- There is a growing demand for increased durability of concrete repairs on both new and existing structures
- The use of corrosion inhibitors is one of the most efficient and cost-effective methods for corrosion protection of reinforced concrete structures
- There are clear guidelines available to assist specifiers on where corrosion inhibitors can be successfully used
Equipment preservation is more than just managing the corrosion of materials and equipment. Preservation is a set of strictly defined routines, schedules, procedures and process actions that keep tagged pieces of equipment – from pumps, engines, bolts and pipes - in working order. Equipment preservation is very important because it has a significant impact on the budget throughout the whole asset lifecycle.
A traditional method of preservation uses Nitrogen; however, this method implies the application of serious health considerations. Another approach is the use of Vapor Corrosion Inhibitor (VpCI) technology, which is based on the use of organic salts with partial vapour pressure allowing them to vaporise, and it provides protection in three phases allowing them to be combined with Nitrogen and Dry air.
VpCI has multiple advantages compared to conventional methods. The key benefits are that VpCI is very environmentally safe, it provides three-phase protection, it has multiple delivery mechanisms, and it is a multi-functional technology.
In order to achieve the best practice in equipment preservation, we need to have an allocated budget and then to develop a plan. After this, we need to identify the stakeholders with proper management and coordination, and we need competent and well-trained people to execute these practices.
The preservation specialist third party is required to coordinate with all of the other parties - from manufacturers and operators, to designers and EPC contractors. The preservation specialists then become part of the management team developing plans and procedures with industry-proven technologies. They also become involved in testing supervision, training, monitoring and inspections.
Corrosion inhibitors for new-build concrete structures
The corrosion mechanism is well described in ACI 22R-01, which is a guide to the Protection of Metal in Concrete Against Corrosion. The first commercial corrosion inhibitor was developed in 1975; however, the first testing method to assess the performance of these inhibitors was developed by ASTM called G109. In 2004, ASTM developed a standard specification (C1582) for corrosion inhibitors that has acceptance criteria. Also in 2004, ASTM developed a quick test method for corrosion testing known as the G180, which offers results within 72 hours.
According to ASTM C1582/C1582M, for a material to be considered a corrosion inhibitor, it must show a reduction in corrosion rate and corroded area of bars in concrete containing chloride at the level that induced corrosion in the reference test specimen. Techniques or materials that reduce the actual intrusion of chloride, while being useful, are not corrosion inhibitors.
The Concrete Society’s CS 163 Guide to the Design of Concrete Structure in the Arabian Peninsula defines special structures as any structure that has a service life in excess of 30 years or is exposed to a severe environment. The guide offers recommendations including conducting a specific durability study and service life prediction, as well as implementing the use of Additional Durability Enhancement Techniques (ADET) through electrochemicals, through the surface, through reinforcement and through admixtures.
Corrosion inhibitors for existing structures
The ACI 562 and BS EN 1504 codes and standards are available to guide engineers on the right path for repair and assessment. When repairs are done in a very unprofessional manner, this creates the anodic ring effect (or the Halo effect) which is discussed in ACI 562. It is a special form of corrosion in which new corrosion develops immediately around the repair area. The ACI 562 also has a section that talks about alternative means of protecting reinforcement, including the application of waterproof membranes, corrosion inhibitors, and various forms of cathodic protection.
The ICRI 5010.2-2019 technical guideline for the use of penetrating surface applied corrosion inhibitors, developed by the International Concrete Repair Institute (ICRI), provides information on SACI treatment for corrosion mitigation of reinforced concrete structures. The information is intended to provide guidance and supplement sound judgment by engineers, consultants or other specialised in the repair and restoration of reinforced concrete structures suffering from corrosion induced damage.
Surface Applied Corrosion Inhibitors (SACI’s) are used in restoration to extend the useful service life, to cut corrosion rates to 1/5 of what they are, to help reduce the ring anode effect, and they are very compatible with other materials such as sealers, coatings, etc.
SACI’s works with a migrating mechanism via capillary action, then vapour diffusion followed by ionic attraction onto the rebar surface. This is where the physical absorption takes place where the monomolecular layer forms on the rebar suppressing the anodic and cathodic reactions. Other types of speciality organic corrosion inhibitors include the converter rust primer, liquid-based rebar preservation, and PT strands protection.
Corrosion of steel in concrete structures plays a significant role in affecting the service life of the concrete structures. Various methods, codes and standards are available from the American Concrete Institute, International Concrete Repair Institute, and British Standards, for example, which offer guidance on the use of concrete inhibitors for both new and existing structures. The type of inhibitors used in concrete is based upon their mode of action and the way of application.