ndt 37, 72,74

CASE STUDY ON NON-DESTRUCTIVE TESTING

ON CONCRETE STRUCTURES

Submitted By :

Ankita Kulkarni (243037)

Sandhya Silotia (243072)

Sangamesh Kotarki (243074)

Non-Destructive Testing on Concrete Structures - A Case Study 1

Guided by : Prof. R. Satish Kumar

Index:

Objective Scope Why NDT? Applications of NDT Various Methods of NDT Case Studies Conclusions Remedial Measures Limitations Bibliography

Non-Destructive Testing on Concrete Structures - A Case Study

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Objective

To Study the use, methodology & applicability of non destructive testing methods to check integrity of concrete structures through a case study.


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Scope:

Suggest the methodology to be followed & applicability of non destructive testing.

Automatic interpretation of data from NDT, with the goal of detecting flaws accurately and efficiently.

To propose retrofitting techniques for structures failing in this kind of testing.


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Case Studies :

1. EIGHT LANE ACCESS CONTROLLED EXPRESSWAY AS OUTER RING ROAD TO HYDERABAD CITY, PHASE II KOLLUR (KM. 12+000 TO PATANCHERU (KM. 23+700)

2. DRDL Laboratory building, single storied at Chandrayangutta, Secunderabad

3. Ambuja cements ltd.,Rajasthan


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Non destructive testing

Non destructive testing is a technique for checking structural integrity after concrete hardening without damaging it.


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Various methods of NDT

UPSV Test (Ultra sonic pulse velocity test)

Schmidt rebound hammer test Carbonation depth measurement test Half-cell potentiometer test Cover meter test Penetration Resistance test Resistivity measurement


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Why NDT?

Strength on concrete depends on material, proper mixing & also workmanship at the time of placing

Conventional methods of testing of concrete does provide solution to assess actual strength or internal structure after hardening of concrete

In some cases, it required to assess of concrete damaged due to fire or any other natural calamity due judge the condition of structure


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Application of NDT

quality control of pre-cast units or construction in situ

confirming or negating doubt concerning the workmanship involved in batching, mixing, placing, compacting or curing of concrete

location and determination of the extent of cracks, voids, honeycombing and similar defects within a concrete structure

determining the position, quantity or condition of reinforcement

confirming or locating suspected deterioration of concrete resulting from such factors as

overloading, fatigue, external or internal chemical attack or change, fire, explosion, environmental effect


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USPV Test

This test is used for determination of the uniformity of concrete in and between members.

Reference code: IS 13311Part I 199 Principle:the velocity of an ultrasonic pulse

through any material depends upon the density, modulus of elasticity and Poisson’s ratio of the material.

Higher is the velocity, better is the quality of concrete


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UPSV Contd…Equipment:

(a) Electrical pulse generator

(b) Pair of transducers (c) Amplifier (d) Electronic timing

machine

UPSV Equipment

•Equipment should be capable of measuring transit time over path lengths ranging from about 100 mm to the maximum thickness to be inspected to an accuracy of ±1%

Cost of equipment: Rs.2.15 lakhs


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UPSV Contd…. Methodology

Calibration: done by measuring transit time on standard calibration rod.

Transducers arrangement: 3 methods

a) Direct Transmission

c) Surface Transmission

b) Semi Direct Transmission


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Contd… USPV

Sr. No.

Ultrasonic Pulse Velocity by Cross probing (Km/Sec)

Concrete quality grading

1 Above 4.5 Excellent

2 3.5 to 4.5 Good

3 3.5 to 4.5 Medium

4 3.5 to 4.5 Doubtful

Velocity criterion for concrete quality grading is given by IS 13311 (Part-I):1992


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SCHMIDT REBOUND HAMMER TEST

The Schmidt rebound hammer is basically a surface hardness tester.

IS: 13311 (Part 2): 1992 & BS 1881: Part 202: 1986

Principle :the rebound of an elastic mass depends on the hardness of the surface against which mass strikes.


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Contd… Rebound Hammer


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Equipment: It Consist of a spring control hammer that slides on a plunger within a tubular housing. When the plunger is pressed against the surface of the concrete, the mass rebound from the plunger. It reacts against the force of spring. The Distance travelled by the mass, is called rebound number.

Contd… Rebound Hammer


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CARBONATION DEPTH MEASUREMENT TEST

Carbonation of concrete occurs when the carbon dioxide, in the atmosphere in the presence of moisture, reacts with hydrated cement minerals to produce carbonates

Due alkaline nature of concrete, reinforcement is protected from corrosion. This is neutralized by carbonation, thus reinforcement becomes prone to in presence moisture and oxygen.


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Contd… Carbonation Test

The extent of carbonation is determined by testing concrete surface with a 1% phenolphthalein solution

The 1% phenolthalein solution is made by dissolving 1gm of phenolthalein in 90 cc of ethanol & the making it to 100cc by adding distilled water.

Change in colour is observed after test: No change in colour layer: Carbonation

affected Purple: No cabonation has taken place


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HALF-CELL ELECTRICAL POTENTIAL METHOD This test is used to assess the corrosion conditions

in a reinforced concrete structure. ASTM C876 - 91 The apparatus includes copper-copper sulphate

half-cell, connecting wires and a high impedance voltmeter

external cathode is provided in the form of copper rod and copper sulphate solution in the cell. Any point on reinforcement bar inside the concrete body functioning as anode when connected electrically to cathodic half-cell generates e.m.f. This is measured by connecting a milli voltmeter in the circuit


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Contd… Half Cell Electrical Method

Half cell potential (mV) reading

Percentage chance of activecorrosion

< -350 90%

-200 to –35050%

> -200 10%

The possibility of active corrosion is found out according to guideline below


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Cover meter test

This test is used to assess the location and diameter of reinforcement bars and concrete cover.

Principle: based measurement of change of an elctromagnetic field caused by steel embedded in the concrete.

Equipment: profometer comprise a search head, meter and interconnecting cable. The concrete surface is scanned, with the search head kept in contact with it while the meter indicates, by analogue or digital means, the proximity of reinforcement


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Case Study 1:EXPRESSWAY, KOLLUR Structure: EIGHT LANE ACCESS

CONTROLLED EXPRESSWAY AS OUTER RING ROAD TO HYDERABAD CITY, PHASE II KOLLUR (KM. 12+000 TO PATANCHERU (KM. 23+700)

Test conducted:A. Rebound Hammer tests to assess the in situ

compressive strength of cover concrete.B. USPV tests to assess the integrity of

concrete


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Case study 1:

Test results: USPV TEST RESULTS Rebound Hammer test results

Results & Inferences: Concrete quality is found from “good to

excellent” according to UPSV tests results Concrete strength is varies from M35- M45

in rebound hammer test


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Case Study 2 : DRDL Hyderabad


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Structure: DRDL laboratory building, single storied Columns size( B1 & B4) : 1’6” x 1’6” Columns size( A1, A2, A3, A4, B2, B3, C1, C2,

C3 & C4 ) : 1’0” x 1’6” Beam size –2’4” x 1’0”

Test conducted:a) UPSVb) Rebound hammer test Test results:a) UPSV test:b) Rebound hammer

Case study 2:

Analysis & Results: Concrete quality is found to be “good” at

maximum locations .At some places it is found “medium & doubtful”.

On analyzing above rebound hammer test, it is found that the strength produced by the structures are more than the strength of Concrete of M-25.


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Case study 2:


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Case Study 3: Ambuja cements ltd.,Rajasthan Structures:

A. Cement silo: Dia 16.7 M & Height 51.0 M Test conducted:

A. Rebound Hammer tests to assess the in situ compressive strength of cover concrete.

B. USPV tests to assess the integrity of concrete.

C. Carbonation test to assess the depth of carbonated concrete.

D. Half cell potentiometer test to assess the probability of active corrosion.

E. Cover Meter test to estimate the cover provided.Non-Destructive Testing on Concrete Structures - A Case

Study

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Case Study 3:

Tests results: UPSV & Rebound hammer: Half cell potentiometer : Cover meter: Carbonation depth:

Results analysis & Inferences: columns ground level wall and Upper level

wall “Medium to good quality concrete” 10% probability of active corrosion exists.


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Case study 3:

Results & Inferences: average cover provided to reinforcement in

columns and wall is about 40 mm which adequate acc. To IS 456

The carbonation test results on cores s as well as drill powder from concrete suggest that average depth of carbonation for columns is upto 10 mm & Wall can be considered upto 20mm, which can be considered as normal considering the age of the structure.


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Case study 3:


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Silo structureFine crack in silo top slab

Conclusion :

Various NDT methods can be used depending upon the type & age of structure to check the integrity of structure.

USPV, rebound hammer & covermeter can be applied to newly constructed structures to check the quality of concrete adequacy of cover before applying live load to the structures.

Half cell potentiometer & carbonation test can be applied to old structure to acess to carbonation depth & amount of corrosion occurred.


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Remedial measures:

Replacement of cover concrete by microconcrete

Polymer Modified Mortar Treatment Protective Coating Jacketing Water proofing to slab


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Limitation:

Lack of access, especially inside silo structures is a serious limitation in assessing the integrity of silo walls

Slabs are covered with water proofing membrane, it becomes difficult to get accurate through NDT.

If spalling or cracks are observed ,concrete remains no longer homogeneous, and tests like UPSV & rebound hammer becomes inapplicable, equipments for NDT are not made in India.

Equipments are very costly and not easily available.


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Biblography:

Guidebook on non-destructive testing of concrete structures - INTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA, 2002.

IS 13311 : Part 1 : 1992 Non-destructive testing of concrete: Part 1 Ultrasonic pluse velocity

IS 13311 : Part 2 : 1992 Methods of non-destructive testing of concrete: Part 2 Rebound hammer

MS shetty:Concrete technologyNon-Destructive Testing on Concrete Structures - A Case

Study

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Thank you for Your Attention…


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ndt 37, 72,74

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