Assessment of potential exposure prior to construction or repair can prevent premature deterioration. Specific cement types, water repellent sealants or chemical resistant barrier coatings are common preventive measures to protect concrete against chemical attack. Steel reinforcement is often used in concrete applications to make the resulting structure much more solid, stronger and safer. But steel can be susceptible to corrosion, especially in winter and cold climates.
Once corrosion starts to spread, it is almost impossible to stop it and therefore repairing an isolated area will probably not solve the problem. Prevent corrosion of steel reinforcement by making sure you have at least 1.5 to 2 inches of concrete over the reinforcement. A waterproof concrete mix with a low water-cement ratio is best to protect the steel. In addition, other corrosion inhibiting materials, such as an epoxy coating and penetrating sealants, help ensure that the steel remains effective.
Corrosion is the deterioration of steel reinforcement in concrete. Corrosion can be induced by chloride or carbonation. Corrosion can lead to the appearance of cracks in the concrete cover, delamination in concrete covers, etc. Concrete degradation can have several causes.
Concrete can be damaged by fire, aggregate expansion, seawater effects, bacterial corrosion, calcium leaching, physical damage and chemical damage (from carbonation, chlorides, sulphates and non-distilled water). This process adversely affects concrete exposed to these damaging stimuli. Durability begins with a concrete mix design appropriate to the service conditions to which the concrete will be exposed. The water-cement ratio and cement content must provide sufficient paste to fill the voids in the compacted concrete.
The main effect of chloride ions in reinforced concrete is pitting corrosion of the reinforcing steel bars (rebar). Due to its low thermal conductivity, a concrete coating is often used for fire protection of steel structures. Concrete in buildings that have suffered a fire and have been standing for several years shows an extensive degree of carbonation due to carbon dioxide being reabsorbed. We use ground penetrating radar accurately and expertly and are familiar with many other methods that can be used where appropriate, such as concrete radiography and electromagnetic conductivity.
In addition, the load-bearing capacity of the structure can be decreased by loss of concrete, loss of bond between the reinforcing bars and the concrete, and decrease in the thickness of the reinforcing bars themselves. Although concrete is very durable, every effort must be made to stop premature deterioration of concrete structures. Some people believe that concrete is born with cracks; that its ingredients and the way it is produced - from the batching plant to pouring, setting and curing - are influenced by so many factors that concrete cracking is no great surprise; and to a large extent, that may be true. Sulphates in solution in contact with concrete can cause chemical changes in the cement, which can cause significant microstructural effects leading to weakening of the cement binder (sulphate chemical attack).
Steel formwork pinches the top surface of a concrete slab due to the weight of the next slab being built. When the concrete temperature exceeds 65 °C for too long at an early age, the crystallisation of ettringite (AFt) does not occur due to its higher solubility at elevated temperature and the then less soluble monosulphate (AFm) is formed. Exposure of concrete structures to neutrons and gamma radiation in nuclear power plants and high flux material test reactors can induce radiation damage to their concrete structural components. The expansion of corrosion products (iron oxides) of carbon steel reinforcement structures can induce mechanical stresses that can cause cracking and disturb the concrete structure.
Carbon dioxide (CO from the atmosphere diffuses easily into the leachate and causes a chemical reaction that precipitates (deposits) calcium carbonate (CaCO) on the outside of the concrete structure. The use of aggregates with similar particle sizes normally results in a concrete that is poorly consolidated and therefore weaker.