For transporting concrete under normal circumstances, what is the specified time before placement after batching?

• A. 1 1/2 hours
• B. 1 hour
• C. 2 hours
• D. 30 minutes

Answer: (A)

The main idea here is the workable life of concrete after batching. Under normal conditions, ready-mix concrete must be placed within 90 minutes (1 1/2 hours) of batching to maintain proper workability and to avoid problems like slump loss, segregation of aggregates, and premature stiffening that make placement and finishing difficult or impossible. This 90-minute window starts when the batch is mixed and ready to pour, and it can shorten in hot weather or with certain mix designs, while cooling or retarders can extend it slightly. The other time options fall outside the typical allowable window for normal circumstances.