Florida DOT Concrete Batchman/Operator Practice Exam

What is re-tempered concrete?

1. Concrete that has been pre-mixed with additives

2. Concrete that has water added after it initially starts to set

3. Concrete that has been mixed multiple times

4. Concrete that has cured for a period before use

The correct answer is: Concrete that has water added after it initially starts to set

Re-tempered concrete refers to concrete that has water added to it after it has initially begun to set. This process is generally done to restore workability when the concrete starts to stiffen, making it easier to work with or place. However, it's essential to do this carefully, as adding too much water can adversely affect the final strength and durability of the concrete by diluting the cement paste. In the context of concrete work, it is crucial to understand that the properties of concrete can change significantly once it starts to set due to the hydration process. The addition of water during this phase is aimed at making the concrete more manageable again, but it's important to comply with accepted practices to ensure the integrity of the final mix. The other choices involve processes that do not accurately describe re-tempered concrete. Pre-mixing with additives refers to the introduction of materials like retarders or accelerators, which is different from simply adding water after setting begins. Mixing multiple times usually does not specifically address the need for re-tempering but might refer to different mixing processes or methods of refreshment. Curing indicates care taken after the concrete is placed, not the addition of water during the setting phase. Understanding these distinctions is important for maintaining the quality of concrete work.