Compressive strength in concrete test
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Transcript of Compressive strength in concrete test
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COMPRESSIVE STRENGTH
CONCRETE IS STRONG IN COMPRESSION AND WEAK IN TENSION
PREPARED BYS.Selvaprakash
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COMPRESSIVE STRENGTH• Compressive strength is the capacity of a
material or structure to withstand axially directed pushing forces.
• When the limit of compressive strength is reached, brittle materials are crushed.
• The compressive strength is used to determine the hardness of cubical and cylindrical specimens of concrete.
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COMPRESSIVE STRENGTH• The strength of concrete specimen depends
upon cement, aggregate, bond, w/c ratio, curing temperature, and size of specimen.
• The cube specimen is of the size 15 x 15 x 15 cm. If the largest nominal size of the aggregate does not exceed 20 mm, 10 cm size cubes may also be used as an alternative.
• Cylindrical test specimens have a length equal to twice the diameter. They are 15 cm in diameter and 30 cm long.
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COMPACTION• compaction of the concrete with neither
segregation nor excessive laitance.• The concrete is filled into the mould in layers
approximately 5 cm deep.Compacting by Hand
• For cubical specimens, in no case should the concrete be subject to less than 35 strokes per layer for 15 cm or 25 strokes per layer for 10 cm cubes.
• For cylindrical specimens, the number of strokes are not less than thirty per layer.
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TEST PROCEDURE
Scope:• The test method covers determination of
compressive strength of cubic concrete specimens.
• It consists of applying a compressive axial load to molded cubes at a rate which is within a prescribed range until failure occurs.
• The compressive strength is calculated by dividing the maximum load attained during the test by the cross sectional area of the specimen.
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APPARATUS
1- Weighing device.2- Tools and containers for mixing.3- Tamper (16mm dia & 600mm height)4- Testing machine.5- Three cubes (150 mm side)
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PROCEDURE
• Prepare a concrete mix with the proportions suggested Such as: 1: 2: 4 with w/c = 0.55 by mechanical mixer.
• Prepare three testing cubes; make sure that they are clean and greased or oiled thinly.
• Metal molds should be sealed to their base plates to prevent loss of water.
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PROCEDURE
• Fill the cubes in three layers, tamping each layer with (35) strokes using a tamper.
• Fill the molds completely, smooth off the tops evenly, and clean up any concrete outside the cubes.
• Leave the specimens in the curing room for 24 hours.
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PROCEDURE
• After that open the molds and immerse the concrete cubes in a water basin for 7 days or 28 days.
• Before testing, ensure that all testing machine bearing surfaces are wiped clean.
• Carefully center the cube on the lower platen and ensure that the load will be applied to two opposite cast faces of the cube.
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PROCEDURE
• Without shock, apply and increase the load continuously at a nominal rate within the range of ( 0.2 N/mm2.s to 0.4 N/mm2.s ) until no greater load can be sustained.
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COMPRESSIVE TEST
BEFORE LOADING AFTER LOADING
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COMPRESSIVE TEST
Compressive strength= (P/A) (N/mm2) Where P =Applied load (N) A=Area of the specimen (mm2)