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Compression Test Compression Test of the Concrete Specimen is most widely used test to measure its compressive strength. Two types of concrete specimen: Cubes for compression test are casted in a steel or cast-iron moulds of prescribed dimensions.
Compaction of each layer is achieved by not less than 35 strokes for mm cubes or 25 strokes for mm cubes. A standard tamping bar of a 25mm square of steel section is used for this purpose.
Compaction by vibration may also be used. After finishing the cube, it should be stored at a temperature of C to C, when the cubes are to be tested at or more than 7 days.
When the test days is less than 7 days the temperature to be maintained is C to C. Also, relative humidity of 90 percent is to be maintained always.
The cube is demoulded just before testing at 24 hours. For greater ages at test, demoulding takes place between 16 to 28 hours after adding water in a concrete mix and the specimens are stored in a curing tank at C to C until the required age.
At the time of testing the specimen is placed in a "Compression Testing Machine" with the position of cubes at right angles to the position of cast.
The load is applied at a constant rate of stress within the range of 0.
Under pure uniaxial compression loading, the failure cracks generated are approximately parallel to the direction of applied load Fig-1 with some cracks formed at an angle to the applied load.
Practically, the compression testing system rather develops a complex system of stresses due to end restraints by steel platens. There exists a differential tendencies of lateral expansion between steel platens and concrete cube faces; as a result of which tangential forces are induced between the end surfaces of the concrete specimen and the adjacent steel platens of the testing machine Fig The degree of platen restraint on the concrete section depends on the friction developed at the concrete-platen interfaces, and on the distance from the end surfaces of the concrete.
Concrete is one of the most widely used building materials in the world, yet people still find it difficult to take samples correctly and manage the testing & certification process. Concrete sample is placed on the lower platen of a compression testing system and carefully aligned with the longitudinal axis. As the axial loading increase, the moment capacity for the concrete will increase as applied axial strains relieve some of the tensile strains resulting from the bending until it reaches the balance point (mob, Nub). The Amerimix Promise. Amerimix offers a full line of preblended mortars, stuccos, core fill grouts and specialty iridis-photo-restoration.com work closely with craftsman to develop innovative products with an unwavering focus on consistency and durability.
As a result, in addition to applied compressive stress, lateral shearing stresses are also effective in the concrete specimen.
As the degree of end restraint depends on the friction at the interfaces, this frictional value can be eliminated by applying grease, graphite or paraffin wax to the bearing surfaces of the specimen.
It helps the specimen to undergo a larger and uniform lateral expansion and eventually splits along its full length. It should be noted that with end restraints in full effect, the compression test yields the higher value of cube strength. When the height of specimen increases with respect to its width, the influence of shear becomes smaller so that the central part of the specimen may fail by lateral splitting; thereby exihibiting the lower compressive strength.
This dependence is known as Specimen Effect. The compressive strength is found to be highest for the cube specimen mm and below.
This is evident from the fact that the probability of occurrence of weak spots is greater when the volume of the concrete is larger for a given stress level to which it is subjected. This is true to some extent because smaller specimen can be better compacted and also exhibit a smaller amount of bleeding, as a result, the concrete would be of better quality, and therefore, stronger.B BACK UP BARS—See GRILLAGE BARS.
BAND—Group of reinforcing bars distributed in a slab or wall or footing. See STRIPS. BANDED TENDONS—Prestressing tendons which are grouped into a narrow “band” 3 to 4 feet wide over the columns. Concrete sample is placed on the lower platen of a compression testing system and carefully aligned with the longitudinal axis.
As the axial loading increase, the moment capacity for the concrete will increase as applied axial strains relieve some of the tensile strains resulting from the bending until it reaches the balance point (mob, Nub).
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General Short All Technical Civil Site Engineer Frequently Asked Questions. Compression Test of the Concrete Specimen is most widely used test to measure its compressive strength. Two types of concrete specimen: Cubes & Cylinders are used for this purpose: Cubes of size mm are more common in Asia, Russia & European countries while Cylinders of mm in diameter & mm high are common in U.S and Australia.
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