What is the recommended procedure for sampling concrete during truck deliveries for field tests?

• A. Take representative samples from the discharge stream per applicable methods, typically after the initial flow, and perform tests promptly using clean containers.
• B. Collect samples from the truck's exterior after discharge.
• C. Sample only from the first portion of discharge.
• D. Delay testing until after the pour is complete.

Answer: (A)

Sampling from the flowing concrete in the discharge stream after the initial flow is cleared is essential to get a representative sample of what is being delivered. The initial portion often contains surface laitance, washout, or segregated material from the chute and truck walls, which isn’t representative of the concrete you’ll place. By collecting from the ongoing stream, you capture the actual mix proportions, aggregate size, and air content that will be in the placed concrete.

Using clean containers and testing the sample promptly are just as important. Clean containers prevent contamination that could skew results for slump, temperature, air content, or unit weight. Testing soon after sampling preserves the concrete’s current properties, avoiding changes that occur with time, such as setting, loss of workability, or further temperature or moisture changes.

Choosing exterior samples, sampling only from the first portion, or delaying testing until after the pour would lead to nonrepresentative or altered results, which is why the recommended approach emphasizes representative samples from the discharge stream after initial flow and prompt testing in clean containers.