Preparing for the Slump Test
All the equipment must be dampened prior to testing, including the base on which the slump cone is set.
Equipment & Dimensions
- Cone dimensions: 4" (top) x 8" (base) x 12" (height), with a tolerance of +/- 1/8"-inch for any of those dimensions.
- Tamping rod: 5/8" in diameter (+/- 1/16-inch) that’s at least 4 inches greater than depth of mold in use, but not greater than 24 inches – with one or both sides having a hemispherical tip. (A rod size of 16 - 24 inches is suitable for use on all the ACI tests.)
- A measuring device at least 12" long with increments of at least 1/4" must be used to measure slump.
- The slump cone mold must be checked annually for irregularities.
- The slump cone can either be metal or plastic. If plastic, it should maintain an average minimum wall thickness no less than .100 of an inch. The metal cone no less than .060 of an inch.
Steps Performed in the Slump Test
- Fill cone in three lifts, rodding each one 25 times through the lift depth, each time penetrating the layer below approximately 1 inch for the second and third lifts. Do not tap the cone.
- Each lift should fill a third of the volume. Height of concrete for first lift should be 2-5/8", and second lift should be 6-1/8".
- After the last rod, screed the material off the top (an 1/8" excess concrete above top of mold is optimum) and wipe any concrete from around the base of the cone.
- Pull cone straight up with no twisting taking anywhere from 3 to 7 full seconds (specs say 5 seconds +/- 2).
- Measure slump from the top of the mold to the displaced original center of the concrete. Record results to the nearest 1/4-inch.
- Begin and complete slump test within 2-1/2 minutes, maximum.
- Maximum size aggregate for slump test is 1-1/2"; if larger, wet sieve through a 1-1/2" sieve.
Remember that slumps less than 1/2" may not be adequately plastic, and slumps greater than 9" may not be adequately cohesive for the slump test to have significance.