May 11 2019 0Comment

5 Tests For Measuring The Workability Of Fresh Concrete

5 Tests For Measuring The Workability Of Fresh Concrete

  • Slump Test

A steel mold which has the shape of a frustum cone with a top diameter of 100mm, bottom diameter of 200mm and height of 300mm is used for a slump test. The maxim size of aggregate in concrete that is used for a slump test is limited to 38mm.

Slump Test

The mould should be free of any moisture after which the concrete is added in three layers. Each layer gets tamped 25 times with a tamping rod. After filling, the cone is slowly elevated for the concrete to subside. The decline in the height in the center of the slumped concrete is referred to as slump and are measured to the closest 5mm.

This test is the most widely used method for measuring the workability of fresh concrete. It can be done either on-site or in a lab setting. The test is performed in batches to assess the quality and workability and to see how the concrete slumps. This method is not suitable for very dry or very wet concrete.

  • Compacting Factor Test

The concrete is gently positioned in the upper hopper to avoid any effort to producing compaction. The bottom door is released so that the concrete falls onto the lower hoper. Again, the bottom door of the lower hopper gets opened so that the concrete lands on the cylinder. After removing excess concrete with the blades, the weight of the cylinder is taken to the closest 10 grams. The weight is referred to as “weight of partially compacted concrete.” The cylinder gets emptied and then filled with the same sample, butted heavily to obtain full compaction. The cylinder is then weighed to the closest 10 grams. This weight is then referred to as “weight of fully compacted concrete.”

This test is done in a laboratory but can be performed on site as well. It is useful for a concrete mix with low workability (very dry concrete) as they are not suitable for slump testing.

  • Vee-Bee Test

This test is done in a laboratory and is suitable for concrete mixes with low or very low workability (stiff). The test involves a metal pot, vibrating table, an iron rod, and a metal cone.

Vee-Bee Test

A slump test is performed (as described above) by placing the slump cone in the sheet metal cylindrical pot. Vibration is started, and a stop watched used for timing. The time it is taking for the concrete to form a cylindrical shape after the cone shape disappears is documented and the time is referred to as Vee-bee seconds or Vee-bee degree.

  •  Flow Test

Performed in a lab and is best suited for flowing concrete which is made by using super plasticizing admixtures. It is used for indicating the quality of concrete relating to cohesiveness, consistency and its prone-ness to segregation. The spread of the concrete’s flow is measured, and workability is assessed.

  • Kelly Ball Test

A simple field test for determining the indentation made by a 15cm (in diameter) metal hemisphere, weighing 13.6kg, being placed freely on fresh concrete.  It is a fast and precise measurement of workability compared to the slump test. However, a large amount of concrete is needed for testing. For more information, you should take concern with concrete contractor Perth.

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