General Contractor Practice Exam

Which type of admixture is typically used to accelerate hydration for high early strength concrete?

1. Retarding

2. Water-reducing

3. Accelerating

4. Air-entraining

The correct answer is: Accelerating

The choice of admixture that is typically used to accelerate hydration for high early strength concrete is indeed an accelerating admixture. These admixtures significantly speed up the setting time and enhance the early strength development of concrete, which is particularly beneficial in cold weather or for projects that require quick turnaround times. Accelerating admixtures usually contain substances that facilitate more rapid hydration of the cement particles, leading to faster gain in strength and reduced setting time. This allows the concrete to cure more effectively and to be used sooner than it would be under normal conditions. On the other hand, retarding admixtures slow down the setting time, which is useful in hot weather to prevent the mix from setting too quickly. Water-reducing admixtures are designed to reduce the amount of water needed for a given workability, improving strength and durability but not necessarily focusing on accelerating the setting time. Air-entraining admixtures introduce tiny air bubbles into the concrete to enhance its resistance to freeze-thaw cycles but do not influence the acceleration of hydration for early strength.