Protection Methods for Concrete StructuresAssociation of Construction and Development
April 12, 2013 — 2,499 views
The continuing deterioration of concrete structures with time is a serious problem. Despite the tragic fall of some massive structures in the recent past, there seems to be lack of guidelines enlisting the dos and the don’ts when it comes to maintaining concrete structures all over the world. There is a need for such guidelines to enable classification, testing, assessment, and ultimately restoring the structures to their former conditions.
In most cases visual inspection is the only source of data available for evaluation. This method does not hold good as most of the structural defects are physically concealed, present underground, or beneath the surface. Moreover the impact of the defect on the structure cannot be correctly determined. Engineers need to keep themselves updated about the latest diagnostic methods, up gradation, rehabilitation techniques, and new materials available in order to provide a better solution when needed.
Major Causes of Damage and Deterioration
The reason for deterioration of concrete structures is primarily extended exposure to adverse climatic conditions such as moisture, acidity, alkalinity, and so on. When concealed from these conditions, a standard concrete structure can stand strong for many decades. Concrete deterioration is a process that starts in the embedded reinforced steel which begins to rust and then expands outside. Chemical reactions between the compounds of the cement matrix and aggregate moisture are the major reasons for concrete deterioration.
Types of Common Damages seen in Concrete Structures
Corrosion: Scientifically, corrosion can be classified into two processes, cathodic and anodic. The anodic process is the dissolution of ferrous ions when the cement protective layer is destroyed. The cathodic process is the reduction of oxygen during reaction with water to form hydroxyl ions. Carbonation of the diffused carbon dioxide reduces pH of the concrete, which causes corrosion of the underlying steel. This phenomenon is seen especially with industrial structures.
Thaw Damage: Moisture along with freezing condition is a bad combination. The continuous expansion and contraction of trapped water creates pressure on the structure eventually cracking it.
Other Damaging Issues: Overloading of certain structures which are not designed to withstand such pressure causes most of the damage. Concrete bridges have always been victim of this phenomenon.
Methods to Protect, Repair, and Strengthen the Structures
In the last 30 years, concrete protection and maintenance techniques have improved considerably. There is a difference between repairing a structure and protecting it from future corrosion. Repair deals with identifying cracks, cavities, and filling these cavities with reinforced steel. Repair should be carried out by qualified engineers. The extent of damage and other specifications should be documented for future reference.
Protection processes, of either repaired concrete structure or newly built ones, always involve limiting the climatic factors to avoid extensive corrosion. Moisture is the main element responsible for corrosion. Successful removal of moisture from the environment provides a standard amount of protection to the structure. This is most often attempted by a combination of protective coating and drainage improvement systems. Along with repair and protection, some structures are strengthened using materials like glass fiber reinforced plastic (GFRP), carbon fiber sheets, and supplemental steel. Structures meant to withstand heavy load often require strengthening.