Updated: May 26
It´s easy! Just grab the cone, fill it with concrete and lift it up....hurry up we have more important things to do! Just another ordinary day at the building site during a casting.
We have already discussed about the importance of the correct workability of concrete (see post “Workability of concrete”), but how to measure it? The most famous way is the Abrams cone test or slump test. Easy? Well, my first boss used to say: “There are no easy or difficult things, only things you know how or things you don´t know how to do”. So let´s start from what you need:
A full Abrams cone is made of a cone (really?!) a plate, a pestle, a meter preferably a funnel and a bailer.
10 steps procedure:
1. Wash the equipment so to have it slippery.
2. Place the plate onto a horizontal flat clean surface at the operator´s feet level.
3. Place the cone onto the plate. The cone comes with two feet where the operator must step onto.
4. Start filling the cone while keeping it in place with the feet, it must be filled up with three similar layers.
5. Compact each layer of concrete with the pestle hitting 25 times with circular patterns carefully avoiding to compact the lower layer again.
6. Ensure the cone is totally filled up right to its limit, not more, not less.
7. While keeping the cone with the feet so as to keep it well fixed on the plate, grab the cone´s handles and push the cone as to keep everything right in place.
8. Remove your feet (the cone is still “fixed” on the plate) and gently lift up the cone straight without vibrations in 5 to 10 seconds.
9. Place the cone beside the dropped mass of concrete and by the help of the pestle and the meter measure the highest point (tolerance ± 1 cm.).
10. Wash carefully all the equipment.
10 common mistakes:
1. Not washing the equipment before using. The internal surface in contact with the concrete will be too dry compromising the concrete´s rheology and invalidating the test.
2. Choosing a dirty, rough, uneven surface where to set the plate. This will allow movements that will nullify the test.
3. Not pushing enough with your feet onto the cone´s feet. Concrete will come out from below nullify the test.
4. Filling the cone in more or lesser than three layer. Irregular method, the test is not valid.
5. Not compacting the layers in the way over described. Irregular method, the test is not valid.
6. Overfill or underfill the cone. The measurement of the concrete´s lowering will not be reliable.
7. Moving the feet before having firmly grabbed the cone, pushing it to the ground. The cone will move, the concrete will flow out nullify the test.
8. Lift up the cone while moving it. The concrete receive more compaction and will most likely lower more. The test is compromised
9. Lift up the cone in lesser than 5 or more than 10 seconds. Modify the rheology of the concrete compromising the test result.
10. Bad washing of the equipment or not washing at all. The internal surface in contact with the concrete will be rough compromising the rheology and nullify the test result.
Everybody at the building site, if well trained, can do that. But please give this responsibility only to the trusted ones, it is a serious task. For more details about the consequences in using a wrong consistency concrete read my post “Workability of concrete”.
This test is the most used and the one you have to refer to whenever you have to cross check the workability declared by the manufacturer if not agreed otherwise.
There are several other methods to measure the workability of concrete, but in this post I´ll tell you briefly only about the Flow table test.
The flow table test measures the horizontal spread of a concrete cone specimen after being subjected to jolting.
The equipment consists of a 700 mm square wooden top plate lined with a thin metal sheet. The plate is hinged on one end to a base, while on the other end, clips allow the plate to be lifted a vertical distance of 40 mm. The cone used is shorter than the Abrams cone.
To perform the test, the cone is placed in the center of the plate and filled in two layers, each of which is compacted with a rod. The plate is lifted with the attached handle a distance of 40 mm and then dropped for 15 times. The horizontal spread of the concrete is measured both axes and considered the average.
The goal of the test is getting to know the aptitude of fresh concrete to settle under a vibration action and is specially advisable for fluid concrete.
The consistency class for this specific test is described in the following table: