8-guidelines for inspection, maintenance and rehabilitation

8/3/2019 8-Guidelines for Inspection, Maintenance and Rehabilitation

1/23

GUIDELINES FOR INSPECTION, MAINTENANCE AND

REHABILITATION OF CONCRETE BRIDGES

CHAPTER IV

NON DESTRUCTIVE EVALUATION OF CONCRETE STRUCTURES

4.1 A variety of Non Destructive Testing (NDT) methods have been developed or are under development forinvestigating and evaluating concrete structures. These methods are aimed at estimation of strength andother properties; monitoring and assessing corrosion; measuring crack size and cover; assessing groutquality; detecting defects and identifying relatively more vulnerable areas in concrete structures.

Many of NDT methods used for concrete testing have their origin to the testing of more homogeneous,metallic system. These methods have a sound scientific basis, but heterogeneity of concrete makes

interpretation of results somewhat difficult. There could be many parameters such as materials, mix,workmanship and environment, which influence the results of measurements. Moreover, these testsmeasure some other property of concrete (e.g. hardness) and the results are interpreted to assess adifferent property of concrete e.g. strength, which is of primary interest. Thus, interpretation of results isvery important and difficult job where generalistion is not possible. As such, operators can carry out testsbut interpretation of results must be left to experts having experience and knowledge of application ofsuch non-destructive tests.

4.2 Purpose of Non-destructive Tests: The non-destructive evaluation techniques are being increasingly

adopted in concrete structures for the following purposes:

(i) Estimating the in-situ compressive strength

(ii) Estimating the uniformity and homogeneity

(iii) Estimating the quality in relation to standard requirement

(iv) Identifying areas of lower integrity in comparison to other parts

(v) Detection of presence of cracks, voids and other imperfections

(vi) Monitoring changes in the structure of the concrete which may occur with time

(vii) Identification of reinforcement profile and measurement of cover, bar diameter, etc.

(viii) Condition of prestressing/reinforcement steel with respect to corrosion

(ix) Chloride, sulphate, alkali contents or degree of carbonation

( ) M t f El ti M d l


2/23

( ) M t f El ti M d l



4.4.1 Rebound Hammer Test

This method is based on the principle thatthe rebound of an elastic mass dependson the hardness of the surface againstwhich the mass impinges. ReboundHammer consists of a spring-controlledmass that slides on a plunger within atubular housing. When the plunger ispressed against the surface of the

concrete, the spring controlled massrebounds and the extent of such rebounddepends upon the surface hardness and,therefore, the rebound is related to thecompressive strength of the concrete. Therebound value is read along a graduatedscale and is designated as the reboundnumber or rebound index. Thecompressive strength can be read directly

from the graph provided on the body ofthe hammer. Depending upon the impact energy, These are classified in to four types i.e. N, L, M and P.Type N test hammer having an impact energy of 2.2 N-m and is suitable for grades of concrete fromM15 to M45. Type P is suitable for grades of concrete below M15. Type L test hammer is suitable forlightweight concrete or small and impact sensitive part of the structure. Type M test hammer is generallyrecommended for heavy structure and mass concrete. A sketch showing various components of ReboundHammer is shown in Figure 4.1.

For taking a measurement, the hammer should be held at right angles to the surface of the structure. Thetest can thus be conducted horizontally on vertical surfaces or vertically upwards or downwards on

horizontal surfaces. If the situation so demands, the hammer can be held at intermediate angles also, butin each case, the rebound number will be different for the same concrete. It is necessary that the testhammer is frequently calibrated and checked against the test anvil to ensure reliable results.


3/23



The rebound hammer method provides a convenient and rapid indication of the compressive strength ofconcrete by means of establishing a suitable correlation between the rebound index and the strength of

concrete.

In general, the rebound number increases as the strength increases, but it is also influenced by a numberof other factors like type of cement and concrete; surface condition and moisture content; age of concreteand extent of carbonation on concrete surface. As such, the estimation of strength of concrete by reboundhammer method can not be considered to be very accurate and the probable accuracy of prediction ofconcrete strength in a structure is +25 percent. If the relationship between rebound index andcompressive strength can be checked by tests on core samples obtained from the structure or standardspecimens made with the same concrete materials and mix proportion, then the accuracy of result and

confidence thereon are greatly increased. It can then be used with greater confidence for differentiatingbetween the questionable and acceptable parts of a structure or for relative comparison between twodifferent structures.

It may also be noted that rebound indices are indicative of compressive strength of concrete to a limiteddepth from the surface. If the concrete in a particular member has internal micro-cracking, flaws orheterogeneity across the section, rebound hammer indices will not indicate the same.

Various types of Rebound Hammer testing equipment are available in market; such as:

(i) Schmidts Rebound Hammer(ii) Smith Rebound Hammer

Digital Rebound Hammers are also available.

4.4.2 Ultrasonic Pulse Velocity (UPV) Test

This is based on the principle that the velocity of an ultrasonic pulse through any material depends uponthe density, modules of elasticity and Poissons ratio. Comparatively higher velocity is obtained when

concrete quality is good in terms of density, uniformity, homogeneity, etc.

Pulse Velocity measurements may be used to assess the homogeneity of concrete, presence of cracks,voids etc., quality of concrete relative to standards requirements, quality of one element of concrete


4/23



concrete member at the pre-determined place and an electric timing circuit enables the transmit time (T)of the pulse to be measured. The pulse velocity is given by V = L/T in unit km/sec.

Once the ultrasonic pulse impinges on the surfaceof the material, the maximum energy is propagatedat right angles to the face of the transmittingtransducer, and best results are therefore obtainedwhen the receiving transducer is placed on theopposite face of the concrete member. This iscalled Direct Transmission or Cross Probing. Inmany situations, the two opposite faces of the

structural member may not be accessible formeasurements. In such cases, the transmitting andreceiving transducers are placed on the same faceof the concrete member. This is called SurfaceTransmission. Surface transmission is not soefficient as Direct Transmission, because thesignal produced at the receiving transducer has anamplitude of only 2 to 3 % of that produced byCross Probing, and the test results may vary from

5 to 20% depending upon the quality of concrete under test.

In view of inherent variability in the test results, sufficient number of readings are taken by dividing thestructural member under test in suitable grid markings of 30x30cm and in some cases even smaller. Each

junction point of the grid becomes a point of observation.

The guidelines for assessing condition of concrete based on pulse velocity are given below:

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

1. Above 4.5 Excellent

2. 3.5 to 4.5 Good3. 3.0 to 3.5 Medium


5/23



compressive strength of the concrete. In other words, larger the exposed length of the probe, greater thecompressive strength of concrete.

This equipment consists of apower-activated gun or driverunit, hardened alloy probe,loaded cartridge and a measuringinstrument such as depth gaugeetc. The probes are 6.35mm indiameter and 79.5mm in length.Larger diameter probes (7.94mm)

are also available for testinglightweight concrete. Probe isthreaded in to the probe-drivinghead and fired into the concreteusing a template. The driverutilizes a standard powercartridge. The power level can bereduced when testing low strength concrete by locating the probe at a fixed position within the driverbarrel. Two types of templates are provided with the equipment e.g. single probe template and a three-

probe triangular template. Exposed length of probe is correlated to the compressive strength of concrete.A typical correlation is shown in Figure 4.2.

The Windsor Probe is basically a hardness tester and provides an excellent means of determining therelative strength of concrete in the same structure or relative strengths in different structures. The test isnot expected to determine the absolute values of strength of concrete in the structure. The method maybe used to assess the uniformity of in-situ concrete, to delineate zones or regions of poor quality ordeteriorated concrete in the structure and to indicate changes with time in characteristics of concrete,when forms and shoring may be removed.

The precision of Windsor probe measurement has been found to vary with the maximum size ofaggregates in concrete. The penetration of the probe in to the concrete is affected by the hardness of theaggregates. Therefore, it is desirable to prepare separate calibration curve for the type of aggregate usedin the concrete under investigation.


6/23



4.4.4 Combined use of Rebound Hammer and Ultrasonic Pulse Velocity

Inview of the relative limitations of either of the two methods for predicting the strength of concrete, bothultrasonic pules velocity (UPV) and rebound hammer methods are sometimes used in combination toalleviate the errors arising out of influence of materials, mix and environmental parameters on therespective measurements. Relationship between UPV, rebound hammer and compressive strength ofconcrete are available based on laboratory test specimen. Better accuracy on the estimation of concretestrength is claimed by use of such combined methods. However, this approach also has the limitation that

the established correlation are valid only for materials and mix having same proportion as used in thetrials. The intrinsic difference between the laboratory test specimen and in-situ concrete (e.g. surfacetexture, moisture content, presence of reinforcement, etc.) also affect the accuracy of test results.

Combination of UPV and rebound hammer methods can be used for the assessment of the quality and


7/23



This test measures the force required to pull out the inserts in the form of specially shaped steel rod ordisc whose enlarged end has been embedded in concrete (Figure 4.3). The force is measured with the

help of a dynamometer. Because of the shape of the steel rod, a cone of concrete is pulled out in the

operation. The pull out strength is calculated as the ratio of the pullout force to the idealized area of thefrustum of the cone. Pullout strength is proportional to compressive strength of concrete. The pulloutstrength is of the same order of magnitude as the direct shear strength of concrete, and is 10 to 30% ofthe compressive strength.

The pull out test is covered in ASTM C 900. The pull out tests fall into two basic categories; those whichinvolves an insert which is cast along with concrete i.e. the test is preplanned for new structures and

secondly those in which insert is fixed by undercutting and subsequent expanding procedure in thehardened concrete and is useful for existing structures and surveys of matured concrete. These methodsare generally known as Cast-in method and drilled hole method respectively. There are variousvariants in cast-in methods like Lok test as well as in drilled hole method like CAPO. In the CAPO (cut


8/23



As per recent approach, break-off test can be conducted in hardened concrete also. Instead of insertingthe tubular disposable forms, the cores are left unbroken at the bottom and the remaining test is carried

out in the same way as described above or the cores are subjected to direct tension test.

Similar to pull out test, the disadvantage of the break-off test is that a small damage to the concrete isrequired to be repaired.

4.4.7 Pull-off Test

The pull-off test is meant for measuring the tensile strength of in-situ concrete. It is equally useful formeasuring the adhesive strength of all kinds of applied coatings (mortars and plastic coating, flexible and

thermo-plastic coating, paint finishes, etc.). The pull-off test method can be used to check the bondstrength of repairs and renovation works on concrete surfaces. The test method is covered by BS-1881Part 207.

Pull-off tester ismicroprocessor based,portable hand operatedand mechanical unit. It isavailable from 5KN to100KN tensile forcecapacities. Theinstrument mechanismmakes it possible to pre-select the rate of loadingand the actual tensileforce being applied isdisplaced on LCDmonitor. The memoryallows transferring of the

recorded data to PC.

This test involves gluing a 50-mm diameter metal disk to the concrete surface, under test, using an epoxyadhesive. If the state of concrete beyond cove is to be assessed or the concrete surface is damp and


9/23



location is so selected with the help of a metal detector that reinforcement disturbance, if any, iscontrolled and minimised during cutting operation.

The test consists of drilling a 100 mm nominal diameter core through the overlay into the parent concretematerial. The drilled core is left without breaking. The top surface of the core is cleaned and dried and acylindrical steel disc 85mm in diameter is fastened to it with epoxy resin and adhesive. After hardening ofthe epoxy, the counter pressure ring with an inside diameter of 105mm is placed concentric with the coreon the overlay surface and connected to the pull bolts with countering plate and coupling. Load is appliedby turning the instrument handle to a required pull force up to failure of the core in tension. Here also thedisadvantage is that a small damage to the concrete is required to be repaired.

4.4.9 Core Drilling Method

Core drilling method is the most direct way of measuring the actual strength of concrete in the structure. Itmostly involves proper selection of location and number of samples to be obtained. Core should be takenso as to avoid the reinforcement. If avoidance of secondary reinforcement or surface reinforcement isinescapable, strength of Core can be taken as 10% less than measured strength. Cylindrical specimen of100mm or 150mm diameter are common; other sizes may also be permitted but the least lateraldimension should not be less than 3 times the maximum size of the aggregates used. The core specimento be tested should preferably have height of specimen as twice the diameter. If there are difficulties ofobtaining samples of such size, the length to diameter ratio is permitted to be lower, but in no case lowerthan 0.95. The samples are to be stored in water for two days prior to testing and are to be tested in moistcondition. The ends of specimens are trimmed and flatten and capped with molten sulphur or highalumina cement or some other permissible capping material to obtain a true flat surface. The specimen isthen tested in compression.

Although drilling of cores and compressive strength test are quite simple (and are covered in IS:1199 andIS:516), but the procedures and influencing factors are to be carefully understood as they affect themeasured value and therefore the assessment of the quality of in-place concrete. The provision of IS 456:2000 vide clause 17.4.3 in this regard is given below:

Concrete in the member represented by a core test shall be considered acceptable if the averageequivalent cube strength of the cores is equal to at least 85% of the cube strength of the grade ofconcrete specified for the corresponding age and no individual core has a strength less than 75 percent.


10/23



These techniques are broadly classified into two groups according to principle of mechanism.

(i) Electrochemical Technique

Open circuit potential measurements

Surface potential measurements

Polarisation resistance technique

Impedence

(ii) Electrical Technique

Resistivity of concrete

Electrical resistance probe

4.5.1 Half-cell Potential Measurement

The most important of the electrochemical techniques that can be adopted for site use is open circuitpotential measuring technique. Based on this principle, ASTM C 876 prescribes a Half Cell PotentialMethod for detection of reinforcement corrosion. The equipment consists of a half-cell, voltmeter andelectrical lead wires. Normally copper copper sulphate half cell is used but other half-cells like silver silver nitrate can also be used.

The method detects the likelihood of corrosion of steel but cannot indicate the rate of corrosion. Thepotential readings obtained can be interpreted as per Table 4.1. Now-a-days sophisticated commercialequipment such as Potential Wheel, Path Finder or Bloodhound are available for which higher speed

and accuracy is claimed.

In Half-cell Potential Test, electrical connection to reinforcing bar is necessary to obtain potentialmeasurements. Normally with connection at one place, sufficient number of readings can be obtained.Sometimes it may not be possible to give connection to reinforcement In such cases the other method


11/23



4.5.2 Magnetic Method for Cover Measurement

Magnetic methods may be usedto determine the location andcover to reinforcement embeddedin concrete. Some of the modelscommercially available in marketare Micro-cover meter,Pachometer, Profometer, Fe-Depth meter, etc. These

equipment are based on theprinciple that the presence

Micro-CoverMeter of steel affects the field ofan electromagnet. Most covermeters consist of a unitcontaining the power source, amplifier and meter and a separate search unit (probe) containing theelectromagnet which is coupled to the main unit by a cable.

Profometer is a portable, batteryoperated equipment used formeasuring the depth of coverconcrete, location and size of thesteel reinforcement embedded inconcrete. The equipment is usefulfor investigating the structureswhere drawings are not available.The equipment consists of datalogger, diameter probe and depth

probe and calibration block.

Profometer Theequipment has sufficient memory


12/23



With = 8 to 12 kcm corrosion is possible

With 8 kcm corrosion is fairly certainwhere, (rho) = resistivity

Resistivity Meter is used tomeasure the electricalresistance of the coverconcrete. With the graphicaldisplay of the major values, it ispossible to determine the spots

in the concrete structure wherecorrosion may occur. Thecombination of resistancemeasurement by ResistivityMeter and potentialmeasurement by

Resistivity Meter CorrosionAnalysing Instrument (described below) furthermore improves the information about the corrosioncondition of the rebar.

4.5.4 Corrosion Analysing Instrument

The method is based on half-cellpotential measurement. By measuringthe corrosion potential of rebars usingcorrosion analysing instrument, it ispossible to differentiate betweencorroding and passive areas of the

concrete structures. Corrosionanalysing instrument is used tomeasure corrosion potential of theembedded reinforcement on the


13/23



Similar equipment are available for rapid determination of sulphates and alkali in concrete. A rotarypercussion drill is used to collect a pulverised sample of concrete and the chlorides are extracted by a

special acid. The amount of acid soluble chloride is determined directly by a chloride sensitive electrodeconnected to a electrometer. If different samples are obtained from different concrete depths, it can beestablished whether the chloride contamination was there in the original concrete or the same has comefrom the environment. The chloride content of concrete can also be determined by chemical analysis ofconcrete in the laboratory.

4.6 TESTS FOR DETECTING DEFECTS IN CONCRETE STRUCTURES

Apart from the above popular non-destructive tests, there are also many NDT tests, which are either

under developmental stages or are being used in other countries for detecting defects in concretestructures. Some of these described below:

4.6.1 Gamma Radiography

Concrete will absorb X-rays or gamma rays, which pass through it and the degree of absorption dependson the density of the concrete. When a ray passes through concrete, it is partly absorbed and partlyscattered. The measuring device should be shielded from the scattered radiation. The density of theconcrete is determined by the degree of absorption of the rays in traversing a direct path of known depth.

The technique involves transmission of wave energy detected by a photographic emulsion or a radiationdetector. The equipment basically consists of a radioactive source, a detector and a remote commandmodule. The equipment is portable and easy to use and exposure time is very small. One suchequipment BETATRON has been developed by CECRI, Karaikudi. However, care has to be taken andproper precautionary measures are to be followed, as such radiation is a health hazard. It is used for:

Defining cracks

Determining the quality of concrete e.g. its homogeneity or the presence of crack

Checking the location and condition of reinforcing bars or prestressing tendons e.g. forerror in positioning, abnormal deformation, steel failures and fractures, corrosion or lackof bond

Checking the quality of grouting


14/23



delamination in concrete bridge decks. This method is quite useful in assessment of deck slab covered bywearing coat.

4.6.4 In-situ Permeability Test

Because of the increasing instances of corrosion in reinforced/prestressed concrete structures, attentionhas been drawn on the significance of permeability in addition to compression strength in assessingquality of concrete.The procedure consists of drilling a small hole in concrete, sealing it with a rubberstopper and then evacuating the air from the hole with a vacuuming pump connected to a manometer.Rate at which the manometer recovers is a measure of permeability of concrete. This method can beused to assess the resistance of concrete to carbonation, penetration of aggressive ions and quality ofgrout in post-tensioned ducts.

4.6.5 Magnetic Field Disturbance Test

This can be used for detecting flaws in the steel embedded in concrete. The test is based on applying asteady magnetic field near a member and scanning the surface of member to detect disturbance in themagnetic field caused by the presence of flaws in reinforcing or prestressing steel.

4.6.6 Acoustic Emission Method

It provides a means of monitoring the initiation of cracking under increasing load. It can be possible tomonitor large structural member for locating the origin of cracking and zones of maximum deterioration.Acoustic emissions are irreversible i.e. emissions are not generated in a material unless it is stressedbeyond prior stress level.As a material is loaded, localised points may be strained beyond their elastic limit, and crushing or microcracking may occur. The kinetic energy released will propagate small amplitude elastic stress waves.These waves known as acoustic emissions are generally not in the audible range and may be detectedas small displacements of transducers positioned on the surface of the material

Acoustic emission method is still under development. However, in future it may be a useful method in

conjunction with in situ load testing as a mean of monitoring cracking origin, its development and toprovide a warning to impending failure.


15/23



This method has been recently developed and successful application has already been made for piletesting. With the help of impact by a hammer or by use of electromechanical transducer, an acoustic

pulse is sent in the structure. The analysis of the reflected waves depicts the voids and internaldiscontinuities and other problems arising out of insufficient compaction, if any, in the structure. Themethod is useful for testing concrete members which provide only one surface for testing. In spite of itsample potential in evaluating in-place concrete, the method suffers from varying interpretations bydifferent operators and is dependent upon skill of the operator.

4.6.10 Ground Penetrating Radar

Radar is analogous to pulse-echo technique, except that pulses of electro-magnetic waves (short radio

waves) are used instead stress waves. An antenna emits a short duration pulse of electromagneticwaves. The pulse travels through the underlying material, and when the pulse encounters an interfacebetween dissimilar materials, some of the energy is reflected back towards the antenna. The antennareceives the reflected portion of the pulse and generates an output signal. By measuring the time from thestart of the pulse until the reception of the echo, the depth of the interface can be determined if thepropagation speed through the material is known. Various elements of Radar System is shown in figure4.6.

4.6.11 Endoscopy technique

Endoscopy consists of inserting a rigid or flexible viewing tube into holes drilled into concrete bridgecomponents or cable ducts and view them with light provided by optical glass fibres from an externalsource. This is a most useful method for inspecting or detecting voids in the grout and corrosion in steel inthe cable ducts. It is also useful for detail examination of other part of the bridge structure, which couldnot otherwise be assessed. Endoscopes are available as attachments for a camera or a TV monitor. It,however, needs an experienced engineer to make assessment of most likely locations of voids in thegrout and probable points of entry of chlorides into the ducts.

4.7 LABORATORY TESTS

The following are some of the main tests which can be conducted in laboratory on representative coresamples of concrete and steel to supplement the results of visual observations and other field tests.


16/23



As a result of special inspection, if condition of any structural member requires evaluation of structure,then load test may be carried out in accordance with clause 10.5 of IRS Concrete Bridge Code, 1997.

This method may also be used for checking the suitability of any structural member for higher standard ofloading or suitability of the member for certain degree of calculated overstress.

The detailed scheme for load test viz. test load, testing procedure, instrumentation for measurement ofrequired parameters, criteria for evaluation, safety precautions, repairs, if any, to be carried out before theload test etc. must be finalised with due care.

4.9 SUMMARY OF TESTS

A general summary of NDT tests is given in Table 4.1. Facilities for a number of tests are still notavailable in India, but have been mentioned, as they might become available later. The engineering

judgement for adoption of a particular test or combination of tests could help in taking effective and fasterdecisions.

The rating and capability of different test methods is given in Table 4.2. The Classification of technique forexamining corrosion of the reinforcement/prestressing steel, potentially the most dangerous problems inconcrete, is compiled in Table 4.3.

Capability of defect detectionTechniqueCracking Scaling Corrosion Wear &

AbrasionChemical

AttackVoids inGrout

Visual G G P G F NHardness N N P N P N

Sonic F N G N N NUltrasonic G N F N P NMagnetic N N F N N NElectrical N N G N N NChemical N N G N N NNuclear N N F N N N


17/23



Chloride Analysis X X X EssentialResistivity X X X Useful

Moisture Content X X X Limited useWater Absorption X X X Limited use

ConcreteStrength

X X X Useful

Permeability X X X UsefulDelamination X X X Useful

UltrasonicMethods

X X X Limited use

Hardness

Methods

X X X X Useful

Radiography X X X For PSConly

Windsor Probe X X X Limiteduse

Coring X X X Limiteduse

X Yes, Blank - No

Table 4.3 Classification of Techniques for examining reinforced Concrete Structures for Corrosion

4.10 REFERENCE OF RELEVANT STANDARDS FOR VARIOUS TESTS

Table 4.4 gives a list of relevant standards for various tests.

4.11 LIST OF NDT EQUIPMENT AVAILABLE IN RDSO

Table 4.5 gives a list of various NDT equipment available in RDSO.


18/23



M

4. Half-cell Potential - - C876

5. Pull-out test - 1881 (Pt.

207)

C900

6. Pull-off test - 1881 (Pt.

207)

-

7. Break-off test - 1881 (Pt.

207)

C1150

8. Maturity Method - - C1074

9. Core drilling Method 1199 & 516 BS EN

12504

-

10 Nuclear Method - - C1040

11. Infrared Thermography - - D4788

12. Electro-magnetic

Covermeter

- 1881 (Pt.

204)

-

13. Radiography - 1881 (Pt.

205)

-


19/23



Compressive strength

Modulus of Elasticity3. Windsor Probe * James Instrument

Inc., USA Compressive strength

4. Pull-off Tester Proceq,

Switzerland Bond strength of overlay and

repair materials to the base

concrete

Tensile and compressive strength5. Resistivity

Meter

Proceq,

Switzerland Quality of cover concrete

Identifying areas where risk ofcorrosion activities is expected.

6. Corrosion

Analysing

Instrument

Proceq,

Switzerland Corrosion potential of embedded

reinforcement

To differentiate between

corroding and passive areas ofconcrete structure.

7. Micro-

covermeter

Corebrand, UK Depth of concrete cover.

8. Profometer Proceq,

Switzerland Depth of concrete cover

Location and size ofreinforcement embedded in

concrete9. Crack Detection

Microscope

Ele International,

UK Width of crack


20/23

GUIDELINES FOR INSPECTION, MAINTENANCE AND REHABILI TATION OF

CONCRETE BRIDGES

Table 4.1

Summary of principal test methods

Method Principalapplication

Principalproperties

assessed

Surface damage Type ofEquipment

Remarks

1 2 3 4 5 6

Pull out test

(cast-insert)

Quality Control

(in-situ-strength)

Strength related Moderate /minor Mechanical Preplanned usage, surface zone

test

Pull out test

(drilled hole)

In situ-strength

measurement

Strength related Moderate /minor Mechanical Drilling difficulties on vertical

surfaces or soffits. Surface zone

test

Break off test In situ-

measurement

Flexural tensile

Strength

Substantial

/moderate

Mechanical High test variability, surface

zone test, very good to checkrepair bond.

Penetration

resistance

In situ-

measurement

Strength related Moderate /minor Mechanical Specific calibrations reqd., limits

on minimum member size,

surface zone test.

Surface-

hardness

Comparative

Surveys

Surface hardness Very minor Mechanical Greatly affected by surface

texture and moisture, surface

test, unpresntative on concrete

more than 3 months old, strength

calibration affected by mix

propertiesInitial surface

absorption

Surface

permeability

assessment

Surface

absorption

Minor Hydraulic Difficult to standardize in situ

moisture conditions and to obtain

watertight seal to surface,

comparative test.

Surface

permeability

Surface

permeability

assessment

Surface

permeability

Minor Hydraulic Surface zone test, water or gas

Resistively

measurements

Durability survey Resistivity Minor Electrical Surface zone test, related to

moisture content, indicate

potential of reinforce-mentcorrosion in zones of high risk.


21/23


CONCRETE BRIDGES

Half cell

potential

measurements

Survey of

reinforcement

corrosion risk

Electrode

potential of

reinforcement

Very minor Electro-chemical Indicates only the probability of

corrosion, Quality of results

depends on moisture content.Placement of half cell has to be

done carefullyAcoustic

emission

Monitoring

testing

Internal crack

development

None Electronic Increasing load required, not

fully developed for site use. Not

very reliable

Dynamicresponse

techniques

Pile integrity Dynamicresponse

None Mechanical/Electronic

Cannot yield bearing capacity


22/23


CONCRETE BRIDGES

(Contd.)

1 2 3 4 5 6

Electromagnet

ic

measurement

Location and depth

of reinforcement

Presence of

embedded steel

None Electromagneti

c

Affected by magnetic-aggregates

and unreliable for congested steel.

Radar Location of voids or

reinforcement

Relative density None Radio active

source or

Radiations

generator

Some safety precautions limit on

member thickness.

Radiography Location of voids or

reinforcement

Relative density None Radioactive

source or

generator

Extensive safety precautions, limit

on member thickness. Essential for

prestressed ducts

Radiometry Quality control Density None Radio active

source or

generator

Safety precautions and limit on

member thickness for direct

method and back scatter method,surface zone test

Neutron

moisture

measurement

Comparative

moisture content

Moisture content None Nuclear Surface zone test, calibration

difficult. Not of much use so far

Depth ofcarbonation

Durability survey ConcreteAlkalinity

Moderate/Minor Chemical Good indications of extent ofcarbonation if area is well sampled

Resonant

frequency

Quality control Dynamic elastic

modulus

None Electronic Specially cast specimen required.

Not very useful

Strain

measurements

Monitoring

movements instructures

Changes in strain Minor Optical,

Mechanical,Electronic

Attachment and reading requires

skill, can only indicate changes instrain

Movement

measurements

at joints

Monitoring

movements

Changes in strain None Mechanical Requires skill to read

Crack

movement

demec gauges

Monitoring crack

widths

Changes in strain None Mechanical Requires skill to read

Spall survey Corrosion risk Indicate extent of

corrosion damage

None Physical recording of all spalls, depth of rebar,

thickness of corrosion and spalled concrete for

chlorides and carbonation


23/23


CONCRETE BRIDGES

ANNEXURE - A(SHEET 2)

REPORT OF DETAILED INSPECTION CONDITION OF VARIOUS COMPONENTS OF THE BRIDGE

Bridge No. Span No.Date ofInspectio

n

Sub-structur

e

Bed blocks Bearings Camber Girders/Beams

Slabs/Decks

Parapet/Railins

Trolleyrefuge/

Footpath

Ballastand

Track

DrainageArrange-

ments

Anyother

compone

nt such

as

diaphrag

m

approach

slab,

jackingbrackets,

etc.

Initial ofinspectio

n official

with

designati

on

1 2 3 4 5 6 7 8 9 10 11 12 13

8-guidelines for inspection, maintenance and rehabilitation

Documents