According to ASTM C 94, within what time after water is added must concrete be delivered and discharged from the truck mixer?

According to ASTM C 94, within what time after water is added must concrete be delivered and discharged from the truck mixer?

• A. 2 1/2 Hours
• B. 2 Hours
• C. 1 1/2 Hours
• D. 1 Hour

Answer: (C)

The main concept is the time limit for a ready-mixed concrete batch after water is added. Once water goes into the mix in the truck drum, hydration starts and the mix begins to stiffen. To keep the concrete workable and ensure designed strength, it must be delivered and discharged within a short, defined window. Specifically, ASTM C94 requires the concrete to be discharged from the mixer within 90 minutes (1 1/2 hours) after the water has been added. This helps prevent excessive loss of slump, segregation, or premature stiffening that would compromise placement and strength. If you can't meet this time, the practice is to delay or reject the batch rather than trying to extend its workability in the field. In context, this means if water was added at 9:00, the discharge should occur by 10:30 at the latest.

The main concept is the time limit for a ready-mixed concrete batch after water is added. Once water goes into the mix in the truck drum, hydration starts and the mix begins to stiffen. To keep the concrete workable and ensure designed strength, it must be delivered and discharged within a short, defined window.

Specifically, ASTM C94 requires the concrete to be discharged from the mixer within 90 minutes (1 1/2 hours) after the water has been added. This helps prevent excessive loss of slump, segregation, or premature stiffening that would compromise placement and strength. If you can't meet this time, the practice is to delay or reject the batch rather than trying to extend its workability in the field.

In context, this means if water was added at 9:00, the discharge should occur by 10:30 at the latest.