Since 1922 slump test has been widely used for check out the concrete workability at the site. This test is also known as the slump cone test. Slump test measures the consistency or workability of concrete. It is used to check the workability of freshly made concrete for the easy placement of concrete. This test indicates the water-cement ratio and the properties of materials and also admixture etc. The test is carried out in accordance with BS EN 12350-2.
Slump test can be done on site to check the concrete mix has expected fluid properties. This test can be used to measures consistency between the individual batches.
It is a simple and low-cost test prepared at the laboratory or at the site during the work. It can be carried out from batch to batch to check the workability of freshly made concrete. It is the most simple test to check out the workability of concrete.
The concrete workability is the property of freshly mixed concrete which determines homogeneity, placed, mixed, consolidated and finished’ as specified by ACI Standard 116R-90 or ACI 1990b. The w/c ratio, amount and type of aggregate and cement, admixtures, and weather conditions are main factors that affect the workability of concrete.
Procedures for slump test [ Step by Step]
The whole concrete slump test is performed under the 5 steps. You have to clean all the apparatus which is going to use with water and then apply the oil on the surface to make then friction free.
The sample of slump test:
Concrete having a different mix (M15 or M20 etc) with the suitable water-cement ratio and can be prepared at the site or casting the 6 cubes after conducting the slump test.
The sampling and the test is performed under the following rules and laws.
American Society for Testing and Materials (ASTM) standards are ASTM C 143 or ASTM C143M.
The American Association of State Highway and Transportation Officials (AASHTO) AASHTO standards AASHTO T119 or AASHTO BS 1881.
British & European standard BS EN 12350-2.
Indian standard: IS 1199 – 1959.
Size of slump cone
The cone both ends are open (Top and bottom). The bottom diameter is more as compared to the top diameter. The standard size is,
Cone internal Top diameter is 3.9 inches (100 mm) and bottom diameter is 7.9 inches (200 mm). The cone height is 12 inches (305 mm).
Metal Tamping road 5/8 (16 mm) in diameter and 2 ft (600 mm) long with bullet-nosed.
The surface of the whole apparatus must be dry or clean.
Place all the apparatus parts together.
By using a trowel, put the first layer of concrete into the mould.
Then done tamping on the first layer (25 times) with the help of the rod.
The second layer of concrete is added into the mould.
Again the (25 times) tamping was done with the rod.
The third layer of concrete added after the proper tamping.
Again 25 strokes were done to do the proper compaction.
The excess concrete was removed from the above.
In four-step, the cone was lifted upward properly.
The cone lifting angle must be 90 degrees.
The value of the slump was noted with the help of measuring tape.
Types of slump test:
1: Zero slumps:
This test indicates the very low water-cement ratio which results in dry mixes. This test is mostly used in road construction works.
A slump occur when the value of slump recorded below 1/4 inch.
In this, the concrete is very stiff or extremely dry consistency.
It is defined as Concrete Terminology (ACI 116R-90).
2: True slump:
This measurement is taken from the top of the concrete when the slump cone has been removed. The true slump is considered as more desirable as compared to shear slump.
This test is mostly used for checking the consistency of lean concrete.
In true slumps, the concrete subsides shortly and maintain its cone shape.
More desirable slump.
3: Shear slump:
The top portion of the concrete surface slips sideways and shear off it is known as a shear slump. If shear is achieved in the concrete, then a sample should be taken and repeat this test again.
The concrete may have a little more water-cement ratio as per design.
Lake of cohesion of the mix.
4: Collapsed slump:
This test indicates the water-cement ratio is too high. It means the concrete is high workability and high concrete mix. This slump test is not appropriate.