When most people think of concrete, they imagine it as a completely inert substance. After all, concrete surfaces and structures can easily last for dozens and dozens of years. Yet, while this may seem like proof of the fact that concrete has a neutral chemical make-up, concrete is still chemically reactive.
This fundamental aspect of concrete makes it susceptible to certain forms of damage as time goes on. If you would like to learn more about concrete on a chemical level, keep reading. This article will educate you about three key facts regarding concrete and its pH value.
1. Concrete Starts Out With a High pH Value
Scientists measure chemical reactivity by means of the pH scale. The pH scale has a range of between 0 and 14, with the midpoint of 7 representing complete chemical neutrality. As pH values drop below 7, something will become more acidic. Likewise, as pH values climb up above 7, they become more basic.
Fresh concrete has a surprisingly high pH value of around 13 - in other words, nearly at the top of the scale. This high pH stems from the cement used to bind the concrete together. Cement contains a large amount of alkalis, a highly basic category of minerals. As the cement dissolves and mixes with the water, it imparts its high pH to the concrete as a whole.
2. Concrete's pH Value Changes Over Time
Although concrete starts out with a high pH, this tends to change as time goes on. Concrete's high pH makes it more volatile on a chemical level. Virtually any substance with a lower pH that comes into contact with the concrete will interact with its alkalis, neutralizing their basic nature. This reaction, in turn, causes the concrete's pH to go down.
Fresh concrete reacts with acidic substances so easily that even carbon dioxide in the air will begin to neutralize the alkalis. This process, known as carbonation, will gradually affect the concrete's pH at deeper levels. In addition, exposure to other acidic substances like acid rain or deicing salts will further hasten the pH change in the concrete.
3. Lower pH Values Increase the Concrete's Chances of Damage
Unfortunately, concrete starts to experience negative effects when its pH dips below a value of around 11. At that point, the cement's chemical nature will have been altered enough that it can no longer bind the aggregate particles tightly. As a result, the concrete may begin to break apart.
This sort of damage affects the outer layers of the concrete first. Patches of flaking, chipping, or otherwise damaged concrete go by the general name of spalling. As the surface of the concrete shears away, the process of carbonation will have an easier time affecting deep portions of the slab. Before long, the concrete may be too damaged to be repaired.
Carbonation poses even more serious problems for concrete that has been reinforced with internal steel supports. The changing pH will leave these structural elements much more prone to corrosion. As rust starts to build up on the outside of the metal, the rust will place large amounts of pressure stress on the surrounding concrete. This stress makes the concrete more prone to developing cracks and potholes.
Fortunately, contractors have a variety of techniques for protecting concrete against unwanted pH changes. To learn more about what you can do to keep carbonation from destroying your concrete or to have damaged contract repaired or replaced to get back to a good state, contact the experts at Capitol City Concrete Cutters LLC. We can help you with all of your concrete needs.