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Understand the technical reason behind this curious difference that confuses many people on construction sites. Learn how the actual yield of the materials used in the concrete mix works and avoid surprises on the construction site.
Anyone who has ever followed a construction project up close or worked with it knows that, often, the amount of gravel and sand used seems to be much greater than the volume of concrete that is left at the end. This leaves many people wondering: Why do we use so much material and the final volume seems smaller?
This difference has an explanation and is totally linked to the way the materials fit together during mixing. In practice, the concrete undergoes a volume reduction when crushed stone, sand, cement and water are mixed. This phenomenon occurs because the voids between the grains of sand and crushed stone are filled, causing the final volume of concrete to be less than the sum of the dry materials. And don't forget about safety: glasses, gloves and masks are essential when working with cement and sand.
Here you will understand in a simple and direct way:
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- How to calculate the correct proportion of materials;
- Why does volume loss occur in concrete;
- How does this affect the work budget;
- And what to do to avoid mistakes when purchasing materials.
Many people think that by mixing 1 cubic meter of gravel with 1 cubic meter of sand and a little cement and water, you will end up with 2 or even 3 cubic meters of concrete. But that's not how it works.
What happens is that the grains of sand settle between the spaces in the gravel, and the cement, together with the water, penetrates between all of this. Result? What seemed like a lot, decreases a lot after mixing. This volume reduction is natural and occurs because of compaction of materials.
This “shrinkage” can reach 20% or more, depending on the type of gravel, sand and proportion used.
Understand concrete calculation
The basis of everything is in the concrete stroke, which is the formula that defines how much of each material will be used per cubic meter. A common ratio, for example, might be 1:2:3 (cement : sand : gravel). This means:
- 1 part cement
- 2 parts of sand
- 3 parts gravel
But when it comes to mixing everything with water, the gaps between the grains are filled, and this reduces the final volume of the mixture. Therefore, whoever calculates the concrete on site needs to already consider this loss, otherwise there will be a lack of material before the concreting is finished.
How does this affect the cost of the work?
If the construction team is not aware of this, it could end up buying less material than necessary. And the losses come immediately: there is a lack of concrete, service is delayed, freight increases and the finishing of the structure is even hindered.
Therefore, it is important to work with safety margin. Many professionals already consider this loss when ordering materials — especially in large volumes, such as slabs, foundations and industrial floors.
How to avoid mistakes when using gravel and sand?
Here are some simple and valuable tips:
- Use standardized strokes based on technical tests or reliable tables;
- Consult an engineer or building technician to calculate exactly what will be needed;
- Do not use buckets or shovels as a measure, as the volume can vary with the humidity of the materials;
- Consider volume loss in the budget — better to have some left over than to have some missing in the middle of concreting.
Bonus tip: use an online concrete tracer or calculator
Nowadays, there are several online tools that help you calculate how much cement, sand and gravel you need for each cubic meter of concrete. Many of them already take into account the loss of volume, helping you avoid headaches during construction.
Concrete “shrinks” because the materials fit together better when they are mixed together. It’s like putting together a jigsaw puzzle: the pieces alone take up more space than when they are organized. Therefore, the amount of gravel and sand used in the construction exceeds the final volume of concrete.
Understanding this helps not only to save money, but also to better plan the work, avoid delays and ensure the quality of what is being built.
What is this ratio 1:1.5:3 yield 7,7?