Team Hashtag - Aalto...Mar 11, 2015 · Aalto University has given us a task to investigate Otaniemi water tower in part of a course named Repair Methods of Structures I. The water

Rak43.3301 Repair Methods of Structures I (4 cr)

Autumn 2015 (Period I)

Team Hashtag Sami Savolainen Roope Haimila Lauri Vainio László Kovács 3.11.2015

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Condition Survey Report

CONTENT

1 Abstract

1.1 Brief summary of the investigation

1.2 Contribution to the report

2 Introduction

2.1 Investigation problem

2.2 Aim and objectives of the investigation

2.3 Investigation methodology

2.4 Scope of the investigation

3 Location Details

3.1 Introduction of the building

3.2 Location

4 Site Investigation

4.1 Visual inspection

4.2 Condition of the investigated case

4.3 Non-Destructive Testing [NDT]

4.4 Destructive Testing [DT] and Laboratory Studies

4.5 Further research needed

5 Conclusion and Recommendations

6 Observations – Individual and Group

7 Appendices



Number Description

Figure 1 A view of water tower from Ring 1 road

Figure 2 Map that indicates location of the water tower

Figure 3 Freeze thaw cracking

Figure 4 Freeze-thaw deterioration of footings of the facade

Figure 5 Some stirrups did not have sufficient concrete cover

Figure 6 Concrete cover was not sufficient on the edges of facade elements

Figure 7 Insufficient concrete covers was found also in foundations

Figure 8 Rock pocketing in walls where was used wooden formwork

Figure 9 Spalling in SW-elements

Figure 10 Spalling in SW-elements

Figure 11 Cracked footing

Figure 12 Cracked footings

Figure 13 Plastic shrinkage

Figure 14 Hole in elastic seam

Figure 15 Defective water barrier

Figure 16 Condensed water behind the paint

Figure 17 Weathering near the air vents

Figure 18 Spalling near the soil

Figure 19 Some places graffities were covered with gray painting

Figure 20 Color difference caused by vegetation

Table 1 Damage class in different building parts

Table 2 Repair recommendations



1. Abstract

1.1. Brief summary of the investigation

The aim of this study is to investigate the deterioration condition of Otaniemi Water Tower and in light of this, we have pointed out the approaches that we think are necessary for an appropriate condition. During the investigation we have found several typical concrete damages, like freeze-thaw, spalling, reinforcement bar corrosion, rock pocketing, finishing and formwork errors, carbonation caused corrosion, plastic shrinkage, weathering, cracks. For planning of repair methods of the serious problems we need to perform some non-destructive and destructive tests. The most common NDT-s are the impact-echo, hammering, profometer, half-cell potential method and rebound hammer tests. For more accurate information we recommend some DT-s as well, such as taking specimens from the facades on which we can measure the tensile strength of the concrete and the carbonation depth. Another option can be the thin-section analysis and measuring the chloride content from a powder sample. After the observation it can be concluded that building condition overall is 4/5. 1.2. Contribution to the report

Every member of the team took part to condition survey on Thursday morning 1.10.2015. After condition survey team continued group work dividing the tasks and writing the report. Work was continued individually for a week. Team finished the report together and made the presentation on 8.10.2015.

Divided main responsibilities:

Sami Savolainen: east facade notes, visual appearance of the report, buildings history and background, presentation

Roope Haimila: south facade notes, weather conditions, pictures and descriptions, observations, conclusions

Lauri Vainio: west facade notes, non-destructive and destructive testing, further needed research methods, repair recommendations, writing the report contribution

László Kovács: north facade notes, introduce the building, pictures and descriptions, presentation, summary

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2. Introduction

2.1. Investigation problem

Aalto University has given us a task to investigate Otaniemi water tower in part of a course named Repair Methods of Structures I. The water tower’s condition has been deteriorating over time by climate conditions and from mischief (graffities and cuts on element seams).

2.2. Aim and objectives of the investigation Our goal is to find and determine plausible sources of founded damages. Based from our investigation we are presenting suggestion to repair and improve the water tower’s condition so that it will stay in good condition also following 45 years.

2.3. Investigation methodology

To begin with we are looking over possible and usual damaging methods of water towers. We had no permission for using destructive methods. That is why our data collection is mainly visual observing.

From data we get from the site we can determine damage type and possible source of the damage. After this we can suggest ways to repair the building and possible improvements for keeping building in condition.

2.4. Scope of the investigation

Because our low funding we can not investigate higher than our eyes (or our cameras) and hands can reach and as mentioned we can use only non-destructive methods. Also we had no permission to go inside of the building what complicates also the investigation in part of windows and doors.



3. Location Details

3.1. Introduce the building

The Otaniemi water tower is a reinforced concrete structure which was built in 1971, designed by a finnish architect, Alvar Aalto. The total capacity of the tower is 6000 m³. The external shape of the building is a dodecagon. An office building and a heating plant are located below it. The height of the tower is 52 metres from the ground level. The water tank is borne by twelve concrete columns and an irregular central pillar containing a spiral staircase. The building is still in use. The tower is surrounded by trees, which cause different circumstances for the lower part of the structure.

Figure 1. A view of water tower from Ring 1 road.



3.2. Location

Address of the water tower: Otaniemen vesitorni, 02150 Espoo

Figure 2. Map that indicates location of the water tower. Picture source: maps.google.com



4. Site Investigation

4.1. Visual inspection

Details and conditions Visiting date / time: 1.10.2015 / 8 am

Weather: cloudy / light rain

RH %: 88 %

Pressure: 1017.6 hPa

T / T (Dewpoint): + 12 °C / + 12 °C

Wind: 270° / 8 m/s

Visibility: 27 km

No hard rain or exceptional weather conditions have occurred within the last 48 hours. Site investigation was carried out by all members of our group. Everyone had one facade to make notes from. First everybody sketched their facade (Appendix) and made first impression notes of defects and other relevant things. After that we inspected all facades as a group so we were able to have as many observations as possible. These observations were documented to our sketched facades (Appendix) and as pictures which is covered in the next chapter.



4.2. Condition of the investigated case

Freeze-thaw

Figure 3. Freeze thaw cracking Figure 4. Freeze-thaw deterioration of footings of the facade

Figure 3 is taken from the east facade and there is clearly freeze-thaw related deterioration. Surface of the concrete fall’s off as large flakes because of the freezed and then melted water / ice. This is only a visual problem and doesn’t affect structural integrity or health and safety.

Figure 4 is taken from a supporting column in south-east side. There is freeze-thaw related deterioration present. This same defect can be found from just above the ground line in all of the columns and footing. In this case the deterioration mechanism is related to defective water barrier which enables the water to rise capillary from ground to concrete. This creates only visual harm.



Defective cover depths, spalling / Corrosion

Figure 5. Some stirrups did not have Figure 6. Concrete cover was not sufficient sufficient concrete cover on the edges of facade elements.

Figure 5 is from north facade. We are able to see that one end of stirup steel rod has been left too close to the surface of the form in construction phase. It has penetrated the surface due expansion of volume when corrosion occurs. This causes mostly cosmetic problems in this case.

In the figure 6 the situation is the same as above.



In figure 7 we can see same work error as in last page, where reinforcement rod has been left too close to the form and thereby isn’t protected against corrosion with thick enough concrete layer.

Figure 7. Insufficient concrete covers wasfound also in foundations



Rock pocketing / finishing & formwork errors

In figure 8 is a lot of rock pocketing present. The wooden form work has had gaps that have enabled the cement to escape around the aggregate and this leaves holes and gaps between aggregate. This creates a situation where the surface is very delicate to mechanical stresses or freeze thaw. This is only a visual problem in this case.

Figure 8. Rock pocketing in walls where was used wooden formwork.

Carbonation caused corrosion

Figure 9. Spalling in SW-elements Figure 10. Spalling in SW-elements



In figures 9 and 10, there is probably carbonation caused corrosion. This happens when concrete loses its alkalinity and after that it does not protect the steel rods from corrosion. Carbonation is a common problem for sandwich elements used in this era. This is due the fact that dense surface slows the carbonation reaction in concrete. Washed concrete finish that has been used a lot in this era is very porous and does not protect from carbonation. Also typically outer shell is very slim so carbonation does not take very long to reach reinforcement steel depth.

What we are unable to see from figures 9 and 10 is the condition of steel parts that hold the outer shell in place in insulation layer. This is very critical for health and safety. Falling outer shell may cause serious injury or even death. But outer shell does not really affect to structural integrity of the whole structure.

Failure in foundations (support cracks)

In figures 11 and 12, there is a upwards V shaped crack from the footing. The most probable cause for this is a change in soil properties under foundations. Maybe a peak in the bedrock which does not allow loads to be carried evenly. This might have very dangerous effects. But when considering structures age this is not so dramatic if the crack do not grow annually. Although corrosion may occur in reinforcement because of the cracks that let water to flow freely to the steel rods.

Figure 11. Cracked footing.



Figure 12. Cracked footing.



Plastic shrinkage

In this surface in figure 13, you can notice small cracks that are born from excessive water used to wash out a graffiti which created plastic shrinkage.

Figure 13. Plastic shrinkage.



Defective elastic seams

Defective elastic seam that enables water to flow freely to the insulation space where outer shells supporting steels are located. This can have very dramatic effects if water starts corrosion in supportings.

Figure 14. Hole in the elastic seam.



Defective water barrier

As you are able to see from figure 15 the water barrier used in foundations is not in very good shape and it does not work anymore. Moisture that penetrates water barrier rise capillary and create freeze thaw related problems that have covered earlier.

Figure 15. Defective water barrier.



Condensation behind paint on footing

In figure 16, the paint that has been used in footings has fallen off. This is due condensation that has occurred under the paint because capillary risen water was not able to diffuse through the paint and the water vapours pressure or freeze thaw have loosen the paint off from concrete surface.

Figure 16. Condensed water behind the paint.

Weathering at air vents Below at figure 17 the air vents we can see some discoloration. This weathering is caused by the flowing rainwater. For the better visual appearance this area should be repaired.



Figure 17. Some weathering at air vents.



Spalling

In figure 18 we can see spalling near the soil. It is caused by freeze-thaw cycling. The corrosion of the embedded steel is due to inappropriate concrete cover.

Figure 18. Spalling near the soil.

Spalling and painting Spalling and grey painting on the column (figure 19), the reason of the painting might be to cover some graffiti.

Figure 19. Some places graffities were covered with gray painting



Column with different colors

The lower part of the column is darker than the upper one due to different circumstances, which are caused by the tree. This is just a cosmetic problem.

Figure 20. Color difference caused by vegetation.



4.3. Non-Destructive Testing [NDT]

Sounding of the sandwich elements should be executed because of the cracks and delamination caused by corrosion of the reinforcement bars. Additional to visual cracks, the facade elements might also have non-visual cracks and delamination. By hammering the elements other possible cracks and delamination can be surveyed. Non-visual cracks and delamination areas can also be surveyed with impact-echo. Impact-echo is more reliable and accurate than sounding because with impact echo one can find the exact location and depth of delamination and cracks. On the other hand hammering is much faster method to detect these failure types and can give sufficient information about the condition of the elements. It is also possible to detect inner damages and reinforcement bars positions in concrete by using x rays. X ray films give a realistic picture of damage and bar positions but it is really time taking and expensive survey method. Using the x ray method the harmful rays to a user and a researcher of a building has to be taken into account.

The corrosion of reinforcement bars can be visually seen on the facade elements and on columns. It can be notified that some of the reinforcement bars lack concrete cover. Profometer should be used to detect general cover depth of the reinforcement bars. Together with carbonation depth measurement (presented in chapter 4.4) the carbonation level and time of concrete and reinforcement bars can be estimated. Having the knowledge of carbonation level it is possible to predict potential cracks in concrete in the future. The corrosion level of the bars itself can be determined with half-cell potential method. Based on an electrical activity of reinforcement bars and concrete bars under more severe corrosion show bigger potential energy values than low corrosion bars.

If the building is going to be repaired in the future the compressive strength of the concrete has to be solved for structural design. Compressive strength of the concrete can be measured with rebound hammer. Although the rebound hammer test is very quick and easy to perform in situ many factors in concrete are affected to the compressive strength results for example depth of the carbonation on concrete surface and moisture content. Compressive strength measurements need to be taken multiple times so distinct results can be made.



4.4. Destructive Testing [DT] and Laboratory Studies

For finding out the more precise condition of the concrete destructive tests need to be organized. Several destructive tests need specimens from the facades and other concrete structure parts. Specimens are taken from the structures with coring. Coring specimens are cylinders whose diameters are from 50 mm to 80 mm. These cylinder diameters are typical because the destructive tests are easy to perform at the laboratory conditions from specimens of this size.

Clear carbonation can be seen on facade elements and concrete columns. To determine the carbonation depth phenolphthalein solution is sprayed on specimens. Phenolphthalein colors the non-carbonated parts from the concrete specimens and carbonation depth can be measured with measuring tape.

Finding out the tensile strength of the concrete is important when the building is going to be renovated. It is very difficult or almost impossible to attach new concrete to old one if the tensile strength is too low. Usually the tensile strength has to be more than 1 MPa if it can be taken advantage. Tensile strength is determined by performing a pull-off test to cylinder specimens. The failure type of the specimen also tells which part of the concrete is the weakest if specimen consists several different types of layers.

In order to inspect corrosion in reinforcement bars visually and with half-cell potential method the bars need to be notched open from the concrete. The best areas to perform notching are areas where concrete is already started to come off. Notching is a good and quick way to find out a realistic reinforcement in concrete.

To determine the quality and quantity of old concrete thin-section analysis is very good research method. A very thin sample is cutted concurrent with the cross section of the cylinder specimen. By using a microscope one can determine several qualitative and quantitative matters from the sample such as internal cracks, carbonation and relative volume of air pores. Chloride content of the concrete is important to determine because large quantity of chlorides in concrete accelerate corrosion and freeze-thaw processes. Chloride content of the concrete is determined from a powder sample drilled in situ from the concrete.



4.5. Further research needed

The scope of the damages needs to be surveyed first. It is very important to determine what is a general condition of the facades, columns and footing. Damage mapping is a good method for this purpose. Damage map includes cracks, visible reinforcement bars, hollow parts and other information found in concrete structure parts. Finding out the quality and composition of concrete with destructive methods and corrosion level are also important because these subjects determine what kind of repair methods can and has to be used.



5. Conclusion and Recommendations

Our groups task was to define the actual condition of the watertowers concrete structures and what kind of mechanisms are causing concrete structures to deteriorate. We investigated this problem by making a site visit which was the main base for our report. From our site finding we evaluated the buildings condition. Found defects and future recommendations are presented in tables 1 and 2 below.

Part Defects Intensity Damage class

Comments

Footing Cracking Spalling Lack of water barrier Color variation Corrosion

10 % 80 % ? % 90 % 25 %

4 Spalling present due freeze thaw cycling and cracks due forced bending of the footing. Improper water barrier also enables water from the soil to transfer to structure. We were unable to determine water barrier defects intensity with NDM. Also color variations present. Corrosion present in the surface.

Columns Cracking Spalling Lack of water barrier Color variation Corrosion

0 % 50 % ? % 30 % 5 %

3 Freeze thaw cycling and cover depth caused spalling. Improper water barrier also enables water from the soil to transfer to structure. We were unable to determine water barrier defects intensity with NDM. Also color variations present. Corrosion present in the surface.

SW-elements Cracking Spalling Damaged seams Color variation Corrosion

75 % 75 % 95 % 5 % 15 %

5 Cracks and spalling in 75 % of the elements. Carbonation and corrosion level inside the outer shell is not evaluated. 95 % of the elastic seams were damaged. Some color



variation. Corrosion marks in the surface and edges.

Casted walls pump room (east facade)

Cracking Spalling Color variation Corrosion

10 % 75 % 20 % 10 %

4 Almost all of the surface layer has damages caused by rock pocketing and formwork errors (uneven surface). Joints to other structures are also uneven or cracked open. Corrosion present in lower parts.

Table 1. Damage class in different building parts.

Part Repair method

Footing Strengthening the foundation with new concrete so that sinking will be terminated. Removing the old waterproofing where it exists and mounting a new waterproofing to outer surface of footing.

Columns Cleaning the visible reinforcement bars, protecting them for corrosion and applying mortar by hand. Spreading the hydrophobic impregnation on column surfaces. Painting the columns with a new facade paint.

SW-elements Cleaning the visible reinforcement bars, protecting them for corrosion and applying mortar by hand. Spreading an anti-carbonation coating to element surfaces. Removing the old element seams and installing a new seam strip and elastic seam mass.

Other parts of facade

Adding non-structural crack sealer to facade cracks. Spreading an anti-carbonation coating to element surfaces.

Table 2. Repair recommendations.

Buildings overall condition 4 / 5, this is due critical defects that can be harmful for health and safety. If no actions to improve structures condition are not carried out damaging will proceed further.



6. Observations – Individual and Group

One major challenge was to determine the mechanism behind deterioration. There were so many problems present that it was hard to point out the most important ones. We also could have familiarize the given literature more aquidently.

We also noticed that all parts of the building which were protected by the upper water tank were in better condition than parts exposed straight to all weather conditions. This is due lower rain and moisture exposure.

As a group we achieved to support each other’s knowledge and we all learned a lot this way. Using english as our groups main communication language added some limitations. None of us were native speakers. This probably didn’t affect a lot to the final outcome but made working more difficult.



7. Appendices

1. Site visit notes, west facade, 1.10.2015 2. Site visit notes, south facade, 1.10.2015 3. Site visit notes, east facade, 1.10.2015 4. Site visit notes, north facade, 1.10.2015









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Team Hashtag - Aalto...Mar 11, 2015 · Aalto University has given us a task to investigate Otaniemi water tower in part of a course named Repair Methods of Structures I. The water