Coastal and Floodplain Construction Inspector's Practice Exam

Under which condition should concrete exposure classes be assigned according to ACI 318?

1. Exposure to wind

2. Exposure to freezing and thawing in moist conditions

3. Exposure to corrosion from electrical currents

4. Exposure to extreme heat

The correct answer is: Exposure to freezing and thawing in moist conditions

Concrete exposure classes are assigned based on specific environmental conditions that can affect the performance and durability of concrete. According to ACI 318, one of the critical conditions influencing the assignment of exposure classes is the exposure to freezing and thawing in moist conditions. This condition is particularly important because when concrete is subjected to these cycles, the repeated freezing and thawing can lead to significant deterioration if the concrete is not designed correctly to withstand such stress. In moist conditions, water can penetrate into the concrete and, upon freezing, expand. This expansion can create internal tensile stresses that may cause cracking and spalling, ultimately compromising the concrete's structural integrity. To mitigate this risk, ACI 318 outlines specific provisions for ensuring the concrete is formulated (including appropriate air entrainment and sufficient strength) to endure these harsh conditions, leading to the assignment of specific exposure classes for freezing and thawing scenarios. The other conditions mentioned, such as wind exposure, corrosion from electrical currents, or extreme heat, while they can be significant in their respective contexts, do not have as direct and defined a link to the classification of exposure classes in the context of freezing and thawing effects specifically outlined in ACI 318.