Concrete slump test is very important test, carried out on site to find out the workability of concrete. Purpose of slump testing is to find out Water Cement Ratio of concrete and its workability that is very important in mixing, transporting, placing and compacting of concrete.
In slump test procedure this is the 1st activity that all equipment should be clean and inside of cone and other equipment should be moisten with oil.
Place the slump cone on a level, rigid surface with the base on the ground. Protect the slump cone with the tamping rod stand to avoid movement.
Slump cone should be filled with three layers, one layer equal to one-third of the cone's height. Each layer should be compacted by rodding with 25 strokes with the tamping rod, ensuring uniform distribution and compaction.
After filling of cone with the final layer, excess concrete should be removed using the tamping rod or a trowel.
Lift up the slump cone vertically without any twisting or tilting motion. Do it smoothly and steadily to avoid disturbing the concrete.
Measure the difference between the height of the slump cone and the top of concrete. This difference is called the "slump," and it is measured in millimeters.
During slump testing, ensure all equipment should be clean and inside of cone and other equipment should be moisten with oil. Clean all the equipment immediately after testing to avoid the concrete hardening on the tools.
After removal of cone, concrete takes various shapes and these different shapes called types of slump. According to the shape of concrete after cone removal slump is distributed in following four types of slump:
In a collapse slump, the concrete collapses completely. Collapse slump shows the excessive quantity of water in the concrete. By reducing the quantity of water, collapse slump should be controlled. Concrete with collapse slump should not be used in any case.
In a shear slump, the concrete shears off and slips sideways. The shear slump shows the result is incomplete, and the test should be done again. If the shear slump continues, as may be the case with harsh mixes, this is an indication of the lack of cohesion of the mix.
In the case of true slump, the concrete simply subsides, keeping more or less to shape. This is the only slump which is used for concreting.
If concrete shows no change in its shape, defined as zero slump. Zero slump shows the very low ratio of water in the concrete.
Conduct the slump test as soon as possible after sampling the concrete to ensure accurate results. Recommended slump range should be followed to achieve the desired strength of the concrete structure.
