The tensile strength of concrete is one of the basic and important properties. Splitting tensile strength test on concrete cylinder is a method to determine the tensile strength of concrete.
The concrete is very weak in tension due to its brittle nature and is not expected to resist the direct tension. The concrete develops cracks when subjected to tensile forces. Thus, it is necessary to determine the tensile strength of concrete to determine the load at which the concrete members may crack.
To determine the splitting tensile of concrete.
Equipment for Splitting Tensile Test of Concrete:
Compression testing machine, two packing strips of plywood 30 cm long and 12mm wide.
Sampling of Concrete Cylinders:
The cylinder mould shall is of metal ,3mm thick. Each mould is capable of being opened longitudinally to facilitate the removal of the specimen and is provided with a means of keeping it closed while in use. The mean internal diameter of the mould is 15 cm ± 0.2 mm and the height is 30 +/- 0.1 cm. Each mould is provided with a metal base plate mould and base plate should be coated with a thin film of mould oil before use, in order to prevent adhesion of concrete.
The tamping bar is a steel bar of 16 mm diameter , 60 cm long and bullet pointed at the lower end.
Compacting of Concrete
The test specimen should be made as soon as practicable after the concrete is filled into the mould in layers approximately 5 cm deep. Each layer is compacted either by hand or by vibration.
Compacting by Hand
When compacting by hand, the standard tamping bar is used and the stroke of the bar should be distributed in a uniform manner. The number of strokes for each layer should not less than 30. The stroke should penetrate in to the underlying layer and the bottom layer should be rodded throughout its depth. After top layer has been compacted,the surface of the concrete should be finished level with the top of the mould,using a trowel and covered with a glass or metal plate to prevent evaporation.
Curing of Specimen:
The test specimen should be stored in a place at a temperature of 27° +/- 2°C for 24 +/- 0.5 hrs. from the time addition of water to the dry ingredients. After this period the specimen should be marked and removed from the woulds and immediately submerged in clean fresh water or saturated lime solution and kept there until taken out just prior to the test. The water or solution in witch the specimen s are kept should be renewed every seven days and should be maintained at a temperature of 27° +/- 2°c.
Concrete cylinder 15 cm diameter &3 0cm long.
Cast 6 cylinders (3 for split test &3 for compression test ).
Procedure of Splitting Tensile Test:
- Take the wet specimen from water after 7 days of curing
- Wipe out water from the surface of specimen
- Draw diametrical lines on the two ends of the specimen to ensure that they are on the same axial place.
- Note the weight and dimension of the specimen.
- Set the compression testing machine for the required range.
- Keep are plywood strip on the lower plate and place the specimen.
- Align the specimen so that the lines marked on the ends are vertical and centered over the bottom plate.
- Place the other plywood strip above the specimen.
- Bring down the upper plate to touch the plywood strip.
- Apply the load continuously without shock at a rate of approximately 14-21kg/cm2/minute (Which corresponds to a total load of 9900kg/minute to 14850kg/minute)
- Note down the breaking load(P)
As per IS456, split tensile strength of concrete.= 0.7Fck
The splitting tensile strength is calculated using the formula
Tsp = 2P/ pi DL
Where P = applied load
D = diameter of the specimen
L = length of the specimen
There fore P = Tsp x pi DL/2
Expected load = P x f.s
Range to be selected is…………..
SPLIT TENSILE STRENGTH
T = 2P/ pi DL
(I) Date of test
(II) Identification mark and size of the specimen
(III) Age of test specimen and date of test
(IV) Curing history,as detailed earlier
(V) Weight of specimen in kg .
(VI) Type of fracture face,if they are unusual.
Splitting tensile strength of given concrete =……………….N/mm²