Using a superplasticizer admixture to increase the workability of concrete has a short-lived time of how many minutes?

Using a superplasticizer admixture to increase the workability of concrete has a short-lived time of how many minutes?

• A. 45 to 90 minutes
• B. 30 to 60 minutes
• C. 15 to 30 minutes
• D. 30 to 45 minutes

Answer: (B)

Superplasticizers boost workability by dispersing cement particles, letting you keep or lower water while still getting a workable mix. But that extra flow isn’t permanent—the slump improves after mixing and then gradually declines as the concrete begins to set. In practice, the increased workability from a superplasticizer lasts for about 30 to 60 minutes, depending on mix design and temperature, which is the window you typically have to transport, pump, place, and finish the concrete before the drag effect wears off. That 30–60 minute range matches common field practice and is broad enough to cover variations in conditions, making it the best fit. A longer window (like 45–90 minutes) would risk the mix starting to stiffen or require additional timing considerations, while shorter ranges (15–30 minutes or 30–45 minutes) don’t align with typical placement timelines for many projects.

Superplasticizers boost workability by dispersing cement particles, letting you keep or lower water while still getting a workable mix. But that extra flow isn’t permanent—the slump improves after mixing and then gradually declines as the concrete begins to set. In practice, the increased workability from a superplasticizer lasts for about 30 to 60 minutes, depending on mix design and temperature, which is the window you typically have to transport, pump, place, and finish the concrete before the drag effect wears off.

That 30–60 minute range matches common field practice and is broad enough to cover variations in conditions, making it the best fit. A longer window (like 45–90 minutes) would risk the mix starting to stiffen or require additional timing considerations, while shorter ranges (15–30 minutes or 30–45 minutes) don’t align with typical placement timelines for many projects.