Machine Design Elements Board Practice Exam

The main disadvantage of excessive air content in a concrete mix is the loss of strength. When the air content in concrete is higher than what is required or optimal, it creates numerous voids within the hardened concrete. These voids reduce the cross-sectional area that bears load, leading to a decrease in the overall strength of the concrete.

A concrete mix is typically engineered to achieve a balance between workability and strength. While some air bubbles can improve workability and freeze-thaw resistance, excessive air can lead to significant reductions in compressive strength, making the concrete more susceptible to cracking and other forms of damage under load.

Therefore, while there might be scenarios where increased workability and improved freeze-thaw resistance could be seen as advantageous, they do not compensate for the detrimental effect of losing structural integrity due to the reduction in strength caused by excess air. Moreover, higher density is not a characteristic associated with high air content; rather, excess air typically results in a lower overall density of the concrete.