WHAT IS CONCRETE ?•Concrete is a composite

material composed of water, coarse granular material (the fine and coarse aggregate or

filler) embedded in a hard matrix of material (the cement or binder) that

fills the space among the aggregate particles

and glues them together.

MEASUREMENT OF WORKABILITY

Workability depends upon –

1.Water content

2.Mix proportions

3.Shape & Size of Aggregates

4.Surface Texture of Aggregates

5.Grading of Aggregates

6.Use of Admixtures

.Workability tests are commonly employed to measure

-1.Slump Test

2.Compacting Factor Test

3.Flow Test

4.Vee Bee ConsistometerTest

5.Kelly Ball Test

TEST OF CONCRETE

CONCRETE SLUMP TEST

Theory and Scope:-The concrete slump test is an empirical test that

measures the workability of fresh concrete.

More specifically, it measures the consistency of the concrete in that specific batch. This test is performed to check the consistency of freshly

made concrete. Consistency is a term very closely related to workability. It is a term which describes

the state of fresh concrete. It refers to the ease with which the concrete flows. It is used to indicate

the degree of wetness. Workability of concrete is mainly affected by consistency i.e. wetter mixes

will be more workable than drier mixes, but concrete of the same consistency may vary in

workability. It is also used to determine consistency between individual batches.

The test is popular due to the simplicity of apparatus used and simple procedure.

Unfortunately, the simplicity of the test often allows a wide variability in the manner that the

test is performed. The slump test is used to ensure uniformity for different batches of similar concrete under field conditions, and to ascertain the effects

of plasticizers on their introduction. In India this test is conducted as per IS specification.

PRINCIPLE OF SLUMP TEST

The slump test result is a slump of the behaviour of a compacted

inverted cone of concrete under the action of gravity. It measures the

consistency or the wetness of concrete.

Apparatus

Metal mould, in the shape of the frustum of a cone, open at both

ends, and provided with the handle, top internal diameter 4 in (102 mm),

and bottom internal diameter 8 in (203 mm) with a height of 1 ft

(305 mm). A 2 ft (610 mm) long bullet nosed metal rod, 5/8 in (16 mm) in

diameter.

Collapse Shear True

In a collapse slump the concrete collapses

completely.

In a shear slump the top portion of the

concrete shears off and slips sideways.

In a true slump the concrete

simply subsides,

keeping more or less to

shape.

The slumped concrete takes various shapes, and according to the profile of slumped concrete, the

slump is termed as true slump, shear slump or collapse slump. If a shear or collapse slump is

achieved, a fresh sample should be taken and the test repeated. A collapse slump is an indication

of too wet a mix. Only a true slump is of any use in the test. A collapse slump will generally mean

that the mix is too wet or that it is a high workability mix, for which slump test is not appropriate.

Very dry mixes; having slump 0 – 25 mm are used in road making, low workability mixes; having

slump 10 – 40 mm are used for foundations with light reinforcement,

INTERPRETATION OF RESULTS

Compaction Factor Test

Aim: To find out the compaction factor for the given fresh mix of concrete.

Theory: Work-ability of concrete is the ability/ease with which concrete can be mixed, transported and placed. This is a major factor which contributes to the other properties of concrete also. If concrete is workable enough then it can be compacted with less compacting effort. So there is a relation between the amount of work required to compact a given fresh concrete and the work-ability of the concrete. This relation is well suited for the concrete of the low water cement ratio. Slump cone test is also used to find out the work-ability of the concrete but only recommended for the concrete of higher work-ability. For less workable concrete(having less water cement ratio), compaction is standardized by various standards.

Apparatus: Compaction factor apparatus/machine, weighing balance, cow/mixing tray.

Let weight of the empty cylinder = W1

Let weight of the cylinder with the partially compacted concrete = W2

Let weight of the fully compacted(Using mechanical vibrator) concrete with cylinder = W3

Compaction Factor = Weight of the partially compacted concrete/ Weight of the fully compacted concrete

i.e., Compaction factor = (W2-W1)/(W3-W1)

Result: The compaction factor of the given fresh concrete mix is .....

(concretNote: Relation between the compaction factor and work-ability is that higher the compaction factor higher is the work-ability. Theoretical maximum value of the compaction factor can be 0.96 to

1.0 packted .

CALCULATIONS

VEE BEE CONSISTOMETER TEST

Vee Bee Consistometer Test: Vee Bee Consistometertest is done on concrete that is either too dry for

slump test or compaction test. It is done to determine the consistency of low slump concrete.

Specifications : The equipment consists of : A Vibrating Table size 380mm long and 260mm wide,

resting upon elastic support at a height of about 305mm above the floor, complete with start/stop

switch, cord and plug. A holder is fixed to the base into which a swivel arm is telescoped with funnel

and guide sleeve. The swivel arm is also detachable from the Vibrating Table. A graduated rod is fixed on a swivel arm and at its end a plastic disc is screwed. The division of scale on the rod record the slump of the concrete in millimeters, supplied complete with a sheet metal container with lifting handles which can easily be fixed to the Vibrating Table. A slump cone open at both ends with lifting handles and a Tamping rod of size 16mm dia and 600mm long,

rounded at one end.

To use a Vee-Bee Consistometer, a conventional slump test is performed. For conducting the test, a slump cone is placed in the inside part of a Vee-Bee Consistometer.

When the mixture is poured, a Glass Disc attached to the swivel arm turns and is placed on top of the concrete in the machine. This triggers an electric vibrator and initiates the stop-

watch as well.Vibration continues till the conical shape of the concrete disappears and the concrete takes a

cylindrical shape.When the mixture assumes a complete cylindrical shape, the stop watch switches off

immediately.This time is recorded to understand the consistency of the mixture, which is generally

expressed in VB Degrees, which is equal to the time recorded in seconds.

USING A VEE-BEE CONSISTOMETER

FLOW TEST The flow table test or flow test is a method to

determine the consistence of fresh concrete.

Application When fresh concrete is delivered to a site by a truck mixer it is sometimes necessary to check its

consistence before pouring it into formwork.

If the consistence is not correct, the concrete will not have the desired qualities once it has set, particularly

the desired strength. If the concrete is too pasty, it may result in cavities within the concrete which leads

to corrosion of the rebar, eventually leading to the formation of cracks (as the rebar expands as it

corrodes) which will accelerate the whole process, rather like insufficient concrete cover. Cavities will

also lower the stress the concrete is able to support.

EquipmentFlow table with a grip and a hinge, 70 centimetres (28 in) square.

Abrams cone, open at the top and at the bottom - 30 centimetres (12 in) high, 17 centimetres(6.7 in) top diameter, 25 centimetres (9.8 in) base diameter.

Water bucket and broom for wetting the flow table.Tamping rod, 60 centimetres (24 in) long

CALCULATION

The flow of the concrete is the percentage increase in diameter of spread concrete over the base diameter of the moulded concrete, calculated from the following

formula.

REPORT

The flow measured is to be reported in terms of percentage.

SAFETY & PRECAUTIONS

Use hand gloves, shoes at the time of test.

Keep the mould & flow table clean, dry & free from sticking concrete.

Keep the vertical shaft lubricated with light oil.

Keep the contact faces of the flow table top & supporting frame oiled.

Keep the hand wheel, the adjustable shaft & universal joint.

KELLY BALL TEST General description

This method is used to determine the penetration of a

hemispherical metal weight into freshly mixed concrete, which is related to the workability of the

concrete.The apparatus consists of a

cylinder with one end having a hemispherical shape and the

other end fit with a graduated handle. The weight assembly is

lowered through a frame into the concrete and the penetration

measured. Weight approx.: 15 kg

Rebound hammer test is done to find out the compressive strength of concrete by using rebound hammer as per IS: 13311 (Part 2) – 1992. The

underlying principle of the rebound hammer test isThe rebound of an elastic mass depends on the hardness of the surface

against which its mass strikes. When the plunger of the rebound hammer is pressed against the surface of the concrete, the pring-controlled mass

rebounds and the extent of such a rebound depends upon the surface hardness of the concrete. The surface hardness and therefore the rebound

is taken to be related to the compressive strength of the concrete. The rebound value is read from a graduated scale and is designated as the

rebound number or rebound index. The compressive strength can be read directly from the graph provided on the body of the hammer.

REBOUND HAMMER

PROCEDURE TO DETERMINE STRENGTH OF

HARDENED CONCRETE BY REBOUND HAMMER

i) Before commencement of a test, the rebound hammer should be tested against the test anvil, to get reliable results, for which the

manufacturer of the rebound hammer indicates the range of readings on the anvil suitable for

different types of rebound hammer.ii) Apply light pressure on the plunger – it will release it from the locked position and allow it

to extend to the ready position for the test.iii) Press the plunger against the surface of the

concrete, keeping the instrument perpendicular to the test surface. Apply a

gradual increase in pressure until the hammer impacts. (Do not touch the button while

depressing the plunger. Press the button after impact, in case it is not convenient to note the

rebound reading in that position.)iv) Take the average of about 15 readings.

The rebound reading on the indicator scale has been calibrated by the

manufacturer of the rebound hammer for horizontal impact, that is, on a vertical

surface, to indicate the compressive strength. When used in any other

position, appropriate correction as given by the manufacturer is to be taken into

account.

INTERPRETATION OF RESULT

This test is done to assess the quality of concrete by ultrasonic pulse velocity

method as per IS: 13311 (Part 1) – 1992. The underlying principle of this test is -The method consists of measuring the

time of travel of an ultrasonic pulse passing through the concrete being

tested. Comparatively higher velocity is obtained when concrete quality is good

in terms of density, uniformity, homogeneity etc

ULTRASONIC PULSE VELOCITY

i) Preparing for use: Before switching on the ‘V’ meter, the transducers should be connected to the sockets marked “TRAN” and ” REC”.

The ‘V’ meter may be operated with either:a) the internal battery,

b) an external battery orc) the A.C line.

ii) Set reference: A reference bar is provided to check the instrument zero. The pulse time for the bar is engraved on it. Apply a smear of grease to the transducer faces before placing it on

the opposite ends of the bar. Adjust the ‘SET REF’ control until the reference bar transit time is obtained on the instrument read-out.

iii) Range selection: For maximum accuracy, it is recommended that the 0.1 microsecond range be selected for path length upto 400mm.

iv) Pulse velocity: Having determined the most suitable test points on the material to be tested, make careful measurement of the path length ‘L’. Apply couplant to the surfaces of the

transducers and press it hard onto the surface of the material. Do not move the transducers while a reading is being taken, as this can generate noise signals and errors in measurements. Continue holding the transducers onto the surface of the material until a consistent reading

appears on the display, which is the time in microsecond for the ultrasonic pulse to travel the distance ‘L’. The mean value of the display readings should be taken when the units digit hunts

between two values

.

PROCEDURE TO DETERMINE STRENGTH OF HARDENED CONCRETE BY ULTRASONIC PULSE VELOCITY.

Pulse velocity=(Path length/Travel time)v) Separation of transducer leads: It is advisable to prevent the two transducer leads from coming into close contact with each other when the transit time measurements are being taken. If

this is not done, the receiver lead might pick-up unwanted signals from the transmitter lead and this would result in an

incorrect display of the transit time.

The quality of concrete in terms of uniformity, incidence or absence of

internal flaws, cracks and segregation, etc,indicative of the level of workmanship employed, can thus be assessed using the guidelines given below, which have been evolved for characterizing the quality of

concrete in structures in terms of the ultrasonic pulse velocity.

INTERPRETATION OF RESULTS

CASE STUDY

Collapse of a reinforced concrete structure,

This factory building included concrete columns and asteel truss for the roof.

• Two people were killed• Design error. No consideration was given in the

calculations of how forces were transmitted through the

joint between the edge beam and column.• Detailing error. Inadequate connection between

beamand column reinforcement.

• Construction error. Column links were excluded forconvenience

SUMMARY

Civil A2Santu DeySurajit MondalSatyajit RoySupriyo SarkarSantunu MondalSumangal Kundu

THE END