1. MIX DESIGN PROCEDURE

AIM:

To design a concrete mix of M40 grade, in accordance with IS 10262- 1982.

DESIGN STIPULATIONS:

a) Characteristic compressive strength required in field at 28 days - 40N/mm b) Maximum size of aggregate - 20mmc) Degree of workability

- 0.9(compaction factor)

d) Degree of quality control

- good

e) Type of exposure

- mild

1.1. SPECIFIC GRAVITY OF CEMENT TEST:

AIM:

To determine the specific gravity of the cement using IS 2720-1980 (part- III).

APPARATUS:

Le Chaterliers flask.

Weighing balance.Kerosene.

PROCEDURES:

Dry the flask carefully and fill with kerosene or naphtha to a point on the stem between zero and 1 ml. Record the level of the liquid in the flask as initial reading. Put a weighted quantity of cement (about 60 gm) into the flask so that level of kerosene rise to about 22 ml mark, care being taken to avoid splashing and to see that cement does not adhere to the sides of the above the liquid.

iv) After putting all the cement to the flask, roll the flask gently in an inclined position to expel air until no further air bubble rises to the surface of the liquid.

v) Note down the new liquid level as final reading.

CALCULATION:

Specific Gravity = (w2-w1)/ [(w2-w1) x (w3-w4) x0.79]

W1 = weight of empty flask

W2 = weight of empty flask + cement

W3 = weight of empty flask + cement + kerosene

W4 =weight of empty flask +kerosene

0.71 = specific gravity of kerosene

RESULT: Specific gravity of cement = 3.15g/cc.

1.2. SPECIFIC GRAVITY AND WATER ABSORPTION TEST- COARSE

AGGREGATE

AIM:

From IS 2386 (Part-III)-1963, the specific gravity and water absorption of coarse aggregate can be determined. APPARATUS USED:

Weighing Balance (capacity not less than 3 kg),

Oven (to maintain temperature of 100 to 110C),

Wire basket (not more than 6.3mm mesh),

Absorbent cloth.

PROCEDURE:

The sample shall be thoroughly washed to remove fine particles and dust, drained and then placed in wire basket and immersed in distilled water at a temperature between 22 to 32, with a cover of at least 5 cm above the top. The basket shall be jolted 25 times to remove the entrapped air and kept immersed in water for a period of 241/2 hours. The basket and the sample shall be weighed in water at a temperature of 22 to 32. The basket and aggregate are taken out from water, after which the aggregates are emptied on a dry cloth. The empty bucker shall be returned to water and weighed in water. The aggregates are surface dried with two dry absorbent cloths and weighed (B). The aggregate shall then be placed I a shallow tray in over at a temperature of 100 to 110 for 241/2 hours. It shall then be removed from oven and weighed after cooling (weight C).FORMULA USED:

a) Specific gravity =

b) Water absorption= x 100(% of dry weight)

Where,

A= Submerged weight in grams.

B= Saturated surface dry weight

C= Oven dried aggregate in air

OBSERVATION:

Submerged weight of bucket + coarse aggregate

=2660 gSubmerged weight of bucket

=899 gSubmerged weight of coarse aggregate(A)

=1761 gSaturated weight of coarse aggregate (B)

=2870 gWeight of oven dried aggregate (C)

=2800 gi. Specific gravity of coarse aggregate=

=

=2.52

ii. Water absorption of coarse aggregate=

=x 100

=2.5 %

CONCLUSION:

Specific gravity of aggregate lies between 2.4-2.8. We obtained the specific gravity of coarse aggregate as 2.52. And also water absorption is obtained as 2.5% which is in the specified limit. It shows that the aggregate can be used in concrete.

1.3. SPECIFIC GRAVITY AND WATER ABSORPTION TEST- FINE

AGGREGATEAIM:

Specific gravity of fine aggregate (particle size less than 10mm) and water absorption test can be determined by following method which is described in IS-2386 (Part III)-1963. APPARATUS USED:

Balance (capacity not less than 3 kg),

Oven (to maintain temperature of 100 to 110C),

Vessel (Pycnometer).

PROCEDURE:

500 g of sample shall be place in a tray and keep covered in water of 24 hours. The water is drained and the saturated and surface dry sand is weighed (A).The aggregate shall then be placed in pycnometer and weighed (B). All the contents in the pycnometeis then emptied in a tray and the pycnometer is filled with distilled water and weighed (C). The sample in the tray is then drained carefully and dried in over at a temperature of 110 for 24 hours. And weighed (D).

Observation:

Weight of bottle

=0.671 g

Weight of bottle+sand

=1.12 g

A- Weight in g of saturated surface dry sample=(1.129-0.671)=0.458 g

B- Weight in g of pycnometer on gas jar containing sample and filled with distilled water

=1.87

C- Weight in g of pycnometer or gas jar filled with distilled water only = 1.597

D- Weight in g of oven dried sample

= 0.449 g

FORMULA USED:

Specific gravity

= QUOTE

QUOTE

Apparent specific gravity

=

Water absorption (% of dry weight)=

SPECIFIC GRAVITY:

=

=

= 2.43

APPARENT SPECIFIC GRAVITY:

=

=

=2.55

WATER ABSORPTION (% OF DRY WEIGHT):

=

=

=2%CONCLUSION:

Specific gravity of aggregate lies between 2.4-2.8. We obtained the specific gravity of sand as 2.44. And also the water absorption is obtained as 2% which is in the specified limit. It shows that the aggregate can be used in concrete. 1.4. SIEVE ANALYSIS FINENESS MODULUS OF FINE AGGREGATEAIM:

The sieve analysis test is used to determine the particle size distribution and fineness modulus of aggregates. APPARATUS USED:

According to IS-2386(Part-I)-1963, the following set of sieves are used for the test 4.75mm, 2.36mm, 1.18mm, 600 micron, 300 micron, 150micron, 90 micron. And sieve shaker.

PROCEDURE:

The sieves are arranged accordingly, pan is kept at the bottom and the 1kg of sample is poured in to the set of sieves. By using sieve shaker the full set of sieve is shaken and the weight retained in each sieve is noted and tabulated. From this observation the fineness modulus of the specimen is calculated.

Table-1: Fineness modulus of Sand

S.NOIS SIEVE SIZE (mm)WEIGHT RETAINEDCUMULATIVE

WEIGHT

RETAINEDCUMULATIVE

% RETAINED% FINER

14.75727.27.292.8

22.36929.216.483.6

31.1819019.035.464.6

4600 micron25525.560.939.1

5300 micron31531.592.47.6

6150 micron636.398.41.3

790 micron50.599.20.8

8Pan50.599.70.3

CONCLUSION:

From the test result, it is observe that the sample is comes under Grading Zone III as per IS 383-1970. This can be used for the Mix design of concrete.TEST DATA FROM MATERIALS:DESIGN STIPULATIONS:

Characteristic compressive strength required in field at 28 days - 40N/mm2 Maximum size of aggregate- 20mm

Degree of workability

- 0.90 (compaction factor)

Degree of quality control- good

Type of exposure

- mild

TEST DATA FROM MATERIALS:

a) Specific gravity of cement

- 3.15

b) Specific gravity of

i. Coarse aggregate

- 2.50

ii. Fine aggregate

- 2.00

c) Water absorption

i. Coarse aggregate

- 2.5percent

ii. Fine aggregate

- 2.0 percent

d) Free surface moisture

i. Coarse aggregate

- nill

ii. Fine aggregate

- 2.0percent CALCULATIONS (according to IS 10262-1982):

1. TARGET MEAN STRENGTH OF CONCRETE:

= 40 + 1.65 X6.6

= 51 N/mm2. SELECTION OF WATER-CEMENT RATIO:

= 0.30

3. DETERMINATION OF CEMENT CONTENT:

Water

=180 l/m

4. DETERMINATION OF WATER CONTENT:

= 0.30

C = 180/0.30

= 600 kg/m

5. DETERMINATION OF AGGREGATES:

Sand as percentage of total aggregate

By absolute volume=25%

CORRECTION:

Decrease in W/C (0.6-0.3)= .30

% of fine aggregate

=25-3.50

=21.50%

Air entrapped

=2%

Required water content = [ 180 + X 3 ]

= 185.40 l/mDETERMINATION OF CEMENT CONTENT :

Water cement ratio = 0.30 Water

= 185.4 l/m

Cement =185.4/0.30

=618 Kg/m3i. DETERMINATION OF FINE AGGREGATE:

V= [ W + + . ] X 0.98 = [ 185.40 + + . ] X = 321.64 kg/m

ii. DETERMINATION OF COARSE AGGREGATE:V= [ W + + . ] X 0.98 = [ 185.4 + + . ] X = 1174 kg/m

6. MIX PROPORTION:

WATERCEMENT(Kg)FINE AGGREGATE(Kg)COARSE AGGREGATE(Kg)

185.406183211174

0.3010.521.90

CONCLUSION:

This design methodology paved the way for adopting required materials in the ratio 1:0.52:1.90. The various tests on fresh mortar and hardened concrete are discussed in the following chapter.

2. FRESH CONCRETE PROPERTIES2.1 SLUMP CONE TEST ON CONCRETE

AIM:

To find the workability of the designed concrete mix using slump cone test, using IS 1199-1959.APPARATUS:

1. Metallic mould in the form of a frustum of a cone with the following inner dimensions.

Bottom diameter = 20cm

Top diameter = 10cm

Height = 30cm

2. Tamping rod.PROCEDURE:

Prepare the representative Samples for the Workability test for Concrete.

Dampen inside of cone and place it on a smooth, moist, non-absorbent, level surface large enough to accommodate both the slumped concrete and the slump cone. Stand or, foot pieces throughout the test procedure to hold the cone firmly in place.

Fill cone 1/3 full by volume and rod 25 times with 5/8-inch diameter x 24-inch-long hemispherical tip steel tamping rod. (This is a specification requirement which will produce nonstandard results unless followed exactly.) Distribute rodding evenly over the entire cross section of the sample.

Fill cone 2/3full by volume. Rod this layer 25 times with rod penetrating into, but not through first layer. Distribute rodding evenly over the entire cross section of the layer.

Fill cone to overflowing. Rod this layer 25 times with rod penetrating into but not through, second layer. Distribute rodding evenly over the entire cross section of this layer.

Remove the excess concrete from the top of the cone, using tamping rod as a screed. Clean overflow from base of cone.

Immediately lift cone vertically with slow, even motion. Do not jar the concrete or tilt the cone during this process. Invert the withdrawn cone, and place next to, but not touching the slumped concrete. (Perform in 5-10 seconds with no lateral or torsional motion.)

Lay a straight edge across the top of the slump cone. Measure the amount of slump in inches from the bottom of the straight edge to the top of the slumped concrete at a point over the original center of the base. The slump operation shall be completed in a maximum elapsed time of 2 1/2 minutes. Discard concrete. DO NOT use in any other tests

TABLE 2: Showing variations of slump values by adding waterSL.NOWATER CEMENT(%)SLUMP VALUEINITIAL HEIGHT(mm)FINAL HEIGHT

(mm)

10.4010300290

20.4525300275

30.5075300225

40.5590300210

Graph 1 : Showing Variations water cement ratio versus Slump value

Fig- 2 a: slump cone test

OBSERVATIONS FROM SLUMP VALUES:

S.NoSlump values(cm)Degree of workabilityUse for which concrete is used

1150Very highFlow table test is more suitable

CONCLUSION:

For a slump value of 75mm, the workability is medium and hence it can be used for manually compacted flat slabs. For all other values >150mm, the workability is very high for which flow table is more suitable.

2.2 COMPACTION FACTOR TEST

AIM:

To find the workability of the concrete using compaction factor test, according to IS 1199-1950.APPARATUS REQUIRED:1. Top hopper:

Top internal diameter = 25.4cm

Bottom internal diameter = 12.7cm

Internal height = 27.9cm

2. Lower hopper:

Top internal diameter = 22.9cm

Bottom internal diameter = 12.7cm

Internal height = 22.9cm

3. Cylinder:

Internal diameter = 15.2cm

Internal height = 30.5cm

Distance between bottom of top hopper and top of lower hopper = 20.3cm

Distance between bottom of lower hopper and top of cylinder = 20.3cmFORMULA: Compaction factor = Weight of partially compacted concrete Weight of fully compacted concretePROCEDURE:A Sample of concrete to be tested is placed on the upper hopper up to the prism. The trap door is opened so that the concrete falls into the lower hopper. The trap door of the lower hopper is opened and the concrete is allowed to fall into the cylinder.The excess concrete remaining above the top level of cylinder is then cut off with the help of plane blades supplied with the apparatus. The outside of the cylinder is wiped clean and is weighed to the nearest 10grams.Thin weight is known as the weight of the partially compacted concrete.

The cylinder in the emptied and again refilled with the concrete from the same sample in layers of approximately 5cm deep. The layers are heavily rammed or preferably vibrated so as to obtain full compaction.

The top level is struck off carefully and is weighed to the nearest 10grams.This weight is known as the weight of the fully compacted concrete.

CALCULATION:

Volume of the cylinder=x

=0.01059 + 20% extra

=0.0127m

Cement content

=volume of cube x weight of cement

=0.0127 x 415

=5.2705 kg

Fine aggregate content=volume of cube x weight of fine aggregate

=0.0127 x 550

=6.985 kg

Coarse aggregate content=volume of cube x weight of coarse aggregate

=0.0127 x 1153.6

=14.65 kg

The volume of the cylinder is found to be 0.01059 cm

And 20% concrete for wastage is found to be 0.0211 cm

Total volume of concrete needed is 0.01247 cm

The volume of cement needed is

=5.175 kg

The volume of fine aggregate needed is

=6.86 kg

The volume of coarse aggregate needed is =14.38 kg

fig-2 b: Compaction factor testTable 3: Showing compaction factor for various water-cement ratioS.NOW/C RATIOWATER ADDEDHEIGHT OF PARTIALLY COMPACTED CONCRETE (kg) W1WEIGHT OF FULLY COMPACTED CONCRETE

(kg) W2COMPACTION FACTOR

W1/W2

1.0.417789.5311.420.84

2.0.45200010.06311.830.85

3.0.5222211.5312.480.924

4.0.55244412.2912.780.962

5.0.60266711.9313.020.926

GRAPH-2: Compaction factor corresponding to water-cement ratios:

INFERENCE:

Degree of workabilityCompaction factorUse of which concrete is suitable

Small apparatus

large apparatus

Very low 0.78 0.8Roads vibrated by power machines. At the more workable end, concrete may be compacted by hand machines

Low 0.85 0.87Roads vibrated by hand operated machines at the more workable end, concrete may be manually compacted using rounded aggregates. Mass concrete foundation without vibration

Medium

0.92 0.935At less workable end manually compacted flat slabs using crushed aggregates, normally compacted concrete is manually compacted

High 0.95 0.96For sections with congested reinforcement. Not normally suitable for vibration. For pumping and termie placing.

CONCLUSION:

It is observed that as the value of water-cement ration increase, the compaction factor also increases and hence the workability. For a compaction factor of 0.91,the concrete can be used for manually compacted flat slabs and for values 0.84,0.85,0.92, they are used for sections with congested reinforcement.

2.3 VEE-BEE CONSISTOMETER METHOD

AIM:

To determine consistency of concrete using Vee-bee consistometer, according to IS 1199-1959.PROCEDURE:A conventional slump test is performed, placing the slump cone inside the cylindrical part of the consistometer. The glass disc attached to the swivel arm is turned and placed on the top of the concrete in the pot. The electrical vibrator is switched on and a stop-watch is started, simultaneously. Vibration is continued till the conical shape of the concrete disappears and the concrete assumes a cylindrical shape. When the concrete fully assumes a cylindrical shape, the stop-watch is switched off immediately. The time is noted. The consistency of the concrete should be expressed in VB-degrees, which is equal to the time in seconds recorded above. A = Cylindrical pot

B = Sheet metal coneC = Glass discD = Swivel armE = Glass disc with adjustable screw

F = Adjustable screw

Fig-2.c: vee-bee consistometer testTABLE-4 : Table showing observation on vee-bee consistometer.

S.NOW/C RATIOVEE-BEE DEGREE (sec)

10.4040

20.4533

30.5012

40.557

GRAPH-3 : Graph showing vee-bee degree corresponding to water cement ratio

INFERENCE:

Tabel-1 shows the vee-bee consistometer readings corresponding to the various water-cement ratio of 0.4, 0.45, 0.5, 0.55. Graph-1 shows the vee-bee degrees corresponding to the water-cement ratio mentioned above.

CONCLUSION:

There is a considerable decrease in vee-bee with increase in water cement ratio from 0.40 to 0.45. Then we found a drastic decrease in vee-bee degrees with a increase in water-cement ratio from 0.45 to 0.50. Again there is a small decrease in vee-bee degree as water-cement ratio increases from 0.50-0.55.

2.4 INFULENCE OF SUPER PLASTICIZER IN THE WORKABLITY OF CONCRETE

AIM:

To study the influence of super plasticizer in the workability of concrete.

APPARATUS REQUIRED:

Slump cone,

Weighing balance,

Conplast sp 430 super plasticizer,

Measuring jar.

PROCEDURE:

Accordance with the provisions of IS 456 the chemical admixtures is used in concrete.The nominal design mix of M30 grade concrete is prepared for slump cone test to find the workability of concrete using super plasticizer.In addition with this 0.2% of chemical admixtures named conplast 240 is added for every trail.The workability of the concrete is obtained by adding super plasticizer to find the slump value.

OBSERVATION :

Table - 5: Showing Influence of Super plasticizer In Fresh concrete

SL.NO% OF SUPERPLASTICIZER IN CONCRETESLUMP VALUE

10.252

20.465

30.671

40.884

GRAPH-4: Showing variations between superplasticizer versus Slump value

CONCLUSION:

The influence of the super plasticizer to find the workability of concrete is obtained in 0.6 percentage.Hence Suplasticizer increases the workability in fresh concrete decreases the adding of water in the concrete Which helps in Site condition`by increasing his workability of concrete by adding Super Plasticizer.3. HARDENED CONCRETE PROPERTIES

The hardened concrete after curing is tested for its strength using Universal Testing Machine. The tests conducted are as follows:

3.1. COMPRESSIVE STRENGTH:

AIM:

The compressive strength of the concrete can be determine as per

IS-516-1959 by using the compression testing machine.

APPARATUS USED:

Universal testing machine (UTM),

Cube mould (15mmX15mmX15mm).

FORMULA USED:

Concrete cube compression strength = Ultimate load

Cross- sectional area

PROCEDURE:

The dimensions of the concrete cube are measured accurately.The concrete cube is then weighed to the nearest whole number. The cube is placed on the testing machine and load is applied gradually. The ultimate load before the failure of the specimen is note.TABLE-6 :OBSERVATION OF LOAD TESTING MACHINE SL.NO

EMPTY

WEIGHT

(kg)

DATE OF CASTINGDATE OF TESTINGULTIMATE

LOAD(T)COMPRESSIVE

STRENGTH

(N/MM2)AGE IN DAYS

18.315/10/1212/11/121004044.6228

28.315/10/1212/11/12997044.3128

Average =44.4 CALCULATION: Compressive strength = Ultimate load

Cross-sectional area

1004*103 =

22500

= 44.62 N/mm2CONCLUSION:

The mix is designed for M40 grade concrete. The average compressive strength of the cube is 44.47 N/mm2.Hence the designed mix is safe.4.SPLIT TENSILE STRENGTH TEST:

AIM:

The tensile strength is obtained by the direct uniaxial tensile test. Concrete is in weak in tension so It will take only lesser amount of tensile load. APPARATUS USED:

Universal testing machine (UTM),

Cylinder mould (150mm diameter, 300mm height)

Frame (to keep specimen in position)

PROCEDURE:

Dimensions of concrete cylinder are measured. The weight of the cylinder is measured and tabulated. The concrete cylinder is placed on compression testing machine horizontally. Pads are placed both top and bottom for the application of load uniformly. The ultimate load was observed before the failure of the specimen

FORMULA :

Split tensile Strength=

Where,

P Maximum load in N

l Breadth of specimen in mm

d Depth of specimen in mm

Table-7: Split tensile Strength Test ObservationsSL.NOWEIGHT(kg)ULTIMATE

LOAD (T)SPLIT TENSILE STRENGTH(N/mm2)

1 13 1667.7 2.36

CONCLUSION:

Split tensile strength of the concrete from the test is given as 2.36 N/mm2. It is observed that the split tensile strength of the prepared mix design within the required limit. Hence the design mix can be used for making concrete for M40 grade concrete.5. YOUNGS MODULUS OF CONCRETE

AIM:

To determine the youngs modulus of the concrete using the stress and strain of the same.APPARATUS REQUIRED:

UTM

Strain gauge

Cylindrical cube of concrete with 28 days desired strength

PROCEDURE:Dimension of the concrete cylinder are measured. The weight of the specimen is also determined. The compressometer is attached to the specimen and the initial reading is made to read zero. The entire setup is placed vertically in the compression testing machine. The load is applied gradually. The compressometer reading for every incremental load is taken and tabulated. The stress strain curve is drawn and from the graph, the youngs modulus is calculated.

CALCULATION:Youngs modulus of the concrete is determined by the following formula:

E = =

Area of specimen = 1763 mm2TABLE -8 : Youngs modulus of concrete for the M40 grade of concrete:S. NOLOAD

(kN)STRESS

= (N/COMPRESSOMETER READINGDEFLECTION

L X 10-4 (mm)STRAIN

e= X 10-5

119.621.110242.353

229.431.666363.529

339.242.2218169.412

449.052.776122414.117

558.863.331142816.471

668.673.886193822.353

778.484.441244828.235

888.294.997285632.942

998.105.552326437.647

10107.916.107387644.706

11117.726.662428449.412

12127.537.211469254.118

13137.347.7725210461.177

14147.158.3285611265.882

GRAPH- 5 : Youngs modulus of concrete for the M40 grade of concrete:

CONCLUSION:

Thus the young modulus of the concrete, tested using a concrete cylinder has been found out to be 0.215 x105. The graph has been plotted to show the stress-strain behaviour of the concrete which shows a uniform variation till the noted value, above which it shows no deflection, pointing out that it has reached its yielding point.6.BOND STRENGTH BETWEEN STEEL AND CONCRETE

AIM:To find bond strength between steel and concrete using pull out test according to IS 2770(part I).APPARATUS REQUIRED:

Pull out test specimen of desired grade of concrete

UTM

PROCEDURE:

Pull out test apparatus has to be fixed in the UTM. The pull out test specimen is to be fixed in the apparatus and the rod is to be fixed to the bottom of the UTM. As the load is applied the pull out apparatus is to be lifted as tension develops in the rod. This causes the pull in the concrete and the rod try to come out of the concrete. The maximum load at which the steel comes out of the concrete denotes the bond strength of the concrete. Sometimes steel fails first, as it denotes there is an excellent bond strength between steel and concrete.

OBSERVATION:

Table - 9: load vs deflection valuesS.NOLOAD (KN)free end sliploaded end slip

divisionDeflection (mm)divisionDeflection (mm)

150000

280000

3100000

415000.020.005

520000.680.17

62220.0051.40.35

7234.80.0121.80.45

8249.60.0242.080.52

92513.20.0332.40.6

1026180.0452.640.66

112722.40.0562.880.72

122827.20.0683.160.79

132930.80.0773.40.85

143034.40.0863.660.915

153137.20.0933.920.98

163241.20.1034.21.05

173344.40.1114.441.11

1834480.124.61.15

193550.40.1264.881.22

203652.80.1325.161.29

213757.20.1435.481.37

223859.20.1485.681.42

2339640.165.81.45

244066.40.1666.041.51

254168.80.1726.241.56

264273.60.1846.641.66

2743760.196.641.66

284478.40.1966.841.71

294583.20.2087.121.78

304684.80.2127.281.82

314789.60.2247.441.86

324892.80.2327.81.95

334997.60.2447.961.99

34501020.2558.162.04

3551105.60.2648.362.09

3652110.80.2778.482.12

37531160.298.762.19

3854122.40.3069.162.29

3955128.80.3229.282.32

4056135.20.3389.562.39

4157142.40.3569.762.44

4258148.80.3729.962.49

43591560.3910.242.56

4460162.40.40610.362.59

4561169.60.42410.62.65

46621760.4410.82.7

4763183.20.458112.75

4864190.40.47611.22.8

4965198.40.49611.442.86

5066207.20.51811.722.93

51672160.5411.962.99

5268225.60.56412.163.04

5369233.60.58412.443.11

5470240.80.60212.643.16

5571288.80.72212.963.24

5672297.60.74413.163.29

5773304.80.76213.43.35

58743120.7813.63.4

59753200.813.83.45

6076330.40.82614.083.52

61773400.8514.283.57

62783520.8814.643.66

63793600.914.83.7

6480369.60.92415.243.81

65813800.9515.443.86

66823920.9815.643.91

ULTIMATE LOAD = 83.3KN CALCULATION:

FREE END:

Load corresponding to 0.025mm=24.1 KN

LOADED END:

Load corresponding to 0.25 mm=21 KN

Bond strength

=P/A

=

=3.83 GRAPH 6.1: Behaviour of load vs free end slip

GRAPH 6.2: behviour of load vs loaded end slip:

RESULT:

Bond strength of concrete is found to be =3.83 INFERENCE:

As per clause 26.2.1.1 of IS 456, the design bond stress for grade of concrete is found to be 1.5 for plan bars under tension. Incase of deformed bars under, IS 1786 the above value can be increased to 60%.1.5x +1.5=2.4N/a) The value obtained theoretically was found to be =2.4b) The value obtained experimentally was found to be=3.83As the experiment value is more than the theoretical value, it is clearly known that there is a perfect bond stress between steel and concrete. Hence the design grade of concrete can be used for construction as it gives a better bond strength which is one of the most important factor to resist seismic effect to the structure.7. REBOUND HAMMER TEST

AIM:

To calculate the Compressive strength of any concreting using Rebound Hammer Test.

PRINCIPLE:

The underlying principle of the rebound hammer test is that the rebound of an elastic mass depends on the hardness of the surface against which its mass strikes.INTRODUCTION

The Rebound hammer has been around late 1940s and developed in 1948 by a swiss engineer Ernst Schmidt, the device also measures hardness of concrete surfaces using rebound principle. The device is often referred to as swiss hammer. Rebound hammer test is done to find out the compressive strength of concrete by using rebound hammer as per IS: 13311 (Part 2) 1992. A steel hammer impacts with a predetermined amount of energy, a steel plunger in contact with the surface of concrete and the distance that the hammer rebounds is measured.Surface hardness measured during the test give an idea about the soundness and quality of cover concrete.DESCRIPTION

The device consist of a plunger rod and an internal spring loaded steel hammer and a latching mechanism. When the extended plunger rod is pushed against a hard surface, the spring connecting the hammer is stretched and when pushed to an internal limit, the latch is released causing the energy stored in the stretched spring to propel the hammer against plunger tip. The hammer strikes the plunger rod and rebounds a certain distance. on the outside of the unit is a slide indicator that records the distance travelled during rebound. This indication is known as rebound number.

Fig- 7 a: Cross sectional view of rebound hammer

Procedure to determine strength of hardened concrete by rebound hammer.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. 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. 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.) Take the average of about 15 readings.

Fig-7b: testing method

Interpretation of ResultThe 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.

Table 10 :- Average Rebound number and quality of concrete

Average rebound numberQuality of concrete

>40Very good hard layer

30-40Good layer

20-30Fair