How does carbonation affect concrete?

Carbonation has a significant impact on concrete, particularly regarding its alkalinity. As carbon dioxide from the atmosphere penetrates the concrete, it reacts with calcium hydroxide to form calcium carbonate. This process reduces the pH level of the concrete, which normally sits around 12 to 13. The normal high pH provides a protective layer to reinforcing steel against corrosion. When carbonation occurs and the pH drops, this protective environment is compromised, increasing the risk of reinforcing steel corrosion. This is particularly important because corrosion of reinforcing steel can lead to structural weaknesses and reduce the longevity of concrete structures.

The other choices do not accurately reflect the effects of carbonation on concrete. While carbonation does not inherently improve strength or workability, its primary concern is its ability to alter the chemical environment within concrete, which can impact its durability and integrity over time.