Slump tests (ASTM C 143) are applicable for concrete with slumps greater than 1/2 inch and less than 9 inches. Once the concrete sample has been remixed, start taking the slump tests within 5 minutes. Start by filling a mold 12 inches high in the shape of the frustum of a cone that is 8 inches in diameter at the bottom and 4 inches in diameter at the top. Fill the mold in three equal layers by volume, not by height. Rod each layer 25 times with a bullet-tipped 5/8-inch diameter rod to compact each layer. After filling and rodding, raise the cone to allow the concrete to subside. The distance the concrete subsides, or slumps, is based on its consistency.

Measure the amount the concrete slumps or settles from the original height of 12 inches to the nearest 1/4 inch and record as the slump in inches. The measurement is made between the original height of 12 inches and the displaced center of the settled mass of the demolded concrete. If the test falls outside of the specified range, a check test is typically performed to confirm test results.

Testing tip: Since concrete setting is time and temperature dependent, this test must be started within 5 minutes after obtaining the composite sample and completed within 2 ½ minutes after the filling process begins.

Return to concrete testing