ndt (non destructive testing) of concrete structure anshul

Under guidance-

Prof. V. K. Gupta HOD CIVIL DEPT.

2/13/2015 1

• Nondestructive testing in the broad sense refers to methods whereby internal characteristics of solid structures can be examined without permanently affecting the structure. Thus, parts that prove to be satisfactory under specified test conditions are not degraded by the test procedures

2/13/2015 2

Nondestructive testing (NDT) is the process of inspecting, testing, or evaluating materials, components or assemblies for discontinuities, or differences in characteristics without destroying the serviceability of the part or system. In other words, when the inspection or test is completed the part can still be used

2/13/2015 3

1)-Assessment of Existing Structures in the Absence of Drawings.

2)-Quick assessment of the structure.

2/13/2015 4

1. Access to hidden items – “see through walls”

2. Better investigations with NDT

3. Rapid accumulation of data

4. Generally less expensive than destructive testing.

2/13/2015 5

1. More than one test method may be required

2. Environmental conditions may effect or distort results

3. Construction details & building components may effect results

4. Some conditions cannot be determined with a reasonable degree of accuracy without destructive testing

2/13/2015 6

1-Rebound Hammer

2-Ultrasonic Pulse Velocity Meter

3-Pull Out

4.Core cutter

5-Covermeter

6- X ray computed tomography

7. Electric resistivity test2/13/2015 7

• The rebound hammer can provide a fairly accurate estimate of concrete compressive strength.

• The concrete should be 14 to 56 days old.• Surface Condition:• The surface of the concrete at the point tested

must be smooth, dry, and free of honeycombing. Otherwise, rebound readings will be low Indicating a weaker concrete than is actually the case. The rubbing stone provided can be used to grind the surface smooth, if necessary.

2/13/2015 8

The concrete to be tested must be at least four inches thick: It is also recommended that readings be taken only where the concrete has been in contact with the form. These conditions are most easily satisfied if the readings are taken along the edge of the tank on the sides and ends where the adjoining concrete face (i.e., wall, top, or bottom) can support the point of contact.

2/13/2015 9

2/13/2015 10

• A). Remove hammer from case and press the plunger end against a hard surface to release the plunger from the locked position. (Do not press lock button while doing this.)

• B). Position hammer horizontally with plunger end against wall at a point.

• C). Slowly apply pressure until hammer fires. This will occur when only approximately 1/2 inch of the plunger is still visible. Do not press the lock button during this step.

2/13/2015 11

• With the hammer still pressed against the wall, read the rebound number off the scale provided on the hammer. If it is necessary to move the hammer before reading, press the lock button. The rebound number should be read to two significant figures.

• Repeat the above procedure at different points around the wall until a total of ten readings has been taken

2/13/2015 12

2/13/2015 13

• This is based on the principle that the velocity of an ultrasonic pulse through any material depends upon the density. Comparatively higher velocity is obtained when concrete quality is good in terms of density, uniformity etc.

• Pulse Velocity measurements can be used to assess the presence of cracks, voids etc., quality of concrete relative to standards requirements.

2/13/2015 14

There are three possible ways of measuring pulse velocity.

i) Direct transmission

ii) Semi direct transmission

iii) Indirect transmission (surface probing)

Out of the three methods, the direct transmission method is considered to be the best.

2/13/2015 15

2/13/2015 16

condition of concrete based on pulse velocity are given below:

S.No. Pulse Velocity Condition of concrete I in(Km/Sec.)

• 1. Above 4.5 Excellent

• 2. 3.5 to 4.5 Good

• 3. 3.0 to 3.5 Medium

• 4. Below 3.0 Poor

2/13/2015 17

• The fundamental principle behind pull out testing with LOK-test and CAPO test is that the test equipment designed to a specific geometry will produce results (pull-out forces) that closely correlate to the compressive strength of concrete.

The first method ,using the cast steel disc is called LOK test. The second method shown in fig.2 using expandable ring is called CAPO test (i.e. Cut and Pull out Test). The diameter of both the disc and ring is 25mm. the distance to the concrete surface is also 25mm. the inner diameter of the counter-pressure is 55mm.2/13/2015 18

2/13/2015 19

The relationship between the pullout force Fu in kN and compressive strength Fc in MPa is given in fig

2/13/2015 20

• Determine in-situ compressive strength of the concrete

• Ascertain the strength of concrete for carrying out post tensioning operations.

• Determine the time of removal of forms and shores based on actual in-situ strength of the structure.

• Terminate curing based on in-situ strength of the structure.

2/13/2015 21

The test should be taken at points where minimum strength and maximum stress are likely to coincide. But, at the same time, the core cutting causes some damage to the member and may impair the future performance of the member. Therefore, in slender members, the core should be taken away from the critical section. For compression testing, the diameter of the core should be at least three times the nominal maximum aggregate size.

2/13/2015 22

Core Cutter is used to cut the core from the existing concrete structure for testing the physical properties of the concrete like compressive strength, density, water absorption, crack depth and chemical test like depth of carbonation and chloride content etc. It can also be used to inspect the interior region of the structural members.

2/13/2015 23

2/13/2015 24

Cover meters are electromagnetic in operation. Electric currents in a coil winding in the search head generate a magnetic field which propagates through the concrete and will interact with any buried metal present, such as reinforcing steel.It is the generic term for equipment used to locate steel reinforcing bar in concrete and to estimate the thickness of the concrete cover over the reinforcement.

2/13/2015 26

Tomography means imaging an object by taking measurements from “slices” of its cross-section.

2/13/2015 27

In computed tomography, the image of an object is reconstructed from projections of the object.

• Most commonly the projections are obtained by using penetrating x-rays, although other modalities for measuring projection data are also available.

2/13/2015 28

2/13/2015 29

2/13/2015 30

This test is carried out to assess the quality / uniformity of concrete at various depths. The instrument consists of a four probe device. Electrical current is passed through the outer probes & the potential drop is measured by the inner probes. From the current & voltage drop measurements, the resistivity of concrete can be measured.

Electrical resistivity = 2(pi)aE/i (in kilo-ohm cm) where a = distance between probes = 5 cm in the 1st set of readings = 10 cm in the 2nd set of readings E = potential difference between inner two probes in mV Most useful test in tunnel structure.

2/13/2015 31

2/13/2015 32

2/13/2015 33