Why Does Concrete Conduct Electricity?

Concrete is a very common building material made up of cement, sand and aggregate (stone), mixed with water. It’s used in the construction industry to build just about everything from roads, damns and bridges to sidewalks, patios and residential homes. The mixture gets hard through a process called curing which in some cases can take over a month to complete. Concrete is a very poor conductor of electricity but it is still a conductor. Completely dry concrete offers high resistance and can actually be classified as an insulator. But there are conditions under which the conductivity of concrete can increase. Moist concrete retains water within it’s pores which makes it a much better conductor of electricity. So in other words, when concrete is wet or damp, it changes and becomes a much better conductor.

Concrete is made up of chemical components that have free ions. Concrete conducts electricity through these ions. The conductivity of any substance is dependent on the resistance it offers. The ions of Silicon, Aluminium, Calcium, sulfur and others, help conduct electricity but there not great conductors. It’s by other factors not native to concrete that help it become a better conductor. Things like water and steel rebar.

There are actually several factors that can affect how well concrete conducts electricity. Let’s go through some of the conditions that influence the conductivity of concrete.

What Makes Something Conduct Electricity?

How conductive a things is has a lot to do with its atoms. In things like wood or glass, the atoms are packed tightly together. The electrons stick close to their atoms. This makes it harder for the electrons to move around. This means a greater electrical charge is needed to conduct electricity through them.

These substances are known as resistors because they resist the flow of electricity through them. Electricity will rarely pass through resistors because of the amount of power that it takes to do so. Electricity takes the path of least resistance so when it meets a resistor it finds another way.

In contrast, good electrical conductors have plenty of free electrons floating around. The atoms and electrons are loose and spread farther apart. In the most conductive substances, like copper or gold, there are so many free electrons that some are actually shared by multiple atoms. This makes it very easy for electricity to pass through because there’s hardly any resistance at all.

Water is a good conductor of electricity and so is metal. So even though natural, dry concrete is a form of resistor, when it gets moist or is filled with steel it loses some resistance.

Concrete is a better conductor than something like glass or wood but not as good as metal or water.

What Makes Concrete Conductive?

In it’s natural dry state, concrete is actually more of a resistor. Dry concrete that’s made from sand, water, aggregate, and cement is not a good conductor of electricity and can actually be used as an insulator. As long as you keep the concrete dry it’s very hard for electricity to pass through it. Especially as the concrete gets thicker.

What makes concrete become more conductive is what you add to it. It’s not the concrete itself that’s carrying the electricity. Water for example is great for conducting electricity. So if your concrete gets wet it will conduct electricity. But it’s the water that’s actually doing it, not the concrete.

When you first mix concrete it’s much much easier for electricity to pass through it because of the high water content. But as the concrete dries out it becomes much more resistant.

Concrete’s exact level of resistance can be a bit unpredictable because it depends on the ingredients that were used. Ingredients have different levels of resistance so the finished product’s overall resistance can vary. But in general, almost all concrete is considered resistant when dry.

It’s also worth noting that each batch of concrete loses conductivity at a different rate. This is also based on the ingredients and water levels used.

Can Concrete Be A Better Conductor?

Yes, if you use the right additives then concrete can be a better conductor. One of the ways you can do it is by including ingredients that conduct electricity, such as metals. By including things like steel rebar you can increase the conductivity of concrete. Although for this to happen the electricity has to reach the rebar.

Increasing the water content in concrete can also increase it’s conductivity. However, the more water you put in the concrete mix the weaker it will generally become. This can be a serious problem if you need your concrete to be strong.

Some companies have also tried using a carbon based aggregate to produce more conductive concrete. This is a promising technique that shows promise. Although it has some adverse effects regarding water absorption.

You could also try including a porous aggregate in your mix. Porous concrete absorbs moisture much better than non porous does. The concrete would have to be damp for this to work but in many areas of the country that’s not a problem.

Additional Factors To Consider

Concrete doesn’t have a lot of conductivity on it’s own. However, there are a couple of situations that occur in construction that can make it more electrically conductive.

Because of these common situations, most concrete used in many building projects is at least a little bit conductive, even if it isn’t that way naturally.

Lets look at them below.

Size

The size of an object can also affect conductivity. A concrete wall that’s 4″ thick won’t resist electricity as well as one that’s 12″. If you resistance is a concern for you then I recommend building a little thicker.

Temperature

The temperature of an object can also effect conductivity. Some resistors, like glass, become better conductors when they’re hot. Superconductors do the opposite. They conduct electricity much better when at low temperatures.

Concrete gets more conductive when it warms up which makes it a better conductor.

Water

Concrete can become conductive when it’s used in a wet environment. It’s good at absorbing water and gets more conductive as the water content increases. If it’s been placed in wet soil or in a rainy environment, as long as it stays wet, it’ll be better at conducting electricity.

Steel Rebar

Another situation where concrete becomes more conductive is when it’s built using steel rebar. Nearly all concrete structures include some form of rebar. Rebar adds a lot of strength to a structure. By including metal in the concrete you can make it a fairly strong conductor. This is because steel is a good conductor so electricity is able to use that steel as a method of transportation. This is much in the same as it uses water.

Why Would Anyone Want Their Concrete To Conduct Electricity?

Concrete has a few valuable uses when it’s able to conduct electricity.

A slight electrical current run through a concrete road can warm the concrete which melts light snow and ice. Japan and many other countries do this rather than plowing light snow.

Another valuable use of conductive concrete is as a grounding for lightning rods. Lightning rods need a counterpart on the ground to redirect the lightning they catch. A building’s concrete foundation can often serve as ground for it’s lightning rod, protecting the people living inside.

It’s important to remember that even though most concrete is a natural resistor, it still might conduct some electricity. You should never count on concrete to keep you safe from electricity.

Summary: Why Does Concrete Conduct Electricity?

Many people believe concrete can’t conduct electricity but that’s not the case. Electricity can pass through just about anything if the current is strong enough. But concrete is definitely resistant in it’s natural, dry form. It’s the additives that make it a better conductor than usual.

Concrete is a very poor conductor of electricity but it is still a conductor. Completely dry concrete offers high resistance and can actually be classified as an insulator. But there are conditions under which the conductivity of concrete can increase. Moist concrete retains water within it’s pores which makes it a much better conductor of electricity.

In general it’s safe to say that concrete is not a good conductor. And in it’s dry form its resistant and sometimes even an insulator. But it definitely can conduct electricity under certain circumstances.

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