Concrete Slump Test March 2010

Concrete Slump Test
Testing Concrete for Strength

Water Amount_________ (Given by the teacher)
The concrete slump test is, in essence, a method of quality control. For a particular mix being used on a construction site, the slump should be consistent. A change in slump height would demonstrate an undesired change in the ratio of the concrete ingredients. If this were to happen, the proportions of the ingredients would be adjusted to keep a concrete batch consistent. This homogeneity improves the quality and structural integrity of the cured concrete. Too much or too little water will weaken the concrete.

Goal: You will be measuring how much “slump” or sag there is in your concrete mix.

Materials Needed per pair: 1 ruler, 1 cup (18 oz)with the bottom cut out, 1 mixing bucket, 1 baggy of 2.5 lbs concrete, 1 scrap piece of OSB approximately 1 foot square, 1 graduated cylinder, and 1 stir stick.

Procedure Per Pair of Students:
1. Take your premeasured ready mix concrete that you received in the food storage baggy and pour it into the mixing bucket provided.

2. Add water to the concrete mix that is in the mixing bucket. Be sure to measure the water amount carefully. This measure is in milliliters. If your water measurement is off slightly, your results will suffer, and thus your grade.

3. Use stir stick and stir the concrete for 3 minutes or until dry spots of concrete are gone.

4. Measure, in inches to the nearest eighth inch, the vertical height of the cup and record. This height is the perpendicular height of the cup. This is the initial height of the concrete needed for #10 below.

5. Pour half the mix into the upside down cup (with the bottom cut out). Be sure cup is on the scrap piece of OSB. Tamp down the concrete by using stir stick to tamp it 25 times. Add the rest of the mix and tamp. Remember to keep the cup full to the top.

6. Scrap off excess concrete that is above the top of the cup.

7. Remove the “form” AKA cup from around the concrete carefully by lifting the cup straight up.

8. After the concrete stabilizes (stops slumping) measure the height of the concrete. The concrete will have various heights so you will need to measure the average height.

9. Find the amount of slump by taking the initial height – the ending height.

10. Record: (amount of water________ , amount of slump_______)

11. Find the average slump of all pairs of students with the same water amount in the class.
Record Average (amount of water________ , amount of slump_________)


12. Collect data from all the groups in class and record in data table below.
Water 110 120 130 140 150
Slump

13. Label the axis appropriately and graph the data on your own graph paper.


14. Write an equation for the line of best fit.


15.Explain the real life meaning of slope.


16. What type of predictions could you make from your equation


17. If you had a 60 lb bag of concrete, how much water would you need to add to give the same ratio of water to concrete mix as you initially had? Hint: You will not need your graph for this.


18. Take your cement to the designated disposal area/person. Wash all of the equipment and return equipment to teacher.



Teacher Instructions:
It is best if you pre bag the ready mix concrete. Bag 2.5 lbs in each bag. Water must be added using milliliters in the amounts of 110 ml, 120 ml, 130 ml, 140 ml, and 150 ml. Each pair of students will do one water amount or one slump test. To clarify, each pair of students will do one water amount (either 110, 120, 130, 140, 150 ml) Repeat the water amounts as needed depending on the number of groups you have.

We do one slump test per pair of students with at least 2 pairs doing each water amount. A 60 lb bag of ready mix will provide about 24 bags of concrete.

The line of best fit will predict the amount of slump per ml of water. Realize that this equation will only be useful for a specific domain. That is, a concrete mix with too little or too much water will not be a mix. The equation gives you an opportunity to discuss the concept of domain of a function. The slump test is one measure of a concrete’s strength. Once again too much or too little water will significantly weaken the concrete.

Make stepping stones with the left over experiments.