Download pdf - Bader Test Report

7/27/2019 Bader Test Report

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ABSTRACT


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Table of Contents

1. Introduction

2. Materials

3. Experimental Procedure

3.1 Concrete mix design

3.2 Testing the properties of the plastic state

3.2.1 Slump Test

3.2.2 VeBe Test

3.2.3 Compacting Factor

3.3 Testing the properties of the hardened concrete

3.3.1 Non Destructive Test

3.3.1.1 Schmidt Hammer Test

3.3.2 Destructive test

3.3.2.1 Compressive Strength

3.3.2.2 Indirect tension

3.3.2.3 Flexure

4. Result

4.1 Slump Test

4.2 VeBe Test

4.3 Compacting Factor


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4.4 Non Destructive Test

4.5 Schmidt Hammer Test

4.6 Destructive test

4.7 Compressive Strength

4.8 Indirect tension

4.9 Flexure

5. Discussion

6. Conclusion

7. References


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Introduction


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Materials


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Experimental Procedure

Concrete mix design and casting specimens


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Testing the properties of the plastic state

Slump Test

The Slump test is the most commonly use method in the concrete construction to measure the

workability of the concrete. Workability is a general term to describe the properties of fresh

concrete. Workability is often defined as the amount of mechanical work required for full

compaction of the concrete without segregation.

The test is carried out using a mould known as a slump cone. The cone is placed on a

hard non-absorbent surface. This cone is filled with fresh concrete in three stages,

each time it is tamped using a rod of standard dimensions. At the end of the third

stage, concrete is struck off flush to the top of the mould. The mould is carefully lifted

vertically upwards, so as not to disturb the concrete cone. Concrete subsides. This

subsidence is termed as slump, and is measured in to the nearest 5 mm. Three different

kinds of possible slumps exist, true slump, shear slump, and collapse slump. Conventionally,

when shear or collapse slump occur, the test is considered invalid. However, due to recent

development of self compact concrete, the term of collapse slump has to be used with caution.

Figure 1 Slump Test


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VeBe Test

The Vebe consistometer was developed in 1940 and is probably the most suitable test for

determining differences in consistency of very dry mixes. This test method is widely used in

Europe and it is, however, only applicable to concrete with a maximum size of aggregate of less

than 40 mm. For the test, a standard cone is cast. The mould is removed, and a transparent disk is

placed on the top of the cone. Then it is vibrated at a controlled frequency and amplitude until the

lower surface of the disk is completely covered with grout. The time in seconds for this to occur is

the Vebe time. The test is probably most suitable for concrete with Vebe times of 5 to 30s. The

only difficulty is that mortar may not wet the disc in a uniform manner, and it may be difficult to

pick out the end point of the test.


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Compacting Factor

The compacting test was developed in Great Britain in 1947. As shown in the figure, the

upper hopper is completely filled with concrete, which is then successively dropped into the

lower hopper and then into the cylindrical mould. The excess of concrete is struck off, and the

compacting factor is defined as the weight ratio of the concrete in the cylinder, mp, to the

same concrete fully compacted in the cylinder (filled in four layers and tamped or vibrated),

mf(i.e., compacting factor = mp/mf). For the normal range of concrete the compacting factor

lies between 0.8 to 0.92 (values less than 0.7 or higher than 0.98 is regarded as unsuitable).

This test is good for very dry mixes.

Three limitations: (i) not suitable for field application; (ii) not consistent; (iii) mixes can stick

to the sides of the hoppers.

The test was started by measuring the weight of the cylindrical mould (W1) and then the final

weight of the levelled cylinder after dropping of the fresh concrete was measured (W2).

Partially compacted concrete was removed from the cylinder and then the cylinder was filled

with fully compacted concrete through the vibration, and the final weight was measured.

Therefore the compacting factor was calculated using (W2-W1)/(W3-W1) ratio.


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Testing the properties of the hardened concrete

Non Destructive Test

Schmidt Hammer Test

The purpose of the Schmidt Hammer test is to be able to calculate the hardness of the hardened

concrete. The method consists of applying a known force to a surface of the concrete concerned

using a spring loaded rod with a head of known diameter (typically 10mm), the rebound of the rod

back into the instrument is measured and from this the result is known as a rebound number[Baker,

p85, 1962]. The number obtained from the experiment is quite variable due to the angle at which

the instrument is held to the surface of the concrete. Typically moulded specimens with a trowelled

surface obtain a higher value than those which are not moulded or trowelled. In the above data it is

noted that some of the results are far lower than what their counterparts are, in particular the small

cylinder of batch B, this is because there may have been an air bubble beneath the surface. The

advantages of the Schmidt Hammer test is it being a very portable instrument which is capable of

giving a rough idea of the concrete being tested.


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3.3.1.2 Pundit Test

This form of testing has a wide variety of purposes ranging from evaluation of cracking bridges to

investigating honeycombing or voids (air pockets) inside concrete. The unique test has a low degree

of accuracy however one of the most excellent characteristics of this test being it is completely non-

destructive. The pundit machine sends stress waves also known as soundwaves through the

concrete.

The velocity through the material can be obtained using the above equation, where V is the velocity

of the sound waves through the material, L is the length of the material in mm or metres and t is the

time in seconds or microseconds.

This obtained velocity is empirically correlated to that materials strength; calibration curves

relating the two properties are usually constructed for each concrete.[Ansari, p95, 1992]

The reasoning behind the velocity being related to the materials strength is the amount of air

pockets entrapped inside the material. Sound waves prefer to travel in straight lines, if there were

air pockets in the concrete the soundwaves would have to travel either through the air void or

around it. Air pockets are considered weaknesses within concrete, if just 1% of the volume of

concrete is made of air the total strength of the concrete is reduced by approximately 5%.


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The pundit or ultrasonic test is obviously important especially for concrete which are needed to be

able to withstand large forces, in particular high performance concretes. If there is any air above a

certain allowable percentage in the concrete it cannot be used for that particular application

Destructive test

Compressive Strength

Strength is defined as the ability of a material to resist stress without failure. The failure of concrete

is due to cracking. Under direct tension, concrete failure is due to the propagation of a single major

crack. In compression, failure involves the propagation of a large number of cracks, leading to a

mode of disintegration commonly referred to as

crushing. The strength is the property generally specified in

construction design and quality control, for the following

reasons: (1) it is relatively easy to measure, and (2) other

properties are related to the strength and can be deducedfrom strength data


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Indirect tension

The splitting test is carried out by applying compression loads along two axial lines

that are diametrically opposite. This test is based on the following observation from elastic

analysis. Under vertical loading acting on the two ends of the vertical diametrical line,

uniform tension is introduced along the central part of the specimen.


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The splitting tensile strength can be obtained using the following formula:

According to the comparison of test results on the same concrete, fst is about 10-15% higher than

direct tensile strength, ft.

Flexure

BS 1881: Part 118: 1983. Flexural test. 150 x 150 x 750 mm or 100 x 100 x 500 (Max. size of

aggregate is less than 25 mm). The arrangement for modulus of rupture is shown in the above

figure.

From Mechanics of Materials, we know that the maximum tension stress should occur at the bottom

of the constant moment region. The modulus of rapture can be calculated as:

This formula is for the case of fracture taking place within the middle one third of the beam. If

fracture occurs outside of the middle one-third (constant moment zone), the modulus of rupture can

be computed from the moment at the crack location according to ASTM standard, with the following

formula.


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However, according to British Standards, once fracture occurs outside of the constant moment zone,

the test result should be discarded.

Although the modulus of rupture is a kind of tensile strength, it is much higher than the results

obtained from a direct tension test. This is because concrete can still carry stress after a crack is

formed. The maximum load in a bending test does not correspond to the start of cracking, but

correspond to a situation when the crack has propagated. The stress distribution along the vertical

section through the crack is no longer varying in a linear manner. The above equations are therefore

not exact.

Result

Dimensions of the specimens casted

Name of the

SpecimenDescription Type Length

Top

Diameter

Bottom

Diameter

Middle

Diameter

C1

Control one

without

Admixtures

Cylinder 200 100.13 100.12 101.57

C2

Control one

without

Admixtures

Cylinder 200 100.1 100.32 100.23


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P1Added with

Super plasticiserCylinder 201 100.04 99.97 99.84

P2Added with

Super plasticiserCylinder 204 101.74 101.73 101.14

A1

Added with

air-entering

Agent

Cylinder 201 99.93 100.37 100.12

A2

Added with

air-entering

Agent

Cylinder 199 100.51 100.79 100.69

P3Added with

Super plastiserCylinder 303 150.44 150.41 151.05

A3Added withair-entering

Agent

Cylinder 302 150.42 150.42 150.73

BeamBeam for the

flexure testBeam 500 N/A N/A N/A

=

Slump Test

VeBe Test


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Compacting Factor

Non Destructive Test


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Schmidt Hammer Test

Destructive test

Compressive Strength


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Indirect tension


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Flexure


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Discussion


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Conclusion


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References