What happens to air content in concrete when the temperature of freshly mixed concrete increases?

When the temperature of freshly mixed concrete increases, the air content generally decreases. This occurrence is largely due to the physical principles governing the behavior of air bubbles within the concrete mixture. As the temperature rises, the viscosity of the concrete decreases, leading to a greater likelihood of air bubbles merging and escaping from the mix.

Higher temperatures can accelerate the rate of hydration as well. As the cement hydrates more quickly, there may not be sufficient time for air-entraining agents to work efficiently and produce stable air bubbles. Therefore, the overall air content can drop, which is why the choice indicating a decrease in air content is accurate. This understanding is crucial for ensuring that the air content remains within desired limits for various environmental conditions, ultimately impacting the durability and performance of the concrete after it sets and cures.