The Weight of Concrete
Concrete—one of the most in-demand substances on the planet—is no gentle touch when it comes to weight. Largely made up of sand and stone-based aggregates, it is a pretty heavy material, but how much does it weigh? And in what state are we taking this measurement?
The exact numbers will vary based on many factors, but for normal concrete, the weight is roughly two thousand and four hundred kilograms per cubic meter. That’s quite a lot of weight!
Of course, a general amount is not applicable in all situations, and that is precisely the case here. For example, our above amount of nearly two and a half tonnes applies to normal concrete, but there is also lightweight concrete, which has a density of around seventeen hundred and fifty kilograms per cubic meter.
Another factor to consider is whether you are just interested in the concrete, or do you need the weight of the final structure? In many cases, concrete is reinforced with steel frameworks that add tensile strength to the mix. Granted, the steel framework accounts for quite a small portion of the overall structure, but the density of steel is over three times that of normal concrete, so it will still have a noticeable effect on the final weight.
Another thing to consider when talking about the weight of concrete is whether you are talking about actual concrete or cement. You may know that concrete and cement are two different things, but many people use these two words interchangeably, which can sometimes cause confusion. Cement is an ingredient in concrete, rather than the final product, and as such, the weight of cement for a given area will be considerably lower than the weight of concrete for that same area. This is because cement is usually the ingredient with the lowest volume in the mix, with the bulk of concrete being made up of sand and aggregate.
Speaking of aggregate, there are plenty of different types of aggregate, and they don’t always come in the same size or density. That means that two different batches of concrete—even if they both use the same mix ratio—could have completely different weights. The aggregate in concrete is the component that makes up the bulk of the strength of the final mix. Cement is strong, of course, but its main purpose is to bind the aggregate together. If the aggregate in one mix is considerably larger than the aggregate in another mix, it will not only mean a weight change on the aggregate, but it will alter the volume of cement in a given area.
Finally, you have water to factor in. Water plays a crucial role in the mixing and curing of concrete, and water is also quite heavy. It may not equal the near-two and a half tonnes that concrete weighs overall per cubic meter, but one cubic meter of water weighs in at around one tonne, so it’s not an ingredient to be discounted in discussions around the weight of concrete.
Which is Heavier – Wet or Dry Concrete?
The first thing to establish when talking about wet and dry concrete is what the asker means by “wet concrete.” There are two possible versions of wet concrete, with the answer to this question being very obvious for one of those versions, and perhaps a little more surprising for the other.
If you are comparing unmixed concrete to concrete that has had water added to it and is ready to pour, then, of course, the wet concrete mix is going to be heavier. The dry concrete mix is missing a component that the wet concrete mix has—water. And water is not a particularly lightweight substance, to begin with. That being said, this not the question that most people are asking when they want to know whether wet or dry concrete is heavier.
There is a common misconception about concrete that it “dries out” as it hardens, and that the drying of the concrete is what makes it cure in the first place. It is the hardened final product of concrete that most people think of as “dry concrete.” This is not the case, however. Concrete hardens through a chemical reaction with the water, forming something called hydrates. The water does not evaporate but becomes part of the concrete’s chemical makeup. This means that, while cured, hard concrete may not be as heavy as wet concrete mix, it is still heavier than unmixed dry concrete, which is essentially just a pile of unrelated powder and aggregates.
In some cases, the concrete may be hydrated further after it has been poured, which could theoretically result in cases where the final cured concrete is heavier than even the wet, pre-poured mix. That being said, the additional hydration typically comes in the form of water or a special hydration liquid being sprayed onto the curing concrete, meaning it is more exposed to the elements than the water contained within the concrete, and thus more prone to evaporating.
Do I Mix Concrete by Weight or Volume?
The ratio of the different ingredients in concrete mix is crucial to getting the desired outcome. Much like how getting the ingredients wrong when baking a cake can result in a cake that doesn’t rise, getting the mix wrong for concrete can result in a final product that is too weak for its intended purpose, or too porous or “crumbly.”
It is not hard to find advice on what ratios you need for different purposes when you mix concrete, but what is not always so obvious is the way you are supposed to determine those amounts. The weight would seem to be the obvious choice, but concrete is a pourable construction medium that has to occupy a specific volume in order to do its job. What is more, the aggregates used in concrete are not compressible—after all, that is kind of the point of concrete aggregates—so measuring by volume would appear to be a good way of determining how much you will need since it can correspond directly to the area you are concreting.
The truth is you can measure your mix out by either weight or volume; it really doesn’t matter as long as the mix is right. The important thing is the ratio, so you will need to know the relevant values of your materials. For example, a standard bag of cement weighs in at around fifty kilograms and is typically good for one-fifth of a cubic meter of concrete. That means you will need five bags—or two hundred and fifty kilograms worth-worth—of cement per cubic meter of concrete. If your mixing ratio of cement to sand is one part cement to four parts sand and you are measuring your mix by volume, you will need to know how much volume a bag of sand represents.
As long as you keep the ratios correct, the worst thing that can happen is you make too much—or not enough—concrete, but the concrete itself should be strong enough.
Does Water Add Weight to Concrete?
Once again, the answer to this question depends on what exactly is meant by adding weight. The finished product that is concrete—cured and hard and ready to use—can not exist without water. It is the chemical reactions between the cement and water that make concrete what it is. In that sense, water doesn’t add any weight to concrete because the concrete doesn’t exist without water.
We should clarify that we are referring to Portland Cement-based concrete here, by far the most commonly used cement. There are other non-hydraulic forms of cement; however, they are not nearly as commonplace as Portland Cement.
If, on the other hand, you are using “concrete” and “cement” interchangeably, or you are comparing dry, unmixed concrete to wet, mixed concrete, then yes, water does add weight.
The important thing to note, as we mentioned above, is that water is not merely a tool to make concrete pourable that then evaporate, leaving a hardened mix of cement, stone, and sand behind. Water is the catalyst that starts the process of cement curing, and most of the water that is mixed in with the cement is then locked up in the structure of the final, cured product.
The process of hydrating concrete can leave some standing water on the surface of the structure, and that water may evaporate away, not adding any weight to the structure, but much of the water will be absorbed by the cement and form more hydrates, further strengthening the material.
How do I Calculate Concrete Mix?
The main factors to consider when calculating your concrete mix are how thick you want the concrete and the size of the area you are covering. The thought process goes something like this;
- Decide how thick you need your concrete to be
- Measure the area (length multiplied by width) that you are going to cover
- Multiply your thickness by the area you are concreting
If this looks familiar, it is because it is the same maths your school teachers had you using to calculate the volume of three-dimensional objects. If the area you are concreting is less conventionally shaped, try to break it down into smaller sections that can be more easily measured, then add the area of all of the sections together.
Once you know roughly how large a volume you are concreting, you can start working out how much of everything you need. Cement is the most important ingredient, so it is usually best to start with that.
Your mix ratio will be determined by what you are building, but essentially it refers to the amount of one ingredient in relation to the others. So one part cement and two parts sand mean that there should be twice as much sand as there is cement. If, as we mentioned above, you need two hundred and fifty kilograms of cement for one cubic meter of mixed and poured concrete, then you would need five hundred kilograms of sand in that same mix.
What’s Heavier, Sand or Concrete?
The first thing to note is that, for this question to be worth answering, “concrete” has to be being used in its interchangeable form with “cement.” The reason for this is that concrete—the mixed construction material that includes cement—is very rarely mixed without sand. Sand is an essential ingredient in making concrete economically viable because cement is relatively expensive to make, especially when compared to the cost of harvesting sand from natural resources, and the addition of sand into the mix allows you to get far more concrete out of a relatively small amount of cement.
So, the question then becomes; is sand heavier than cement? This is an important piece of information if you are measuring out your concrete mix by weight rather than volume. As it turns out, cement is quite a bit lighter than sand. A cubic meter of pure cement would weigh in at around three hundred and fifty kilograms. Conversely, a cubic meter of sand would weigh in at close to sixteen hundred kilograms, or nearly five times heavier than cement.
This difference may go some way to illustrating why sand is so useful in concrete. Essentially acting as a tiny aggregate, sand offers the mix a great deal of strength, as well as filling out the final mix so that it doesn’t require an obscenely large amount of cement.
How Many Bags of Cement do I Need for 1 Cubic Meter?
How many bags of cement you need for one cubic meter of concrete is a question that has a lot of variables, such as what size bags of cement you are buying, and how much of that cement is going into your mix. We mentioned above that a typical bag of cement weighs in at roughly fifty kilograms, but there are other standard sizes of cement bags. For consumer-centric DIY outlets, you are as likely to find a twenty-five-kilogram bag of cement as you are a fifty-kilogram one. And, if you are in the trade and getting large quantities of cement, you could be buying much larger bags of around eight hundred kilograms!
Obviously, things like these will make a huge difference in how many bags you need for a given volume of concrete. As a general rule, you should be looking at around two hundred and fifty kilograms of cement per cubic meter of concrete, which translates to around five bags of cement if your bags are fifty kilograms, and ten bags if they are twenty-five kilograms.
It is also worth remembering that, though cubic meters are a relatively common way of measuring volume for things like this, the areas that you are pouring your concrete into may not always be cube-shaped, meaning you may have to get inventive to accurately measure how much you need. As a general rule, you should allow for some wastage during the mixing process—usually around three percent for cement—and if you can’t estimate the required volume of concrete accurately, be sure to over-estimate so that you have enough to finish the job, since pouring fresh concrete onto curing concrete will result in weaker structural integrity between the two separate batches.
What Does 1 Cubic Meter of Concrete Weigh?
As we mentioned at the very top, a cubic meter of normal cement weighs in at just under two and a half tons—two thousand and four hundred to be more precise. That being said, being precise about the weight of concrete without knowing the exact ingredients going into said concrete is something of a futile task. This number assumes a typical concrete ratio with the most commonly used sand and aggregates. If you were to change that ratio or use a different aggregate, you would be looking at different weights. And, as we also mentioned above, you may also want to factor in the weight of any reinforcements, such as steel bars.
What is the Best Way to Calculate How Much Cement I Will Need for a Project?
As tricky as it can often be, the best way to measure how much cement you will need for a project is to figure out how much volume you are going to be filling with concrete. A certain amount of wastage is to be expected in any concreting job, so don’t expect to be able to get the volume measured absolutely perfectly—it simply won’t happen.
Once you know the volume you are concreting, you can move on to the amount of cement you will be using per unit of measurement. We have been using cubic meters because the numbers line up much easier in the metric system, but you may want to do your maths in imperial. Regardless, once you know how much cement you need per unit of measurement, and you know how many of those units of measurement you are filling with concrete, all you need to do is multiply the two to get your magic number.
It is recommended that you add at least three percent to your total amount of cement for wastage—more if the area you are filling is particularly difficult to measure accurately.