When concrete for a slab placement will be discharged from the truck chute, truck arrivals should usually be spaced about how many minutes?

When concrete for a slab placement will be discharged from the truck chute, truck arrivals should usually be spaced about how many minutes?

• A. 5
• B. 15
• C. 25
• D. 30

Answer: (B)

Coordinating truck deliveries with the placement rate keeps the slab moving smoothly and minimizes weak joints. If trucks arrive too quickly, the crew may have to rush to place, consolidate, and finish each load, increasing the risk of poor consolidation, segregation, or early stiffening. If the interval is too long, concrete in the earlier load can begin to stiffen before the next batch arrives, creating cold joints and bonding issues between pours. A spacing of about fifteen minutes lines up with a typical pour rate, giving the crew time to place, vibrate, strike off, and finish each load before the next one arrives. This helps maintain workability and a clean, continuous finish. Shorter intervals (around five minutes) tend to overwhelm the crew, while longer intervals (twenty-five to thirty minutes) raise the chance of cold joints and weaker bonds between loads.

Coordinating truck deliveries with the placement rate keeps the slab moving smoothly and minimizes weak joints. If trucks arrive too quickly, the crew may have to rush to place, consolidate, and finish each load, increasing the risk of poor consolidation, segregation, or early stiffening. If the interval is too long, concrete in the earlier load can begin to stiffen before the next batch arrives, creating cold joints and bonding issues between pours. A spacing of about fifteen minutes lines up with a typical pour rate, giving the crew time to place, vibrate, strike off, and finish each load before the next one arrives. This helps maintain workability and a clean, continuous finish. Shorter intervals (around five minutes) tend to overwhelm the crew, while longer intervals (twenty-five to thirty minutes) raise the chance of cold joints and weaker bonds between loads.