sähkömiehentie 4 wind tunnel m. umar riaz, farid ullah 08 ... · non-destructive testing of...

Rak-43.3301 Repair Methods of Structures I (4 cr)Autumn 2015 (Period I)

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Sähkömiehentie 4

Wind Tunnel

M. Umar Riaz, Farid Ullah

08/10/2015


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Contents1. ABSTRACT .................................................................................................................................................. 4

1.1 Brief Summary ......................................................................................................................................... 4

1.2 Contribution to the Report ....................................................................................................................... 4

2. INTRODUCTION .......................................................................................................................................... 4

2.1 Investigation Problem .............................................................................................................................. 4

2.2 Aim and Objectives of the Investigation ................................................................................................... 5

2.3 Investigation Methodology....................................................................................................................... 5

2.4 Scope of the Investigation ........................................................................................................................ 5

3. LOCATON DETAILS...................................................................................................................................... 6

3.1 INTRODUCE THE BUILDING AND ITS SITE .................................................................................................. 6

3.2 LOCATION ................................................................................................................................................ 6

4. Site Investigation ....................................................................................................................................... 7

4.1 Visual Inspection ...................................................................................................................................... 7

4.2 Condition of the Investigated Case ..................................................................................................... 8

4.2.1 Corrosion Induced Spalling ................................................................................................................ 8

4.2.2 Aggression by mechanical and physical elements ........................................................................ 9

4.2.3 Weathering of Concrete .................................................................................................................. 11

4.2.4 Protective paint over steel plate and concrete surface damaged ..................................................... 13

4.2.5 Construction Errors ......................................................................................................................... 14

4.3 Non-Destructive Testing [NDT] ............................................................................................................... 16

4.3.1 Methodology of testing: .................................................................................................................. 17

4.3.2 Interpretation of Results:................................................................................................................. 17

4.3.3 Recommendations for additional Testing and Research: .................................................................. 18

5 Conclusion and Recommendations ............................................................................................................... 19

6 Observations – Individual and Group ............................................................................................................ 19

7. Appendices .................................................................................................................................................. 20


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S/no Description

Figure - a Google map- location of wind tunnel

Figure – b Google map- street view of wind tunnel

Figure – 1 Corroded steel leading to spalling of concrete

Figure – 2 Repair works

Figure – 3 Visible loss of fine particles, exposed aggregate.

Figure – 4 Local repair work on the concrete surface

Figure – 5 Local repair work on the concrete surface

Figure – 6 Degradation of appearance (Change of concrete color)



Figure – 9 Moss and lichen growth on concrete surface

Figure – 10 Rusting of steel surface

Figure – 11 Damage to protective paint layer from top of the structure

Figure – 12 Spalling and Rusting of exposed reinforcement due to insufficient concrete cover

Figure – 13 Improper joint construction, fines not filling up the formwork

Figure – 14 Exposed and corroded steel

Figure – 15 Aggregates exposed, poor construction practice

Figure – 16 Schmidt Hammer Testing

Figure – 17 Schmidt Hammer Testing

Figure – 18 Graph for cubic compressive strength of concrete

Figure – 19 Concrete strength Criteria against Rebound number

Figure - 20 Classification of Concrete based on Rebound Number


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1. ABSTRACT

1.1 Brief Summary

A condition survey report has been prepared for the wind tunnel structure located inOtaniemi as part of coursework of ‘Repair Methods of Structures I’. The survey wasconducted with an aim to learn the practical application of condition assessment. Thereport is based on the qualitative findings of the physical assessment. A number ofvisual inspection and non-destructive testing techniques were utilized in theinvestigation and pictures were taken to augment the explanation of the results. Thefindings of visual inspection were abrasion damage, spalling of concrete due tocorrosive reinforcement, construction defects, coloration of concrete, growth of moss,lichens and fungi, rusting of the cylindrical steel protective layer of the tunnel andremoval of protective paint layer from the top surface of the steel protective layer. Asnon-destructive testing of concrete, Schmidt Hammer test was performed on columns,beam, RC wall and main tube of the wind tunnel structure with satisfactory results. Itwas measured that the strength concrete is very good (rebound number > 40). Thedamages of the structure can be categorized as that of local nature with no immediaterisk to the structural performance. The abrasion damage should be fixed before itreaches any serious level of concern. However, endemic cases of fresh repair workswarrants a more comprehensive test of rusting of reinforcement in the structure and apermanent solution must be achieved for spalling.

1.2 Contribution to the Report

There are only two members in group namely M. Umar Riaz and Farid Ullah. Fromplanning and carrying out of the condition survey to the documentation andcompilation of the report, all the work was done in a collaborative manner.

2. INTRODUCTION

2.1 Investigation Problem

The scope was to carry out an inspection and prepare a report on the condition of theselected assignment case; the wind tunnel. This was done in two visits, first theinspection visit primarily included qualitative evaluation of the physical condition of thestructure to evaluate the equipment required for the condition evaluation of this


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structure. The next visit comprised of visual inspection of the wind tunnel structurealong with onsite non-destructive testing.

2.2 Aim and Objectives of the Investigation

The objective of the investigation is to gain an insight into the building deterioration, ifany, with an attempt to further assess the damage using standard techniques. Thebasic techniques involve visual inspection, non-destructive tests and destructive tests.However, in this case destructive testing was not used. In strict meaning of thetechniques, usually the inspection is performed by qualified observers and results aredocumented for further explanation. The aim was to learn the process of inspection ofconcrete structures that are useful in early or timely identification of deterioration anddamage. The results of such survey are very useful in taking an executive decisionregarding repair and maintenance works or further destructive testing, whichever isdeemed necessary.

2.3 Investigation Methodology

A condition survey was planned after an initial visit of the wind tunnel. The scope of thesurvey was defined and a list of instruments required for the condition survey wasprepared. Due to the sensitivity and accessibility, only the exterior of the concretestructure has been included. Consequently, physical condition of the wind tunnel wasexamined using the following two techniques:Visual Inspection

· Crack-width measurement gauge using handheld microscope.

· Infra-red camera.

· Endoscope.

· Camera.

Non-Destructive Tests

· Schmidt Hammer Test

2.4 Scope of the Investigation

Due to restriction to access and out of bound classification for the students, onlyexterior part of the superstructure was included in the survey. Visual inspectionmethods were used to find out any damages to the surface of the concrete. Theseinspection methods are important as they can give valuable insight regarding the


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health of the exposed concrete surface. Whereas, only one non-destructive test(Schmidt Hammer Test) was used to give a representative strength of the variouselements (column, shear wall, beam, and box-girder main tube). However, due tounavailability of test samples, chemical and physical properties in laboratory could notbe tested.

3. LOCATON DETAILS

3.1 INTRODUCE THE BUILDING AND ITS SITE

The wind tunnel is located in Otaniemi, Espoo. It is a massive high strength concretestructure with both functional and aesthetic value. It is located very near to a vastwater body as shown by the map. The wind tunnel experiences large temperaturedifferences (freeze and thaw cycle) every year and high relative humidity all around theyear. Moreover, there are connections between cylindrical steel and supportingconcrete load bearing members.

3.2 LOCATION

Figure-a


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Figure - b

4. Site Investigation 4.1 Visual Inspection

A preliminary survey of the site was performed by the group, on 30th-September-2015,to get a general idea about the physical condition of the wind tunnel structure. Theinitial visit allowed to gather information regarding the surface defects of the concrete.Based on the scope of investigation, the equipment required for the detailed conditionsurvey were acquired and a detailed survey of the structure was conducted on 2nd-October-2015. The inspection started at 3:50 PM. As the survey is greatly affected bythe weather conditions on the survey day, therefore for a careful and accurate


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estimation the Temperature and Relative Humidity were measured by using a DigitalHumidity and Temperature Probe apparatus. The temperature at the start of survey at3:51 PM was 19.5 0C and relative humidity of air was measured to be 45.7%. Handheldmicroscope for observing concrete surface cracks was not used as the structure iscomposed mostly of crack free sections.

4.2 Condition of the Investigated Case

The structure under investigation is a wind tunnel, a heavy concrete structure cast in-situ. As such no structural defects of global nature were observed. But, there is visiblesurface deterioration because of abrasion and weathering, along with some localconstructional defects. The main defects found in this structure are as follows:

4.2.1 Corrosion Induced SpallingMultiple occurrences of spalling were documented. There are numerous small repairson the concrete structure. Most of the repair words are on the bottom side of the windtunnel structure. Spalling is accompanied by the rusting of reinforcement as shown bythe pictures. The reasons for spalling could be the chloride attack induced rusting fromthe use of deicing agents in winter and carbonation induced rusting as being near tosea. Following pictures support the argument.

Figure-1


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Figure-2

In the above pictures, massive repair works can be seen. And such repair works areendemic on the wind tunnel. An educated guess can be made that the spalling ofconcrete is due to rusting. The products of rusting cause expansion as they occupy tentime more volume than the reinforcement itself.

4.2.2 Aggression by mechanical and physical elements

Almost all the concrete surface of the structure seems to have this kind of defect but itis prominent in columns, beams and walls exposed to incoming slanted rains andwinds. Visible loss of fine particles from the concrete led to this conclusion assupported by the picture evidence. This loss of fine particles suggests erosion, abrasionand cavitation (by rain). Also freeze and thaw cycles could have played a huge part asFinland faces serious temperature variations in winters. At places repairs were foundwhich means this problem has occurred in the past and is being taken care of fromtime to time. Below are some pictures to support the argument:


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Figure - 3

Figure - 4

Figure - 5


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4.2.3 Weathering of Concrete

Another main observation was the presence of coloration other than the natural colorof the concrete structure. Although only a surface defect, but this kind of phenomenoncould be attributed to dirt deposit and rain water flow variations which might result indegradation of overall appearance and moss and lichen growth on concrete. Despitenot affecting the structural performance of the wind tunnel structure, such kind ofdefects harms the aesthetic value. This problem was also carefully documented usingcamera, as shown in below:

Figure - 6

Figure - 7 Figure - 8


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Growth of moss and lichens can be seen in the following pictures.

Figure - 9

Figure - 8


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4.2.4 Protective paint over steel plate and concrete surface damaged

There is a considerable portion of cylindrical steel structure in the wind tunnel as well.The steel portion of the structure has been protected against damage by a protectivepaint covering on its surface. The protective coating of paint is damaged at numerousplaces, where presence of rust is visible. Other places don’t show rust yet but are proneto rust with passage of time. This was carefully documented with camera as shown inpictures below:

Similarly, the application of the protective layer of paint on the top of structure isalmost gone. Thus, exposing the concrete surface to damages due to water and snow.

Figure - 10


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4.2.5 Construction Errors

Construction errors like honeycombing, formwork displacement and low concretecover leading to spalling, pop outs and consequent steel exposure at various places.However, due to local nature of these defects, they don’t pose any risk to the wholestructure.

Figure - 11

Figure - 13

Figure - 12


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Figure- 15

Figure - 14


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In the above picture there appears to be exposed aggregate particles all along theedge. One of the primary reasons for this could be that fine particles didn’t fill out theformwork properly or that there exists segregation of aggregates along this surface. Itis something which should be further analyzed.

4.3 Non-Destructive Testing [NDT]

SCHMIDT HAMMER TESTAs the structure doesn’t show any structural damage hence non-destructive testingmethod was applied on the structure to get an idea about the extent of damage. Forthis purpose Schmidt Hammer was used to estimate the strength of concrete. Theelements tested include columns, beams, RCC wall and main tube consisting of boxgirder beam. The pictures of testing are given as follows:

Figure - 16 Figure - 17


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For the cubic compressive strength calculation of concrete following graph was used:

Ref: http://www.academia.edu/8396599/Rebound_Hammer_Test-priciple_procedure_cons_and_pros.....

4.3.1 Methodology of testing:

For every element, a small area was selected. A total of ten readings were recordedand averaged for accuracy of results.

S/No. Element Rebound Values AverageRebound value

(R)

value fc’(MPa)

1 Column 1 48,50,49,48,46,50,52,48,47,49 48.7 0 532 Column 2 49,46,54,44,40,44,48,44,54,38 46.1 0 483 Beam 46,48,48,50,47,53,45,44,44,45 47 90 424 RCC wall 44,48,44,52,40,47,39,51,48,49 46.2 0 485 Tube 51,46,42,51,52,55,54,48,54,43 49.6 90 48

4.3.2 Interpretation of Results:

The rebound reading on the indicator scale has been calibrated by the manufacturer ofthe rebound hammer for horizontal impact.

Figure - 18

Figure - 19


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Ref: http://www.academia.edu/8396599/Rebound_Hammer_Test-priciple_procedure_cons_and_pros.....

As per Figure-20 and values for fc’ from Figure-19 one can say that concrete ofstructure has very good compressive strength and comes under the category of highstrength concrete.

4.3.3 Recommendations for additional Testing and Research:

The minimal exposure of steel at random places shows local defects which cannot begeneralized for the structure hence just GalvaPulse-Surface Corrosion Rate system testcan be done on those localities for checking the extent of corrosion and applying therequisite repair technique for that. This test is chosen on the basis that it is reliable,speedy, and easy to perform and the damage is only local. For destructive testing,samples shall be extracted and Carbonation Depth shall be performed in order toevaluate the cause of corrosion of steel. However, for lifecycle management purpose,the current scope of observations and analysis is insufficient to suggest any repair andmaintenance of the structure.Further research is needed as the outer surface of structure shows loss of fine particles,a special survey shall be designed to check the inner surface of concrete as it being awind tunnel, chance of heavy erosion is there due to high velocity of fluid motion insideduring testing.

Figure - 20


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5 Conclusion and Recommendations

After careful documentation and explanation of the observed facts regarding thephysical condition of the concrete structure, it can be confidently stated that the windtunnel structure is in a good condition. Spalling of concrete seems to be the maindamage to the wind tunnel structure. The growth of fungi, moss and lichens also marthe aesthetics of the structure in this case. The partial coloration of concrete surfacewhich could be attributed to rain and dirt also has a negative effect on appearance. Therusting marks on the concrete surface and large amount of repairs suggest that rustingis widespread. The reasons for rusting could be insufficient concrete cover, carbonationor chloride induced corrosion. Rusting of cylindrical steel surface due to the removal ofprotective paint layer was also observed.

There is scope for the aesthetic improvement of the wind tunnel structure by:

Ø Timely application of the anti-corrosive paint on the top surface of concrete aswell on the steel portion.

Ø Cleaning of moss, lichens and fungus is strongly suggested.Ø A solution for the abrasion damage on surface of concrete should be worked out.Ø Cases of corrosion of steel reinforcements should be treated accordingly. To

make sure of any loss of structural strength due to corrosion, samples should betaken out and tested in laboratory. And a suitable response should be made.

6 Observations – Individual and Group

Condition survey report is a vital tool to make big financial decisions regarding repairand maintenance of existing structures. Therefore, it should be made by a qualifiedprofessional. In the current case, there was no observation regarding crackinghowever, spalling and repair works on the underside of the wind tunnel structure wascommon. The wind tunnel is operated by a private company and is officially out ofbound for students unless official permission has been granted. Due to lack ofaccessibility, the inside surface of the wind tunnel could not be observed. The lack ofdestructive testing also limits the depth of data for analysis. So, the findings of thisreport are somewhat limited. However, this report could serve as a guiding documentif in-detail physical condition assessment is to be made in future.

There were only two members in this group, so all the work was done together.


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7. Appendices


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