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Slump test for concrete

Slump test is used extensively at construction fields because of the simplicity of conducting the test at the field. it is a common practice to check the slump for every concrete truck. slump test measured the consistency of concrete. a flowable concrete mix will have greater slump value compared a to a drier concrete mix.

Procedure for conducting slump test

the apparatus used in this test is metal mold with a conical shape and tamping rod. the dimension of the mold shall be as shown in the figure below. the metal mold shall be opened from both directions. fresh concrete will be filled at three layers. each layer will receive 25 blows by tamping rod. then the mold will be lifted carefully and the amount of slump shall be measured.

Slump types
  1. collapse slump: in this type of slump concrete collapse completely
  2. shear slump:in this type of slump concrete top portion shears off and slide away
  3. true slump: in this type of slump concrete keep almost same shape

Limitation of slump test

slump test is simple and easy to conduct but the results of the test are not accurate. the test doesn't stimulate the process of pumping, placing and compacting of concrete. the slump occurred under concrete self-weight.
slump results for mixes with different size of aggregate can be similar even the workability of the mixes are different. also, it is impractical to use slump test to measure the workability for stiff mix as it shows no slump. it is not recommended to use slump test for mixed with size if aggregate greater than 40 mm.


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