Concrete is one of the most durable substances known to man, but it is not impervious to the passage of time. Over time concrete will begin to build up corrosion and erode away, this can be due to many factors. Human error, aggregate quality and natural elements can all be causes of concrete erosion.
This guide will go through how erosion happens to concrete, ways to prevent it (including regular use of cement mixers) and how to repair erosion that has already occurred. The first thing that will need to be discussed is some basic terminology and differences so that there is no confusion further on. A good place to start would be the difference between erosion and corrosion.
Difference Between Erosion and Corrosion
Corrosion is a chemical reaction that occurs within metals where they begin to change their oxidation levels and begin to actually change their states by combining with something within their environment. This new state is usually more brittle and weak compared to the previous state. For example, iron or steel reacts with oxygen in the air over time and will begin to corrode and form rust and this is why rust will form on your cement mixers over time if you don’t maintain them properly.
Erosion on the other hand is a natural process where physical elements such as rain and wind will modify the shapes of the geography and in the case of concrete, more than likely degrade the structural integrity. It is important to understand the difference between corrosion and erosion as even though there is no such thing as concrete corrosion, the corrosion of the metals within the concrete pour can erode if not properly prepared and this will in turn lead to concrete erosion. This happens even if there is very little air for the metal to react to.
Corrosion can also occur within concrete if two different types of metals are touching inside of it. Metals such as aluminum and steel have different properties and if put in contact, such as a railing being driven into a concrete foundation, this will begin to cause corrosion. This is similar to what happens inside of a battery when left for too long.
In this instance, the metal is reacting to the concrete itself to begin this reaction and as the steel used in things like rebar are not naturally occurring metals, they will naturally want to either oxidize or turn to rust. Ways to prevent this from happening will be discussed below. This is just one factor that can lead to erosion of your concrete and damage to your projects.
Other Causes of Concrete Erosion
As stated previously, erosion can happen due to natural elements over time. Either rain water hitting the surface or wind dragging particles across it, although negligible at the time will eventually affect the surface of the concrete at a molecular level. The level that it is affected can vary based on the type of concrete used, types of particles the wind drags across the surface and frequency of rain.
Particles such as dust are constantly moving and in areas with high winds or levels of sand, these particles can actually be extremely abrasive. This also applies to surfaces that are used for every day work as this can be an even more abrasive type of erosion. An obvious example of this would be roads and driveways that have cars constantly driving over them, any made with concrete will need to be maintained regularly.
Rain can have a particularly bad effect on concrete as it is used in its creation. Water that is trapped in close proximity to concrete and that is given no space to evaporate, such as rainwater that has been trapped under broken waterproofing, can very quickly start to seep into the concrete and cause damage. Damaged waterproofing that is actually trapping water can be a very common cause of erosion.
Concrete that is frequently exposed to sea or saltwater can be even more susceptible to corrosion as the chloride ions within them can seep through cracks or fissures in the concrete and reach the steel rebar within. This will exponentially increase the rate of corrosion.
Another natural cause of erosion is extremely cold temperatures. Concrete is made using water that is then evaporated during the curing process, but not all the water evaporates. In cold enough temperatures this can lead to the water still within the concrete freezing and expanding up to as much as 10%.
This frozen water will then thaw again when the temperature rises and return to its original state and size. Over time, this constant expansion and regression can cause the cavities within the concrete to crack and form deep fissures. This process can be exasperated if the concrete is not prepared properly or given enough time to finish the curing process as there will be even more water within it.
Some people may place salt to prevent this, but this can actually aggravate the erosion. Besides that, if done frequently enough, the sodium can begin to seep into the concrete. Although this won’t do anything to the concrete itself, as mentioned this salt can be incredibly corrosive to any metals that are inside the concrete.
The quality of aggregates used and how the original concrete pour is conducted are very important factors to consider. This may seem simple but there are actually many different types of concrete that can be created using different aggregates from sand types to types of cement. Some cement types are better suited to different environments or temperatures whereas others are for more aesthetic means and should be used indoors.
Besides the quality of the aggregates, the way in which they come together is also very important. Concrete that is not mixed together or not divided into ratios properly will not undergo a proper chemical reaction and will be weak or will have sections that are weaker than others. Even if everything is mixed properly with cement mixers or delivered premade, if the pour is not properly cared for during the curing process this could leave too much water trapped in the surface that will either cause erosion or form cracks as it tries to go to the surface that has already dried.
Concrete can withstand very well in high temperatures but extreme ones such as those encountered in a fire can still be very damaging. The heat generated can cause the concrete to become stiff and brittle and lose much of its strength. The water within will evaporate too quickly and if this is not allowed to escape then the strength of the concrete will be greatly reduced and in some circumstances it can actually force its way out and cause cracks and fissures, any concrete that has been exposed to a fire should be removed and rebuilt rather than repaired.
Ways to Prevent Concrete Erosion including cement mixers
Corrosion of metals within a concrete structure is actually fairly easy to prevent. Steel that is completely submerged inside concrete will corrode at a negligible rate if the concrete mixture is created and cured properly. If however, any steel is exposed from the beginning or becomes exposed due to damage, this can very quickly lead to corrosion and further damage.
In the designs, no metal should be exposed from any concrete, this is a given. But care must also be taken in sections of a pour where metal is close to the surface. For these areas, protective coatings can be used to further increase the durability and longevity, but a professional company will need to be brought out to assess the best coating for the situation and apply it.
Professionals should always be used when applying protective coatings as they can actually be extremely damaging if not done correctly. As mentioned above, a damaged waterproofing layer can trap water against a layer of concrete and cause water damage. This is just as, if not more, likely to happen if the waterproofing is installed incorrectly by an amateur.
In the beginning of the article, you may have wondered, why mention the use of cement mixers? As mentioned above, if concrete is not mixed together properly it can cause weaknesses later on. Using a cement mixer can help alleviate some of the problems here by ensuring your aggregates are always properly mixed together.
As long as you have ratioed your concrete out properly, you can throw it all in your cement mixers and watch the concrete form before your eyes. This will also allow you to easily pour the concrete from your cement mixers straight onto the surface you intend to cover. If you do not own any cement mixers, it may be worth renting one before a pour simply because of the quality they can provide.
For larger pours a cement truck loaded with premade concrete can also be used. As long as this is from a reputable supplier you can trust that they have properly ratioed the concrete and it has definitely been properly agitated in the cement truck. Cement mixers and trucks will obviously come with their own challenges and costs and these will need to be weighed up against the benefits.
If you are truly serious about your pour lasting a long time, it may be worth hiring a company that has their own team and cement mixers. They will be able to assess the correct cement and aggregates for your specific needs and will have all the experience in the actual pour process doing things such as aerating the pour before it hardens and keeping the surface moist during curing. They will of course have their own cement mixers, concrete vibrators and any other machinery needed, turning multiple costs into one hiring fee.
For climates where temperatures consistently go below freezing and then rise again, research may be needed. Certain cement mixtures and aggregates that have smaller particles that are less likely to expand will be needed. These ingredients may be costly to acquire but will provide long-term benefits and structural stability.
For concrete that is constantly exposed to vehicles or rough winds and abrasions, besides applying a cover there is not much that can be done to completely mitigate erosion. Depending on how often the surface is used the erosion will always continue. Constant maintenance and structural tests can at least mitigate truly large damages.
Concrete is literally the pillars on which we have built our civilization and we have been led to believe that it is nearly indestructible. But unfortunately, nothing is truly invincible against time. Although erosion can never truly be stopped, through the use of specific aggregates, machinery such as cement mixers, the experience of others and proper precautions it can be slowed down to such an extent that it will be negligible and regular maintenance will ensure that it will always stand tall.