What Happens if You Put too Much Cement in Concrete?

Concrete is a versatile and powerful tool in many forms of construction. Its strength comes from a fine balance in the different components that make it up. Understanding these ratios and their value allows you to create the most effective concrete form. But what happens if you put too much cement in concrete?

Putting too much cement in concrete can result in several disadvantages. If too much is added to the mix, the concrete’s workability will suffer, and some of the aggregates won’t properly bond to the cement. The final product’s structural integrity will likely decrease if too much is used versus the aggregate.

We will focus on the risks of using the wrong ratios for making concrete and what each could lead to. Careful attention should always be placed on how much of each of these elements is involved.

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Adding Too Much Cement to The Mix

Since the paste that makes up concrete is an important part of the process, adding too much of a specific element can have some significant downsides. 

It is important to note at this point that, ideally, you want to add as little water as possible to the paste mixture. The greater the ratio of cement to water, the better the resulting paste will be for the concrete.

That being said, there are, obviously, downsides to adding too much cement to the paste mixture. Fortunately, the primary one is easy to spot immediately.

Makes The Paste Too Thick

The primary disadvantage of adding too much cement to the paste mixture is based on the final consistency. More cement means the paste will be less liquid and struggle to flow properly. This means that when you combine it with the aggregate, the bonding between these two components does not properly occur.

The paste will sufficiently encompass all the necessary gaps between the larger, more porous aggregate in a good concrete mixture.

Creates Air Pockets

When the paste is too thick from too much cement, holes can develop in the final mixture. This is called honeycombing and can have some notable side effects (source). 

These air pockets can create spaces for water to seep into the concrete, leading to deterioration over time. This happens during freeze-thaw cycles that cause the moisture trapped inside to expand and contract. This can create cracks on the surface and directly affect the structural integrity of the concrete.

Porous concrete is also susceptible to acidic and corrosive substances from the surrounding soil. This reacts with the cement, which contains a significant amount of water and can cause further degradation (source). 

Adding Too Little Cement to the Mix

While we are looking at the negative effects of too much cement in concrete, it is certainly worth noting that the reverse is also true. This is particularly true when too little cement is added to the paste mixture.

Weakens The Concrete

When cement and water mix, they undergo a process called hydration. This results in the solidifying and hardening of the cement. If the ratio of water to cement is done correctly, this process will leave the concrete strong and durable.

However, if too little cement and too much water are involved, the hydration process leaves behind some excess water. 

This water will then stay inside the concrete and result in cavities within the final product as the water evaporates. These holes weaken the structural integrity of concrete and reduce its compressive strength, which is one of the primary attributes sought when using concrete (source).

Shrinkage

Another downside of too much water in the paste is shrinkage. Cement will always undergo some form of mild shrinkage as the hydration process occurs. However, if there is too much water, this shrinkage can be excessive as the remaining water evaporates. 

Significant shrinkage can lead to cracks forming in the concrete, weakening the tensile strength of the final product.

Dusting

Excess water can also lead to a process known as dusting. This is when the paste allows the finer aggregate particles to float to the surface of the mixture. This will settle there before the drying process is complete and leave a thin layer at the top. Again, this can affect the integrity of the end product.

As you can see, excess water has more disadvantages than excess cement in the paste mixture. This means that it is best to err on the side of cement when combining these two.

While speaking of concrete, you may wonder if it’s possible to make concrete with only two ingredients – sand and cement. Get detailed insights in the guide.

Too Much Paste in Proportion to Aggregate

Another consideration for the relative proportions of concrete components is paste versus aggregate.

As you know, the paste consists of cement, water, and air. However, even if you get this ratio perfect, you must consider the amount of this paste you use for the aggregate you have.

The resulting mix will be easier to use and place when you use too much paste. This is because it is more liquid and will flow into the required spaces. While this is a benefit, there is also a significant drawback.

Less aggregate means less structural integrity, and the concrete is more likely to crack. This is especially true under the extreme pressures concrete is often subjected to. These cracks can lead to further degradation and open spaces in the concrete that can fall victim to the freeze-thaw problems mentioned above.

Another, perhaps less serious factor to consider with this ratio is the costs involved. Cement is the most expensive component of the concrete mix, and using more than you have to will incur unnecessary costs. While this can be minimal, the more concrete you require for your project, the more this stacks up.

Creating and working with concrete is a balancing act and requires dedication and understanding. Utilize these warning signs to note potentially incorrect proportions in your concrete mix and adjust accordingly.

Image by Vic Shen via Unsplash

The Relationship Between Concrete and Cement

Though you are likely familiar with cement and concrete, a quick refresher can help before we dive further into it.

What Is Concrete

In basic terms, concrete is the final product, while cement is just a component of the mixture that makes concrete.

Concrete is typically made up of four specific parts. The largest portion, around 60%–75%, is the aggregates (source). These aggregates will vary in size based on the task the concrete is being used for.

The aggregate usually consists of rocks, sand, or gravel. The finer the aggregate used, the more malleable the wet concrete will be and the smoother the final product.

Gravel is a common aggregate ingredient, but is it possible to make concrete without gravel? Learn more about it in the guide.

The Concrete Paste

The next part of concrete construction involves what is known as the paste. This comprises three primary elements: water, cement, and air. The ratio of this mixture defines much of the strength and durability of concrete when it sets.

According to the Portland Cement Association, the typical ratios for the different components of concrete are 60–75% aggregate, 7–15% cement, 14–21% water, and up to 8% air.

Once your concrete project is complete, you may be left with some old bags. Get tips on creative ways to reuse old concrete bags.

Making Concrete

To make concrete, you must combine each of the above parts. The first step is to mix the cement and water to form the paste. At this point, air can be added to the cement and water mixture.

You can let the air enter in several ways, even just through mixing, to increase the workability of the concrete.

Air voids added to the mixture will also increase resistance to freeze-thaw cycles that may occur. However, the entrained air will also reduce the strength of the concrete, so this must be done with care and caution (source). 

The hydration process will begin once the cement and water have been combined. Hydration happens when cement is introduced to water. Each cement particle will form a node that allows it to bond to the adjacent particles. This includes other cement particles but, most importantly, the various aggregate pieces.

This is why you must mix it quickly with the aggregate before this bonding occurs and the cement hardens. Wait too long, and you could be stuck with hardened bags of concrete, though options are still available to you should this happen. Check out what to do with hardened bags of concrete.

Mixing is an important part of the process because it allows the cement to get into the spaces between all the aggregates and bonds everything together.

Once all these parts are combined, the result is concrete. However, understanding this concrete’s efficacy requires looking at the disadvantages of excess used in the ratios between the cement, water, and aggregate.

Remember, concrete can deteriorate over time, even if it’s just stored. Learn more about the shelf life of concrete here.

Final Thoughts

While there are not many components involved in the construction of concrete, each of them requires deliberation and understanding to get right. This is particularly the case with how much cement is used in the process, as this is the most reactive and important part of the entire operation.

Too much cement in the paste can lead to improper aggregate bonding, and too little risks even worse due to the excess water. Too much paste can lead to a decrease in the integrity of the concrete and a hike in the project’s price due to the relative costs of cement.

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