non destructive testing mr nr patil

8/14/2019 Non Destructive Testing Mr NR Patil

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t i S _ O SRES College of Engineering Kopargaon Maharashtra - 423 603

NON DESTRUCTIVE TESTING (NDT)ADVANTAGES AND LIMITATIONSAuthorN.R. fatil

Assistant ProfessorBharati Vidyapeeth University I

College of Engineering DhankawadiPune-43.

[email protected]

AuthorJ.R. Patil

Professor Y Patil College of Engineering

Akurdi Pune-44jalinder [email protected]

ABSTRACT: Non destructive testing is a form of testing to be carried out on variousconstruction members and materials without causing any permanent damage tothem. As T isused in concrete it can also be used very effectively for other building members and materials.

Thispaper covers case study of T on concrete as well as other elements of building.Concrete has been used in construction industry for its compressive strength and for protectionof reinforcement of steel. T is used to test concrete by two methods namely surface testingtechnique and through testing technique. In surface testing Schmidt Hammer pull out tester etc.are carried out and compressive strength is determined by using imperial formulaIn through testing technique ultrasonic pulse velocity impact echo X-ray etc. are the techniquesusedINTRODUCTION:Non- Destructive Testing is a form of testing to be carried out on various construction materials. and members without causing any permanent damage to them members. Though,' N.D.T. ispredominantly used on concrete, the same can be very effectively used for other building.materials/members also. This paper covers case studies of NDT on concrete as well as otherbuilding elements.Concrete has been used in construction industry for its compressive strength and for-protection toreinforcing steel. NDT application to concrete can be broadly divided into 2 methods i.e. surfacetesting and through testing. Surface Testing Technique:Schmidt Hammer, pull off tester, Windsor probe test etc. fall in this category. These tests arepractically used to determine the compressive strength of concrete. It is interesting to note thatnoNDT can measure the compressive strength of in situ concrete directly but all the testsmeasure some other property of concrete like surfacehardness, toughness, penetration resistanceetc. and the compressive strength is deduced based on empirical formulae.B Through Testing Techniques: .Ultrasonic Pulse Velocity, impact echo, X Ray, RADAR, etc. are the techniques which fall inthis category. All these techniques have a common theory of passing some form of waves, eitherhigh frequency sound or electromagnetic or mechanical or light etc., through the body ofconcrete to assess the interiors of the same. Some of these techniques have been successfully

'.' in laboratories to preduct the compressive strength of concrete but due to extreme variables t ISPracticallynearing impossible task to do the same on site. .',.In Indian construction industry NDT finds its application on several fronts. Prediction of. ;compressive strength by using any of the techniques has maximum demand. Compressive

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strength of in situ concrete of age less than one year can be predicted by using Schmidt Hto an accuracy 15%. After this age the concrete starts getting carbonated thereby beco .hard on surface. Since, the technique of rebound hammer is based on surface hardness,inaccuracy in measuring the compressive strength of older concrete goes up. It is recommeby international codes and manufacturers of Rebound Hammer that the carbonated concrete sbe ground off using grinders to the depth of uncarbonated concrete before 'using this techniThis procedure has several practical limitations and cannot be meticulously followed on .Hence, Schmidt Hammer becomes practically not suitable for older concretes.Another popular technique to find out compressive strength is Ultrasonic Pulse Velocity TUltrasonic Velocity in concrete depends on 3 properties of the-sameviz. Dynamic Moduluselasticity, density, Poisson's ratio. These properties in turn depend on the stress in the conmember, the water content, the methods of production of the concrete member etc. Due to,fact that all the codes recommend that substantial No. of cubes shall be tested with Ultrasand cube crushing strength on a site before using USPV technique to predict comprestrength of structural concrete for the site.

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Case study-Application ofNDT for testing ofRCC buildingRCC building constructed in 1970 in Mumbai containing 13 floors and 25 flats was tested for t ssafety by using rebound hammer test, ultrasonic pulse velocity test and carbonation test. Alsovisual and delam survey was carried out and the observations and instrumentation test resultspresented in this paperVISUAL SURVEY:The structure was investigated flat by flat for ease in observation. Each column, beam and swithin the section was observed for a range of defects such as cracks, spalls, rust stains, c .seepage (water) etc. These defects were noted on the observation sheets which formed the bof the date collected. Each section observation was plotted on an individual observation shVarious symbols used in definition of observed defects were as per attached legend sheet.DELAM SURVEY:Every column, beam was subjected to tapping by three different types of hammers. effective was the medium hammer which gave the delams from 15 mm to 25 mm depth.hollow sound was recorded as Hollow and that part was evaluated for remedial measure.results of each structural members viz., columns beams were again recorded onto observati'sheet and the cumulative area of defect was simultaneously recorded. \,INSTRUMENTATION:Three different tests were carried out on a representative spread of columns and beams.tests thatwere carried out identified the damage potential due to four different defects.The tests carried out comprised of:

1 CARBONATION TESTS to identify the depth of carbonation.2 REBOUND HAMMER TESTS to give a picture of the surface strength of thesection. ULTRASONIC PUSLE VELOCITY TESTS to define the integrity and dof defect in the RC section.

CARBONATION TEST:Chemical reaction of the concrete surface to a Phenolphthalein based' staining agentrecorded at varying depth at the same location. The first depth were the stain turned pink,record s the depth of carbonation. These tests were carried out jn close proximity to the s 'strength profile test locations to note the densification effect of carbonation on surface strength. :

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SURFACE STRENGTH PROFILE: REBOUND HAMMER METHODThe hammer is principally a surface hardness tester. The principle is that when a spring-loadedshaft strikes a surface, its rebound is a function of the surface. The force on the shaft and itsrebound developed are measured by the hammer. The Operations are very simple. They consistof releasing the plunger from locked position by pressing gently against the hard surface andcheck for zero setting of rebound number indicator on the graduated scale.The hammer is then strongly pressed against the prepared spot of the surface under investigationwhich leases the spring-loaded weight which strikes the plunger and causes the impact Theposition of the indicator on the scale is read as rebound number and recorded in test data log.This recorded data log is then corrected for position of the hammer position of the reinforcement,moisture contents in the elements and carbonation depth. This together with other data wouldhelp design of other actions .INTEGRITY TESTING: ULTRASONIC PULSE VELOCITY MEmOD:.It is known that speed of a sound wave varies with the density of its propagation medium. The'Jl}ncreteis a medium through which ultrasonic pulse is made to propagate. The pulse is sentough transmitting transducer acoustically coupled with the surface and is received by a similaruansducer placed in position. The time elapsed from transmittance to receipt of pulse ismeasured in microseconds and displayed. The pulse velocity is calculated by expressions: -

Pulse travel pathPulseVelocity Pulse travel timeIs converted to rnIsec or KmIsecThe Pulse velocity in concrete ranges from 3 krnI see to 4.8 krnI seeTheULTRASONIC PUSLE VELOCITY in concrete is a function of density and compactness ofconcrete, which within limits bears a relationship with strengths and elastic properties ofconcrete. Beyond these limits, the relationship is very weak.OBSERVED DEECTS AND DISTRESS SYMPTOMS:RCCFRAME:The observations are based on visual and delam survey conducted by team of engineers andtechnicians as per standard methodology. The frame element shows presence of distress in the. form of cracks and delams, seepages. The cracks are mostly longitudinal and at some places.hese cracks are observed to be transverse. Most of the longitudinal cracks are along the rebars,mdicating high corrosion activity. The cracks extend from ground floor in some of the. Comer columns show cracks 10mm wide within permissible limits. The crack width is varyingfrom 1mm to 10 mm. Cracks wider than 20mm indicate severity of distress. The crack depth asrecorded varied from superficial to about 20mm deep. Few cracks on the exterior face are deepand extend up to the rebar depth. The crack depth of about 30mm indicates that the crackextends up to the rebar location. The cover depth on an average is 40mm. The depth of crackbeingwithin the cover concrete, it can be concluded that the core concrete is not affected in mostof the columns. Beams also show a similar distress level but compared to columns they arehavingless distress. Slab cover shown crazing seepage marks efflorescence in most of the'. flats. Delamination is observed in stilt areas. Most of the columns beams in this area are.shOwingcracks. Instrumentation results correlate with the observed distress pattern. UPVresultsprove that the integrity of the columns tested is poor but in some of the locations they are.beyondpermissible limits. Surface strength tests show uniform deterioration l strength. Beams

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in stilt area show porosity honeycombing, this being a construction defect affecting the ensection, for which grouting will have to done. The UPV readings being taken on plaster s plaster of paris, the effect of plaster carbonation and hardening is accounted and it tconcluded that the member shows uniformdeterioration, Carbonation test is carried out vthe carbonation depth as being 10 to 30mm in locations indicating the part cover is becarbonated. Carbonation is normally extensive along the face of the columnslbeams and 1on other sides. Assuming concrete has been manually made and casting has been in stagesdiscounting for carbonation induced increase in surface strength. The grade of concreteexists today is about to MIS to M20. However as most of the core being unaffectedcarbonation and corrosion affected distress, the frame is safe, if cover is repaired. The staira jlanding beams and soffit show distress in the form of cracks hollowness delamination.FAC;ADEThe facade of the building shows weathering effect. The facade shows beam wall delaminatland column wall delamination to some extent This is a potential area for seepage propagatiThe plaster on all faces shows crazing, cracking. Cracks arising due to thermal variation arenoticed around most of the openings. All theses defects lead to common defect mainly seepSeepage near to any RC member leads to further propagation of defects like carbonationcorrosion. The terrace Parapet wall is also seepage prone. Plumbing and sanitation lines aremaintained well. Hence they need to be repaired. Most of the lines are covered with vegetatigrowth around it which will lead to the seepage problems in future. Vegetation growth tendspenetrate the roots in to the RC section and wall section. These roots create cracks in the sectiand should be removed immediately. In general no vegetation or plants should be allowedgrow on .the building elements. Defects in soffit of balcony slab and lintel are in the formdelaminating cracks, hollowness. Stair case waist slab shows hollowness and crazing. Re .to such areas are essential.WATER PROOFING:Terrace water proofing is reported to be in good condition as same has been done recent)There are no leakages reported. Most of the external walls show seepage in the building.parapet wall show crazing on most of the locations. It has been reported that in many flatsis seepage from flat above. This seepage is from toilet and sunken area and this being an intematter needs to be appraisal to every member of society to rectify this defect beforerahabilization work is completed. In case it is decided to rectify such defects from societythen the bill of quantity shall undergo changes accordingly.GENERAL:General cleanliness is maintained and can positively be enhanced overhead water tanks sheleakage marks. Surface crazing and seepage marks will require repairs and replasteriPlumbing lines are not maintained. During replastering it will be essential for a total retrofitall lines as during working damage can occur to the same.

TABLE NO .. LEGEND SHEETLEGEND DESCRIPTIONSOMC MINOR CRACK.OC OPEN CRACK..WC WIDE CRACK RC CRACK ALONG MAIN REINFORCEMENT

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5. DC DIAGONAL CRACK6. HNC BEARlNGSHOULDER HAUNCm/CRACK

i 7. DL DELAMINATED SECTION

8. SPL SPALLING

9. RP CRACK PERPENDICULAR TO THE MAIN- REINFORCEMENT10. .rs JUNCTION S P ARA TION11. CWD COLUMN WALL DELAMINATION

d 12. BWE BEAM WALL DELAMINATIONtr 13. SG/ F , C , B) S) SAG IN FOUNDATION, COLUMN, BEAM,SLAB.

14. CRA CRAZING 15 BG BUILDINGa 16. STL SETTLMENT

17. TL TILT -- rJif 18 SC STEEL CORRODED q a D 19. SPM SEEPAGE MARKS1I t 20. OSPM OIL SEPAGE MARKS 21. SPE SEEP AGE EVIDENTn o s 22. PO POROUS;e 23. H HOLLOWNESS SECTIONSiV e d 24. PTP CARBONAGTED SECTION1- 25. PTN NON CARBONATED SECTION 26. BF BOTTOM FACE

27. SF SIDE FACE

28. GRN GRID REFERENCE NO.ll 29 PPT PRECIPITATION

m e 30. HC HONEY COMBING

l 31. RS RUSTINGr 32. ENC ENCASEMENT: 33. SE STEEL EXPOSED

34. NA NOT AVAILABLEINOT ACCESSIBLE- 35. PP PAINT PEELING

36. PL LOOSE PLASTER37. POP PLASTER OF PARIS38 FC FALSE CEILING39. LC LINTEL CRACK

40 BSD BEAM SLAB DELAMINATIONU Observations and instrumentation test results of arcand floor external side .eOL OBSERVATIONS TAPPING BEAM OBSERVATIONS -TAPING REMARKSNO NO. 1 RC,DC,CRA H 1/2 RP,CRA,RC H2 RC,CRA H 2/3 RP,CRA,RC H3 RC H 34 RP,CRA,RC H

4 RC H 9 RP,CRA,RC -H

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5 RC,SC,SWD H 3/10 RP,CRA H

6 SPL,RC,SPM H 4/11 RP,CRA H14 CWD,SPM H 5/7 RP,CRA H13 CWO H. 118 RP,CRA H15 RC,CWO,CRA H 4/5 CRA,RP H h'17 RC,CWD H 16/21 RC,RP H 18 RC,CWD,CRA H 18124 RP H I N

14/18 BWD,RP,CRA H 14/23 RP,CRA H LOt 22123 CRA,DL H22129 RC,SC,SPM,DL H 29/30 SPM,DL,SPL H --

INSTRUMENTATION: \ OCATION REBOUND HAMMER ULTRA PULSE REMARKTEST VELOCITY TEST Est 2 ro AVG DIST READ VEL

15 22 30 28 26 260 99 2.63 POOR 1 48 38 32 39 1.26 UNCERTAIN 24 20 20 21 260 200 POOR \5 36 40 40 38 UNCERTAIN ,--24 22 30 28 26 260 121 2.15 POOR CN23 24 20 20 21 260 175 1.33 POOR -

CARBONATION TEST: LOCATION CHANGE IN COLOUR REMARK Cl COLOURLESS 30MM - iC2 COLOURLESS 25MM , --;--2) Observations and instrumentation test results of flat no101 ,--

COL OBSERVATIONS TAPPING BEAM OBSERVATIONS TAPING REMAf''''NO NO.

15 CWO H 15/13 LC,RC H13 CWO H 13/20 POP H19 CWO H 19120 POP H . \20 CWO H 15/19 POP H 21 CWO H 13A116 POP,RP H ilN2 POP,OK H 20/21 OK H r8 CWO H 1/2 POP H16 OK H 2/9 POP,MC H 10 F.C. POP H 9/10 POP H -

POP H 3/10 POP, RP H 1- ,,,3 , -II CWO, POP H 2/3 RP H 'I17 F.C. H 2A13A L.C, SPM H

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.. INSTRUMENTATION-

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.SRES College of Engineering Kopargaon Maharashtra - 423 603

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SLAB OBSERVATIONS A 4A LC RP HI FC 3/4 RP POP HII SPM 4/11 OK HIII OK 11/12 RP H

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NSTRUMENTATION:LOCATION REBOUND HAMMER ULTRA PULSE REMARK

TEST VELOCITY TESTt 2na 3ra AVG DIST READ VEL9-10 14 16 18 16 200 72 2.78 POOR14-11 20 22 22 22 200 79 2.53 POOR

r: CARBONATION TEST:V LOCATION CHANGE IN COLOUR REMARKI Cl COLOURLESS 20MMr CI8 PINK

3 Observations and instrumentation t est results of flat no 402COL OBSERVATIONS TAPPING BEAM OBSERVATIONS TAPING RE .1ARKSNO NO.3 CWD H 10/11 RP H4 OK H 3/10 RP BWD H5 OK H 4/11 OK H10 CWD H 3/4 OK H11 CWD H 7 RP H7 CWD H 4/5 RC H17 OK H 5/7 OK H18 OK H 14/18 Me H 14 OK H 18/24 OK H22 OK H 23/24 RC CRA HSLAB OBSERVATIONS 14/17 MC HV CRAVI SPMVII CRA

LOCATION REBOUND HAMMER ULTRA PULSE REMARKTEST VELOCITY TEST st 2nd 3ra AVG DIST READ VEL10/11 14 . 14 14 14 300 126 2.38 POOR 3/4 26 28 28 28 300 174 1.72 POOR

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CARBONATION TEST: LOCATIONSRES College of Engineering Kopargaon Maharashtra - 423 603

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C5CHANGE IN COLOUR REMARK

P N KOBSERVATIONS & RECOMMENDATIONS

1. The defects in the RC members are due to a combined effect of carbonation, corrosion giveffect of continuous drying and wetting in the vicinity of thin RC Sections. The results of vi reiand tapping prompt us to following observations. The Combined results ofUPV surface stre corand carbonation all confirm that the distress is restrictive in the surface cover of the RC mem Tl:Surface rehabilitation of external surfaces is essential. RC section in stilt is exposed ext T h tcarbonation and corrosion. 2. The propagation of defects will proceed faster once the entire cover has deteriorated. C cowidth and depth of.crack in most ofthe column is within acceptable safety limits Instrumentati v 1 Jalso confirms the prognosis that the cover of most the RC sections shows distress but it is wi ' ;acceptable limits. Surface strength shows a major reduction. Carbonation has reached p ,cover depth on some of the RC members. Corrosion potentials are 90 to 95 percent at soexternal locations where tests have been conducted Core concrete is in good condition butcover will require repairs.3. The external plaster has failed due to delamination; crazing and cracks hence total retrofit'essential:4. Water Proofing will not require retrofitting as it is reported to be in good condition.5. Overhead Water tanks will require repairs including grouting and replastering.

replumbing of sanitary lines will be required.6. A well-defmed and specified rehabilitation plan is essential and this programme shobe carried out under expert's guidance. Some items of repairs should be taken up immediatelyone or two column/beam locations in the stilt area. Thelest of the repairs can proceed inphased manner .. Due to the expected monsoon season. It will be of advantageous to take uprepairs right now and start with the internal repairs during monsoon. Also the effect ofmocan be noted by the Supervisory staff at site during monsoon. The external repairs cansuitably modified to take that into account. The phased plan can extend to over l O.to 12 monHowever 'above points are based on observation and are fairly accurate. Foundation assessmhas not been carried out.7. The cost of rehabilitation will be about Rs. 42 lakh to Rs. 45 lakh. The costs are based onmarket prices as of 1st August 2001. The split up and essential list can be worked out basedthe budgetary constraints. It is our opined that repairs are essential should be carriedimmediately. The committee is suggested to plan their repair fund mobilization based on 'realistic figure. This budget does not consist of any provision for extra structural supportfor the sunshades that will be essential. It also does not cover any defect not identified due to'inaccessibility during inspection. However the budget is realistic and should not vary beyopercent of the stated figure. ..8. All observations and test results are based on factual records. No suppressionextrapolations have been adopted. Foundation status survey has not been carried out due to..availability of details. The observation and facts presented here relate to the findings as of.date of investigation. The process of deterioration is continuous and the level of distress will

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non destructive testing mr nr patil

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