Various tests on concrete

      There are many tests which are conducted to check the quality of concrete. These tests are  basically divided into two categories

1. Various Test On Fresh Concrete.
       a) Slump Test
       b) Compacting Factor
       c) Vee- Bee Test
2.Various Test On Hardened Concrete.

          There are two kinds of tests which are done on hardened concrete. These are non destructive test and destructive tests. In non destructive test, the sample is not destroyed and this test is very useful in determining the strength of existing buildings or structures where as in destructive test a sample is made and then destroyed to find out the strength of concrete.Compression test is the example of destructive test. Here are the nondestructive tests.

        a) Rebound Hammer Test
        b) Ultrasonic Pulse Velocity Test

A) SLUMP TEST: 
      
 SCOPE: It is a method for determining the consistency, or the ability of fresh concrete to flow.

 APPARATUS:      
                   
i) Mould made of metal not readily attacked by cement paste and not thinner than 1.5mm, upper diameter 100mm, lower diameter 200 mm and height of the cone 300mm.

ii) Scope approximately 100 mm wide

iii) Tamping rod, made of straight iron or steel bar of circular cross section of 16mm diameter and 600mm long

iv) Rule, graduated from 0 mm to 300 mm at 5 mm intervals, the zero point being at one end of the rule.

SAMPLING:  

1. Obtain at least two samples to make a composite sample.
2.  Do not take samples from the very first or last portions of the batch.
3. Take samples after all water and admixtures have been added to the mix.
4. Carefully observe time limitations to ensure results of field tests are consistent.
5. Protect samples from sun, wind, rapid evaporation, and contamination.

PROCEDURE:

• Ensure that the internal surface of the mould is clean and damp but free from superfluous moisture before commencing the test.
• Place the mould on a smooth, horizontal, rigid and non-absorbent surface free from vibration and shock.
• Hold the mould firmly against the surface below with the funnel, if used, in position at the top whilst it is filled in three layers, each approximately one-third of the height of the mould when tamped.
• Tamp each layer with 25 strokes of the tamping rod, the strokes being distributed uniformly over the cross-section of the layer. 
• Tamp each layer to its full depth, ensuring that the tamping rod does not forcibly strike the surface below when tamping the first layer and just passes through the second and top layers into the layers immediately below. 
• Heap the concrete above the mould before the top layer is tamped. If necessary, add further concrete to maintain an excess above the top of the mould throughout the tamping operation. 
• After the top layer has been tamped, remove the funnel, if fitted, and strike off the concrete level with the top of the mould with a sawing and rolling motion of the tamping rod. 
• With the mould still held down, clean from the surface below any concrete which may have fallen onto it or leaked from the lower edge of the mould.
• Remove the mould from the concrete by raising it vertically, slowly and carefully, in 5 s to 10 s, in such a manner as to impart minimum lateral or torsional movement to the concrete. 
• The entire operation from the start of filling to the removal of the mould shall be carried out without interruption and shall be completed within 150 s.
• Immediately after the mould is removed, measure the slump to the nearest 5 mm by using the rule to determine the difference between the height of the mould and of the highest point of the specimen being tested.

 In brief 1-6 procedure

Information to be included in the test report:

Mandatory information: The following information shall be included in the test report:

a) date, time of completion, place and method (general or alternative) of sampling and sample identity number; 

b) time and place of test;

c) time lapse from sampling to commencement of test;

d) form of slump, whether true, shear or collapse;

e) measured true slump;

f) name of person carrying out test.

Optional information: If requested the following information shall be included in the test report:

a) name of project and place concrete used;

b) name of supplier and source of concrete;

c) date and time of production of concrete or delivery to site;

d) specification of concrete mix (e.g. strength grade).
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B) COMPACTING FACTOR TEST: 

      
 SCOPE: It is a method for determining the compacting factor or workability of fresh concrete

 APPARATUS:      

                   
i) Iron pan to mix concrete
ii) Slump cone
iii) Spatula for mixing purpose
iv) Trowels
v) Tamping rod
vi) Graduated cylinder

PROCEDURE:

• Keep the apparatus on the ground and apply grease on the inner surface of  the  cylinders.
• 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.
• 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.
• 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.

• 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.
• 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.
• Struck off level the concrete and weigh and cylinder filled with fully compacted concrete. Let the mass be W3 kg.

• Calculate compaction factor by using the formula:-                                                                
•  C.F = W2 – W1 / W3 – W1

Compacting factor = (Weight of partially compacted concrete)/(Weight of fully compacted concrete)