Part of Lesson Plan: Slump Test

Activity Overview / Details

Hour 2: Teacher Demonstration - Performing a Slump Test. To perform the demonstration the teacher will need; a slump cone & rod, either a cement mixer or a wheelbarrow and square point shovel for hand mixing and a water hose. The instructor needs to buy ahead of time either two - 60 lb bags or one - 90 lb bag of Sack Mix Concrete (Sackrete or Quikcrete) from a local hardware store and several aluminum pie pans as forms. Begin mixing your concrete - First trial run add a small amount of water to the mix and perform a slump test, have students record the readings (concrete should be relatively stiff), place a sample of the mix into one of the pie pans (leveling / screeding to top of the pie pan). Place the remainder of concrete from the first trial batch back into the mix and add a little more water. Mix thoroughly and perform a second slump test, record the readings and place that batch into another pie pan. Continue with this sequence as many times as you feel necessary - each time adding a little more water. Try to have at least one sample on the dry side and at least one sample on the extreme soupy side. The students will begin to observe as more water is added to the mix the slump will also be greater. After all trials are complete, place the pie pans somewhere to set where they will not be disturbed. Give the samples a chance to set (cure) completely 3-7 days. Once concrete has set or cured, remove the concrete from the pie forms. Have students make visual observations about the samples, then test each sample for strength.

Testing the samples for strength- using a hydraulic bottle jack (2 ton or greater) and the class wearing their safety glasses. Set the bottle jack securely propped up between two heavy shop tables.  Place the concrete batch on top of and in the center of the bottle jack.  Slowly jack up the batch under the edges of the table tops.  Then have the class count how many pumps it takes to split each of the concrete batches.  You will note that the batches ranging in the 5-6 gallons paste mixes (5-6 slump) will require more pumps than those above and below those slump ranges (greater strength).  Have the class record the amount of pumps (on the bottle jack) required for each concrete slump batch. students will observe the obvious strength differences with the differences of slump (water to cement ratio) each batch delivers.

Note to teacher- The batch with an accurate 3-2-1 ratio mix and a 5 gallon paste mix (slump) should have the greatest strength results.