Sunday, July 24, 2011

Slump of Hydraulic Cement Concrete

Slump test is one of the process to control quality of water cement ratio in field condition. It conforms ASTM Designation C 143. Now the procedure is discussed below.  

Equipment and Materials
Frustum of a cone made of noncorrosive sheet metal, not less than 1.14 mm (0.045 inch) thick, 30.5 cm (12 inches) in height, with a 20.8-cm (8-inch) base, having a diameter at the top of 10.2 cm (4 inches), with foot pieces and handles as shown in Figure 1. There should also be a metal base plate with clamps that engages the foot pieces while the concrete is being poured into the slump cone and tamped with the tamping rod.

• Round steel tamping rod 16 mm (⅝ inch) in diameter, having the tamping end rounded to a hemispherical tip, approximately 60 cm (24 inches) long. Suitable, graduated metal scale approximately 25 cm (1 ft) in length.


Test Procedure
1. Dampen the slump cone and the metal base plate; then engage the slump cone with the base plate clamps. The base plate should rest on a level surface.

2. Fill the slump cone in three lifts, tamping each lift 25 times with the tamping rod, starting from the center and working toward the perimeter. The bottom lift should be rodded the full depth down to the base plate. For the two other lifts, the strokes of the tamping rod should penetrate into the underlying concrete layer. The top lift should remain heaped above the top of the slump cone after completing the rodding. Each of the three lifts should contain approximately an equal volume of concrete. Therefore, the bottom layer should have a rodded depth of about 7 cm (2½ inches) and the second lift to about 15 cm (6 inches).
3. Strike off the excess concrete with a screeding and rolling motion of the tamping rod.

4. Remove the cone carefully with a slow vertical motion without any rotational or lateral motion. The entire procedure from the time the fresh concrete is ready for testing to this point should be no more than five minutes. The time from the filling of the slump cone to determining the slump should be within 2½ minutes.

Fig -2

5. Set the slump cone in an inverted position next to the concrete and measure the distance to the top of the original center of the specimen as shown in Figure 2.


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