Why Investigation of Reinforced Concrete Structures for Repair and Maintenance Required?
Concrete is one of the most adaptable man-made building materials available today. Concrete has earned a reputation as the most generally acceptable material for most sorts of modern buildings due to its flowability in the most convoluted forms while wet, and its strength, development, and durability properties when hardened.
The embedded reinforcement in the concrete is widely known to be protected by the high alkalinity of the concrete, which lends durability to the reinforced cement concrete. Concrete should be made to last for a long time.
However, due to the numerous criteria and requirements that must be met, as well as the unfavourable environmental circumstances, the engineer on site encounters numerous practical issues that reflect the concrete’s long-term endurance.
As a result, it is a fallacy that even good concrete requires no maintenance; it does, however, necessitate frequent inspection, maintenance, and timely repairs in order to maintain the intended durability.
Due to the owner’s lack of awareness of the structures’ maintenance and repair, timely remedial measures are neglected, and the results are the same problems that manifest themselves in greater magnitudes after a period of time, where the durability and stability are not only compromised, but also the cost of rehabilitation is increased multiple times.
A minor rust stain on the exterior, if ignored, can lead to the protective cover splitting and spalling, and if not addressed, can progress to reinforcement corrosion, potentially jeopardising the structure’s structural stability.
It’s also worth noting that the repair or rehabilitation of distressed or damaged structures differs significantly from the design of new structures, when the unknowns are either known or assumed. Before proceeding with repairs, the cause of the discomfort must be precisely determined.
The most up-to-date diagnostic procedures and advances in the field of materials for such repairs should be used. As a result, total proficiency in both investigation and material science is required. An early diagnosis and rapid remedial steps are significantly less expensive than ignoring the problem.
Visual Signs and Type of Repairs for Reinforced Concrete Structures
Cracks of various patterns and sizes, rust stains or rust spots, peeling of plasters, etc., spalling of concrete, and rusty reinforcement if exposed are all common visual symptoms of a distressed or damaged structure.
The first step is to figure out whether the damage is structural or non-structural. Structural repairs are made to restore the structure’s structural stability so that it can withstand the current stresses in service. Non-structural repairs are carried out to restore the structure’s long-term durability but do not increase its load-bearing capability. If a nonstructural or aesthetic repair isn’t done at the right time, it can cause structural damage.
Possible Causes of Structural Concrete Deterioration
Before beginning an examination into a structure’s distress, it’s important to grasp the elements that influence concrete deterioration. Knowing why and conducting an in-depth examination can only lead to a correct diagnosis. The deterioration of concrete might occur in one of two stages.
To a large extent, we can stop or slow the deterioration of concrete in its early stages, such as before or during construction, by taking the right precautions. In the second scenario, however, the majority of the elements determining concrete’s durability are outside our control. At this point, all we can do is maintain the status quo and take quick effort to alleviate the repercussions.
Cracks in Concrete
Tensile stresses are applied to concrete in structures. When these tensile stresses exceed the concrete’s tensile strength, however, it splits. This happens frequently, and cracks constitute one of the inherent flaws. The reasons for cracking in concrete are varied.
The Causes of Cracks in Concrete
It is critical to be aware of the flaws. The presence of cracks does not imply that there are flaws that need to be repaired. It must first be determined whether the cracks are structural or non-structural.
Preliminary Investigation and Detailed Investigation of RCC Structures
The primary goal of an inquiry is to identify the level of damage or distress, whether it is structural or non-structural, and the grounds for that judgement. The remedial procedures will be meaningless until the cause of the distress is identified, as it is the cause of the distress that has to be addressed, not the appearance of the damaged structure.
The age of the structure, nature of construction, structural design assumptions, current loading conditions, if repairs have been completed, and their durability should all be acquired.
Semi-destructive and non-destructive tests should be included in structural repair investigations. Before passing judgement on the concrete, the findings of the tests should be double-checked.
Diagnosis is the process of interpreting the findings of an investigation. The analysis of the data necessitates extensive knowledge and experience in this subject, and it should primarily be performed by competent engineers.
Concrete Repair Methods Specifications Because repairs and maintenance is such a specialist sector, it’s critical that precise specifications are established for carrying out the necessary repairs.
Surface Preparations of Damaged Concrete
For entire repairs, two different types of materials may be required: one for crack filling and the other for cosmetic restorations. When choosing materials, economic aspects must also be taken into account.
Damaged Concrete Surface Preparation This is a very crucial phase that rarely receives the attention it deserves. Because of incorrect pretreatment and lack of sufficient surface preparation, many systems including proper requirements and material selection fail.
Without delving into specifics, hammer testing should be used to check for cavities in the concrete surface. A chisel and hammer should be used to chisel all loose parts. In either direction, the reinforcement should be exposed roughly 50 mm more than the corroded reinforcement.
Suitable mechanical or other means should be used to clean the steel. To guarantee proper bonding of the successive coats, the surfaces should be solid and devoid of oils and fats.
Actual Repairs Methods for Concrete Structures
The actual repairs will be determined by the type of structural or non-structural damage to the structure. In both circumstances, the steps overlap and are essentially the same. The fundamentals of civil and structural engineering must be strictly followed; else, the same difficulties will recur at larger scales.
Periodical Maintenance of Reinforced Concrete Structures
Periodic inspections are critical because they can detect damage at an early stage and allow for quick repair. Periodic inspections should be carried out to avoid the incidents listed below.
(i) Cracks’ appearance
(ii) Rustt staining
(iii) Concrete spalling
(iv) Reinforcement exposure
Correcting these flaws in a timely manner can save money and extend the life of structures. Inspections can be done once every three years by qualified engineers and documented. The owners should be informed that any damage or degradation should be reported as soon as possible.
Exterior paints are used for more than just decoration; they also provide additional protection to concrete, seal fine fractures, and prevent water and oxygen from entering the concrete body, reducing corrosion.
Precautions for Concrete Structure Repair, Maintenance, and Rehabilitation
Though it is an accepted truth that errors sometimes occur during construction, reducing concrete’s durability, it is still possible to cast good concrete with long-term durability and minimal maintenance if some simple and not-so-difficult procedures are followed.
(a) At the design office, proper detailing should be done to show the specifics of reinforcements and other details at junctions where reinforcements are congested. Formwork should be constructed to accommodate not only alignment but also prop settlements.
(b) Proper shuttering must be done on the job site, and the reinforcement should be aligned with appropriately built constant covers utilising bar spacers.
(c) The slump of the concrete should be appropriate for flowability in the formwork. The water-to-cement ratio must be rigorously followed. The mix should be built with the right amount of cement, keeping in mind that the right amount of cement is needed not only for strength but also for durability. The use of chloride-free aggregates and potable water is recommended.
(d) For proper compaction, optimal vibration is essential. When in doubt, it’s preferable to be over vibration than under vibration.
(e) Form work should be withdrawn once adequate strength has been achieved. Honeycombs and cracks should be filled right away, since waiting can cause dirt, oil, and other contaminants to accumulate in joints and other areas.
f) Proper curing is critical. Even in the early phases of curing, using membrane-forming curing agents protects the concrete.Precautions are clearly preferable to cure, as evidenced by the preceding debate. It is critical to have qualified engineers supervise construction sites. Codes of conduct should be scrupulously followed.
Experienced engineers should do the diagnosis and interpretation of the investigation data. Material selection demands more than just logic.