Which feature serves as the reference point when measuring slump?

• A. Center of the bottom surface
• B. Edge of the top surface
• C. Displaced original center of the top surface of the specimen
• D. The center of the mold tip

Answer: (C)

The measurement in a slump test is all about how far the top surface of the concrete has moved downward from its original position. To get a consistent, repeatable value, this drop is read at the center of the specimen, because edge effects can distort readings near the sides. So the slump height is defined as the vertical distance between the original center line of the top surface and the actual top surface after the mold is removed—the displaced original center of the top surface of the specimen. This reference point gives a standard way to quantify how workable the concrete is: a larger drop means higher workability.