Test

TESTING FOR FRESH AND HARDENED CONCRETE

Concrete concrete is a mixture of cement, coarse aggregate (metal or crushed stone) , fine aggregate (sand of size < 4.75mm)and water .The prepared concrete is in semi-liquid stage this is as called fresh concrete or green concrete or plastic concrete.Cement initial setting time – not less than 30 min Cement Final setting time – not more than 10 hours After 28 day concrete fully hardened

Tests on fresh concrete Various tests can be carried out on fresh concrete . All these test are used to determine the workability of concrete . Some important test carried out on fresh concrete are Slump cone test Flow Test and Compaction factor test.

Slump cone test Slump cone test is used to

determine the workability of concrete. This test can be conducted in the field (or) in

laboratory .This test is not suitable for very wet (or) very

dry concrete .APPARATUS Cone is about 20cm@ bottom gradually

reduced to 10cm at top. With a height of 30mm.

Steel tamping rod 16mm dia , 60mm long

Procedure •The vessel is placed on a flat non-absorbent surface • Then specimen is filled with concrete mix in four different layers of equal thickness.•Compact each layer with 25 blows •Then cone is lifted up wards from the concrete immediately

10mm 30mm 20mm

Slump commonly adopted for various concrete mixes Sl.no Type of concrete work Slump adopted in

mm

123

456

Concrete for road workBeam and slabsColumns, retaining walls and thin vertical members etc.Impermeable workVibrated concrete Mass concrete

20 to 3050 to 10075 to 150

75 to 15012 to 2525 to 50

Compaction factor test In the compaction factor test the degree of

workability of concrete is measured in terms of internal energy required to compact the concrete thoroughly .

Apparatus Upper hopperLower hopperCylinder

Procedure involved in compaction factor testA standard amount of concrete is allowed to

fall from a standard height procedureThe concrete sample to be tested is first

placed in the top hopper.The trap door is opened and concrete is

allowed to fall to the lower hopper.Similarly from the lower hopper concrete is

allowed to fall in the cylinder kept below.

•Now the cylinder is weighed and the weight is called as weight of partially compacted concrete .•Now the cylinder is emptied and refilled with concrete by the same sample .it is vibrated heavily and weighted.

Compaction factor=weight of partially compacted concrete weight of fully compacted concrete

Workability compaction factor

corresponding slump

Very lowLowMediumhigh

0.800.850.920.95

0 to 25mm25 to 50mm50 to 100mm100 to 180mm

FLOW TEST The spread or the flow of the concrete is

measured and this flow is related to workability

Procedure The mould is kept on the center of the table and

is filled with concrete in two layer. Each layer is rammed 25 times with a tamping

rod 1.6 cm in dia and 61cm long rounded at lower tamping end.

The mould lifted vertically upward and concrete stands on its own without support.

• The table is then raised and dropped 12.5mm height for 15 times (or)for 15 seconds. The diameter of the spread concrete is measured in about 6 directions to the nearest 5mm and the average spread is noted .

Flow , percent =(spread diameter in cm-25)*100/25

The value could range anything from 0 to 150 percent

Testing for hardened concrete • Compressive strength test.• Flexural strength test.• Split-tension test .

Compressive strength test.The Compression test is used to determine the

hardness of cubical (or) cylindrical specimens of concrete.

The strength of a concrete specimen depends upon concrete , aggregate bond, w/c ratio ,curing temperature ,and age and size of specimen .

procedureThe largest nominal size of the aggregates does

not exceed 20mmEach layer of the concrete is compacted by 25

to 35 blows .Then remolded the concrete after 24 hours.Submerged the specimen in clean water.Then the specimen is tested after 7days and

28days .Normally strength of cylindrical specimen is

taken as 0.8 times of the strength of cubical.Compressive strength= maximum load cross-sectional area of

cube

Flexural strength test The concrete is strong in compression & weak in

tension. Stress develop in concrete due to drying shrinkage.

In this test load is applied.

central .Two-point

central Two-point

LOAD LOAD

L/2 L/2 L/2 L/2 L/2 L L

Size of specimen = 15x15x70cmBeam size = 10x10x50cm

Split- tension test This is an indirect tension test. In this test

cylindrical specimen is placed horizontal.

The load is applied until failure of the cylinder along the vertical diameter .

But a larger portion about 5/6th of the depth is subjected to tension stress.

p compression

cylinder

Quality of concreteIn order to make concrete a quality one there

division are used Engineering division Manufacturing division Piecing division

Engineering division look after all forms reinforcement details

and installation of all embedded parts.

Manufacturing This division takes care of the

control of materials , batching and mixing of concrete.

Placing division This division take care of placing

other subsequent works.Following are the General requirements for

quality of concrete Air bubbles should be completely removed from

the concrete .Compaction of concrete should be minimize the

voids presented in the concrete.A adequate curing for 28 days is done.

To attain high quality of concreteProper ingredientsProper batching & mixingProper transportation Careful placing Adequate curingCareful removal of form work Necessary finishing Admixture

Admixture These are substances other than cement ,

aggregate and water , those are used to modify the properties of concrete .

Admixture are two type Mineral andChemical admixture

Mineral admixtureSilica fume Rice husk ashGround granulated blast furnace slagFly ash

Chemical admixtureAccelerators(decreases the setting time)Retarders(increase the setting time)PlasticizerSuper plasticizerDpc and water proof material

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