Measuring the properties of fresh concrete is an essential process that should be carried out in the site before placing the concrete. The main reason for carrying out these tests is to ensure whether the desired properties are associated in the fresh concrete which influencing the strength and durability of the structures.
As we discussed under the topic, What is Concrete?, the various concrete mixture can be prepared to form the different types of concretes. So, again the properties of fresh concrete are highly depending on the type of concrete that is going to be used for the structure. The main properties of the fresh concrete are,
- Workability
- Temperature
- Setting
- Segregation of the concrete
- Plastic shrinkage on the concrete
- Thermal shrinkage and thermal expansion on the concrete
- Water cement ratio
Workability is a key property of the fresh concrete for all the types of the concrete. Workability defines as a measure of consistency of the fresh concrete or simply can be explained as it is about how easily the concrete can be poured into the mold and compacted to form the required shape without any segregation and defects with the required strength and durability. Having the moisture higher than the designed is giving rise to the defects and cracks on the concrete surface especially due to the thermal shrinkage.
The slump test, compacting factor test and V-B test are the three tests that can be used to point out the workability of the concrete. Among all three, slump test is generally preferred in the site to assess the consistency of the fresh concrete as it is easy to do at the site with very low cost and low labor skills. Slump test is one of the tests that are performed in the fresh state concrete at the site once the concrete truck is arrived.
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Slump test is carried out in accordance with ASTM C143 in US and EN 12350-2 in Europe. And other countries will define the slump test procedures according to their own standards.
General Procedure for Slump Test
Slump test sketch
After cleaning the slump cone, cone should be kept on planer tray. Then the concrete should be poured into the cone in 3 layers, and each layer should compact for 25 times using a tamping rod. After filling up to top level, the top surface should be smoothened, and then the cone will be lifted in vertical manner. The concrete will be left to slump and after slumping, the slump will be measured. The slump used in sites will be differing according to the concrete mix proportion with the tolerance of 20 mm or appropriate values.
