Monu Report.pdf

Asemi narr epor t on

NONDESTRUCTI VETESTI NGOFCONCRETE submi t t edby

MANMOHANLODHA 15CE25 I npar t i al f ul f i l l mentoft heawar doft hedegr ee of

BACHELOROFTECHNOLOGY i n

CI VI LENGI NEERI NG

at DEPARTMENTOFCI VI LENGI NEERI NG GOVERNMENTENGI NEERI NGCOLLEGE AJMER

ACKNOWLEDGEMENT It gives me immense pleasure to express my deepest sense of gratitude to my supervisors Mr. Pravesh Saini Sir and Mr. Anurag Kumar Singh Sir for their invaluable guidance, comments and help throughout the course of the project. Their useful suggestions for this whole work and cooperative behavior are sincerely acknowledged. I would also like to thank Dr. Ganpat Singh Sir, HOD Civil Engineering Department for his constant motivation and support during the seminar report. I also wish to express my indebtedness to my parents as well as my family members whose blessings and support always helped me to face the challenges ahead. In the end I would like to express my sincere thanks to all my friends and others who helped me directly or indirectly during this project work.

Manmohan Lodha B.Tech IVth Year Civil Engg.

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ABSTRACT Concrete is the combination of cement mortar and binders and is of wide use in many places. Its applications range from small covering slabs to huge buildings. The necessity to know the strength its ability to withstand load and durability is a factor of grave concern. The existence of the building is entirely relied on the concrete structure it is made of. Based on the mixing proportions, composition and wetting the properties of concrete can vary. Hence it is necessary to test concrete strength wherever possible. Although there can be no direct measurement of the strength properties of structural concrete for the simple reason that strength determination involves destructive stresses, several non destructive methods of assessment have been developed. These depend on the fact that certain physical properties of concrete can be related to strength and can be measured by non-destructive methods.

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TABLE OF CONTENT ACKNOWLEDGEMENT

(i)

ABSTRACT

(ii)

1. INTRODUCTION

1

1.1. NON-DESTRUCTIVE TESTING OF CONCRETE 2. LITERATURE REVIEW

1 3

2.1. DESTRUCTIVE TESTING OF CONCRETE

3

2.2. NON-DESTRUCTIVE TESTING OF CONCRETE

3

3. OJECTIVES AND IMPORTANCE OF NDT

5

3.1. OBJECTIVES

5

3.2. IMPORTANCE

5

4. NON-DESTRUCTIVE TESTING METHODS 4.1. SURFACE HARDNESS METHODS

6 6

4.1.1. PRINCIPLE OF TEST

6

4.1.2. PROCEDURE

8

4.2. PENETRATION RESISTANCE METHOD

8

4.2.1. TEST EQUIPMENT

8

4.2.2. LIMITATIONS AND ADVANTAGES

10

4.3. PULL-OUT RESISTANCE METHOD

10

4.3.1. PROCEDURE

11

4.3.2. LIMITATIONS AND ADVANTAGES

11

4.4. RESONANCE FREQUENCY METHOD

11

4.4.1. TEST EQUIPMENT

11

4.4.2. PRINCIPLE OF TEST

11

4.5. MATURITY TEST METHOD

13

4.5.1. PRINCIPLE OF TEST

13

4.6. PERMEATION TEST METHOD

14

4.6.1. PROCEDURE

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4.7. IMPACT-ECHO METHOD

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4.7.1. PRINCIPLE OF TEST

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4.8. ULTRA SONIC PULSE VELOCITY METHOD

15

4.8.1. TEST EQUIPMENT

16

4.8.2. TRANSDUCER ARRANGEMENT

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4.9. CORE CUTTER METHOD

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4.9.1. PROCEDURE

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5. CONCLUSIONS

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5.1. FOR REBOUND HAMMER TEST

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5.2. FOR PENETRATION TEST

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5.3. FOR PULL-OUT TECHNIQUE

19

5.4. FOR RESONANCE FREQUENCY METHOD

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5.5. FOR MATURITY TEST

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5.6. FOR PERMEATION TEST

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5.7. FOR IMPACT-ECHO METHOD

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5.8. FOR ULTRASONIC PULSE VELOCITY TEST

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5.9. FOR CORE CUTTER TEST

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6. FUTURE OF NON-DESTRUCTIVE TESTING

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REFERENCES

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LIST OF FIGURES 1. SCHMIDT REBOUND HAMMER

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2. SCHMIDT REBOUND HAMMER PROCEDURE

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3. WINDSOR PROBE SYSTEM

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4. PROBE PENETRATION

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5. PULL-OUT RESISTANCE METHOD

10

6. RESONANCE FREQUENCY TEST METHOD

12

7. MATURITY TEST APPARATUS

13

8. ULTRASONIC PULSE VELOCITY TEST APPARATUS

16

9. CORE CUTTING APPARATUS

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CHAPTER 1 INTRODUCTION 1.1. NON-DESTRUCTIVE TESTING OF CONCRETE :- Non-destructive testing (NDT) is defined as the course of inspecting, testing or evaluating materials, components or assemblies without destroying the serviceability of the part or system (Workman and O. Moore, 2012).  Non-destructive testing (NDT) is a wide group of analysis techniques used in science and technology industry to evaluate the properties of a material, component or system without causing damage.  When the inspection and test is done, that part of structure can still be used.  The destructive test are often used to determine physical properties of material such as impact resistance, ductility, yield and ultimate tensile strength, fracture toughness and fatigue strength, but discontinuities and differences in material characteristics are more effectively found by NDT.  These tests are used in manufacturing, fabrication and in-service inspection to ensure product integrity and reliability, to control manufacturing processes, lower production costs and to maintain a uniform quality level.  It is a highly valuable technique that can save both money and time in product evaluation, troubleshooting and research.  It is commonly used in forensic engineering, mechanical engineering, petroleum engineering, electrical engineering, civil engineering, systems engineering, aeronautical engineering, medicine, and art.  The purpose of NDT is to determine the quality and integrity of materials, components or assemblies without affecting the ability to perform their intended functions. For example, Coring is a common NDT method which alters the appearance of the component and marginally affects its structural integrity. If done correctly, coring maintains the serviceability of the structural component and is thus considered to be non-destructive.

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The non-destructive Testing (NDT) plays an important role in assuring that structural and mechanical components perform their function in a safe, reliable, and cost-effective manner. NDT is typically used at various points in a part's life cycle. NDT can be used prior to the use of a component for the sake of quality control. NDT is also employed while components are in use to detect service related conditions caused by wear, fatigue, corrosion, stress or other factors which affect reliability. NDT methods have materialized as a response to the need for structural damage detection and prevention. The extensive use of NDT is driven by economics and safety. In a pre-emptive attempt to eradicate the problems associated with structural deterioration, novel in-site testing techniques have been invented to allow for the assessment of concrete during the construction, commissioning and servicing lifecycle stages of a structure

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CHAPTER 2 LITERATURE REVIEW Concrete may be tested by two methods on the basis of destruction:1.) Destructive testing of concrete 2.) Non-destructive testing of concrete 2.1. DESTRUCTIVE TESTING OF CONCRETE : In destructive testing, tests are carried out to the specimen's failure in order to understand a specimen's performance or material behavior under different loads.  These tests are generally much easier to carry out, yield more information and are easier to interpret than non-destructive testing.  Destructive testing is most suitable and economic for mass production as the cost of destroying a small number of specimens is negligible.  It is usually not economical to do destructive testing where only one or very few items are to be produced. For example, in the case of a building. The following primary destructive tests are performed on hardened concrete :1.) Cube test 2.) Flexure test 2.2. NON-DESTRUCTIVE TESTING OF CONCRETE : Non-destructive testing (NDT) is a wide group of analysis techniques used in science and technology industry to evaluate the properties of a material, component or system without causing damage.  It is a highly valuable technique that can save both money and time in product evaluation, troubleshooting and research.  NDT is commonly used in forensic engineering, mechanical engineering, petroleum engineering, electrical engineering, civil engineering, systems engineering, aeronautical engineering, medicine, and art. The following non-destructive tests are performed on hardened concrete :1.) Penetration test 3

2.) Ultrasonic pulse velocity test 3.) Rebound hammer test 4.) Core cutter test etc. Extensive attempts and advancement have been made to develop NDT methods capable of indicating mechanical, acoustical, chemical, electrical, magnetic and physical properties of materials. The first recorded uses of NDT was in 1868, when Englishman S.H. Saxby relied on the magnetic characteristics of a compass to find cracks in gun barrels. One of the earliest attempts of NDT dates to the 19th century where cracks were detected in railroad wheels by means of acoustic tap testing (Stanley, 1995). The first NDT method to come into industrial application was the X-ray technology. In 1895, German physicist Wilhelm Conrad Rontgen’s experiment led him to discover X-rays, an invention that earned him the first-ever Nobel Prize. In 1929, a Russian named Sokolov proposed the use of ultrasound for testing castings. More sensitive, reliable and quantifiable NDT methods have expansively emerged in recent years. NDT has come a long way since the early years, and those of us involved in the industry today owe a debt of gratitude to these pioneers, many of whom never lived to see the fruit of their labor. Had it not been for their efforts, non-destructive testing as an industry might not even exist.

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CHAPTER 3 OBJECTIVES AND IMPORTANCE OF NDT 3.1. OBJECTIVES : To control manufacturing processes.  Lower manufacturing costs.  Maintain uniform quality level.  Ensure operational readiness.  Make a profit for the user.  To aid in better product design.  To avoid failures, prevent accidents and save human life.

3.2. IMPORTANCE : Various tests can be performed on the same product.  Tests parts are not damaged.  Specimen preparation not required.  Can be performed on parts that are in service.  Low time consumption.  Low labor cost.

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CHAPTER 4 NON-DESTRUCTIVE TESTING METHODS The steps to choosing an adequate NDT method are : Understanding the physical nature of the material property or discontinuity to be inspected.  Understanding the underlying physical processes that govern the NDT method.  Understanding the physical nature of the interaction of the probing field with the test material.  Understanding the potential limitations of available NDT technology.  Considering economic, environmental, regulatory and other factors. There is a wide range of NDT methods which are used by the civil and structural engineering industry. the most common methods of NDT as applied to concrete structures are as follow :4.1. SURFACE HARDNESS METHODS :- The two categories that define concrete surface hardness techniques are indentation methods and rebound methods. These methods attempt to exploit empirical correlations between strength properties of concrete and surface hardness as measured by indentation or rebound. The most commonly used surface hardness procedure is the standard rebound hammer test. The test was developed in 1948 by Swiss engineer Ernst Schmidt and is commonly referred to as the Schmidt Rebound Hammer. The rebound hammer method could be used for : Assessing the likely compressive strength of concrete with the help of suitable correlations between rebound index and compressive strength.  Assessing the uniformity of concrete.  Assessing the quality of the concrete in relation to standard requirements.  Assessing the quality of one element of concrete in relation to another. 4.1.1. PRINCIPLE OF TEST :- Upon impact with the concrete surface, the rebounded hammer records a rebound number which presents an indication of strength properties by referencing established empirical correlations between strength properties of concrete (compressive and flexural) and the rebound number. 6

Figure 4.1(a) : Schmidt Rebound Hammer

Figure 4.1(b) : Schmidt Rebound Hammer Procedure 7

4.1.2. PROCEDURE : A visual examination of the concrete surface should be conducted prior to the test in order to identify a smooth surface suitable for testing.  The test can be conducted in any directional angle where calibration charts are used to mitigate the different effects of gravity.  The hammer is pressed against the concrete surface until a spring loaded mass is released causing the plunger to impact against the surface and rebound a distanced measured by a slide indicator.  The measured distance is referred to as the rebound number. 4.2. PENETRATION RESISTANCE METHOD :- These methods involve driving probes into concrete samples using a uniform force. Measuring the probe's depth of penetration provides an indication of concrete compressive strength by referring to correlations. The most commonly used penetration resistance method is the Windsor probe system. The system consists of a powder-actuated gun, which drives hardened allow-steel probes into concrete samples while measuring penetration distance via a depth gauge.

Figure 4.2(a) : Windsor Probe System 4.2.1. TEST EQUIPMENT :

A powder actuated gun or driver, 8



Hardened alloy probe (diameter 6.5mm and length 80mm) (Driven into the concrete by means of a precision powder charge),



Loaded cartridges and



A depth gauge for measuring penetration of probes.

The strength properties of both mortar and stone aggregate influence the penetration depth of the probe in a concrete. Thus the type of stone aggregate has a strong effect on the relation of concrete strength v/s depth of penetration. For two samples of concrete with equal cube crushing strength, penetration depth would be more in the sample with softer aggregate than the one with harder aggregates. Correlation of the penetration resistance to compressive strength is based on calibration curves obtained from laboratory test on specific concrete with particular type of aggregates.

Figure 4.2(b) : Probe Penetration 9

4.2.2. LIMITATIONS AND ADVANTAGES : The Windsor probe system is quick, cheap and simple to operate.  As with surface hardness methods, the penetration resistance methods do not yield absolute values of strength and must therefore be used as a method of testing variability of strength properties between concrete samples.  It also provides a means of assessing strength development with curing.  This test is essentially non-destructive, since concrete and structural members can be tested in situ, with only minor patching of holes on exposed faces. 4.3. PULL-OUT RESISTANCE METHOD :- Pull-out resistance methods measure the force required to extract standard embedded inserts from the concrete surface. Using established correlations, the force required to remove the inserts provides an estimate of concrete strength properties. Two types of inserts, cast-in and fixed-in-place, define the two types of pull-out methods. Cast-in tests require an insert to be positioned within the fresh concrete prior to its placement. Fixed-in-place tests require less foresight and involve positioning an insert into a drilled hole within hardened concrete.

Figure 4.3(a) : Pull-out Resistance Method

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4.3.1. PROCEDURE :- The most commonly used pull-out test method is the LOK test developed in 1962 by Kierkegaard-Hansen (Kierkegaard-Hansen, 1975). The test requires an insert embedment of 25 mm to insure sufficient testing of concrete with coarse aggregates. A pull-out test measures, with a special ram, the force require to pull from the concrete a specially shaped steel rod whose enlarged end has been cast into the concrete to a depth of 7.6 cm. The concrete is simultaneously in tension and in shear, but the force required to pull the concrete out can be related to its compressive strength. 4.3.2. LIMITATIONS AND ADVANTAGES : Pull-out tests do not measure the interior strength of mass concrete, they do give information on the maturity and development of strength of are preventative part of it.  Such tests have the advantage of measuring quantitatively the strength of concrete in place.  Their main disadvantage is that they have to be planned in advance and pull out assemblies set into the formwork before the concrete is placed.  The pull-out of course creates some minor damage. 4.4. RESONANCE FREQUENCY METHOD :- Resonant frequency methods are noninvasive non-destructive tests that are conducted to determine material properties by measuring their natural frequency of vibration. The two categories of resonant frequency methods are resonant frequency by vibration and resonant frequency by impact. 4.4.1. TEST EQUIPMENT :

An oscillator which generates mechanical vibrations and



Sensors that detect the vibrations. The three most commonly used sensors are displacement sensors, velocity sensors and accelerometers.

4.4.2. PRINCIPLE OF TEST :- The natural frequency of a vibrating structural member is a function of its dimensions, dynamic modulus of elasticity and density. Therefore, measuring either the transverse or longitudinal natural frequency of vibrations of a structural member of known dimensions and material allows the determination of its modulus of elasticity. 11

N=(m²k/2πL²)√(E/d) E=(4π²L⁴N²d)/(m⁴k²) where E = dynamic modulus of elasticity, d = density of the material, L = length of the specimen, N = fundamental flexural frequency, k = radius of gyration, and m = a constant (4.73 for the fundamental mode of vibration).

Figure 4.4(a) : Resonance Frequency Test Method The dynamic modulus of elasticity provides an indication of the mechanical integrity of structural components. Dynamic modulus of elasticity is generally higher than the static modulus of elasticity, which is the recommended parameter in design calculations. The factors affecting resonant frequency and dynamic modulus of elasticity are the concrete mix proportions, aggregate properties, structural specimen size and curing conditions.

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Resonant frequency methods provide an excellent means for studying the effects of extreme temperature changes and loading. 4.5. MATURITY TEST METHOD :- The maturity method is a NDT technique for determining strength gain of concrete based on the measured temperature history during curing. The maturity method has various applications in concrete construction such as formwork removal and post-tensioning.

Figure 4.5(a) : Maturity Test Apparatus 4.5.1. PRINCIPLE OF TEST :- The maturity function is presented to quantify the effects of time and temperature. Temperature versus time is recorded by means of thermocouples inserted into fresh concrete. The measured time history could be used to compute a maturity index which provides a reliable estimate of early age concrete strength as a function of time. 13

The resulting maturity factor is then used to determine the strength of concrete based on established correlations. The factors that lead to variability in testing are :

Aggregate properties,



Cement properties,



Water-cement ratio and



Curing temperature.

4.6. PERMEATION TEST METHOD :- The permeability of aggressive substances into concrete is the main cause for concrete deterioration. Permeability represents the governing property for estimating the durability of concrete structures. Permeation tests are non-destructive testing methods that measure the near-surface transport properties of concrete. The three categories of measuring concrete permeability are : Hydraulic permeability which is the movement of water through concrete,  Gas permeability which is the movement of air through concrete and  Chloride-ion permeability which involves the movement of electric charge. 4.6.1. PROCEDURE : The measuring of chloride penetrability is the most commonly used non-destructive method that provides an indication of concrete permeability through established correlations.  The test involves coring a standard sized cylinder from the in-situ concrete.  The sample is then trimmed, sealed with an epoxy coating from two sides, saturated in water and then placed in a split testing device filled with a sodium chloride solution with an applied voltage potential.  The charge passing through the concrete is then measured where :1.) A value of between 100 and 1000 Coulombs represents low permeability and 2.) A value greater than 4000 Coulombs represents high permeability.

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4.7. IMPACT-ECHO METHOD :- The impact-echo system is a recent development of ultrasonic methods which involves the measuring of concrete thickness and integrity using one surface. The test is also applied to determine the location of cracking, voids and delamination. It is based on monitoring the surface motion of concrete resulting from a short-duration mechanical impact. Specifically, the test measures the amplitude of reflected shock waves to detect flaws in concrete. 4.7.1. PRINCIPLE OF TEST :- The impact-echo system uses an electro-mechanical transducer to generate a short pulse of ultrasonic stress waves that propagates into concrete plate-like structures. The different materials of different densities and elastic properties will reflect the stress pulse at their boundaries. The reflected pulse travels back to the transducer, which also acts as a receiver. An oscilloscope displays the received signal and the round trip travel time of the pulse is measured electronically. The distance of the reflecting interface can be determined by knowing the speed of the stress wave. The factors that affect the detection of a flaw within concrete are :

The type of the flaw and its orientation,



The depth of the flaw and



The contact time of the impact.

4.8. ULTRA SONIC PULSE VELOCITY METHOD : Ultrasonic pulse velocity methods involve propagating ultrasonic waves in solids while measuring the time taken for the waves to propagate between a sending and receiving point.  The features of ultrasonic wave propagation can be used to characterize a composition, structure, elastic properties, density and geometry using previously established correlations, known patterns and mathematical relationships.  This non-invasive technique is also used to detect and describe flaws in material as well as their severity of damage by observing the scattering of ultrasonic waves.

The ultrasonic pulse velocity method can be used to establish :1. The homogeneity of the concrete, 15

2. The presence of cracks, void sand other imperfections, 3. Changes in the structure of the concrete which may occur with time, 4. The quality of the concrete in relation to standard requirements, 5. The quality of one element of concrete in relation to another and 6. The values of dynamic elastic modulus of the concrete.

Figure 4.8(a) : Ultrasonic Pulse Velocity Test Apparatus 4.8.1. TEST EQUIPMENT : Electrical pulse generator, 16

 Transducer-one pair,  Amplifier and  Electronic timing device. 4.8.2. TRANSDUCER ARRANGEMENT : Opposite faces (direct transmission)  Adjacent faces (semi-direct transmission)  Same face (indirect transmission

4.9. CORE CUTTER METHOD : Concrete cores are used for testing of actual properties of concrete in existing structures such as strength, permeability, chemical analysis, carbonation etc. Sampling of concrete cores and testing its strength is described. While Rebound Hammer, Pullout, Windsor probe and ultrasonic pulse velocity tests give indirect evidence of concrete quality, a more direct assessment on strength can be made by core sampling and testing. 

The strength of a concrete core test specimen depends on its shape, proportions and size. The influence of height/diameter (H/D) ratio on the recorded strength of cylinder is an established fact.

Figure 4.9(a) : Core Cutting Apparatus  Strength of core have to be related to the standard cylinder strengths, i.e. for H/D ratio of 2. Thus core should be preferably have this ration near to 2.  For values of H/D less than 1, between 1 and 2, a correction factor has to be applied. 17

 The general rule adopted for fixing the core size, besides the H/D ratio, is the nominal size of stone aggregate and the dia. should be not less than 3 times the maximum size of stone aggregate.  For diameter of core less than 3 times the size of the stone aggregate, an increased

number of cores have to be tested. The core samples can also be used for the following: 1.) Strength and density determination 2.) Depth of carbonation of concrete 3.) Chemical analysis 4.) Water/gas permeability 5.) Petrographic analysis 4.9.1. PROCEDURE : Concrete cores are usually cut by means of a rotary cutting tool with diamond bits.  In this manner, a cylindrical specimen is obtained usually with its ends being uneven, parallel and square and sometimes with embedded pieces of reinforcement.  The cores are visually described and photographed, giving specific attention to compaction, distribution of aggregates, presence of steel etc. 

The core should then be soaked in water, capped with molten sulphur to make its ends plane, parallel, at right angle and then tested in compression in a moist condition.

Factors Affecting Strength of Concrete Cores :

Size of stone aggregate,



Presence of transverse reinforcement steel,



H/D ratio,



Age of concrete,



Strength of concrete and



Drilling operations.

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CHAPTER 5 CONCLUSIONS 5.1. FOR REBOUND HAMMER TEST :- The rebound hammer method could be used for :1. Assessing the likely compressive strength of concrete with the help of suitable correlations between rebound index and compressive strength. 2. Assessing the uniformity of concrete. 3. Assessing the quality of the concrete in relation to standard requirements. 4. Assessing the quality of one element of concrete in relation to another. 5.2. FOR PENETRATION TEST :- Penetration resistance tests on concrete offers a means of determining relative strengths of concrete in the same structure or relative strength of different structures. 5.3. FOR PULL-OUT TECHNIQUE :- The test measures the force required to pull out a previously cast-in steel insert with an embedded enlarged end in the concrete which can be related to the compressive strength of concrete. 5.4. FOR RESONANCE FREQUENCY METHOD :1. To determine the dynamic modulus of elasticity which provides an indication of the mechanical integrity of structural components. 2.

Resonant frequency methods provide an excellent means for studying the effects of extreme temperature changes and loading

5.5. FOR MATURITY TEST :- The maturity function is presented to quantify the effects of time and temperature. The measured time history could be used to compute a maturity index which provides a reliable estimate of early age concrete strength as a function of time. The resulting maturity factor is then used to determine the strength of concrete based on established correlations. 5.6. FOR PERMEATION TEST :- To determine the permeability of concrete. The invasion of aggressive substances into concrete is the main cause for concrete deterioration. Permeability represents the governing property for estimating the durability of concrete structures.

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5.7. FOR IMPACT-ECHO METHOD :- The impact-echo system involves the measuring of concrete thickness and integrity using one surface. The test can be applied to determine the location of cracking, voids, delamination and flaws in concrete. 5.8. FOR ULTRASONIC PULSE VELOCITY TEST :1. An ultrasonic pulse velocity test is an in-situ, non-destructive test to check the quality of concrete and natural rocks. 2. In this test, the strength and quality of concrete or rock is assessed by measuring the velocity of an ultrasonic pulse passing through a concrete structure or natural rock formation. 5.9. FOR CORE CUTTER TEST :- The core samples can also be used for the following :1. Strength and density determination 2. Depth of carbonation of concrete

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CHAPTER 6 FUTURE OF NON-DESTRUCTIVE TESTING Advances in sensors, development of new materials, and miniaturization of devices are all paving the way for new NDT methods. Data fusion techniques are being developed to integrate several NDT methods in the aim of enabling effective data-acquisition, processing, and interpretation of test parameters in relation to material integrity. Much research interest and industry attention have been devoted to acoustic techniques of NDT. This is a result of a clear trend in testing concrete structures using acoustic signals processed by software using advanced data analysis algorithms. NDT of concrete is increasingly gaining acceptance as a means of evaluating material integrity. Low awareness regarding NDT methods is hindering its uptake and is attributable to a lack of understanding construction materials and NDT methods themselves.

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REFERENCES 1. IS: 13311 - 1992, Methods of non-destructive testing of concrete for all methods. 2. Concrete technology by M.L.GAMBHIR, Tata Mc Graw Hill Publication. 3. Concrete technology by M.S. Shetty. S. Chand Publication. 4. J. Helal, M. Sofi, P. Mendis. Non-Destructive Testing of Concrete: A Review of Methods. University of Melbourne, Australia. 5. Workman, G. & O. Moore, P. (2012). Nondestructive Testing Handbook 10: Overview. Columbus: American Society of Nondestructive Testing. 6. Shull, P. (2002). Nondestructive Evaluation: Theory, Techniques and Applications. New York: Marcel Dekker, Inc.

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