The following tests are commonly employed to measure work ability.
(a) Slump Test
(b) Compacting Factor Test
(c) Flow Test
(d) Kelly Ball Test
(e) Vee Bee Consistometer Test.
Here we will discus about Slump test. Because slump test is one of the most important test while we are determining the work ability of concrete.
Slump Test :-
Slump test is the most commonly used method of measuring consistency of concrete which can be employed either in laboratory or at site of work. It is not a suitable method for very wet or very dry concrete. It does not measure all factors contributing to work ability, nor is it always representative of the place ability of the concrete.
The pattern of slump is shown in Fig. It indicates the characteristic of concrete in addition to the slump value. If the concrete slumps evenly it is called true slump. If one half of the cone slides down, it is called shear slump. In case of a shear slump, the slump value is measured as the difference in height between the height of the mold and the average value of the subsidence.
Apparatus :-
The Slump Cone apparatus for conducting the slump test essentially consists of a metallic mold in the form of a frustum of a cone having the internal dimensions as under: Bottom diameter : 20 cm, Top diameter : 10 cm, Height : 30 cm and the thickness of the metallic sheet for the mold should not be thinner than 1.6 mm Weights and weighing device, Tamper ( 16 mm in diameter and 600 mm length), Ruler, Tools and containers for mixing, or concrete mixer etc.
Procedure :
- Dampen the mold and place it on a flat, moist, nonabsorbent (rigid) surface. It shall be held firmly in place during filling by the operator standing on the two foot pieces. Immediately fill the mold in three layers, each approximately one third the volume of the mold.
- Rod each layer with 25 strokes of the tamping rod. Uniformly distribute the strokes over the cross section of each layer.
- In filling and ridding the top layer, heap the concrete above the mold before ridding start. If the ridding operation results in subsidence of the concrete below the top edge of the mold, add additional concrete to keep an excess of concrete above the top of the mold at all time.
- After the top layer has been rodded, strike off the surface of the concrete by means of screeding and rolling motion of the tamping rod.
- Remove the mold immediately from the concrete by raising it carefully in the vertical direction. Raise the mold a distance of 300 mm in 5 ± 2 sec by a steady upward lift with no lateral or torsional motion.
- Immediately measure the slump by determining the vertical difference between top of the mold and the displaces original center of the top surface of the specimen. Complete the entire test from the start.of the filling through removal of the mold without interruption and complete it within 2½ min.
- If a decided falling away or shearing off of concrete from one side or portion of the mass occurs, disregard the test and make a new test on another portion of the sample. If two consecutive tests on a sample of concrete show a falling away or shearing off of a portion of concrete from the mass of specimen, the concrete lacks necessary plasticity and cohesiveness for the slump test to be applicable.
- After completion of the test, the sample may be used for casting of the specimens for the future testing.
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| Slump Test |
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| measurement of slump test |
Observation :
- The vertical difference between top of the mold and the displaces original center of the top surface of the specimen ………… mm
- The pattern of slump is shown True Slump/Shear Slump/ Collapse Slump/Zero Slump.
Result :
The slump of concrete ……….. mm indicate Low/ Medium/ High Degree of work ability