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Reinforced Concrete

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Facts of Early Detection of Concrete Cancer and our Best Solution

The Middle East is well known for the presence of a very aggressive salty water table that sits barely a few meters below the surface. As we all know, salt and water coupled with heat are the perfect blend to create corrosion nightmare of concrete structures.

Some Facts

Concrete Cancer, often identified by flaking concrete or rust stains, which originate deep within the concrete is a serious problem caused by corroding/rusted reinforcing steel from within the concrete. As steel rusts it can expand up to 7 times its original size causing the surrounding concrete to crack. As the steel pushes the concrete away, more water gets to the steel expediting the process.

The process is generally due to:

·       Presence of large quantities of water and salt

·       The ends of reinforcing being too close to the surface allowing water to seep through concrete and react with the steel

·       Poorly treated reinforcing steel being used in the original pour of the slab

·       Fractures in the concrete allowing water to penetrate the concrete and react with the steel

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What do we do?

Spalled concrete can be a safety hazard. Concrete cancer and delaminated concrete should be treated immediately as deferring the treatment will inevitably lead to increased problems into the future.

Similarly, treating the visual aspects such as rendering over the steel are short-term solutions as the rusting process will continue below the surface causing the steel to again displace the concrete and in some cases, rust so badly the steel eventually needs replacement. This approach – we call it the ‘make up’ approach – is aesthetic. In essence, the ugly bits are removed and given a nice clean looking finish, however the underlying problem is very much still present. Within a short time, the area adjacent to the area repaired is cracking and breaking and requires repair. You are back to square one.

The Real Stuff…

The appropriate and effective treatment necessary is cathodic protection – an electrochemical method of arresting corrosion for an extended period of time – ranging from 5 years to 50 years.

Ducorr’s SHIELD™ technology is easy to install into dilapidated atmospherically exposed concrete areas and achieve excellent corrosion protection. The system uses permanent power to provide sustained protection by simply making the corrosion reaction impossible to occur. There’s lots of thermodynamic theory behind, which would be too long for this article – but in essence cathodic protection is the ONLY method that address corrosion at an elemental level eliminating the possibility of any further damage.



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3 Reasons Why Corrosion Protection is the Sustainable Way for Buildings - Part 1

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In the UAE and in the region in general, the geology of our coastal cities in the Middle East require the use of pile or raft slab foundations built from reinforced concrete to be used. These very large underground structures are typically constructed in the water table. Waterproofing attempts typically fail to stop all water ingress, and the basements are often times leaky and inundated with groundwater or significant leaks. Sometimes I have seen entire basements flooded almost to the ceiling of the basement.

 The question we should be asking ourselves is, once the leaks are plugged and the water pumped out, do we still have a problem or are we in the clear?

Do we still have a problem or are we in the clear?

To be sure this is not a one liner. Let’s consider the situation. The floor is made from reinforced concrete. It is now fully laden with chlorides, even after removing all the offending water...

We certainly can’t see the chlorides, but they are there – unless you have somehow managed to miraculously to suction out the chlorides from within the concrete matrix.

With the chlorides present in party like quantities, you now have the main recipe for corrosion;

  • Salt

  • Water (moisture in the concrete)

  • Oxygen

Unfortunately for corrosion engineers, and fortunately for owners, the initiation of corrosion is not something that you can see. If the waterproofing fails…poof….and there is a leak

If corrosion begins….there is only silence. You won’t hear anything, you won’t see anything, at least not until it is too late.

So while the owner goes about renting out his building and counting his rental income, the corrosion reaction also goes about eating away at his steel foundation.

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What are the owner’s options?

 There are a plethora of remedies available. All claim to stop this phenomenon in some way or form. But to be honest there is only one method, which will in effect freeze the corrosion in its tracks. Cathodic Protection. In the next part of this blog, we discuss in more detail the corrosion problem, cathodic protection and sustainability.

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Cathodic Protection of Reinforced Concrete Diaphragm Walls

The Middle East with its high temperatures and extremely high saline content of its sea-water & ground water forms an extremely aggressive environment in terms of corrosion. When constructing structures that are exposed to this environment the challenge is how to ensure corrosion durability.

For diaphragm walls that are cast in situ, this is a special challenge for two reasons.

The first reason is that during construction, some methods employed involve the boring of the excavation, lowering the steel cage into the bored excavation and then casting. The excavation is typically inundated with bore -hole chemicals to ensure that the excavation does not collapse. During this period, it can be expected that chlorides from the surrounding groundwater permeate the excavation walls. Therefore it follows that the reinforcing steel cage will, once it is lowered, be immediately exposed to potentially high levels of chloride.  

The second reason that diaphragm walls are a challenge in terms of ensuring durability, is the exposure after construction. On one side the reinforcing steel is exposed to highly saline sea-water, while on the soil side, the wall is exposed to highly saline ground-water. The wall is seemingly sandwiched between to very corrosion environments.

By deploying a well-designed cathodic protection system using impressed current, the corrosion of the reinforcing steel can be stopped or significantly reduced to a negligible amount. Cathodic protection (CP) is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. A simple method of protection connects the metal to be protected to a more easily corroded "sacrificial metal" to act as the anode. These systems (also known as sacrificial cathodic protection)  can be designed with a service of approaching 20 years.

For longer service life systems, the ‘sacrificial metal’ method above is not sufficient. Metals made from coated titanium cast into the concrete matrix. These provide a means to create electrochemical cell, by introducing direct current onto the steel to be protected, in this case the reinforcing steel. The source of the direct current is typically located close to the structure in an electrical room. These systems can be designed in excess of 50 years.

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Once deployed, these systems can be monitored with extreme ease remotely. Many asset owners fret about the upkeep of these systems. In fact, the upkeep is insignificant. With IoT devices, Ducorr has already developed systems that can be monitored from your smart phone or tablet, sending you updates at intervals you chose.

These systems are extremely powerful durability tools providing a hands-on and active approach for managing corrosion – almost unheard off a few decades ago.

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Beyond The Pool: Corrosion Problems Involved in Swimming Pools

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Many swimming pools were built as part of leisure facilities or schools. These typically comprised of a cast in situ reinforced concrete base and walls with cast in situ promenade decks around the pool. These structures are now often in severe distress due to corrosion of the reinforcement in the walls and promenade decks.

All swimming pools experience galvanic corrosion if they use chlorine sanitizer. Chlorine is salt based, so by adding chlorine to a pool you are actually adding salt. A saltwater pool, however, has approximately ten times the salt level of a traditional chlorine pool. If a saltwater pool has ten times as much salt as a traditional chlorine pool, it means that the rate of galvanic corrosion also increases ten times.

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Corrosion prevention, often referred to as "cathodic corrosion prevention," is a massive field that touches an incredibly broad spectrum of industries, including maritime shipping, manufacturing, petrochemical, water distribution, food processing, major construction and even dairy farming.

The use of cathodic protection to stop this degradation of the reinforcement has been developed to be the standard repair method. The use of anodes in the pool water has become the most popular system of cathodic protection of swimming pools. The anodes are installed in boxes, recessed into the pool side walls of the swimming pool. The economic benefits of this form of repair are so impressive that it is now being used worldwide.  

In this installation, the swimming pool walls and base are protected using anodes in the pool water. The support columns and other concrete parts which also suffer from reinforcement corrosion are protected by internal anodes placed in holes drilled in the concrete. The cathodic protection system is computer-controlled. This gives an accurate continuous control of the output current to each part of the structure based on real-time readings from reference electrodes. This gives a better and more even protection from corrosion, increases the life of the anodes and switches off the anodes in the water when bathers are in the pool. The computer control system has a modem and a telephone connection allowing remote monitoring and control of the system.

Every swimming pool, and especially every saltwater pool, should have a sacrificial anode installed. The addition of this simple and low-cost device will dramatically reduce the damage a pool experiences as a result of galvanic corrosion. While you may still experience localized anodization and oxidation of metals in a pool, especially in situations where two different metals are in direct contact, a sacrificial anode is the bare minimum level of protection that every pool needs. It is absolutely silly to not have one of these — plus they can easily be adapted to any existing system.

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Problems of Durability and Reinforcement Measures for Concrete Tunnel Structures

A tunnel or bridge structure exposed to salt water can expect corrosion of the embedded steel during its service life. Cathodic Protection (CP) has proven itself as the only permanent repair of existing corroded steel reinforced concrete.

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Many underwater tunnel structures have been experiencing water leakages worldwide. Tunnel structures experiencing water leakages are not only old, but also new in some case. The concrete tunnels structures located underwater are generally protected by waterproof membranes as the first defence to prevent water leakages and rebar corrosion. However, once water leakage occurs, the corrosion mechanism is quite different from other concrete structures which are exposed to marine or de-icing salt environments. When rebars corrode in concrete, the accumulating corrosion products develop expansive force and crack the concrete. When the concrete cracks grow, the concrete spalls and falls to the roadway. For the based slab, concrete spalls create potholes on the driveway. Therefore, it is important to clearly understand the corrosion condition of the rebars in the tunnel caused by salt water leakage.

Loss of Durability

Why does the durability of bridges, multi-level car parks, supporting walls, tunnels and sea water structures decrease?

The main problem is the de-icing salt on the streets. These salts contain chlorides which penetrate into the constructions and destroy the protective layer of the rebar - the consequence: corrosion.

These factors together with a too thin concrete cover and too low density as well as changing weather conditions and humidity lead to an increased risk of corrosion. Corrosion of the rebar reduces the steel cross section and as a consequence the support safety. Furthermore, it cause cracks due to the increased volume of the rust.

Factors of influence on the corrosion risk of the rebar.

Factors of influence on the corrosion risk of the rebar.

Concrete Remediation Works

Certain methodology must be developed to remediate the corroding steel and mitigate further corrosion on mild steel components and reinforcement. This would allow the tunnel to achieve its required life with minimal ongoing maintenance. This involved the repair of damaged concrete, encapsulation of mild steel bolts and application of cathodic protection.

Design Options for Cathodic Protection System

There are various design options to be considered to provide cathodic protection for tunnel reinforcement. The three main options were:

a) Ribbon/discrete anodes in slots/ drilled holes in the concrete.

b) A distributed anode system along the full length of the tunnel.

c) Installation of remote anode groundbeds at the two ends of the tunnel

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Treating Reinforced Concrete Corrosion In Parking Structures- Part 2

Levels of Corrosion Protection for Reinforced Concrete

There are three basic levels of active (electrochemical) corrosion protection available. These are generally referred to as:

• Corrosion prevention;

• Corrosion control; and

• Cathodic protection

All levels are essentially similar in that a protective current is provided to prevent or reduce the corrosion activity of the reinforcing steel. They differ in terms of the intensity of the protective current and suitability for a given range of applications.

Corrosion Prevention

Corrosion prevention is defined by the National Association of Corrosion Engineers (NACE) as “Preventing corrosion from initiating even though the concrete may be sufficiently contaminated with chlorides to favor corrosion.”


For owners or managers who suspect corrosion is already underway and damage is occurring, the first step is to identify the extent of the problem. Unless corrosion is severe enough to force off the outer face of the concrete, reinforcing steel is generally hidden within the concrete slab, making any visual identification of early stages of corrosion difficult or impossible. Instead, the concrete is evaluated through field and laboratory testing to determine whether conditions conducive to corrosion exist within the concrete structure.

Chloride ion content testing identifies the concentration of chlorides in concrete at various depths to evaluate the probability a corrosive environment exists. Dust samples from incremental depths through the concrete slab are extracted and sent to a testing laboratory for analysis.

Half-cell potential testing determines the electrochemical behavior of embedded steel by measuring its electrical potential (i.e. the difference in charge from one area to the next). The greater the electrical potential, the greater the risk corrosion is occurring. Conducted onsite, the test involves removal of concrete cover over reinforcing bar, followed by the connection of exposed steel to an electrode through a voltmeter. Half-cell potential readings can be used to generate an electrical potential map, indicating areas with the greatest and least risk of corrosion.

Loss of steel reinforcement is a concern for areas where corrosion has progressed at an advanced rate. Where reinforcing bar is exposed or where concrete is cracked, delaminated, or spalled, a structural engineer should evaluate the remaining slab’s structural capacity to determine whether corrosion has compromised its loadbearing ability.

Where corrosion-induced spalls have been previously repaired, a characteristic ‘halo effect’ might be observed, with a ring of corrosion staining appearing around the patch site. Patching delaminated and spalled concrete with conventional concrete can lead to an electrochemical reaction at the interface between the existing chloride-contaminated concrete and the new concrete. The large difference in electrical potential between the two, combined with the short distance between anode and cathode, leads to accelerated corrosion. Usually, such patches need to be repaired again in just a year or two.

CORROSION CONTROL

Corrosion control is defined by NACE as “Providing a significant reduction in the corrosion rate of actively corroding steel in concrete.” Corrosion control can result in an increased service life of the rehabilitated targeted sections of precast members at a relatively low incremental cost. This is how sacrificial corrosion protection or mitigation is most often used. Corrosion control may or may not completely stop ongoing corrosion, but the reduction in corrosion activity will significantly extend the service life of existing corroding structures. In corrosion control applications, the conditions for corrosion (such as chloride contamination) already exist and corrosion may have already initiated in some areas, although have not progressed to the point of concrete damage. The applied current necessary to address corrosion activity (after corrosion initiation) is higher than the current required for corrosion prevention. Therefore, either larger and/or closer spaced galvanic anodes will be required to provide corrosion control.

CATHODIC PROTECTION

One way of protecting the steel is through cathodic protection. ln this method, the corrosion is stopped by reversing the processes of electrochemical action that cause the corrosion. By applying a direct current to the rebar in opposition to the current causing the corrosion, the corrosion causing current is overcome.

An effective way to achieve long-term corrosion protection of existing chloride contaminated structures, or to provide extended service life to target locations on new precast members, is to use sacrificial protection systems. Galvanic protection is achieved when two dissimilar metals are connected. The metal with the higher potential for corrosion will corrode in preference to the more noble metal. As the sacrificial metal corrodes, it generates electrical current to protect the reinforcing steel. With this type of cathodic protection system, the galvanic protection system voltage is fixed and the amount of current generated is a function of the surrounding environment. Galvanic anodes will generate higher current output when the environment is more corrosive or conductive—for example, where there is higher chloride concentrations, and where current output exhibits a daily and seasonal variation based on moisture and temperature changes. Sacrificial protection systems are low-maintenance, do not require an external power supply, and are compatible with prestressed and post-tensioned steel.

As discussed with our previous Blog article, when sacrificial anodes cannot deliver sufficient current to prevent corrosion, impressed current cathodic protection (ICCP) may be used. As with passive cathodic protection, ICCP reverses the electrochemical process of corrosion through the action of an applied electric potential—in this case, the current arises not from the inherent properties of the materials themselves, as it does with galvanic coupling, but from an external power source.

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Treating Reinforced Concrete Corrosion in Parking Structures - Part 1

Facility Management Contractors are often tasked with maintenance of parking structures. Made of concrete and steel, these multi-level hubs provide visitors and their vehicles with shelter from the elements and often provide access to housing or office space. However, protecting the structure itself from the constant attack of environmental stressors and wear-and-tear comes with its own set of challenges.

Vehicles regularly entering parking garages leave water, oil and dirt behind that can corrode the structure’s concrete and steel support system.

One of the greatest issues related to the deterioration of parking structures is the corrosion of embedded reinforcement. Structural concrete used in parking structures is strengthened by means of steel reinforcement bars, or “rebar,” which is embedded into the concrete to improve resistance to tensile and compressive stresses. Ordinarily, the surrounding concrete protects this embedded steel from the corrosive effects of water and dissolved salts in the environment. However, breaches in the concrete, whether due to cracks, flaws, thin coverage, or poor concrete composition, can allow steel reinforcement to come into prolonged contact with corrosive elements. As the steel corrodes, it expands, leading to further damage to the concrete, greater water infiltration, and additional corrosion in a self-perpetuating cycle of deterioration. If not arrested early on, the progressive nature of the cracking and corrosion can eventually lead to an unsafe structure and can cause costly repair.

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There are several ways contractors can retrofit concrete parking structures to ward off the effects of chloride-induced corrosion. 

One of the effective ways to stop corrosion is the use of a cathodic protection system.

Corrosion is the electrochemical process of reinforcing steel losing electrons and decomposing to iron oxide. Reinforcing steel that loses electrons acts as an anode. One way to stop further loss of electrons, and t h e re f o re stop corrosion, is to reverse the current flow and turn the steel into a cathode.

Passive cathodic protection controls steel corrosion by connecting the reinforcing bar to a sacrificial anode, a metal that is more active than steel and so will corrode preferentially. In the presence of the sacrificial metal, the steel surface becomes polarized to a more negative potential, until the driving force for the oxidation of the steel is removed. The galvanic anode will continue to corrode until it is consumed by the electrochemical reaction and must be replaced. Galvanized rebar is one example of passive cathodic protection, where the zinc coating acts as the sacrificial anode. Other commonly used galvanic anodes include magnesium and aluminum-based alloys.

Where galvanic anodes cannot deliver sufficient current to prevent corrosion, impressed current cathodic protection (ICCP) may be used. As with passive cathodic protection, ICCP reverses the electrochemical process of corrosion through the action of an applied electric potential; in this case, the current arises not from the inherent properties of the materials themselves, as it does with galvanic coupling, but from an external power source. Care must be taken in designing and installing ICCP systems in parking structures, however; excessive current density may cause the alkaline concrete to react with acid generated by the anode, leading to concrete damage. In an ICCP system, it is difficult to provide protection at any significant distance from the anode, since current distribution within concrete is poor. Therefore, anodes must be placed no more than about a foot apart, and the anode material must remain continuous throughout the structure. The ICCP system must take into consideration differing proportion and placement of reinforcement throughout the parking structure, so as to avoid voltage drops from one area to another.

Choosing the Right Strategy

Different approaches nowadays may or may not guarantee protection against reinforcement corrosion for all parking structures. Determining the best way to prevent and treat the underlying causes of corrosion involves consideration of garage conditions and exposure, concrete quality and construction, environmental contaminants, and other factors specific to the structure and situation. Initial cost and maintenance demands are also important decision criteria. Often, the most successful strategy involves a multi-component approach, one which combines preventive treatment with an ongoing program of assessment and repair to keep corrosion at bay. Ultimately, the time and expense required to prevent corrosion and treat early warning signs is far less than that of rehabilitating a garage that succumbs to corrosion induced structural failure.

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Concrete Corrosion Problems of Hotels near Marine Environment

Corrosion of reinforcing steel in concrete is a worldwide problem that causes a range of economic, aesthetic and utilization issues. However, if corrosion effects are considered in the design phase and the right decisions are made prior to construction, public-use buildings such as hotels can be built to last and protect against corrosion for 50 and more years.

Regular and planned asset maintenance is vital for reinforced concrete structures. Such maintenance should not be a ‘cosmetic repair’ but rather a proper root cause analysis that must be carried out to identify and understand the actual source of the problem.

Many of the hotels in MENA Region are situated near marine environments that results in rapid occurrence of concrete corrosion.

Usually, the most exposed elements deteriorate first – but the underlying corrosion is unseen. Active corrosion in the steel beneath may take five to 15 years to initiate cracks in the concrete, but much of the corroded reinforcement is not visible.

Corrosion affects all concrete buildings and structures around the world to some extent, with annual costs in the billions to national economies. With hotel assets, corrosion is often an issue of aesthetics and falling concrete where spalling occurs creates public safety risks. Hotel operators do not want scaffolds, cables, and exposed metalwork on display for extended periods of time. The corrosion of steel in concrete is accelerated in harsh environments, especially in coastal, tropical or desert environments where high salt levels or extreme temperatures can accelerate the rate of decay.

Common Causes of Concrete Corrosion

The two most common causes of concrete corrosion are carbonation and chloride (salt attack). In broad terms, when carbonation, chlorides and other aggressive agents penetrate concrete, they initiate corrosion that produces cracking, spalling and weakening of the concrete infrastructure. As reinforcing rods rust the volume of rust product can increase up to six times that of the original steel, thus increasing pressure on the surrounding material, which slowly cracks the concrete. Over the course of many years, the cracks eventually appear on the surface and concrete starts to flake off or spall.

Degradation of reinforcing steel and the subsequent weakening of the concrete occurs from the inside and may be unseen for many years. It is often referred to as “concrete cancer.”

Repair and Prevention

Impressed Current Cathodic Protection

One of the alternative ways to protect assets from corrosion is by deploying a Cathodic Protection System. One type of CP is  impressed current cathodic protection (ICCP) which is a technique where a small permanent current is passed through the concrete to the reinforcement in order to virtually stop steel corrosion.

The main benefit of ICCP is that the removal and repair of concrete is vastly reduced, with only the spalled and delaminated concrete requiring repairs.

Once installed, corrosion can be controlled for the long term, eliminating future spalling and deterioration even in severe chloride or carbonation contaminated concrete.

Proper anode system selection is the most vital design consideration for a durable and efficient ICCP system. Incorrect selection and placement of the anode system can result in poor performance and a vastly reduced installation lifetime.

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Corrosion in Reinforced Concrete Structures in the Middle East

Corrosion of reinforced concrete structures, both underground and above ground are a significant drain on the economy of most Middle Eastern countries. The majority of reinforced concrete structures in the Arabian Peninsula are chloride contaminated. As buildings and structures age, the chloride levels increase due to both chloride loading from atmospherically carried chlorides, and from capillary action which transports chloride laden ground water into concrete structures, where the water evaporates concentrating the salt above ground level. Allowing reinforced concrete structures to corrode freely results in buildings and structures that require repair or demolition due to structural failure.

One scenario of concrete damage due to corrosion happened in one of the Port in the Emirates which was constructed during 1970 and consists of pre-cast reinforced concrete beams and slabs with in situ concrete topping, supported by tubular steel piles. The first signs of deterioration were recorded after 7 years, evidenced by cracking of the lower corners of the pre-cast beams. Observing this, a series of detailed inspections were carried out.

An impressed current cathodic protection system incorporating metal oxide coated titanium anode was used to prevent further deterioration. The main advantage of impressed current cathodic protection (ICCP) lies in its much greater output capacity as compared to galvanic anode systems. Therefore, whenever corrosion protection is required for large poorly coated or bare structures, ICCP would be the system of choice. ICCP systems requires the use of an external DC power supply and metal anode in direct contact with concrete. This is achieved by embedding a durable conductive anodic overlay. This method is called reinforced concrete cathodic protection (CP).

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The Impact of Corrosion on Concrete Infrastructures

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In the past 50 years, U.S. Department of Transportation’s Federal Highway Administration (Washington DC & Florida) have done research on the bridges and offshore platforms that have aggressive chloride environments and show evidence of corrosion after short service periods. They found that, since mid of 1970’s, the cost of repairing or replacing of deteriorated structures has become a major liability for highway agencies. $20 Billion was spent on repairing corrosion problems in the past 10 years and it is increasing at $500 Million per year. The primary cause of this deterioration (cracking, delamination, and spalling) are due to the chloride attacking the reinforced steel.

Various Cathodic Protection techniques were developed to prevent corrosion in their bridges & offshore platforms. The U.S. Department of Transportation’s Federal Highway Administration (Publication no. 00-081, August 2000) is applying cathodic protection on their major bridges/tunnels, etc. The advantage of deploying Cathodic Protection System are:

1.    100% guaranteed service life (10 to 100 years life span)

2.    Easy installation

3.    Low maintenance

4.    Decreases (stop) the risk of corrosion in the reinforced concrete structures

In recent years, Road and Transportation Authority (RTA) of Dubai, have taken the approach of deploying Cathodic Protection System on their assets such as Dubai Water Canal and Shindagha Tunnel since it is a simpler option that allows to decrease the risk of corrosion on their reinforced concrete assets.

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Culprits That Caused Miami Bridge Corrosion

#corrosion #Infrastructure #bridge

3 Culprits That Caused Miami Bridge Corrosion

Jet Skis, waverunners and other personal watercraft shooting salt water up at the underside of the MacArthur Causeway have caused extensive corrosion on one end of the bridge, necessitating repairs to beams and columns. It's also time to replace the top three inches of concrete on the bridge's surface.

The bridge connects the city of Miami to the barrier island of Miami Beach.

Residents and commuters of the notoriously traffic-jammed region should brace themselves for a long stretch of headaches on the main causeway connecting South Beach to mainland Miami.

The Miami Herald reports the Florida Department of Transportation began a two-year, $12.9 million rehabilitation project on the corrosion of the bridge in June 2018.

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Reference: https://www.nbcmiami.com/news/local/Waverunners-Jet-Skis-to-Blame-in-Miami-Bridge-Corrosion-488207961.html

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