Corrosion, Repair and Maintenance of Structures Essay Example for Free

wearing, recompense and Maintenance of Structures EssayChapter 1.0 IntroductionIn many places around the world, there are expressions that generate existed for a long time and either they are still being used or they are patently left there standing with no use at tot full-pagey to the open. For that reason, these complex body parts that are no longer being used must be restored in order for them to be re-used in few government agency. When pertaining to structures, to rehabilitate promoter to restore, to repair, to rescue from a state of erosion.The idea of rehabilitation came after the World state of war II when old buildings were starting to show damage through time or damage from charitable intervention. The easiest way to fix them was to restore them. That process today is very widely used and is a very familiar process, which applies to al closely every structure on earthfrom structures that desire to be repaired to structures that need to submit a comple tely un deal look or structures that need to unfold. It shtup also be use on structures that need to be potentialened in order to prolong its living for an an some other(prenominal) circumstances of years.Rehabilitation of structures, as a process, flush toilet save time, money and work. That is be possess there is no need for the demolition of an already existing structure and building again from scratch. Simply bewilder, rehabilitation means that some changes or improvements need to be made. This process also saves seat since there is no need for a crude area in order to build a new structure. In this paper, I am deviation to divide this process into triad stages. The first stage is the wearing away, where I am going to explain all the parts that lead to corrosion of structures and how it affects them. The second stage is the part of repairing a structure after it has undergone corrosion. In this stage, I will mention ideas and ways that consume been developed thr ough the years which discharge be utilize to existing structures that pay off been affected by corrosion. The third and final stage that will be discussed in this paper are the ways on how to maintain a structure and how to prevent further disablement after repair in order to minimise its cost efficiency.Chapter 2.0 eating away FactorsIntroductionCorrosion is begetd by a lot of federal agents and it often results to the bereavement of a structure. All these factors have to be studied in order to prevent structure unsuccessful persons. Corrosion, most of the time, is caused by extreme weather conditions except it is not the whole factor that causes corrosion and it is also not the main cause of structure losers. By analysing corrosion and explaining how it happens, we can separate it in antithetical areas.Factors of CorrosionCorrosion dep displaces on many factors which we will focus on such as literal, environment, stress, temperature and time factors. These factors ar e dependent and interconnected with each(prenominal) other.Material Factor The material factor has to do with the materials that are used for the structure. Materials also has a connection with the environment where the structure is put up (i.e. weather, temperature, moisture, etc.), which we will discuss later in this report. The material factor is important as it all starts from the conveyion and planning before being able to build the structure. The selection process is divided into tether stages. The first one is listing the requirements taking into consideration the strength and other properties of the material. The second stage is choosing the most convenient material focusing on its technical properties and evaluating them. The last stage is base on the scotch factor, which means that after going through the first two stages, we came up with a variety of materials and the notwithstanding thing left to do is to choose the cheapest and most suitable material for the struc ture. The final process has to do with the fact that the structure is for repair and that redesigning the whole structure is not easy which means that more tending should be given on delivery time and completion.Environmental factorEnvironment is a all-important(a) factor in corrosion of materials. This is caused by a lot of factors and the main factor that needs to be considered is that the materials have a tendency to widen or shrink depending on the changes in the temperature (Table 2 to a lower place shows some data on expansion of different materials) and also in areas where the weather changes from rainy to juiceless or vice versa in a short span of time. Moreover, water as a factor greatly affects a structure because it can disseminate in the material and cause it to crack. If the material is steel, its painting to water will cause it to rust and the rust can spread and also affect other materials. Another factor to be considered is moisture that can be caused by rain, condensation, leakage from pipes or drains and insurrection damp. For the underwater structures and especially for those in salty waters (i.e. sea) more problems arise because salt can revive the phases of corrosion, and due to that, extra care has to be provided in choosing the materials. Wind also has to be considered. In some areas, winds can prove to be very strong. And strong wind coupled with the effects of some other factors can cause extreme deterioration also because it can bring dust and dirt, which can penetrate materials causing discolouration and corrosion. Finally, pollution is another factor that contributes to the environmental corrosion of a structure. As we know, atmospherical pollution can be transferred to the ground in the form of acid rain. This acid rain can react with the materials that were used for the structure and can cause its rapid deterioration. Regular cleaning of the structure would be helpful in preventing any unwanted deterioration.Stress facto rStress connects and interacts mostly with the environmental and the temperature factors. Changes in temperature followed by expansion and contraction causes cracks on structure which can result in structure failure in a worst case scenario. In some situations, the structure fails without showing outside(a) tortuousness making it hard to avoid. Even though cracks cannot be seen by the human eye, there are quadruple cracks attacking the materials under the surfaces of a structure. These cracks in microstructures can form intergranular or transgranular morphology. These kinds of cracks can cause a big problem because they are difficult to detect. The photo on the right is shows an intergranular SCC (Stress Corrosion Cracking) following the whit boundaries. Problems like this can cause an unpredictable failure of the structure resulting in loss of materials.Temperature factorChanges in local temperature can affect the stability of a structure in a major way because of the expansion and contraction that the structure is being exposed to. Usually materials tend to contract during low temperatures and expand during graduate(prenominal) temperatures which can cause small but dangerous cracks that can further lead to the failure of the structure. In order to prevent such a disaster from happening, the most common recourse is to select proper materials that can adapt to the environment where the structure will be erected. The temperature factor, of course, depends on the environment factor and the stress factor that we talked about earlier in the report.Time factorTime in corrosion is a very big issue. Time is the factor that produces all the problems and is the one that makes all the others affect the structure. Without time, corrosion would not happen. Of course, time is not the only factor that causes corrosion as we have already discussed. The ones that have a clear connection with the time factor is the environment, temperature and stress factor. From all tha t were mentioned, one final but very important factor must be pick outn into consideration. Corrosion does not have the equal effects on all materials different type of material will have a different kind of reaction with the various factors.Types of Corrosion Affecting StructuresFirst of all, let us consider that we have a reinforced cover structure.The mild steel that is used for this structure to reinforce the cover creates a class on its surface in order to keep it in a passive state. This shape is caused by the alkalinity of the concrete. Therefore, the corrosion that will affect the structure will be caused by the steel that is reinforcing the concrete, and there are three types of such based on the steel corrosion. These are Chloride Contamination, the Patch Accelerated Corrosion and Carbonation.Chloride ContaminationThe heraldic bearing of chloride ions in the atmosphere, which are formed usually where structures are exposed to de-icing salts (used to maintain pencil eraser transportation during winter time) or to a marine environment, can cause the destruction of the protective oxide seam of the reinforcing steel and lead to its corrosion.Patch Accelerated CorrosionThis type of corrosion is either kn profess to the public as the Ring Anode Corrosion or the Halo Effect. This phenomenon is often detected on concrete restoration projects where there is movement of concrete spalling on previous patch repairs. It is most commonly put up on the exterior of the structure and is caused by its moving picture to icing and thaw cycles.CarbonationThis process is very like to Chloride Contamination. A state called ampere-secondation, it is caused by the reaction of carbon dioxide within calcium hydroxide in the presence of water. It can cause the loss of alkalinity in concrete. This loss of alkalinity that happens to the surrounding concrete of the steel can cause the destruction of the oxide layer that is protecting the reinforcing steel. This kind of corrosion is a big threat to old buildings.Areas where Corrosion AppliesCorrosion can be found in different kinds of structures. One of them is the bridges where there can be corrosion on the reinforced concrete caused by the presence of de-icing salts or by their exposure to marine environments. Parking garages are also exposed to corrosion, and this can be caused again by the presence of de-icing salts transferred there by the parked cars. Of course, buildings are exposed to corrosion too, and it most likely applies on spandril beams, columns and balconies.The types of corrosion usually found on these structures are the types of corrosion that were discussed earlier, namely, chloride contamination and carbonation, which can also be caused by exposure to sea spay usually to buildings close to the sea, and also through contact with atmospheric carbon dioxide. Another area where corrosion can be applied are the marine structures, like concrete piers and wharfs since they are expo sed to chloride contaminated salt water and airborne chlorides along with high temperatures and high humidity. stultification of Concrete in GeneralConcrete, like other materials deteriorate due to internal and external forces causing concrete failure. Other causes are water infiltration, carbonation, corrosion of reinforcing steel, shrinkage, drying, thermal contraction and poor view practices. From that, water can cause a big problem to concrete since it can penetrate and freeze during low temperatures. This can apply extreme pressure to concrete and make it weak and finally cause it to fail. Also, water carries chemicals like acids, sulphates or chlorides that can attack concrete and corrode the reinforcing steel inside it and expand the corrosion from inside to outside.Another cause is carbonation, where water from rain can be combined with carbon dioxide in air and after some time infiltrate concrete and react with the calcium hydroxide and create calcium carbonate which can d ecrease the concretes pH level and attack the surrounding layer of the reinforced steel. This can cause corrosion of the steel since it is no longer protected and this as we verbalize before can affect concrete as well because of the presence of moisture.Deterioration of Structures and Service livenessThe deterioration of structures is a process that comes in stages and from that, we can point out the starting stages of the actual corrosion which is the concrete cracking and the excessive deflection. This can result in a reinforced concrete failure due to loss of structural strength.Service Life of a StructureEach structure has its own do support. This service life is said to be the time power point that when ended will need human intervention such as conducting repairs, strengthening, maintenance or rehabilitation. By knowing the service life of a structure, we can determine the time when such actions will be required. The service life of a structure is separated into four sta ges.The first of the four phases is the time period from completion of building the structure to its corrosion initiation. The second phase starts after the corrosion initiation and until corrosion induced cracking. In the third phase, we have the time period from the concrete cracking up to the excessive deflection of the reinforced concrete members. As a fourth and final phase, it is the time from the loss of serviceability to the final collapse of the structure, which means that the structure arrived to a point where it had lost its flexural and shear strength.By determining the corrosion stage of the structure, its service life can be made known and as result, the phase in which the structure is soon experiencing at the moment can be identified. Furthermore, the time period of each of the four phases of the service life of a structure can be indomitable once a performance-based assessment criterion is established. The period of each phase can be calculated with the help of the following formula S (t) = morphological Response (Load Effect) L (t) = Acceptable Limit for Structural Response (Structural Resistance)By knowing the time periods of each of the four phases of the service life of a structure, a probable failure can be determined by using the following formula pf (t) = Probability of an eventDeterioration Stages of a Structure allow us go back through to the stages of deterioration of a structure and discuss it. First we have the concrete cracking which comes at the end of the second phase of the service life of a structure and is after the initiation of reinforcement corrosion. So, after the initiation of corrosion, some rust is produced on the reinforcement. That covers more space than the initiation and as a result, some pressure propagates on the surrounding concrete which by itself cannot take the pressure since it exceeds its tensile capacity and starts cracking. Furthermore, after the concrete cracking and at the end of phase three of the s ervice life of a structure, the excessive deflection comes which is restrained within an acceptable limit. After the end of the fourth phase, we have the loss of strength of the structure which can lead to a structure failure. In that stage the corrosion on the reinforcement reduces the strength of the RC structure and results to a break at the lively cross section of a structural member.Deterioration of StrengthThere are two different ways of determining the strength deterioration of an RC structure, namely, the destructive load test and the non-destructive measurement of corrosion menstruum density. Both of those methods can be used in the laboratory in order to measure the strength deterioration of a structure, but in practice and on the field, it can only be mensurable based on the reduction of the cross sectional area of the reinforcement bars.Deterioration of Stiffnessdecision the stiffness deterioration of RC structural members is very important for the deterioration of the structure as a whole system where the load redistribution and the failure mode both depend on the stiffness of its members.Rate of DeteriorationThe rate of strength and stiffness deterioration is different since the stiffness is deteriorating much more severely than the strength. This is based on the fact that stiffness is measuring mechanical properties related to geometry and the cross sections of a structure way more than strength does. Factors that are related to corrosion and can affect the geometry of a structure are concrete cracking, delamination and debonding. After all those factors, and once the corrosion actively propagates, it results to a severe increase of deflection. thusly again, deterioration of strength is not that affected from those factors which can only damage tensile sections of RC members.