In the first pouring of concrete on a project, a quality engineer and a consultant representative should be present to supervise or to check the concrete delivered on-site and eventually the slump test of concrete. But first here is the definition of Slump Test ” A measure of the consistency of freshly mixed concrete equal to the subsidence measured to the nearest 1/4 inch in a molded specimen immediately after removal of the slump cone.”
You should provide the equipment needed shown in the list below, and make sure to clean it before starting a slump test. The test should be done by a concrete technician provided by the concrete ready mix supplier.
A quality engineer shall prepare a concrete pour card to note down each concrete delivery at the site, including slump, temperature, location of placement and quantity of concrete.
|Equipment's For Slump Test|
|Slump cone||Tamping rod|
|Slump tray||Concrete scoop (small)|
|Wheel borrow||Bucket or pail|
Here are the steps to do the slump test of concrete.
1. Get a concrete sample. When a truck mixer reaches the checkpoint, the quality engineer should check the delivery note to ensure that the concrete delivered is in compliance with the concrete grade required for the concrete element to be cast.
Roll the drum for a certain time to completely mix the concrete inside. Place the wheelbarrow below the chutes to get the fresh concrete, and avoid overfilling the wheelbarrow and causing an overflow. Check the temperature with a concrete thermometer. Please note that the fresh concrete should not exceed 30 degrees Celsius.
2. Remix the fresh concrete. Mix the fresh concrete again with a round-mouthed-shovel or concrete scoop. Dig back and forth and sideways. Do it three times until the concrete is properly mixed.
3. Place the slump cone on a flat surface. Firstly, make sure that the slump table and cone are damp. Place the slump table on level and stable ground and make sure it will not vibrate while placing the concrete. Place the slump cone on the table and stand on the foot-pieces built-in with the cone.
4. Filling the cone. Fill the cone with concrete to 3 equal heights in turn, After pouring the first layer, it must be rodded 25 times with 16mm diameter rounded steel. Fill the cone again for the second layer and do rodding as the first layer. Fill the cone again for the last layer, making sure that the cone is completely filled with concrete. Rod the concrete 25 times make sure that the rod just penetrates the surface of the preceding layer.
5. Lifting the cone. Before lifting make sure that the table around the cone is clean. Remove the concrete debris, and while cleaning don’t move the foot pressure on the foot-pieces. Carefully lift the cone straight up to a count of between 5 and 10.
6. Checking the slump. Place the upturned cone just beside the slumped concrete and lay the rod above it, then measure the slump from the underside of the rod to the topmost portion of the concrete.
Record the distance to the nearest 10mm and also check and record the kind of slump. If not a true slump, take a new concrete sample and redo the slump test.
Quality Engineer Tips:
a. You should ensure that the wheel borrow is cleaned prior to fetching fresh concrete from the truck mixer.
b. Ensure that before placing the slump cone on the slump table the table must be cleaned and tidy.
c. There should be only 3 layers of filling.
What is Slump Test of Concrete?
Slump – A measure of consistency of freshly mixed concrete or mortar equal to the subsidence measured to the nearest 1/4 in. (6 mm) molded specimen immediately after removal of the slump cone.
What is Structural Concrete?
A special type of concrete that is capable of carrying a structural load or forming an integral part of a structure.
What is the Allowed Temperature of Fresh Concrete?
It is 32 deg Celcius. More than that the concrete is rejected.