Types of Concrete Deterioration
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How do They Make Concrete?
Before talking about how it degrades, let’s cover how concrete is made briefly.
Concrete is made of three main ingredients: Portland cement, water, and aggregates (either coarse/large or fine/sand).
The mix is then poured into a mold where it is allowed to hydrate, a process where the cement and water chemically bond to form a solid matrix.
Concrete and Steel: A Perfect Match
Concrete and steel pair up perfectly.
Concrete is highly alkaline and has great compressive strength, but low tensile strength. Steel has excellent tensile strength and thermal properties, but it is susceptible to corrosion.
Steel makes up for the lack of tensile strength of concrete, while alkalinity of concrete protects steel from corroding to some degree. This is why reinforced concrete is used so often.
Types of Concrete Deterioration
Corrosion:
Before it can occur, carbon dioxide or chloride must penetrate the concrete to make contact with the reinforcement in sufficiently high concentrations.
Since steel corrosion is an expansive process, it also damages surrounding concrete in addition to weakening the steel as it rusts.
Corrosion is actually two processes labeled anodic and cathodic. The anodic process occurs when the protective surface layer of steel reinforcement is compromised. It is where the iron atoms dissolute to ferrous ions.
The cathodic process is where oxygen is reduced to hydroxyl ions due to water exposure.
Before either process can proceed, the alkalinity of the concrete must be compromised. Calcium hydroxide and the other soluble alkalies in the concrete give it a pH of about 12.5. This is threatened by carbon dioxide in the air that penetrates small pores in the concrete mold.
When carbon dioxide reacts with calcium hydroxide, the resulting carbonation decreases the pH of concrete which endangers the integrity of the underlying steel which depends on the alkalinity for protection.
Moisture is required for the perpetuation of deterioration, however it is interesting that marine structures are unaffected by this since they are fully submerged in water which prevents carbon dioxide from penetrating the mold.
Corrosion is one of the most well known types of concrete deterioration and is caused by chlorides as well as carbonation. Chlorides are present in higher concentrations in desert and coastal regions. They can even be found in the mixing water, contaminating the aggregate during the mixing process which accelerates corrosion of the embedded steel.
In the 1980′s they would add calcium chloride to the mix in order to speed up the setting process, but this has recently discouraged due to the reasons aforementioned.
The most common source of destructive chloride in the northern United States comes from salts intended for deicing.
Both calcium chloride and sodium chloride are applied to the roads and bridges of areas known for their wintery conditions.
Seawater is not as aggressive due to the way that magnesium sulfate and sodium chloride act together to clog surface pores on a concrete structure which actually slows the rate of corrosion.
Freeze and Thaw Damage:
This is one of the types of concrete deterioration that apply to some geographic areas more than others.
Freezing conditions and wet concrete are a poor match. When water is trapped in concrete and then expands, the outward pressure damages surrounding material.
In places where standing water collects on horizontal surfaces, such as a parking deck, the surface will erode and widen the existing pores which further expose the concrete. The increased exposure promotes further deterioration substantially. When the erosion grows into full blown cracks, the embedded reinforcement may be directly exposed to water and other hazardous substances.
Other Types of Concrete Deterioration:
- Shock heating coming from fire
- Overloading or underdesign
- Alkali-aggregate reactivity
- Other forms of chemical attack
- Lightning damage
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So you know you’re in need of a solution for your concrete deterioration issue in Maryland or Northern Virginia, but not sure who to turn to?
Concrete Restoration is the leading concrete services contractor in VA, DC, and MD with decades of experience in concrete repair, concrete restoration, concrete resurfacing, and concrete waterproofing.
If you would like to ask questions or schedule an appointment, call us today at 301-261-4933 or
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