How to Determine the Proper Slump for Concrete

How concrete is mixed varies from one use to another. A bricklayer, for example, may want a concrete that is wetter than someone pouring a sidewalk. The wetter the concrete, the higher the slump factor. A higher slump is more gravy-like in consistency whereas a lower slump will look more like oatmeal. It is important to test the slump factor particularly on large jobs to make sure that the clump is consistent throughout the project. Determining the proper slump is done by calculating it and then matching it to the right slump for the job.

Bucket
12-by-12-inch plywood piece
Trowel
Slump cone
Yardstick
Tape measure

Instructions

- 1
  Fill a bucket with a sample of the concrete you are using as it's being poured.
- 2
  Place a slump cone on a flat, smooth surface, such as a piece of metal or plywood with the narrow end up. A piece 12 inches by 12 inches should work. Dampen the cone with water.
- 3
  Fill the cone about one-fourth full, using a trowel to scoop up the concrete. Insert a 5/8-inch diameter steel rod into the concrete and lift it up and down 25 times.
- 4
  Fill the cone about halfway up the length of the cone and repeat the rodding process, only penetrating the second layer -- not the first.
- 5
  Fill the cone the rest of way until it is overflowing and repeat the rodding process, not penetrating the second layer.
- 6
  Scrape the excess concrete off the top of the cone with your trowel.
- 7
  Lift the cone up slowly, as you would a sand castle mold, in a smooth, even motion. Try not to tilt the concrete or push it anyway.
- 8
  Flip the cone over once it has cleared the concrete and place it with the wide base up next to, but not touching, the concrete pile.
- 9
  Lay a straight edge, such as a yard stick, across the top of the cone's base and over the pile of concrete. Use a ruler or tape measure alongside the concrete pile to measure, after the pile has sat for 2 1/2 minutes, the difference between the top of the cone and the top of the concrete pile. The resulting measurement, often rounded to the nearest inch or millimeter, is the slump.
- 10
  Match your slump to the slump range needed and adjust the moisture or mix accordingly.

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