Various external hostile environmental substances, such as, water, carbon dioxide, oxygen, chlorides, sulphides and biological organisms are transported from the atmosphere into the concrete and attack steel and concrete in different mechanisms causing premature deterioration of reinforced concrete challenging its durability resulting in premature failure of the structures.
- Concrete is a porous material having high gas, vapour and liquid permeability leading to deterioration of reinforced concrete structures. chemicals can penetrate the pores and attack the paste. The paste and aggregate can also be worn down by physical impact and abrasion. Water can penetrate concrete, freeze and expand inside it when the temperature drops, and ultimately weaken the concrete from within. In addition, if the concrete has reinforcing steel bar (rebar) to impart additional strength and other properties, the rebar can corrode if moisture, oxygen and chloride ions penetrate the concrete. Corrosion of rebar contributes to the deterioration of concrete.
2. The protection of concrete should actually begin at the conceptual stage and meticulous strategies are adopted for protecting the concrete from both internal and external environments. Various coating materials and application methods for concrete surface repair and strengthening have been developed. However, selection criterion for these materials has not been established yet at the current moment. Selecting procedures of concrete coating materials must focus on deteriorating mechanisms diagnosed carefully by the conditions of target structures. For instance, in case of salt damage, repair policy should consider corrosion environment and deteriorating condition to determine symptomatic indications such as, 1) removal of permeated chloride ions, 2) penetration block of chloride ions, moisture, and oxygen, 3)derusting of rebar, 4) corrosion-control method (coating or potential control). However, it is still ambiguous to determine which is the best material and coating system, because there is not enough, durability data to estimate.
3. it should be noted that all resin materials are not totally resistant and impermeable to all aggressive agents and do not provide a total protection. Chemical/physical degradation of resins and debonding of coatings are the major phenomena affecting the durability of surface protection. The mechanisms of destructive processes in such heterogeneous materials as resin composites are complicated and not completely understood. Degradation of resins mainly involves swelling, dissolution and scission of molecular chain bonds. A wide variety of reactions is possible for resin degradation. The transport of gases and liquids aggressive to substrate into or through the coating is the major problem of its delamination. There are many parameters that influence the deterioration process of coatings, such as chemical agents, temperature, solar radiation, pressure, abrasion, cyclic temperature-moisture changes etc. All these parameters can occur simultaneously or they can be complementary to one another.
- Diffusion rate of corrosive ingredients is higher than FBEC
5. Concrete coatings suffers from poor durability of the coating and loss of corrosion protection in the areas where the coating is damaged
- Concrete requires continuous maintenance and therefore recurring cost.