A contractor is building a CMU wall and discovers that the mortar is setting too quickly in Florida's heat. What type of mortar additive should be used?
Correct Answer
B) Retarder
A retarder slows down the setting time of mortar, which is beneficial in hot weather conditions. This allows masons more working time and prevents premature stiffening of the mortar.
Why This Is the Correct Answer
A retarder is the correct additive because it chemically slows down the hydration process of cement, extending the working time of mortar. In Florida's hot climate, high temperatures accelerate the setting process, causing mortar to become unworkable too quickly. Retarders counteract this effect by allowing masons adequate time to place, level, and tool the mortar joints properly. This prevents waste and ensures proper bond strength between CMU blocks.
Why the Other Options Are Wrong
Option A: Air entrainer
An air entrainer adds microscopic air bubbles to improve freeze-thaw resistance and workability, but it doesn't address the rapid setting time issue caused by heat.
Option C: Plasticizer
A plasticizer improves workability and reduces water content but doesn't significantly slow down the setting time, which is the primary problem in hot weather.
Memory Technique
Think 'RETARD the HEAT' - when it's hot, you need to retard (slow down) the mortar setting time. Also remember: Accelerator = Faster (hot weather makes it worse), Retarder = Slower (hot weather solution).
Reference Hint
ACI 530 Building Code Requirements for Masonry Structures, Chapter 3 - Materials, or Florida Building Code Chapter 21 - Masonry
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