This is a site test to determine the workability of the ready mixed concrete just before its placing to final position inside the formwork and is always conducted by the supervisor on site. However, in mid of concreting process, should the site supervisor visually finds that the green concrete becomes dry or the placement of concrete has been interrupted, a re-test on the remaining concrete should be conducted in particular of the pour for congested reinforcement area. The procedure of the test in brief is as follows;
1. Ensure the standard Slump Cone and associated equipment are clean before the test and free from hardened concrete.
2. Wet the Slump Cone and drain away the superfluous water.
3. Request the mixer or concrete truck to well mix the concrete for additional 5 minutes.
4. Place the Slump Cone on one side ( ie. not in middle ) of the base plate on the leveled ground and stand with feet on the foot-pieces of cone.
5. Using a scoop and fill the cone with sampled concrete in 3 equal layers, each about 100mm thick.
6. Compact each layer of concrete exactly 25 times with a Slump Rod, allowing the rod just passes into the underlying layer.
7. While tamping the top layer, top up the cone with a slight surcharge of concrete after the tamping operation.
8. Level the top by a “ sawing and rolling ” motion of the Slump Rod across the cone.
9. With feet still firmly on the foot-pieces, wipe the cone and base plate clean and remove any leaked concrete from the bottom edge of the Slump Cone.
10. Leave the foot-pieces and lift the cone carefully in a vertical up motion in a few seconds’ time.
11. Invert the cone on the other side and next to the mound of concrete .
12. Lay the Slump Rod across the inverted cone such that it passes above the slumped concrete at its highest point.
13. Measure the distance between the underside of rod and the highest point of concrete to the nearest 5mm ( see Fig 7 – 3 ).
14. This reading is the amount that the sampled concrete has slumped.
15. If the concrete does not show an acceptable slump ( see Fig 7 – 4 ), repeat the test with another sample.
16. If the repeated test still does not show an acceptable slump, record this fact in the report, or reject that load of concrete.