Posted by Engin Seyhan - 30 September, 2019
Corrosion never sleeps and especially in case of steel-reinforced concrete structures the proper method is required to mitigate and prevent it. Corrosion can be defined as the conversion of a refined metal into its more stable oxides, with the consumption of oxygen and water. Concrete provides a natural shield, protecting the steel reinforcement against corrosion. The highly alkaline environment created by the cement matrix surrounding the steel reinforcement results in the formation of a passive layer around the rebar, which is an impermeable oxide film preventing further corrosion reactions by full isolation of the steel surface. However, this protective film is maintained only as long as the highly alkaline environment provided by the concrete matrix persists. Carbonation due to exposure to carbon dioxide dissolved in water reduces the pH of the cement matrix. In addition, chloride ions also disrupt the passive layer and lead to corrosion. When the passive layer has broken down, corrosion reactions start and damage the steel reinforcement.
Although the corrosion process cannot be avoided, there is a great deal that can be done to inhibit it. Several types of corrosion inhibitors on the market. These are based on chemical compounds which prevent corrosion reactions on the reinforcing steel. All inhibitors need to reach the concrete near to the steel reinforcement to protect it. To do so, corrosion inhibitors can either be added to concrete admixtures and mixed directly with the fresh concrete or applied to the surface of the hardened concrete (SACI - surface applied corrosion inhibitors). The first type of inhibitors can be applied only in the case of new structures; the second has been specifically developed for the refurbishment of existing structures.
MasterProtect 8500 CI: state-of-the-art protection for steel reinforcement
It is no longer necessary to choose between the perfect solution for new or existing structures. MasterProtect 8500 CI by Master Builders Solution is a new corrosion inhibitor developed for application to new and existing structures which has been proved to be effective even in the case of post-application cracks. MasterProtect 8500 CI is a dual-function, silane-based, surface-applied corrosion inhibitor, ideal for use as part of a corrosion prevention, protection, or inhibition strategy. It is a revolutionary blend of high-quality silanes combined with selective corrosion inhibitors, which lie dormant within the concrete until activated by moisture which penetrates the surface due to cracking or aging of the concrete. The inhibitor cannot be visually detected in dry conditions since MasterProtect 8500 CI does not change the appearance of the concrete. However, when the concrete is wet, it's water repellence - the beading effect - on the concrete surface can be easily observed. In addition, MasterProtect 8500 CI has a very low viscosity to improve penetration into the concrete over a wide temperature range, a lower VOC content and a higher flash point, which together makes the handling of the product and its application much easier and safer than many other inhibitors.
What is the dual functionality of MasterProtect 8500 CI and how does it work?
Typical surface-applied corrosion inhibitors require the inhibitor to penetrate deep into the concrete to reach the steel reinforcement, where the functional group acts right at the surface of the rebars, re-passivating the steel and reducing active and future corrosion. MasterProtect 8500CI goes a step further by employee dual functionality.
The first part of the dual functionality of MasterProtect 8500 CI is the hydrophobic effect provided by the high-quality blend of silanes, which prevents moisture and chlorides from penetrating the concrete. Depending on the chemical reaction that takes place, silanes can be created with different functions. MasterProtect 8500CI utilizes multiple silane functions to create different effects on the concrete substrate; these include a corrosion inhibition effect and the formation of a hydrophobic layer which protects concrete against the penetration of liquid water while being permeable to water vapor. This way, new moisture is prevented from penetrating into the concrete, while any moisture contained in the substrate can evaporate. This phenomenon keeps concrete constantly dry and increases its electrical resistivity; as concrete can be considered an electrolyte for steel reinforcement, higher resistivities prevents electrochemical reactions. Besides, in dry and alkaline concrete, steel reinforcement is quickly passivated. Together with the Lack of water and the high resistivity of the concrete, this means that the corrosion rate is dramatically reduced.
The latent-phase inhibitor is blended in the silanes of the second element in the dual functionality of MasterProtect 8500 CI. The presence of latent inhibitors is key to ensuring long term corrosion protection for reinforced concrete structures. Regardless of the age and quality of the concrete, cracking is very likely at any time in the service life of the structures. Concrete, with steel reinforcement, tends to crack for several reasons. The most common causes of cracking are explained in the article Why does concrete crack?. Cracking means also that the hydrophobic shield provided by the silanes of MasterProtect 8500 CI is broken. Water and chloride ions can penetrate through the crack and may cause damage to the steel reinforcement. At this point, the dual functionality comes into play and MasterProtect 8500 CI continues to protect the reinforcement. The latent inhibitors remain dormant in the concrete until the water repellence diminishes over time, or until the concrete cracks. At this point, they are activated, become mobile, and are carried deeper into the concrete by moisture, The steel reinforcement therefore continues to be protected.
The dual functionality of MasterProtect 8500 CI separates it from the crowd of existing inhibitors on the market: in addition to the hydrophobic shield provided by the revolutionary blend of silanes, the latent phase inhibitor guarantees long-term protection. This ensures an extended service life for all types of reinforced concrete structures. The effect has been demonstrated by various independent tests as we will described in Part 2 of this article, soon online.