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Buying extra cement is not worth it. With prolonged storage, even in a dry room, it loses its strength. In a year it will be 50% of the nominal value. That is why when purchasing it is worth knowing how much binder is required. But there may be problems here. Proportions for concrete mortar are often given in volume fractions, and cement is sold by weight with packaging in bags. The calculation may require the volume of cement in the bag. You can use the average value and calculate approximately.
Cement bag volume
In general, the question of how much cement is contained in the bag is not so easy to answer. Let’s start with the fact that the packaging comes in bags of 25 kg, 40 kg and 50 kg. So you need to specify the mass. The second point is that cement is different. With and without additives. And additives are also different and different types differ in density. This means that the same weight occupies a different volume.
There is one more moment. The density of any cement changes over time. Immediately after production, when it was poured into bags, the density is the lowest. While the ground powder is poured, its particles are charged and capture air molecules. Therefore, freshly poured, it weighs less. During transportation and storage, the charge decreases, part of the air escapes, and the density increases. So a month later, more weight is placed in the same volume. Moreover, after about a year of storage, the difference with bulk density is significant – up to 35% of the original value.
In the calculations, they take the average figure, which is called the specific gravity. For each type of cement, it has its own and in the calculations when determining the amount of material required, you can build on it.
Design procedure
The specific gravity of cement is the mass of one cubic meter. For Portland cement, for example, it is 1300 kg / m³. To determine the volume of cement in a bag of 50 kg, you need to solve a simple proportion:
We found what percentage of one cubic meter is contained in one bag of Portland cement per 50 kg. This is 3,85%. This means that this container contains 0,0385 m³ (we simply “take a percentage” of a cubic meter).
summary table
For a bag of 25 kilograms, you can not count, but divide the resulting figure by two. One bag of Portland cement 25 kg contains 0,019 m³. For a bag of 40 kg, you will have to calculate everything in a new way. It will turn out 0,031 m³. Similar calculations must be done for all grades of cement with different densities. We did this and brought the data into a table.
Average values are calculated in the table. If you know exactly the weight of a cube of your material (may be listed on the bag, or you can weigh and calculate), it’s best to recalculate. The difference is unlikely to be large, but still. And how to count? Take a liter container, put it on the scales and weigh it. Pour cement – do not shake, do not compact. Simply pour and weigh and then tare. You will find how much a kilogram of cement you bought weighs. Then you multiply by 1000 (one thousand liters in one cube) and you get the exact (almost) density of your material. You can use it later in your calculations.
How much concrete will come out of a bag of cement
Often the proportions are indicated in volume fractions and therefore, when calculating, it is useful to know how much concrete can be made from one bag of cement. But it is necessary to talk about a specific brand and about a specific concrete solution. The proportions are different and you first need to decide on this. The difference is significant – this can be seen from the following table.
For each binder and each brand, again, you will have to count separately. For each concrete, the approximate consumption of cement for the manufacture of one cube of mortar is known. Based on these data, you can calculate how much mortar can be obtained from a kilogram of cement. Further, it is easy to find out the amount of concrete that can be obtained from a bag of cement.
For example, 300 kilograms of M350 cement go to a cube of M400 grade concrete. That is, from one kilogram, 1 m³ / 350 kg = 0,0028 m³ is obtained. To find out how much concrete of the M400 brand will turn out from a bag of 50 kg, we multiply by 50. We get 0,14 m³. As you can see, the calculations are simple.
To consolidate the information, we calculate for the M200 solution and the same M400 Portland cement. It is necessary for this type of concrete 250 kg. Then, from a kilogram, 1 cube / 250 kg = 0,004 cubic meters is obtained. Then from 50 kg it will turn out: 0,004 * 50 u0,2d 40 cubic meters, from 0,004 kg – 40 * 0,16 uXNUMXd XNUMX cubic meters.