Perhaps the most important advance in using new building materials is the development of concrete which is more durable. New- age concrete is flexible and endows all kinds of structures, buildings, roads, sewers and bridges which last for a very long time. The construction industry in the world is becoming modern and advance, however, there is still the problem of building defects which need to be addressed.
Defects to concrete facades of different buildings pose safety danger to the public; hence there is a need and formidable challenge to rethink on the issue. Successful remediation requires an adequate understanding of defects, correct diagnosis and appropriate repair materials and methods. Different articles discuss different exposure conditions, construction techniques and probable remedies to such defects.
Structural defects are majorly seen to be caused by incorrect design, lack of quality, faulty construction and overloading. Poor workmanship is widely seen to be a major cause of structural defects in floors, despite good use of reinforcement and quality concrete.
Cracks are one of the majorly seen concrete defect explored by different researchers, perhaps because it one of the most common defects. It can be caused by structural defects seen above, or non- structural defects like moisture, elastic deformation, moisture changes and chemical reactions. Concrete can support great weight, but has low tensile strength; hence break or crack when stretched. Therefore, the need to reinforce it with steel bars.
Interestingly, authors like Jefrey Coleman, explores whether cracking is a defect or whether it is a behavior of concrete. In his opinion, some kind of cracking is acceptable, and other forms are unacceptable. An excellent example is cracking in a concrete aquarium is unacceptable if it causes leaks, but if the crack is on an elevated slab, concrete beam or slab on grand, should be acceptable because they do not interfere with the application. Similarly, such tests can be applied to bridges, walls, footings, dams and other facilities. He also discusses the different implications cracks may have; they may affect appearance or may indicate the lack of durability or distress on the structure. His theory on whether a crack is normal or a defect, is further explored using a case Docketey v Mahoney, where the court held that, in at least one case patio, cracking is expected hence not a defect and thus normal. This shows considerable litigation in terms of certain concrete defects which are sometimes somehow unavoidable.
Similarly, other literature explores cracking as a defect which can be prevented. This is especially in cases where contractors are responsible for cracks. This is by ensuring proper placement, finishing, putting adequate amount of water, proper curing and preventing structural overloading. On the other hand, if a crack occurs, measures which can be used to control cracking can be used depending on economics of the cracking.
Jefrey also explores, when concrete cracks can be considered a construction defect. His article explores causes of cracks like shrinkage, internal expansion or external effects. External effects include thawing, thermal stress effects on concrete, freezing and differential settlement. This literature supports the literature by Allien, which shows how different temperatures can lead to concrete defects. He also corroborates the literature that errors in design, poor construction, excessive water additions, inaccurate mixing and overloading concrete lead to concrete defects. Cracks can be diagnosed through observation of cracks and determining whether they are minor or not.
Other common types of construction defects shown by different literature are form failures, rock pockets, honey combing, finishing and dimensional errors. Honey combs are areas where voids are left because of failure of the cement mortar to fill in spaces among and around coarse congregate particles. In concrete construction, there are many opportunities to create dimensional errors. However, it is important not to attempt repair resulting deficiency but to accept it. If the deficiency is of a nature that is unacceptable, reconstruction or complete removal can probably be the best cause of action. Dimensional errors can also be corrected occasionally; by removing or replacing defective concrete with replacement concrete or epoxy- bonded concrete.
Finishing defects include over finishing, or cement or water addition to the surface; during the finishing procedures. This result into a permeable surface or porous with low durability. Poorly finished surfaces exhibit spalling of surfaces early in their life. Surface spalling can be repaired through removal of weakened concrete, and replacement with concrete with proxy- bonded characteristics. If there is early detection of deterioration, surface can be extended by use of concrete sealing compounds. In the same point, according to Woodson, most common causes of concrete failure include a lot of water. He asserts that too much water can lead to increased curing time, reduced strength, increased porosity, increased drying shrinkage and reduced abrasion resistance.
On the other hand, Lee’s article discusses the construction defect of concrete pop- outs. Such pop- outs are caused by electric arc furnace (EAF). His article suggests the used of FE in appropriate repair depth and determining the rate of deterioration of concrete. Lee’s study shows that internal members do not show frost damages. Also, frost damage and alkali frost reactions are causes of other concrete- pop-outs. Similarly, different articles show that pop-outs are caused by expansive reactions between alkali hydroxides and in the concrete and reactive salacious material in the coarse aggregate particles. Accordingly, pop offs can be as a result of improper finishing, poor quality concrete mixture and inadequate curing. Such pop offs can be determined using petrographic examination.
Gambir explores surface defects such as surface aberrations and blowholes which affect the appearance of the concrete face. He also explores other problems with the concrete such as cold joints, scaling, honeycombing and cracking which may affect structure integrity.
Seizer and Christopher explore honey comb and rock –pocket defects which are responsible for impairing overall stiffness, reduce service life, accelerate aging and reduce structural life because of hardening of concrete. According to them such defects can be identified using traditional methods such as localized non- destructive methods or traditional methods. These methods are time-consuming, non- intensive, sensitive to test conditions and require a lot of knowledge in terms of locations of defects. The authors, Christopher and Seizer, propose a vibration response, which is non- destructive, to be used in identifying the severity of defects, location and internal defects of non- concrete members.
Their mode of experiment involves collecting mode curvatures from laboratory beam specimens with honey combs and rock-pocket defects. Their numerical components are then stimulated in a vibration response through a vibration response through an element which is finite (FE) model which has three parameters. The parameters have three defect- identifying variables which identify location (x coordinate which is along the beam length), severity of the damage (a mass reduction, b stiffness reduction). From this defects can be detected through comparison of predictions and measurements from FE, and inferring defect identifying variables.
This method, however is seen to be suitable for inspecting members with simple geometric forms and rapid cost- effective quality assurance for concrete members. This method, therefore has its shortcomings because it cannot be widely used in attempting to identify defects, let alone honey-combs and rock pocket defects. In any case, it is still an excellent procedure which saves time and takes less time compared to other methods. There is little research in terms of methods to be used in identifying defects; hence future research can be vital in identifying more reliable and cost- effective methods of identifying defects. Different non- destructive techniques have proven to be efficient and effective; however, research should be done to incorporate their use in different construction defects.
Strikingly, there are a few unique papers which discuss repair solutions to high-rise facades which pose a threat to public security. In consideration of the facades buildings, notably, it is similar to other forms of concrete defects, as they are mostly ignored or not detected early. Similarly, they are not normally acted upon until they become severe, visibly dislodged and at risk of falling or when a piece has fallen off a facade. Such defects are commonly caused by construction defects, design defects, resistivity and erection related defects. Further research is needed especially in defects of such buildings as they pose the greatest risk and can cause greater damages.
Accordingly, a few articles explore the causes of fire in damage to constructions and being the causes of concrete defects. They also provide details in methodologies adopted in investigating, assessing structural health for damaged structures damaged by fire. When concrete is subjected to fire, its properties deteriorate. Particularly, concrete loses its strength, in the modern era, fire is unpredictable and is also the cause of accidental damage of structures. Such articles provide that structures should be reinforced to make them less susceptible to damage. Such reinforcement may require fewer repairs depending on the extent of damage and duration of the fire. Concrete photographers may be helpful in exploring the extent of damage and in assessing the damage to concrete and steel families. Also, a combination of non- destructive tools and micro- structural investigation can be necessary for assessing damage to structural elements and before rehabilitating structures.
On the other hand, Allen explores the risk factors affecting the durability of concrete, such as environment. An excellent example is exposure of structures in the sea. His article explores how different temperatures affect different chemical processes, and the deteriorations of structures, or concrete defects are affected by the latitude of the structure. He suggests that areas around the coast, adjacent to arid zones represent worst deterioration conditions. Water level strongly affects durability, with the strongest deterioration occurring average water level and above (Allien, p.74). He explores various chemistry behind the difference in deterioration levels. This is helpful in understanding concrete defects occurring at different areas, which may vary depending on temperature and exposure.
Diagnosis
Successful repair projects require understanding of the causes, defects and repair techniques. Certain studies show on diagnosis of post- stress concrete pile defects, have applied artificial neural networks (ANN) on diagnosing other forms of post- stress defects.
Woodson explores troubleshooting defects of concrete and what is required to make a proper repair. Notably, he recognizes that some defects can be hard to troubleshoot. However, in his opinion one should know elements of defects, as they may be mimicking one cause, while they are caused by different factors, hence leading to improper repair. Holland also recognizes the need to bear in mind that defects may result from a combination of various causes (Holland, p. 54.). According to him, one should find out the cause or if caused by multiple causes, hence saving a lot of money; because of proper diagnosis from the relevant information. Also, according to him, a concrete sealer can provide a repair sealer can provide a repair option.
Gambhir recommends the use of SCC formulation with white cement in an attempt to repair different concrete defects; however, the use of different colors can be used by different designers to express aesthetics (Gambhir, p. 616). In his opinion, SCCis not widely used, and only used in a few scenarios. Importantly, it can be vital to examine the surrounding conditions when identifying concrete defects. There has not been much literature in terms of consideration of temperature when examining defects. It can be a crucial factor which is ignored by different literatures, but can be put into consideration.
David in his literature recognizes the importance of prevention in the beginning of every project. This is because even at the end of a project, inappropriate and unplanned interventions can lead to failure, even during the project.
Rock pockets and honey combs can be repaired with cement mortar if minor and if 24 hours have not passed since the removal. If the repair is delayed over 24 hours since removal, and if the rock pocket is extensive, defective concrete must be removed and replaced with dry pack, and the area must be removed. Minor defects can be repaired from grinding; the ones resulting from movement or failure.
If cracks are minor, they can be sealed with mortar cement, this is cracks, less than 1mm wide. If the width of the cracks changes with seasons, they can be filled up with a polyurethane compound or elastic filters. Shear keys made of RCC concrete can be used with reinforcement of 1.5% steel when a sheer crack is observed. The steel can be provided at 1-1.5 m intervals. Cracks caused by soil movements around them, can be prevented by surrounding the areas affected with waterproof blanket around the plinth.
Conclusion
Holland shows on the need to explore various mechanisms which can cause concrete defects. According to him proper diagnosis includes evaluation of residual service life of the structure, and appropriate strategies put in place. Additionally, according to him delays associated with various defects have been well researched and well documented. However, there is still a gap on the need to explore on various decays, especially in relation to how varied temperatures cause defects.
Generally, most literature provides the cause of defects as occurring overtime in a number of instances, however, in other constructions; they occur immediately after construction. Notably, it is crucial to explore the period when defects occur, this can be helpful in keenly watching for occurrence of such defects and repairing them at an early stage. There is also need for an identifiable literature in terms of damage caused by such defects, and the consequences such as unwarranted maintenance costs. Similarly, there is a need for further research on the defects which are hard to diagnose, and how they can be made easier. Also, there is a need for further research in terms of prevention strategies to almost all concrete defects. The use of FE is a promising tool in the diagnosis of concrete defects, however, there should be further research in terms of how viable it can be in measuring different concrete defects apart from a few, which FE is used. Also, historical index can be used in examining damage ratio, and providing various solutions to concrete defects.
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