How long can a batch of concrete be in the truck before considerations of quality arise?

How long can a batch of concrete be in the truck before considerations of quality arise?

• A. 30 minutes
• B. 45 minutes
• C. 60 minutes
• D. 15 minutes

Answer: (B)

Concrete has a limited working life after mixing—the time it remains workable in transit. While the batch is in the truck, it keeps hydrating, and the slump tends to drop as the mix stiffens. The drum helps keep it moving, but it doesn’t stop the chemical set, so the farther it travels, the more the quality and finish can be affected. If the batch sits too long, you risk reduced workability, improper placement, segregation, and weaker or uneven finishes. The 45-minute window is the standard guideline used in field practice and on exams as the point beyond which quality issues become more likely under typical conditions. In hot weather, this window shrinks; in cooler weather it can extend somewhat, but 45 minutes is the commonly accepted limit. Shorter times (like 15 or 30 minutes) would be overly restrictive for many jobs, while a full hour (60 minutes) generally exceeds acceptable transit time under standard conditions.

Concrete has a limited working life after mixing—the time it remains workable in transit. While the batch is in the truck, it keeps hydrating, and the slump tends to drop as the mix stiffens. The drum helps keep it moving, but it doesn’t stop the chemical set, so the farther it travels, the more the quality and finish can be affected. If the batch sits too long, you risk reduced workability, improper placement, segregation, and weaker or uneven finishes.

The 45-minute window is the standard guideline used in field practice and on exams as the point beyond which quality issues become more likely under typical conditions. In hot weather, this window shrinks; in cooler weather it can extend somewhat, but 45 minutes is the commonly accepted limit. Shorter times (like 15 or 30 minutes) would be overly restrictive for many jobs, while a full hour (60 minutes) generally exceeds acceptable transit time under standard conditions.