What is Concrete Mixing Formula?
In this guide we will see how to calculate the volume of concrete needed to cover the affected surface, and the proportions for a perfect mix.
First of all, you need to know that there are various concrete mixes based on the hardness we want to obtain.
If we want to prepare a mixture that will not have to support anything but only to level a floor or the last line of a low wall (also called wall coping), then a lean concrete will suffice. While, to cast a beam, a floor or a pillar we must necessarily rely on reinforced concrete.
How To Calculate The Volume Of Concrete?
When we have to prepare concrete for medium and large surfaces, we need to calculate the volume, in order to cover the entire affected area with a single casting. It is important to throw the whole area without creating restarts (seams) due to an error in the calculation of the mixture. The seams will always remain only a weak point of the structure, therefore to be avoided absolutely. To calculate the volume perfectly we need three measurements: side a, side b and height.
Let’s imagine that we have to prepare the dough for a floor 2 meters long (200cm), 2.5 meters wide (250cm) and 0.2 meters high (20cm), so it will be enough to multiply the length by the width, finally, the result by the ‘height, in this case we will do:
2 x 2.5 = 5 x 0.2 = 1mt³ (volume of mix ) From the calculation we can accurately establish that we will need 1 cubic meter of concrete to cast the entire floor.
Concrete is a compound of sand, gravel (coarse-stony aggregate), cement (binder) and water. The different proportions of the mixture can characterize its hardness. But what are the doses indicated for preparing reinforced concrete?
The Doses For A Perfect Blend
Now that we know the volume of the dough and the components, we just have to divide it into portions. In our case we are preparing a reinforced cement mixture, which will be subjected to continuous vibrations, pressures and stresses, and must therefore resist these effects for at least 100 years.
Let’s see how to obtain a perfect mix for 1mt³ of reinforced concrete:
0.33 m³ of sand (1/3 of a cubic meter)
0.66 m³ of gravel or other large stony aggregate (2/3 of a cubic meter)
12 25kg bags of R425 cement (300kg)
100 Liters of water (1 quintal)
Even if we have apparently exceeded the imposed volume, the components mixed together with the water will form exactly one cubic meter, as the water molecules taking the place of the air molecules will decrease their volume. If we wanted to create a lean concrete for floors, wall coverings, leveling sections, etc.
The recommended doses are these:
0.40 m³ sand (2/5 of a cubic meter)
0.60 m³ fine gravel or other fine stony aggregate (3/5 of a cubic meter)
10 bags of R325 cement (250 kg)
150/180 liters of water (in this case the proportions of the water are indicative and may vary according to needs).
Even if we know the doses for a perfect blend, we must also know the right way for a perfect preparation. How to do?
First, it is important to mix sand and gravel together, then add the cement by distributing the bags all over the compound. Now you need to dry mix the mixture so that the cement integrates perfectly. When we are sure that the three components have been perfectly combined, we can slowly add the water and at the same time turn and turn the mixture until a workable mixture is obtained, neither too liquid nor too hard.
Water has a negative impact if it has a greater or lesser proportion than indicated. A too liquid mixture will make the concrete weak inside, vice versa, a hard mixture will not adhere perfectly to the iron and / or steel cage, moreover it will not be easily leveled. To make the concrete 100% reinforced it must be incorporated with iron or steel bars (nets and cages), we will talk about this in a new article.
Mixing and laying must be carried out as quickly as possible, for this reason it is recommended to use concrete mixers for medium-sized castings , and tools for laying such as aluminum straightedge , spirit level , etc. .. Faster preparation will be and laying the concrete, the better the stability and hardness over time.
For better concrete adhesion (especially when casting pillars and beams) it is recommended to use a concrete vibrator . What are concrete vibrators? By means of the vibrating probe or needle it is possible to reach all the cavities, ensuring (thanks to the strong vibration) a perfect laying of the concrete.