WORKABILITY OF CONCRETE COMPACTING FACTOR TEST
AIM: To determine the workability of concrete mix of given proportions by compacting factor test.
APPARATUS: Compacting factor apparatus, Balance, Weights, Trays, Tamping rod and Trowels.
DESCRIPTION: Compacting factor apparatus consists of two conical hoppers mounted above a cylindrical mould and fixed to a stand one above the other. The hoppers are provided with trap doors at the bottom. The dimensions of various parts are given below.
Upper Hopper Dimensions in cm.
Top internal dia. 25.4
Bottom 12.7
Internal height 27.9
Lower Hopper Dimension in cm.
Top internal dia. 22.9
Bottom 12.7
Internal height 22.9
Cylinder Dimension in cm.
Internal Diameter 15.2
Internal Height 30.5
Distance between bottom of upper hopper and top of lower hopper is 20.3 cm. Distance between bottom of lower hopper and top of cylinder is 20.3 cm.
DEFINITION:
Compacting factor is defined as the ratio of weight of partially compacted concrete to the weight of fully compacted concrete.
PROCEDURE:
Four mixes are prepared with W/C., ratios 0.4, 0.5, 0.55, 0.6 and 0.65. For each mix take 2.5 kg of cement, 5 kg of fine aggregate and 10 kg of coarse aggregate.
- Mix the dry constituents to get a uniform color and then add water.
- The internal surfaces of the hoppers and cylinder are thoroughly cleaned.
- The sample of concrete to be tested is placed gently in the upper hopper.
- The hopper is filled level with its brim and the trap door is opened so that the concrete falls into the lower hopper.
- If concrete has a tendency to stick to the sides of the hopper, the concrete should be slowly pushed down by inserting the tamping rod into the concrete.
- Immediately after the concrete comes to door of the lower hopper, it is opened and the concrete is allowed to fall into the cylinder.
- The excess of concrete in the cylinder above the top is cut off and made level with trowels. The outside of cylinder is wiped clean.
- The weight of the concrete in the cylinder is then determined. This weight is known as weight of partially compacted concrete.
- The cylinder is refilled with concrete from the same sample in six layers and each is rammed thoroughly.
- The top of fully compacted concrete should be carefully struck off level with top cylinder. The outside of the cylinder is wiped a clean and the weight of fully compacted concrete is found.
RESULTS:
Maximum workability of concrete is occurring at a water / cement ratio of
SPECIFICATIONS:
According to IS 456, the degree of workability in classified as follows:
Degree of workability Compacting factor.
Very Low 0.75 to 0.8
Low 0.8 to 0.85
Medium 0.85 to 0.92
High 0.92 & above.
GRAPH:
A graph is drawn with water / cement ratio on x-axis and values of compaction factor on y-axis.
