weight and can affect constructability.