Splitting tensile strength test of concrete – lab Procedure

Splitting tensile strength is generally greater than the direct tensile strength and lower than the flexural strength (modulus of rupture). Splitting tensile strength is used in the design of structural light weight concrete members to evaluate the shear resistance provided by concrete and to determine the development length of the reinforcement.This test method consists of applying a diametrical force along the length of a cylindrical concrete at a rate that is within a prescribed range until failure.

This loading induces tensile stresses on the plane containing the applied load and relatively high compressive stresses in the area immediately around the applied load. Although we are applying a compressive load but due to Poisson’s effect, tension is produced and the specimen fails in tension. Tensile failure occurs rather than compressive failure because the areas of load application are in a state of triaxial compression, thereby allowing them to withstand much higher compressive stresses than would be indicated by a uniaxial compressive strength test result. Thin, bearing strips are used to distribute the load applied along the length of the cylinder. The maximum load sustained by the specimen is divided by appropriate geometrical factors to obtain the splitting tensile strength.

Objective: To determine splitting tensile strength of cylindrical concrete specimens.

Reference: IS: 5816 – 1999, IS: 1199-1959, SP: 23-1982, IS: 10086-1982.

Apparatus: Cylindrical mould confirming to IS: 10086-1982 for splitting tensile strength,tamping rod, metallic sheet, universal testing machine.

Material: Cement, sand, aggregate and water, grease

Procedure:

1. Sampling of Materials: Samples of aggregates for each batch of concrete shall be of the desired grading and shall be in an air-dried condition. The cement samples, on arrival at the laboratory, shall be thoroughly mixed dry either by hand or in a suitable mixer in such a manner as to ensure the greatest possible blending and uniformity in the material.
2. Proportioning : The proportions of the materials, including water, in concrete mixes used for determining the suitability of the materials available, shall be similar in all respects to those to be employed in the work.
3. Weighing: The quantities of cement, each size of aggregate, and water for each batch shall be determined by weight, to an accuracy of 0.1 percent of the total weight of the batch.
4. Mixing of concrete: The concrete shall be mixed by hand, or preferably, in a laboratory batch mixer, in such a manner as to avoid loss of water or other materials. Each batch of concrete shall be of such a size as to leave about 10 percent excess after moulding the desired number of test specimens.
5. Mould: The cylindrical mould shall be of 150 mm diameter and 300 mm height conforming to IS: 10086-1982.
6. Compacting: The test specimens shall be made as soon as practicable after mixing, and in such a way as to produce full compaction of the concrete with neither segregation nor excessive laitance.
7. Curing: The test specimens shall be stored in a place, free from vibration, in moist air of at least 90 percent relative humidity and at a temperature of 27° ±2°C for 24 hours ± ½ hour from the time of addition of water to the dry ingredients.
8. 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.
9. Two bearings strips of nominal (1/8 in i.e 3.175mm) thick plywood, free of imperfections, approximately (25mm) wide, and of length equal to or slightly longer than that of the specimen should be provided for each specimen.
10. The bearing strips are placed between the specimen and both upper and lower bearing blocks of the testing machine or between the specimen and the supplemental bars or plates.
11. Draw diametric lines an each end of the specimen using a suitable device that will ensure that they are in the same axial plane. Canter one of the plywood strips along the centerof the lower bearing block.
12. Place the specimen on the plywood strip and align so that the lines marked on the ends of the specimen are vertical and centred over the plywood strip.
13. Place a second plywood strip lengthwise on the cylinder, centeredon the lines marked on the ends of the cylinder. Apply the load continuously and without shock, at a constant rate within, the range of 689 to 1380 kPa/min splitting tensile stress until failure of the specimen
14. Record the maximum applied load indicated by the testing machine at failure.

Note the type of failure and appearance of fracture.

Observation

• Length of Specimen (l) : _______ mm
• diameter of the specimen (d) : _______ mm

Results:

• The average 7 days tensile strength of concrete sample is : _______ MPa
• The average 28 days tensile strength of concrete sample is : _______ MPa

Precautions: (Discuss about the precautions to be taken while conducting this experiment)