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Corrosion Factors That Attack Buildings

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    5       Real Life Example

    5.1     Introduction

    This chapter will explain and analyze a real life example of a building that was affected by corrosion factors and had to be repaired. This section of the project will help the reader to understand the need for repair under specific circumstances and how such repairs can be applied on a real building. This chapter will examine the corrosion factors that affected the specific building. Subsequently the building will be analysed from a variety of perspectives in order to understand how the corrosion affected the building itself and its components. Furthermore, this chapter will discuss how repair methods can take place and apply to the building, and how those methods can be used to replace and improve the properties of the building.

    Drawings and pictures of the building will be used to explain how the building has deteriorated and the areas that were more seriously affected. The use of these images will help the reader to better understand the situation. The drawings that will be used are actual images of the building taken by the company that was responsible for its restoration. In addition to these drawings that were done in order to facilitate the redesigning of the building, the initial drawings of the original building were collected as well. These two sets of drawings will help the reader to see exactly where the repairs took place and the effect they had on the building and its properties. Furthermore pictures were taken from the site to further assist with explanation and analysis and to give the reader a better view of what the repairs look like.

    In terms of the location and environment surrounding the project area it must be indicated, first of all, that the project consists of three different buildings. These buildings range from three to four floors each. The first two buildings have three floors each and the last one has four floors. The building is located in a city named Kavala which is in the Northern part of Greece. It is situated in the suburban area of the city and is on a hill with at a height of between 500 to 600 meters. For the purpose of understanding the deterioration factors it should be noted that the city it self is on the sea side and, especially during the winter, it suffers from extreme weather conditions. The temperature of the area varies tremendously from time to time. Temperatures can reach 40o C during the summer and even -10o C during the winter. As previously indicated in a preceding chapter of this report, temperature is a factor of corrosion for buildings because it facilitates contraction and expansion of the building material and this lead to the formation of cracks on the surface. Moreover since the city in which the project is taking place is close to the sea, sea salts along with moisture can also affect the building and cause it to deteriorate. This kind of deterioration is called chloride contamination as it discussed in a previous Chapter of this paper. In addition to the sea salts, de-icing salts affect the building during the winter period. This is because the building is surrounded by main roads that lead in and out of the city. The presence of main roads and highways around the building also implies that the building is under attack from pollution factors, especially the carbon dioxide that is produced from cars. This kind of corrosion is called carbonation and was also explained earlier in this report.

    The building was initially completed in 1975 when it was first used as a College. A few years ago, in 2000 a decision was made to cease using the building for that purpose because of the level of corrosion on it. For that reason it was closed to the public. Two years later it was proposed that this building should be repaired so that it could be reused in the future. The designing part of the project took two (2) years to complete and in 2004 the work on the site started. The work went well initially but soon serious problems developed with the payment of workers and so the repairs on the building stopped. In 2006 work started again, and, with no further delays, all the work was completed this time. The project was completed at the beginning of 2008 and will now be used as a part of a hospital that was built very close to it.

    5.2        Dimensions of the Structure

    As mentioned before the structure consists of three buildings of three to four floors. However this does not include those floors over ground level. More specifically, the buildings consist of one or two floors under ground level and two to three floors above it, including the ground floor. The highest point of the building is at 9.95m above ground level with the ground floor being 3.45m in height and the other floors above it 3.25m. For those floors under ground level, the first floor has a height of 3.15m and the second, where there is one, is just 3m high. This can also be seen from images of the sections of the buildings that are provided below (Figures 5.1, 5.2, 5.3).

    Figure 5.1 – Building A

                For Building A it can be seen from its section (Figure 5.1) that it consists of three levels above ground and one below it.

    Figure 5.2 – Building B

    Building B (Figure 5.2) also has three levels above ground level and one below it and has the same shape as the first one and is an extension of Building A. It must be noted that all three buildings are extensions of each other and are all somewhat connected together. Although they are three separate buildings they work as one. For the third and final building (Figure 5.3 – Building C) as it can be seen from the images below, it also consists of three levels above ground level as the other two buildings, but there is a difference in this building since it has two levels below the ground giving a total height of 16.1 meters. The other two buildings (Building A and B) have a height of 13.1 meters each.

    Figure 5.3 – Building C

                The dimensions of the three buildings vary from floor to floor. Each one of the three buildings has a length of about 33 meters giving a total of 100 meters when placed together. In width they are 18 meters each. However the width of the top floor for each building, at a level of 9.95 meters above the ground, is less than the rest of the floors as can be seen from the images above (Figures 5.1, 5.2 & 5.3). It was measured to be 12 meters. Finally, for Buildings A and B ( Figures 5.1 & 5.2) it can be seen that the width of the second floor, at a level of 6.7 meters above ground level, is again less than the floors below it but more than the top floor. The second floor measures 16 meters.

                When all three buildings are put together their formation is that of half a circle and that is how the entire building appears on the plan. Even though it was not possible to provide a copy of the plan, Figure 5.4 gives a reasonable idea of what the building looks like. This picture was taken on site and from one of the sides of the building. The picture also shows that the structure itself is located on a hill at a level of 500 – 600 meters above sea level, as mentioned before. From this picture (Figure 5.4) it is possible to see the difference in the width of the levels between the floors that are below the ground level. It can be seen that the ground is slopping down and the building is placed on the side of the hill using the difference in the levels. For that last reason, Buildings A and B have only one level below the ground and Building C has two as mentioned earlier.

    Figure 5.4 – Side Picture of the Structure

    5.3        Selection of Materials according to Greek Regulations

    The structure was initially built in 1975 with building materials that were common at that time. Construction practices have changed since then and different materials are used nowadays. In order to shows some of these differences examples of materials used will be given in this report. These examples will also help the reader understand some of the building regulations that are in place in Greece, the location of the project.

    First of all the main part of the building that was constructed in 1975 was made out of reinforced concrete. At that time the name for the concrete that was used was B160. This is what is now referred to as C12/15 nowadays. Concrete grade C12/15 (C fck/fck, cube) means that the concrete characteristic compressive strength (fck) as a cylinder is 12MPa and the characteristic compressive strength of a concrete cube is 15MPa. The elastic modulus for such concrete is 26GPa. Moreover the steel that was used at that time was of the grade ST I and had an elastic modulus of 200GPa. This same classification is used today. At that time the grade of the steel implied how flexible the steel was in terms of its capacity to be bent on site by the personnel who were handling the steel. That grade of steel also implies that the steel used was not fluted steel but had a smooth surface [17, 18].

    In repairing the structure the materials used were not the same as the ones used before. The concrete that was used during repairs was C20/25 which also has an elastic modulus of 29GPa, implying that it has a compressive strength of a concrete cylinder of 20MPa and a compressive strength pf concrete cube of 25MPa. Additionally during the repair of the structure, extra reinforcement was used and was of the grade S500 where 500 is the strength of the steel measured in MPa. The way the reinforcement was placed on the structure during repairs will be discussed later in this report.

    Here it should be mentioned that structures in Greece have to meet regulations to protect against damage from earthquakes. In Greece the country is divided into three zones where each zone has a different seismic factor (α) (Table 5.1).

    Seismic Zones
    I
    II
    III
    α
    0.16
    0.24
    0.36

    Table 5.1 – Seismic Zones (EAK2000, Greek Antiseismic Regulation) [17]

    The area in which the structure was build is within seismic zone I and therefore the factor (α) for that zone is 0.16.

    Furthermore, the environmental conditions that exist in the area are also important because they are taken under consideration when deciding on the nominal cover of the reinforcement. The Greek Standards divide the environmental conditions in four stages. The first stage is the mild environment that covers the inside spaces of buildings where the moisture is high only for a small period of time throughout the year. The second stage is the moderate environment, that includes the inside spaces of buildings that are exposed to high levels of moisture and other corrosive substances such as structures that are exposed to natural water that is running slowly or steadily, and structures that are in areas with low contents of corrosive substances. The third stage is the severe environment that includes all the areas that are less than one kilometre away from the sea. Finally, the fourth stage covers the most severe environment that includes industrial areas that are exposed to corrosive and chemical substances (fumes, liquids or solids). The current structure, as was mentioned earlier in this report, is located in a sea-side city, and for that reason it falls within the third stage environmental condition. According to Greece’s specifications the nominal cover should not be less that 30mm. In the case of this building the nominal covers that used were 35mm for the slabs, 40mm for the beams and the columns and 50mm for the footings.

    5.4        Analysis of the Structure

    5.4.1  Introduction

    In this report different aspects of the building will be analyzed in order to explain and describe the methods that were used to repair the building. First, the structure will be described as it was in its initial stage, when it was first built. This will be achieved by using the technical drawings and explanations of different parts of the structure. Next pictures of the deterioration of the structure will be examined so as to better show the various aspects of the building that were in need of repairs and how the methods of repair were applied to the structure. This will give to the reader a more clear idea of the techniques used in the completion of the project. Finally technical drawings of the structure in the final stage, after the repairs were done, will be compared to pre-repair images in order to discuss and explain the repair methods that were used.

    5.4.2  Initial State of the Structure

    As mentioned before, the structure is divided in three buildings that are connected together forming one building. Drawings below show the plans of the ground level slab for each building. These plans are the technical drawings of the slabs and they include all the steelwork used for the slabs along with the dimensions and the steelwork of the columns and the beams of the floor. The drawing shows the slab of Building A (Figure 5.5) with the columns of that floor in green; the connections between them are the beams. On the slab itself the placement and specifications of the slabs are also shown. At the bottom of the drawing the balconies of that floor are indicated in red; these images also show the steelwork connecting them to the main building.

    Figure 5.5 – Plan of Slab for Building A

    Figure 5.6 – Plan of Slab for Building B

                The same descriptions apply to Building B (Figure 5.6) where the steelwork of the slab, the beams and the columns are illustrated on that drawing in like colours. At the bottom of the drawing (Figure 5.6) the balconies of that floor are also shown in red. These descriptions are also true of the technical drawings provided for Building C (Figure 5.7).

    Figure 5.7 – Plan of Slab for Building C

    In the foundations of each building there are footings under each column and in some cases there are beams connecting the columns together. For example, in the drawing below (Figure 5.8) the columns are highlighted in green; these columns, highlighted in red, are placed on footings that have a conical shape.

    Figure 5.8 – Plan of Foundation

    In more detail it can be seen in the drawing below (Figure 5.9) that the specific column with dimensions of 30cm by 40cm is placed on a footing of 1.30m by 1.40m. In this same drawing it can be seen that the H of the footing is 0.50m. This means that its base, which has the shape of a rectangle, is 0.5m high. Subsequently another 0.40m (h) of the footing is rising in a conical shape until its top reaches the dimensions of the column. At the base of the footing reinforcement bars are placed on both axes (x and y). These bars measure [email protected] Also in this drawing it can be seen that the bars that are used for the column are [email protected]

    Figure 5.9 – Footing of the column

    In some instances two of the footings are connected with beams. In the drawing below (Figure 5.10), for example, it can be seen that two footings, with dimensions of 1.40m ´ 1.60m, with the one on the left measuring a total height of 1.00m and the one on the right measuring 0.95m, are connected together with a beam with the dimensions 25cm wide and 60cm high. The beam starts at the top of the footing (where the column starts) and goes 60cm to the bottom of the footing. The remaining distance between the beam and the ground is filled with soil. It should be indicated that the beams are connected to the top part of the footing because this is where the slabs are grounded so that they form some kind of a support to the slab. From this same drawing (Figure 5.10) it can also be seen that the beams are also reinforced with 2T12 at the top, and 4T10 at the bottom, in addition to stirrups, which used [email protected] bars.

    Figure 5.10 – Footings Connected with Beams

    One of the columns was randomly selected to show the bars that are used and how they are connected together in the column. In the next drawing (Figure 5.11) it can be seen that the column with dimensions 40cm ´  60cm contains reinforced bars [email protected] and stirrups of [email protected] again. The hook that the stirrups make is always measured to be 100mm on the inside (Figure 5.12).

    Figure 5.11 – Columns

    Figure 5.12 – Stirrups

    Referring to the drawings of the slabs (Figures 5.5, 5.6 and 5.7) it can be seen that bars going parallel on the y-axis and then bars going parallel on the x-axis are placed on the slabs. In places where a beam might be crossing from underneath, and because of the reinforcing bars that this beam might have, the bars on the slab are rising a bit so that they can cross over the other bars (Figure 5.13) and after they do they fall back to their initial height.

    Figure 5.13 – Bars crossing over beams

    A different kind of reinforcement is used for the balconies. In the following drawing (Figure 5.14), for example, it can be seen that a bar is coming towards the balcony parallel to the y-axis and stops at the end of if, where it makes a U-shape in order to go around the bars at the edge of the slab and stretch again to the inside of the slab with a length of more than two times the thickness of the slab.

    Figure 5.14 – Reinforcement in balconies

    5.4.3  Design of the Repaired Structure

    After estimating the grade of deterioration of the structure, the contractors designed and later applied the repair methods to the structure. The structure was found to have multiple cracks in many areas indicating that steel reinforcements inside the concrete might have been corroded. For that reason, and as was mentioned earlier in this report, parts of the structure were cut off up to the steel bars in order to estimate and check the extent of the corrosion. After cutting out the concrete the bars were cleaned and the area surrounding them was also cleared from dust before new concrete was applied. Also before applying the new concrete on the structure, the surface was roughened and adhesion resins were placed on the old concrete in order to make a better connection between the old and the new applied concrete. In areas where small cracks were found, epoxy resins were applied in order to seal them. The contractors then proceeded with the restoration of the surface of the structural parts.

    In order to apply the concrete to the new ready surface of the structure, gunite was used, applying the sprayed concrete method discussed earlier in this report. Of course Gunite was applied to columns and beams only wherever it was needed since in some areas the structure was not affected by environmental conditions and thus corrosion did not affect the reinforcing bars or the concrete. The application of the sprayed concrete on the structure was not only used to restore the building to its original state. From the drawings it can be seen that, the thickness of the structural members was also increased in order to increase the strength of the structure itself. For that reason extra reinforcement was applied with the concrete.

    Changes were made even from the level of the foundation since more beams were added to connect the footings and the thickness of the columns changed as well. In the following drawing (Figure 5.15), for example, it can be seen that beams were thickened in some areas and in some other areas that did not have any, beams were added because of the new needs of the buildings.

    Figure 5.15 – Repaired Foundations

    In the drawing above (Figure 5.15) it can be seen that new beams were added, these beams are surrounded by red lines. It should also be indicated that the footings in these areas were connected to each other to form a uniform one with the same dimensions and heights. The beams that were added were for placing the slabs on top of them. Moreover the thickness of almost all the columns was increased. In Figure 5.15 the columns highlighted in red were the existing ones and around them in green are the new ones added. A better depiction of how the columns were changed is shown in Figure 5.16. In this drawing it can be seen that the new concrete was reinforced by extra bars. More specifically the existing columns that were deteriorated, highlighted in red, were cut in some parts and lost some of their thickness. Before the repair work began the columns were 40cm ´ 40cm but afterwards they were 36cm ´ 36cm. The columns were then surrounded by the new concrete and the new extra reinforcement in order to strengthen them. It can be seen from the drawings that dowels are used and are bolded in the existing concrete to better connect the new with the old. Before the repair the column had 4T20 reinforcement. This was later increased with an extra 16T18. For the completion of the repair for that column a 10cm thickness of gunite was used on every side and an extra 2cm was left for applying the finishing later in order to level the surface of the sprayed concrete.

    Figure 5.16 – Repaired Column

    Many parts of the structure were repaired and restored to the original volume but some were strengthened on only some of their sides. This was probably because not all of them were affected by deterioration. This may also be due to the fact that some of these parts were towards the inside of the structure and therefore were not that significantly affected by environment and thus did not deteriorate as much as the others did. The drawing in Figure 5.17, for example, shows a column that was repaired on only three of its sides, leaving one not repaired nor strengthened. Another type of repair might have been applied to it such as epoxy resins, usually used to fill a minor crack. Even though it was not strengthened on one side an extra cover was applied to it.

    Figure 5.17 – Partly Repaired Column

    In some parts beams and also slabs were also repaired, in addition to the repairs to the columns. Beams were all strengthened by increasing their thickness. This increased the load they could take as well as their flexibility. Beams were also cut in some parts in order to more clearly see the reinforcement so that they could be cleaned from rust and then repaired. Extra reinforcement and stirrups were used here as well. This time in order to ensure that they stayed in place while being repaired, stirrups were forced into the existing concrete as can be seen from the picture below (Figure 5.18). The stirrups were placed in such a way with the horizontal bars in order to form a kind of cage around the existing beam and helped the new concrete stay in place.

    Figure 5.18 – Reinforcing Bars on Beams

    In beams that were continuous and that connected with other beams of the structure, the reinforcement was placed in such a way that it formed a kind of anchor from beam to beam. The drawing below (Figure 5.19) reveals how this works and how the bars entered other beams.

    Figure 5.19 – Repaired Beams and Reinforcement Bars

    As can be seen from the drawing above (Figure 5.19), the bars that were reinforcing the middle beam in this instance entered the beams on the right and left at such a length that they could be anchored there. The beams were reinforced at the top and bottom, where the top bars entered the area of the other beams with a length equal to that of two times the thickness of the beam and so did the bottom one. Alternative lengths of penetration could have been, for the top bars, one third of the length of the beam that the bar was entering.

    Figure 5.20 demonstrates how the bars came from the columns in order to be anchored to the beams. From this figure it can be seen that the bars coming from the column vertically entered the beam and with a small turn formed a kind of hook and could then be anchored to the beam. The anchorage length of the bars is called Lbnet and the length of the straight part of the bar before it turns is Lbmin and should not be less than five times its diameter.

    Figure 5.20 – Anchorage of Reinforcement to Beams

    Another part of the structure that was reinforced was the balconies that, through deterioration, became weak and needed to be strengthened. For that reason repairs needed to be applied and the following drawing (Figure 5.21) shows how this was done. The balconies already had some bars coming to them and stopping before their edge. The U-shape that was placed is an extra part of the reinforced bars that were connected to those bars coming from the slab and was chosen as shown in the drawing (Figure 5.21). This U-bar, as seen from that drawing (Figure 5.21), surrounds the bars at the edge of the balcony.

    Figure 5.21 – U shaped Reinforcement Bars for balconies

    As can be seen from the drawing above (Figure 5.21) the U-shaped bars for this building used 4T8 every square meter and the bars at the edge of the balcony that were placed parallel to the length of the balcony were chosen based on the thickness of that part of the structure. For example, if the thickness of the slab (h) was less that 0.15m then 2T8 were used. For an h between 0.15m and 0.20m 2T10 are used based on the table shown in Figure 5.15. For the length of the U-shaped bars, which is also shown in Figure 5.21 as L, it should be observed that it is proportional to the thickness of the slab, since normally it should be more than two times that thickness.

                No further applications on the slabs took place since they were found to be good without any strengthening applied on them. Pictures of the structure after the application of the methods are shown below (Figures 5.22 and 5.23), showing beams, columns and balconies that were repaired. In these pictures the difference in repaired parts and non repaired can be seen. Through those pictures (Figures 5.22 and 5.23) the reader can also see the difference in thickness between the columns, beams and balconies (repaired and not repaired).

    Figure 5.22 – Repaired Columns and Beams

    Figure 5.23 – Repaired and not Repaired Beams and Columns

    6       Discussion

    6.1        Introduction

    The aim of this project is to help the reader first to understand why repair and strengthening of the existing structures was more appropriate than reconstruction and to demonstrate the advantages of such a move, and its effects. The effects were measured not only based on their human impact, from an economical point of view, but also from the environmental aspect as well. The report is intended to inform the reader of the factors that contributed to the deterioration of the structure and why repairs are sometimes needed in order to avoid demolition. Also through this report the reader is able to see the different methods that were used to accomplish this kind of construction. The reader is able to understand the different methods chosen to repair the different types of structures and their appropriateness in meeting the needs of the building since different methods are used in different situations either because of the environmental factors or the needs of the structure itself, according to its existing usage as well as potential needs in the future. The aim of the repair was to improve the structure or restore it to the state it was in prior to the initiation of deterioration, and to do it in such a way that minimum maintenance would be needed during its new service life. Even though some structures did not need maintenance the methods proposed in this report can also be used on buildings after some sort of repair takes place.

    6.2        Further Discussion on the Real Life Example

    The building used as an example in this report was chosen so that the reader could understand the different types of repair methods that are used in every-day real life situations and how different methods are used based on the surrounding environment and local building requirements. This building employed a sample of all the repair methods that are widely used in the world and, of course, does not represent all of them, just the main idea of repair. Although it is just a sample, it consists of ideas that are ideal for similar structures needing similar repairs.

    Before such repair methods are put into action they need to be clarified. For that reason a static analysis check must take place first in order to see what can work under each occasion and the methods that are required. A static analysis is run using computer programs after a specialist in the field inputs all the appropriate data required. The program then analyzes the data input into it and produces the results, showing exactly what kinds of concrete and steel would be needed and where these are to be applied on the structure. So that the results are accurate, a static analysis of the initial structure is required, in order to see what existed and the performance of the structure at the time. Later the results are used to improve the buildings performance, if of course such is needed.

    In the building that was chosen to be described, though, the static analysis of the building as it was before was not available and for that reason various tests had to be made on the structure in order to see what materials were used, their current performance and their volume. For example, compaction tests were made on site in order to evaluate the concrete that was used before, for the initial structure, and laser machinery was used in order to have a look under the concrete surface to see what already existed there (mainly to count how many bars were placed, their spacing, their dimensions etc.) since a report of the structure was not available. Later and after these procedures where done and results produced, they were taken to specialists who input them into the computer program in order to run the static analysis.

    As for that aspect there were also some problems found on the way, since the structure was built many years before, with different standards. Here, it should be mentioned, that in Greece the standards changed many times over the years before arriving at the ones that are used today. For example, the structure was initially built in 1975, and was built under the regulations that were first introduced in 1959 for the Earthquake Standards (under the name of EAK2000, which in English means Greek Antiseismic Regulation ) and in 1954 for the Reinforced Concrete Standards (under the name of EKΩΣ2000, which in English means Greek Regulation of Reinforced Concrete). These regulations changed once since then when in 1984 the Earthquake Standards were introduced with new information and changes, although the Concrete one remained the same. Then, in 1995 both Standards were changed once more. The final was in 2000 when new requirements included in both Standards.

    During the analysis of the building the specialist person had to run the analysis initially with the regulations that were used in 1975, the period during which the building was constructed. Then some methods were also analysed using the regulations that were used at 1975 in order to bring the building back to its initial state. So that the building could be returned to its initial performance, repair methods were designed that could be applied based on the new regulations in place at the time of the repairs in order to meet the standards that are being used today in Greece. The results from the static analysis were then applied in reality. These results showed which parts needed repair to be applied on them, and how this was going to happen. For example, it showed how many bars and what dimensions their dimensions would be on every part, and then what quantity of concrete was to be used, its thickness, along with the cover that was required. Along with the reinforcements and the concrete it shows any connections that might have be needed to be used in order to connect new and old members and materials together. The program recommended every aspect that would help to improve the performance of the existing building and bring it to the desired state and performance. After the program provided the engineers with the methods and results they then had to apply them on the building and complete the project.

    Although the repair methods that were applied on the structure were very appropriate for the situation, some problems occurred during repairs. Though these problems were not very serious such problems should not have arisen after such careful planning. On the new concrete that was applied on the building, for example, some discoloration occurred as can be seen from the pictures that were taken on site (Figure 6.1). This discoloration of the concrete is called efflorescence, and this represents the chalky white salt that can be found wherever cement exists. It can be caused by the presence of rain water or moisture. What happens is that as moisture is transferred from within the concrete, it carries calcium salts that are present, and when those salts reach the surface of the concrete they react with CO2 and they form a layer of calcium carbonate. This phenomenon is very common on structures with concrete and it can affect the structure in either a small way or cause serious problems. This depends on the calcium salts that are present in the concrete and how much of them reach the surface.

    Figure 6.1 – Efflorescence Presented on Concrete

                After this deposit reaches the concrete surface it is very hard to disappear by its own and will take up to 15 years to do so. For that reason, and in order to fix the area that it is affected, this area should be cleaned with materials that are produced by manufacturers. Some of those materials that can help remove the efflorescence are acids that can be applied on the surface of the concrete and remove it. Moreover there are special efflorescence removers that are specially designed for this situation. After applying these efflorescence removers to the concrete surface, some sealants should be applied in order to prevent it from happening again. Moreover, covers can be applied on it and protect it from moisture and further damage. Further in this paper, other construction materials will be presented, that could have been used instead of normal concrete that are very high in density and can prevent any intrusion of moisture in the concrete. This problem could have been prevented if during the drying process of the newly applied concrete, the parts were temporarily covered with materials that would protect it from rain water and moisture.

                After the completion of the repair methods that are applied on the building, some more techniques can be applied in order to increase its service life and make it more resistant to environmental and weather influence. For that reason, some coatings can be applied on the surface of the concrete in order to prevent any direct contact of the concrete with the environment that is surrounded with. That way, the building will no more be exposed to atmospheric pollution, because of the highway that is close to it, as it was mentioned earlier in this paper. Moreover, there are coatings that will help the concrete expand and contract during temperature changes, without cracking and causing problems to the structural performance or the intrusion of unwanted substances to the reinforcement of the concrete, causing it to corrode and after that attack the surrounding concrete. Finally, as it mentioned earlier in one of the chapters, the coatings that should be applied on the structure should also protect it from the salt presence in the atmosphere, because of the fact that the building is placed to an area that is surrounded by sea and with extreme weather conditions throughout the year, that during the winter are mainly focused on snow, and with the presence of that, de-icing salts are needed and that can also affect the building.

    6.3        Alternative Applying Methods

    The methods that were used for that building were appropriate and worked well. The objective of the construction was accomplished and the structure was strengthened. Although this method was the one used, other methods could have been used for the repair of the particular building. Such methods could be the usage of the Ultra High Performance Fibre Reinforced Concrete (UHPFRC) that is stronger than many kinds of concrete but more expensive than the normal Portland cement, and one more method could be the usage of the Fibre Reinforced Plastics (FRP) where high strength filaments are used, like Glass, Carbon and Kevlar.

    6.3.1  Ultra High Performance Fibre Reinforced Concrete (UHPFRC)

    6.3.1.1              Introduction to UHPFRC

    The Ultra High Performance Fibre Reinforced Concrete is not yet widely used and is somewhat expensive at the moment in the industry, so in many situations other types are used. Although it is expensive for small constructions, its properties are excellent since it provides very high strength, with compression more than 150MPa and the tensile at more than 8MPa [13]. Moreover, its extremely high density leads to a very low permeability which by its turn increases its durability. It was said that the UHPFRC is very expensive, and that is because it is using very expensive materials. For that reason it is not used in small structures and wherever it is used, it is applied on the areas of a structure that are exposed to aggressive substances, such as chlorides and where high mechanical loads are resisted by the structure. The rest of the parts that need repair on a structure but a re not exposed in such situations can be repaired with normal strength concrete in order to minimise the cost of the repair.

    6.3.1.2              Application Methods for UHPFRC

    This kind of concrete (UHPFRC) is usually used in three different ways. The first method is to apply the UHPFRC as a thin layer on the existing concrete so that it works as a protective layer but does not strengthen nor repair it (Figure 6.2, Method 1). The second way is to use tensile reinforcement in order to replace existing ones that might have been corroded. The new ones are after their application in the new UHPFRC layer, and at the same time this layer works as protective and also it can be designed in such a way that it can increase the tensile strength of the structural member since the tensile bars can be adjusted to the design requirements (Figure 6.2, Method 2). Finally the last application method of UHPFRC is to apply an extra reinforced concrete section on the existing one using the UHPFRC layer (Figure 6.2, Method 3). This method can be used in order to increase the resistant of the structural element and can also provide protection to it at the same time.

    Figure 6.2 – UHPFRC Methods of Application [13]

                The first application method of UHPFRC on structures aims for the protection of the structural member where that is applied and for that reason its interest lies on its cracking behaviour. Furthermore and for the second application method, the application of the UHPFRC is accompanied by the application of steel reinforcement that can be adapted to the requirements of the structure in order to make it safer. In this situation the maximum moment of the part that this method is applied increases. Finally the last application method can protect and at the same time strengthen the structural member wherever it is applied. For that reason, resistance of the member is increased but that means, at the same time that its rotation is decreased making the member stiffer than it was before. This method makes the member stiffer than the other two methods do.

    It must also be mentioned that all these methods have a maximum moment that occurs when all the tensile reinforcement yields. After that point the force applied on the tensile reinforcement becomes smaller and macro cracks forms on the UHPFRC layer and, as a result, the force decreases faster than the stress increases and the bending moment starts decreasing. Because of the decrease in the bending moment softening occurs to the members.

    6.3.1.3              UHPFRC Layer Thickness

    The thickness of the UHPFRC layer that is applied on the existing concrete is controlled by the diameter of the bars that are used to reinforce it and the cover of that reinforcement in order to guarantee that the force is transferred from the bars to the surrounding layer safely. Of course the moment of the particular member increases with an increase at the thickness of that member because of the fact that an increase to the concrete layer leads to an increase of the static height of the reinforcement. As said in the third case of the application of the UHPFRC layer, an extra set of reinforcement bars can be placed in the UHPFRC layer and this can increase the strength of the structural member. This increase in the reinforcement can increase the resistance but also reduce the rotation capacity, as mentioned earlier. Although if a required rotation capacity is needed, then the reinforcement ratio can be limited. In addition to the increase of the resistance, by adding more reinforcement, this method also leads to an increase to the stiffness of the member, and as said before it also leads to increase of the bending moment in the macro cracks at that point. This increase can lead then to an increase at the curvature but only in a small amount. As a result it can be said that with increasing ration of the reinforcement, an increase is happening to the bending moment, which then decreases the possibility of macro cracks forming in these areas [13].

    6.3.2  Fibre Reinforced Plastics (FRP)

    Again it should be mentioned that repairing a structure might come up to be more economical than demolishing it and constructing it again from the beginning. For that reason and in order to make the structures even cheaper, alternative materials were put under testing and research in order to replace the normal concrete that was used. One of those materials was that were tested was the Fibre Reinforced Plastics. As it was said before, high strength filaments are used for this type such as glass, carbon and Kevlar. These materials that are used are not only economical but sustainable as well.

    One of those plastics are the Glass Fibre Reinforced Plastics (GRP), which are composites that can be found in no time and are not expensive at all ( at least less expensive than normal materials used in concrete). Moreover, they have already used in construction where concrete is involved.

    Then we have the Carbon Fibre Reinforced Plastics (CFRP), which have an outstanding performance, since they can overcome the 1,200 MPa in a typical tensile strength and the 140GPa for the modulus of elasticity. Moreover, this kind of fibre reinforced plastics is very light since it weighs less than one fifth of the steel and even more it is corrosion resistant [9].

    7                Conclusion

    The aim of this project was review the corrosion factors that attack buildings and the damages that they can cause to structures. After specifying all the known factors, a discussion carried out on methods that are used worldwide to repair these problems that might have been caused by corrosion and deterioration of the structures. These methods were fully explained and analysed so that the reader could have a better idea of how they work on site and the results of using such methods. Finally, after discussing the methods used to repair already damaged structures, a brief discussion on methods used to maintain structures was also provided. That way, the reader could also understand ways that a structure can be maintained after being repaired, and why maintenance is necessary particularly in order to increase the service life of those structures and protect them from further deterioration.

    There were mainly five corrosion factors that were provided at the beginning of this report. They have to do with the environment that the structure is built in, the temperatures that the area experiences throughout the year, the materials that were used in the construction the structure, the amount of time that the structure has been exposed to corrosion, and finally the stress that the structure has been placed under. Some of those factors or even all of them, can act at the same time and affect the structure leading to damages. Each of the factors that attack the structures were analysed and the ways that they affect the structures were explained. Their impact on structures can range from very harmful, attacking the whole structure and resulting in the structure needing to be completely demolished, or they can affect the structures in such a way and in such places that repairs and maintenance would be adequate to restore it. The second aspect is the one on which this report was focused, which was to discuss occasions in which structures can be repaired and to highlight some methods that can be employed to accomplish this end.

    The repair of structures can happen in many ways, and depends on many factors as well. For instance, different structures with different states of deterioration will need to employ different kinds of treatment. Not all methods are used in the repairs of all structures. There are different methods for each kind of damage. For example, there are some kinds of methods that apply to cracked concrete and other methods that apply to spalled concrete. All these methods are already being used around the world on many types of structures, whether these are buildings, bridges or highways, or even underwater structures. The methods that are described and explained in this report are methods that can be applied to many situations and can be used to restore similar structures to their initial state, or make them even stronger than they were before.

    Furthermore, methods of maintaining structures were also given in this paper, and those methods can also be applied on newly developed structures, or repaired structures. These are methods that can be used to protect the structures from being affected by the corrosion aforementioned factors and can mostly prevent environmental conditions from attacking the structures and causing further damages. The methods that are recommended in this paper are different types of coatings that can be applied to the structures to protect them. That way the structure is protected from damages and this can also increase their service life. However many checks must be made on them after their application in order to make sure that they are working properly and that they do not need any further maintenance.

    The final aspect of this report analysed a building that was affected by corrosion. The corrosion factors that affected the building were highlighted and the damage they caused were explained. In this way the reader was able to understand the state that the building was in at the time. Later, different parts of the structure were analysed in order to give a better idea of the damage that occurred to them. After the analysis of the damages that took place on the building the methods of the repair that were chosen to be applied were also explained, by again using parts of the building that were repaired in order to bring them back to the state that they were before damages occurred or even to make them stronger in order to withstand more loads and improve their performance. Explanation on the way the static analysis was conducted was also provided in order to understand the procedure before arriving at the application of the repair methods on the real building.

    Finally some alternative methods of how to repair the building, that was chosen to be analysed, were provided, in order to propose other ways of repairing other structures that might have been found to be in the same situation.  Also further improvements for its maintenance were recommended in order to further extend the service life of the building and protect it from further damages.

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    Corrosion Factors That Attack Buildings. (2016, Aug 16). Retrieved from https://graduateway.com/corrosion-factors-that-attack-buildings/

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