What Concrete Slump Indicates

Rule: the slump test measures how far a cone of fresh concrete sags once the mould is lifted. That drop shows the concrete's consistency, which is the standard field indicator of workability. How to read the figure: the rod across the top of the empty cone marks the original height; slump is the vertical drop from there to the top of the slumped pile. Why the other choices are wrong: strength is measured later on hardened cylinders, not on fresh concrete. Density is found by weighing a known volume. Air content is measured with a pressure meter, not a slump cone.