CONCRETE TESTING PROCEDURE

SL NO	DESCRIPTION OF DOCUMENT	REMARKS
1	DETERMINATION OF WORKABILITY OF CONCRETE ( SLUMP TEST )
2	DETERMINATION OF COMPRESSIVE STRENGTH OF CONCRETE
3	DETERMINATION OF FLEXURAL STRENGTH OF CONCRETE

 

1. DETERMINATION OF WORKABILITY OF CONCRETE (SLUMP TEST)

( IS : 1199 – 1959 )

Object:

This method of test specifies the procedure to be adopted, either in the laboratory or during the progress of work in the field, for determining, by the slump test, the consistency of concrete.

Apparatus:

a) Mould: the mould for the test specimen shall be in the form of the frustum of a cone having the following internal dimensions:

Dimensions in cm

Bottom diameter. 20

Top diameter. 10

Height. 30

 

b) Tamping Rod: The tamping rod shall be of steel or other suitable material, 16 mm in diameter, 0.6m long and rounded at one end.

Procedure:

The internal surface of the mould shall be thoroughly cleaned and freed from superfluous moisture and any set concrete before commencing the test. The mould shall be placed on a smooth, horizontal, rigid and non-absorbent surface, such as a carefully leveled metal plate, the mould being firmly held in place while it is being filled. The mould shall be filled in four layers, each approximately one-quarter of the height of the mould. Each layer shall be tamped with 25 strokes of the rounded end of the tamping rod. The strokes shall be distributed in a uniform manner over the cross-section of the mould and for the second and subsequent layers shall penetrate into the underlying layer.

 

Fig. Slump Cone filling & Checking

The bottom layer shall be tamped throughout its depth. After the top layer has been rodded, the concrete shall be struck off level with a trowel or the tamping the rod, so that the mould is exactly filled. Any mortar, which may have leaked out between the mould and the base plate, shall be cleaned away. The mould shall be removed from the concrete immediately by raising it slowly and carefully in a vertical direction. This allows the concrete to subside and the slump shall be measured immediately by determining the difference between the height of the mould and that of the highest point of the specimen being tested. The above operation shall be carried out at a place free from vibration or shock, and within a period of two minutes after sampling.

The slump measured shall be recorded in terms of millimetres of subsidence of the specimen during the test. Any slump specimen which collapses or shears off laterally gives incorrect result and if this occurs the test shall be repeated with another sample.

   

    

 Fig. Measuring & Types of slump

 

2. DETERMINATION OF COMPRESSIVE STRENGTH OF CONCRETE.

( IS : 516 – 1959 )

Object:

 Determination of compressive strength of concrete.

 Apparatus:

 

Fig. Compressive Testing Machine

Testing Machine: The testing machine may be of any reliable type of sufficient capacity for the tests and capable of applying the load at the specified rate. The permissible error shall not be greater than 2 percent of the maximum load. The testing machine shall be equipped with two steel bearing platens with hardened faces. One of the platens shall be fitted with a ball seating in the form the portion of a sphere, the center of which coincides with the central point of the face of the platen. The other compression platen shall be plain rigid bearing block. The bearing faces of both platens shall be at least as larger as, and preferably larger than the nominal size of the specimen to which the load is applied.

The bearing surface of the platens, when new, shall not depart from a plane by more than 0.01mm at any point, and they shall be maintained with a permissible variation limit of 0.02mm. the movable portion of the spherical seated compression platen shall be held on the spherical seat, but the design shall be such that the bearing face can be rotated freely and tilted through small angles in any direction.

Age at test: Tests shall be made at recognized ages of the test specimens, the most usual being 7 and 28 days. The ages shall be calculated from the time of the addition of water of the dry ingredients.

Number of Specimens:

At least three specimens, preferably from different batches, shall be made for testing at each selected age.

Procedure:

Specimens stored in water shall be tested immediately on removal from the water and while they are still in the wet condition. Surface water and grit shall be wiped off the specimens and any projecting find removed specimens when received dry shall be kept in water for 24 hours before they are taken for testing. The dimensions of the specimens to the nearest 0.2mm and their weight shall be noted before testing.

Placing the specimen in the testing machine the bearing surface of the testing machine shall be wiped clean and any loose sand or other material removed from the surface of the specimen, which are to be in contact with the compression platens. In the case of cubes, the specimen shall be placed in the machine in such a manner that the load shall be applied to opposite sides of the cubes as cast, that is, not to the top and bottom. The axise of the specimen shall be carefully aligned with the center of thrust of the spherically seated platen. No packing shall be used between the faces of the test specimen and the steel platen of the testing machine. As the spherically seated block is brought to bear on the specimen the movable portion shall be rotated gently by hand so that uniform seating

may be obtained. The load shall be applied without shock and increased continuously at a rate of approximately 140 kg/cm2/min.until the resistance of the specimen to the increasing load breaks down and no grater load can be sustained. The maximum load applied to the specimen shall then be recorded and the appearance of the concrete and any unusual features in the type of failure shall be noted.

 

Fig: Concrete Cylinder and Cubes failure Types

Calculation: The measured compressive strength of the specimen shall be calculated by dividing the maximum load applied to the specimen during the test by the cross sectional area, calculated from the mean dimensions of the section and shall be expressed to the nearest kg per cm2. Average of three values shall be taken as the representative of the batch provided the individual variation is not more than +/-15 percent of the average. Otherwise repeat tests shall be made.

A correction factor according to the height / diameter ratio of specimen after capping shall be obtained from the curve shown in Fig.1 of IS:516-1959. The product of this correction factor and the measured compressive strength shall be known as the corrected compressive strength this being the equivalent strength of a cylinder having a height/diameter ratio of two. The equivalent cube strength of the concrete shall be determined by multiplying the corrected cylinder strength by 5/4.

 

3. DETERMINATION OF FLEXURAL STRENGTH OF CONCRETE.

( IS : 516 – 1959 )

Object: Determination of the flexural strength of concrete specimen.

Apparatus:

a) Standard moulds of size 15 X 15 X 70 cms for preparing the specimen.

b) Tamping bar.

c) Testing Machine.

Procedure:

Test specimens stored in water at a temperature of 250C to 300C for 48 hours before testing shall be tested immediately on removal from the water, whilst they are still in a wet condition. The dimensions of each specimen shall be noted before testing. No preparation of the surface is required.

 

Fig. Placing of Beam For Testing

Placing the specimen in the testing machine: The bearing surfaces of the supporting and loading rollers shall be wiped clean, and any loose sand or other material removed from the surfaces of the specimen where they are to make contact with the rollers. The specimen shall then be placed in the machine in such a manner that the load shall be applied to the upper most surface as cast in the mould, along two lines spaced 20 or 13.30 cms apart. The axis of the specimen shall be carefully aligned with the axis of the loading device. No packing shall be used between the bearing surface of the specimen and the rollers. The load shall be applied with shock and increasing continuously at a rate such that the extreme fiber stress increases at approximately 7 kgs/cm2/mm for the 10 cm

specimens, the load shall be increased until the specimen falls, and the maximum load applied to the specimen during the test shall be recorded. The appearance of the fractured faces of the concrete and any unusual features in the type of failure shall be noted.

 

Fig: Breaking of Concrete Beam

Calculation:

The flexural strength of the specimen shall be expressed as the modules of rapture ‘ fb’ which if ‘a’ equals the distance between the line of fracture and the nearer support measured on the centerline of the tensile side of the specimen, in cm, shall be calculated to the nearest 0.5 kg/cm2 as follows.

 fb = ( p X l ) / ( b X d2 )

 When ‘a’ is greater than 20.0 cm . for 15.0 cm specimen or greater than 13.30 cm for a 10.0 cm specimen, or

fb = ( 3p X a ) / ( b X d2 )

 When ‘a’ is less than 20.0 cms. but greater than 17.0 cms for 15.00 cms specimen, or less than 13.30 cms but greater than 11.0 cms for a 10.0 cms specimen, where b = measured width in cms of the specimen, d = measured depth in cms of the specimen at the point of failure, l = length in cm. of the span on which the specimen was supported, and p = maximum load in kg. applied to the specimen.

If ‘a’ is less than 17.0 cm. for a 15 cm specimen or less than 11.0 cm for a 10.0 cm specimen, the result of the test shall be discarded.