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Making your own concrete is no easy task. Moreover, the problems begin at the start, when you start to deal with the amount of materials that will need to be purchased. First you have to guess how much concrete / mortar will be required. Then it turns out that the proportions are given in mass fraction. And even having calculated how much of the same concrete is required, it will not become easier, because they sell cement not by volume, but in bags of 25 kg and 50 kg. And in order to understand how much you need, you need to find out how much a cube of cement weighs. But it’s also not easy. There is specific gravity, volumetric weight, and there is true density.
Why know the weight of a cube of cement
In stores, cement is sold in bags of 25 kg or 50 kg, and the proportions of concrete, plaster, and mortar are given in volume fractions. That is, it is necessary to measure the components not by weight, but by volume, and this is the difficulty. That is, you need to know how many kg of cement are in 1 m³, or buckets in a bag, how many kilograms of the same cement are in a bucket, etc.
It is easier with buckets, since it is possible to determine how many buckets of cement in one bag experimentally. We bought one bag of binder, poured it into buckets, counted the amount. When pouring, we do not coward the bucket, we do not compact the binder in any way. In general, everything is simple. With a cubic meter, this will not work.
How many kilograms of cement in a cubic meter
In general, answering this question is not as easy as it seems. Firstly, cement can be of different grades. Depending on the brand, it changes its density, and hence the weight. Portland cement weighs more than low-grade cement and the difference is significant.
The second point, Portland cement is obtained by grinding special clinker. As a result of grinding, a dusty substance is obtained, which is called Portland cement. The true density of cement is 3100 kg/m³. But each particle holds a certain amount of air and therefore the volumetric mass of cement is less. But this is also a variable value. Immediately after production, the cement retains the maximum amount of air, so it weighs less. The mass of a cube of cement grades M400 and M500 immediately after production is about 1100 kg / m³.
During storage and transportation, it is compacted, moistened. So in one cubic meter of cement there can already be 1600 kg. For calculations, take the average value – 1300 kg / m³. So if you need to know how much a cube of cement weighs, we take the average values. For M400 and M500, 1,3 tons per cubic meter are taken into account. If you need to convert cubic meters of Portland cement to tons or kilograms, use these numbers.
How many kilograms of cement in a bucket
When mixing concrete in a concrete mixer, the components are often thrown in buckets. You can find out exactly how much a bucket of cement weighs if you have ordinary scales. First, weigh the container, pour the binder. But it should not be compacted in any way. Just pour the substance from the bag or use a shovel to pour from the pile. Put on the scales and subtract the tare weight from the resulting figure. According to statistics, there are 12 kilograms in a standard 15,6-liter bucket.
If there is less cement in your bucket or your container is not 12 liters, or the cement is fresh, which is very good, or you were sold a low-grade binder, one of the distinguishing features is a smaller mass. You can also focus on color. Portland cement has a grayish green color, Portland slag cement is gray with a bluish tinge. These are the brands that can be called good. The rest are gray, yellowish-gray or gray-brown. If your material does not have a bluish or greenish tint at low weight, you have been sold a lower strength binder.
A few words about strength
In recent years, cement has been used grades M400 and not lower, despite the fact that it is more expensive. The usual argument is that manufacturers claim strength is greater than it actually is. Maybe so, but keep in mind that the manufacturer guarantees the declared strength for 2-3 months from the date of production. So when buying, pay attention to the “freshness” of the binder. During storage, the strength of cement decreases, and noticeably:
- after 3 months it becomes lower by 20%;
- after 6 months of storage is reduced by 30%;
- after a year, the drop in strength is 50%.
So buying cement for future use is a so-so decision. If you have stale, when kneading, the amount should be increased by 2-4 times, depending on the shelf life. It is also desirable to add hardening accelerators to the composition. Since, in addition to loss of strength, long-term storage greatly increases the hardening time. That is, concrete is very slowly gaining strength.
So you should not buy cement packaged in building materials warehouses, because it is not clear when it was produced. If Portland cement is packed at the factory, the date is immediately put down. It’s easy to navigate here. It is not known how long the cement has been in the warehouse. The packing date, if they set it, does not give us anything. So, we are looking for factory packaging with a production date.
The second point that forces the use of high-quality cements is that they gain strength faster than low-quality ones. For example, concrete from Portland cement M500 will gain 50% strength in 3-4 days (at a temperature not lower than + 20 ° C and sufficient humidity). When using the M400 brand under the same conditions, 50% of the strength must be expected for 7-8 days. If you are pressed for time, this may be more important than a higher price.