Experiment :- To determine the workability of Fresh Concrete of given proportions by Slump Test and Compacting Factor Test.
Workability of a concrete signifies the full compaction of concrete using a required or reasonable amount of work which helps to achieve the desired possible density or void of fresh concrete resulting better strength and durable concrete structure and helpful to maintain durability throughout the job.
For the determination of Workability of Fresh Concrete the tests which are used mostly are :-
(i) Slump Test
Slump Test is perform to measure the consistency and workability of fresh concrete through an idea which it gives of water content needed for concrete to be used for different ideal works. A concrete is called as workable if it can be easily mixed, placed, compacted and finished and does not show any segregation or bleeding.
(a) Iron Pan to mix Concrete
(b) Slump cone
(c) Spatula for mixing purpose
(e) Tamping Rod
(f) Graduated Cylinder
Slump Test Apparatus
Using the above apparatus, we have to done the test.
Steps which are to be followed in the test are:-
Step 1:- Mix all dry ingredient thoroughly and carefully to get uniform result and then add water.
Step 2:- The slump test cone is placed on a smooth, level surface with the smaller opening at the top. Slump cone is filled in three layers of equal volume, each approximately ¼ of the height of the mould. and each layer is to be compacted 25 times with a standard rod having a hemispherical tip
Step 3:- Struck off the rod, and then cone is slowly lifted and set beside the unsupported concrete Such that the tamping rod should penetrate in to the underlying layer.
Step 4:- The rod is laid across the cone and a measure of the distance from the bottom of the rod to the average top of the concrete is taken .A very stiff mix will have near zero slumps. Lean mixes tend to be harsh and slumps can vary from true to shear in different sample of the same mixes.
(ii) Compacting Factor Test:-
This test is usually used in laboratory and determines the workability of fresh concrete when size is about 40 mm maximum. The test is carried out as per specification of IS: 1199-1959.
(a) Compacting Factor apparatus
(c) Graduated cylinder
(e) Tamping rod and iron buckets
Steps for performing the experiment:-
Step 1:- keep the apparatus on the ground and apply grease on the inner surface of the cylinders.
Step 2:- Measure the mass as w1 kg by weighing the cylinder accurately and fix the cylinder on the base in such a way that the central points of hoppers and cylinder lie on one vertical line and cover the cylinder with a plate.
Step 3:- For each 5 kg of aggregate mixes are to be prepared with water-cement ratio by weight with 2.5 kg sand and 1.25 kg of cement and then add required amount of water thoroughly until and unless concrete appears to be homogeneous.
Step 4:- With the help of hand scoop without compacting fill the freshly mixed concrete in upper hopper part gently and carefully and within two minutes release the trap door so that the concrete may fall into the lower hopper such that it bring the concrete into standard compaction.
Step 5:- Fall the concrete to into the cylinder by bringing the concrete into standard Compaction immediately after the concrete has come to rest and open the trap door of lower hopper and then remove the excess concrete above the top of the cylinder by a pair of trowels, one in each hand will blades horizontal slide them from the opposite edges of the mould inward to the center with a sawing motion.
Step 6:- Clean the cylinder from all sides properly. Find the mass of partially compacted concrete thus filled in the cylinder and say it W2 kg. After this refill the cylinder with the same sample of concrete in approximately 50 mm layers, by vibrating each layer heavily so as to expel all the air and obtain full compaction of the Concrete.
Step 7:- Struck off level the concrete and weigh and cylinder filled with fully compacted concrete. Let the mass be W3 kg.
Step 8:- Calculate compaction factor by using the formula:- C.F = W2 – W1 / W3 – W1
1.What are the main differences between Slump Test and Compacting Factor Test.
Ans:-The main difference between both is that compaction factor test is more sensitive and precise than slump test and is particularly useful for concrete mixes of low workability and also able to indicate small variations in workability over a wide range.
2.List the different types of Slump.
Ans:- There are three main type of slump namely
(a) True slump.
(b) Shear slump .
3. What is the actual proportion or ratio of water and cement to built a concrete structure.
Ans:- The actual proportion of water and cement in concrete is 1:5.
4.What are the standard used in slump test and compacting factor test.
Ans:- The standard used in slump test is ASTM: C143 and B.S: 1882 part 2, and the standard used in compaction factor test is IS: 1199-1959.
5. What are the main precaution that has to be taken during the both test.
Ans:- The precaution that has to be taken are:-
(i) Accurate amount of water, cement and sand are to be taken to avoid collapsing of sample.
(ii) Maintain the consistency throughout the experiment to avoid the failure.