CE 39007 – Concrete Lab Tests on Hardened Concrete

peletonwhoopUrban and Civil

Nov 26, 2013 (3 years and 11 months ago)

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1
CE 39007 – Concrete Lab
Mondays/Thursdays/Fridays
Instructors:
L S Ramachandra (CE, Monday)
Amit Shaw (CE, Monday)
Sushanta Chakrabarti (CE, Thursday)
Nilanjan Mitra (CE, Thursday)
Sudhirkumar Barai (CE, Friday)
S P Bhattacharya (ARP, Friday)
Tests on Hardened Concrete
2
Tests on Hardened Concrete
1.
Compressive Strength of the Concrete
2.
Tensile Strength of Concrete
3.
Non-Destructive Tests –
Rebound Hammer Test/Ultrasonic Pulse Velocity
Test
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1. Compressive Strength Test
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Compressive Strength

Tests on Cubes and Cylinders

Results of individual cubes should not differ by  15% of the
average

A correction factor from graph shall be applied to correct cylinder
strength

Equivalent cube strength = 1.25 times cylinder strength
Correction factor for
height/diameter ration
4
Failure modes of Cubes:
Non-explosive/explosive
Failure modes of Cylinders:
Splitting/ Shear (Cone)/ Splitting and Shear (Cone)
5
2. Tensile Strength of Concrete
Tensile strength of Concrete

Tensile strength of concrete ranges from 10 to 18% of the
compressive strength

Indirect Approaches

Standard Beam Test – Modulus of Rupture Test

Split Cylinder Test
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Determination of Modulus of
Rupture

Both two-point loading and centre point loading can be used

Normally, tests are conducted in the laboratory after keeping the
concrete in wet condition for 48 hours and at 24 degree Celsius

Rate of loading is 180 Kgf / min

f
cr
= pl/bd
2
for the distance between line of fracture and the nearer
support greater than 133 mm (i.e. the fracture occurs within the
middle 1/3 rd of the beamand also when maximumsize of
middle

1/3

rd

of

the

beam

and

also

when

maximum

size

of

aggregate is 20 mm and sample of size 100 x 100 x 500 is used).

If fracture occurs outside this range, the test should be repeated
Modulus of Rupture Test
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Modulus of Rupture Chart
Determination of Tensile Strength
by Split Tensile Test

Results are observed to be 5-12% higher than f
cr

The main advantage and cause of popularity is that same
specimen and instrument is used for compression testing.

Loading condition produced high compressive stress immediately
below the contact generators but after that almost uniform tensile
stresses prevail

Rate of loading is 0.02 to 0.04 MPa per second

The tensile splitting strength is calculated by
f
st
=2P/LD
P= The Compressive load on the Cylinder
L = Length of the Cylinder
D = Diameter of the Cylinder

The Compressive strength of for an element on the vertical
diameter = 2P/ LD * [D
2
/r(D-r))-1]
8
Split Cylinder Test
Split Cylinder Test
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3. Non-Destructive Tests –
Rebound Hammer Test
Ultrasonic Pulse Velocity Test
NDT with Schmidt’s Rebound
Hammer (IS: 13311 Part 2)

This is used for measuring surface hardness of existing concrete mass
which in turn is correlated with the grade of concrete, calibration curves
are available to relate the rebound number (distance travelled by the
mass as a percentage of the initial extension of the spring) with the grade
of concrete for the hammer held either horizontal or vertical (down or up)
for both dry and wet condition of surface

Unfortunately the result depends upon-

Type and nature of aggregate used

Surface and internal moisture condition, presence of void

Smoothness of surface

It can be best used to compare strength of one concrete against another
but usually not reliable in determining absolute strength. Moreover, each
hammer varies considerably in performance and require individual
calibration
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Rebound Hammer
Rebound Hammer
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Compressive Strength and
Rebound Number
NDT with Ultrasonic Pulse Velocity
Meter (IS: 13311 Part 1)

This is used for measuring the time of travel of pulse of vibrations
in ultrasonic ranges, passing through the concrete to judge
qualitatively, how good or bad the concrete is. It can be operated
in direct, semi-direct or indirect, i.e. surface mode

Unfortunately the result depends upon-

Heterogeneity of concrete within a short length

Presence of reinforcing steel or other impurities in concrete
Presence

of

reinforcing

steel

or

other

impurities

in

concrete

It can be best used to judge uniformity of concrete and to establish
acceptance criteria, correlation with strength is possible but not
popular
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Ultrasonic Test:
Direct Transmission/Semi-direct Transmission/
Indirect Surface Transmission
Ultrasonic Test Results
Interpretation

> 4500 m/s Excellent

3500-4500 m/s Good

3000-3500 m/s Doubtful

2000-3000 m/s Poor

<2000 m/s Very poor
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4. Short-term Static Modulus of
Elasticity
Modulus of Elasticity Test
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Stress-Strain Behaviour of
Concrete