Concrete is a building material desired for its core strength and longevity. But just like any other building material, it is highly exposed to multiple environmental hazards.
Such exposure not only affects its durability but also its ability to enhance the aesthetics of a structure.
Choosing concrete as your preferred building material means you have chosen durability. But what happens when the durability aspect is threatened?
You have to come up with equally durable solutions to safeguard the usefulness of the concrete. One such solution accepted industry-wide is the application of protective coatings on concrete surfaces and structures.
Such coatings are ideal in all kinds of environmental and climatic conditions to ensure your concrete structures maintain their durability across all seasons.
What are concrete protective coatings?
These refer to coating solutions applied on concrete structures and surfaces to increase durability or enhance aesthetics.
They serve to restrict anti-durability agents such as water and chemical permeation as well as sealing severe cracks on the concrete’s surface.
Concrete protective coatings are warranted by the fact that concrete structures and surfaces are always subjected to a wide array of exposure conditions. The exposure levels may vary according to location or use of a particular concrete structure.
External forces like heavily polluted urban atmosphere, chemical pollution, marine pollution, and atmospheric carbonation, altogether present some serious threats to the condition of concrete along with its entrenched steel reinforcement.
Therefore, concrete protective coatings essentially reduce the impact of these external forces on the concrete material.
What are the common concrete exposure conditions?
Understanding the agents that affect the durability of concrete is crucial in determining the appropriate protective coating to apply. Below are some of the commonest agents:
Carbon dioxide
Atmospheric carbon dioxide may react with the calcium hydroxide element in the cement combination forming the concrete structure. This intense reaction produces a compound called calcium carbonate.
This carbonation process tends to affect the concrete reinforcement bars embedded within the concrete structure. The calcium carbonate compound effectively weakens the metal bars, reducing the protection and support of the concrete.
However, since CO2 concentration in urban environments is 5-10% higher than CO2 concentration in rural environments, the carbonation-induced corrosion mostly affects urban concrete structures.
Further, carbonation occurs well in concrete relative humidity of between 50-75% pointing to the importance of maintaining a proper cement-water mix when putting up concrete structures.
Structure load weight capacity
Overloading a concrete structure, wrongly designing it, impact from earth tremors, as well as mechanical impact due to car crashes can cause severe damage to the core of the structure. All these forces exert extra stress on the structure hence affecting its overall load capacity.
Water invasion
The capillary pores on any concrete structure allow water to percolate through to the steel reinforcement. Water is a good facilitator of abrasive chemical reactions.
If the concrete structure is carbonated or infested with high chloride concentrations, the steel reinforcement bars may suffer corrosion, consequently resulting in concrete cracks on the surface.
Extreme temperature distortion
Building structures and bridges tend to undergo extreme temperature variations on different seasons or on different sections of the concrete.
That constant contraction and expansion under different temperature conditions may interfere with the thermal conditioning of the concrete structure. Such rapid interference may result in movement of the structure, causing damaging cracks to surface. The same level of stress is also experienced during the freezing and thawing process.
Chemical exposure
Depending on the type, location, and purpose of a concrete structure, chemical threats are rampant. This is a common scenario in sewer systems, water treatment plants, as well as chemical plants. These chemical concentrations breed a conducive environment for corrosion and weakening of concrete structures.
Fire exposure
Intense fire can cause ravaging effects on reinforced concrete. Beyond disfiguring the aesthetics of the concrete structure, fire also weakens the surrounding support components of the structure by releasing gases that react with vapor to form corrosive compounds.
As a rule of thumb, healthy, secure concrete can only withstand heating up to a hundred degree Celsius. Beyond that, the concrete structure becomes exposed to heat damage.
What are the common concrete structural damages?
The structural damages may manifest as either damages due to concrete defects or damages due to corrosion of steel reinforcement.
The most rampant structural defects experienced in concrete structures are:
- Concrete surface scaling or spalling caused by water and chloride ingress
- Corrosion of steel reinforcement due to chemical attacks
- Gradual structural cracks
- Gradual non-structural cracks
- Severe chemical disfiguring
Steps followed in applying the right concrete protective coating
Assessment of the concrete structure
This is done to determine the potential defects staring at a concrete structure.
Evaluating the cause and extent of damage
Understanding the cause of the defect helps in determining the right solution.
Removing the damaged concrete
This entails chiseling the damaged section of the concrete to pave the way for steel access.
Cleaning the exposed reinforcement steel
This is thoroughly done to rid the steel bars of any rust and corrosion elements.
Protecting the exposed steel
This is done by application of active corrosion inhibitors such as paint protection, based on the environmental exposure level of the steel.
Protecting the embedded steel
This involves providing additional protection to the embedded steel that stands the risk of corrosion, especially for carbonated concrete. The extra protection is applied by mixing concrete with corrosion inhibitors such as amino-alcohol or nitrite technology materials.
What should I consider when selecting a concrete protective coating?
The following parameters are to be applied:
- The proximity of the concrete structure to water bodies
- The ability of the concrete protective coating to inhibit chloride movement
- The amount of vapor breathing space allowed within the concrete structure
- The ability of the concrete protective coating to inhibit carbon dioxide diffusion
- The minimum temperature at which the protective coating can be applied to bridge cracks
- The ability of the protective coating to resist weathering
- The ability of the protective coating to hide reinforced concrete
- The ability of the protective coating to resist dirt buildup
What are the types of concrete protective coatings commonly used?
The selection of concrete protective coatings may vary as follows:
Cement based coating
This is preferred where the designer intends to retain the original aesthetics of the concrete structure while still protecting it from adverse environmental conditions.
Reactive coatings
These are used to keep off chemical attacks, carbon dioxide diffusion, chloride penetration, as well as water percolation, which are all agents of corrosion. They react with the corrosive agents before reaching the concrete.
The most common structures ideal for these coatings are tunnels and marine structures.
Organic coatings
These may come in form of elastic coatings and protective coatings. Elastic coatings are ideal for winter seasons because they tend to retain their elastic properties in extremely low temperatures.
Protective coatings are applied where elastic coatings fail to detect the presence of especially severe structural cracks. They provide adequate protection by bridging any potential structural cracks.
Metallic coatings
This involves application of corrosion-resistant metals to concrete surfaces to provide a barrier coating. With such a barrier, the reinforcement steel is protected.
Want to build structures that last longer? Protect your concrete by coating it with the right solution. Consult an expert to determine the appropriate protective coating for your structure.
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