How to make concrete with your own hands

What is important to know

Concrete is the most common building material. It is an artificial stone, which is obtained as a result of hardening of a mixture of binder (cement) and aggregate (sand, crushed stone). Oddly enough, this thing is quite simple and complex at the same time. That is why, before getting started, it is worth understanding some basics.

About the “structure” of concrete

Concrete consists of cement, water, sand and crushed stone mixed in certain proportions. We'll look at which ones below. Sometimes the composition also includes plasticizers - chemical additives, which improve the plasticity, strength, frost resistance and other characteristics of the mixture.

Crushed stone, which occupies almost the entire volume of concrete, acts as a supporting frame. The crushed stones are quite large and do not fit tightly together, so fine aggregate - sand - is added to the mixture. Finally, even smaller particles of cement, when mixed, fill the microscopic voids left between the grains of sand and hold the entire structure together.

About choosing components

Cement

It is allowed to use the M400 and M500 brands, but it is better not to save money and take the M500, since with it it is easier for a beginner to get a high-quality result.

The cement must be absolutely dry and fresh. This can be determined by the date on the packaging, as well as by touch - the bags are soft and do not hold their shape. You should buy it immediately before starting work or at most a few weeks in advance.

Store the material in a dry, ventilated area on pallets so that it does not absorb moisture from the ground. Wrap it in film to protect it from condensate.

Sand

For high-quality concrete you need clean sand without any admixture of clay, silt, or plants. Both river and quarry sand with a fraction of 1.5–5 mm are suitable. The main condition is cleanliness. If there is debris, soil or grass in the sand, it should be sifted first.

Crushed stone

Coarse aggregate must also be clean, free of foreign inclusions, dust, and screenings. The best option is granite crushed stone, since it has “torn” edges with which the mixture adheres better. The crushed stone fraction can be 5–20 mm or 10–20 mm. It is better when the stones are not the same, but of different sizes. This is necessary to more effectively fill voids.

Water

There are no special requirements for it. It should be fresh and clean. Regular tap water quite suitable.

Plasticizers

Additives are useful if you need to simplify installation and get the most durable concrete possible. Plasticizers will allow you to consume 10–30% less water without losing the mobility of the mixture and the quality of concrete after hardening. They can also be useful when working in cold weather to speed up setting and prevent freezing.

About brands and classes of concrete

The main characteristic of concrete is its compressive strength before failure, which is measured in megapascals (MPa). It is this value that is tied to brands and classes.

The grade (M150, M250, M300, and so on) reflects the average strength of concrete in the batch, while the class includes the guaranteed strength of any concrete in the batch.

Brand is an older concept and is used less frequently. There are coefficients and formulas for converting one quantity to another. Without going into details, we present addiction between them and the scope of application in the table:

About the water-cement ratio

The water-cement ratio, or W/C, directly affects the quality of concrete. The less water, the greater the concentration of cement in the mixture and the higher the strength of concrete. But at the same time, its mobility is also less, that is, the ability to spread under its own weight and fill the formwork.

To mix the cement and successfully complete the chemical reaction, 18–20% of water from the amount of cement is sufficient. In practice, more is required - 40%–50% and even 70%–80%, since mixing the dry mixture well is quite problematic.

The thesis that there is no such thing as too much water and it will simply come out over time is fundamentally wrong. Yes, the liquid will evaporate, but pores will form in its place, which will make the concrete more brittle.

It is the W/C that affects the class of concrete. By adding water beyond measure, you increase the workability of the mixture, but inevitably reduce the quality of the concrete. To get as close as possible to the design class and grade of concrete, you should use M500 cement and observe the following ratio:

About the proportions of components

The classic “recipe” for self-mixed concrete is cement, sand and crushed stone in proportions 1: 3: 5 plus water “to taste.” However, it is better to follow the recommendations of cement manufacturers and add water to a minimum.

The proportions, according to the instructions on the bags, are usually closer to 1:2:3. That is, you need to take 1 part cement, 2 parts sand, 3 parts crushed stone and mix, adding enough water to maintain the W/C indicator required for the selected brand.

It is convenient to measure with a 10-liter bucket with measuring marks inside. Also keep in mind that if the sand and gravel are wet, less water will be needed.

About hardening time

Concrete gains full strength in 28 days, provided it is 100% humidity and ambient temperature 20°C. The warmer it is outside, the faster the process goes and, accordingly, the colder it is, the longer the concrete hardens.

12–20 hours after pouring, you can carefully walk on the surface. After 7–10 days, the concrete gains 70% strength and you can safely dismantle the formwork. If the structure is not very important, such as a blind area, the formwork can be removed after 3–5 days.

About concrete care

After pouring, the evaporation of moisture, which is necessary for hydration of the cement, should be prevented. Otherwise, it will come out before the process is completed and the cement in the thickness of the concrete will remain dry without reacting. Which, in turn, will reduce the strength of concrete.

The easiest way is to cover the flooded surfaces with film or pour water, but only when the top layer has already set, so as not to wash it away.

About the concrete mixer and work organization

It is possible to make concrete without a mixer, but it will be more difficult and difficult. It is justified to resort to manual mixing only when very little concrete is needed. In other cases, it is better to buy or rent the simplest mixer.

Keep in mind that the batch volume is only 25-30% of the total tank volume as stated by the manufacturer. This is due to the fact that for good mixing the bowl has to be tilted almost horizontally, and it won’t even be possible to load it halfway - the contents will simply spill out.

Also keep in mind that the volume (and weight!) of materials is 50–60% greater than ready-made concrete. Therefore, it makes sense to place the mixer closer to the piles of sand and crushed stone in order to carry or transport ready-made concrete to the work site. And not vice versa.

How to make concrete in a concrete mixer

What you will need

• Cement;
• sand;
• crushed stone;
• water;
• plasticizer (optional);
• concrete mixer;
• buckets;
• container for ready-mixed concrete;
• shovel.

How to do

1. Prepare cement, sand, crushed stone, water. If the materials are not near the mixer, no problem. In this case, it is more convenient to pick up and pour them one by one, so that while you go for the next portion, the concrete is mixed.
2. Start the concrete mixer and add half the required amount of water or a little more, but not all. If you use a plasticizer, immediately add it to the water according to the dosage in the instructions.
3. Fill in about half of the total crushed stone for mixing. Wait a couple of minutes for the ingredients to wet, and in the meantime go get some sand.
4. Gradually add about half of the sand to the bowl and wait a little until the mixture is well mixed.
5. By changing the angle of inclination, install the tank as close to a horizontal position as possible, but so that the contents do not splash out when the mixer is operating. Maintain the desired inclination, adjusting the angle as you go so that the ingredients are mixed as well as possible.
6. Gradually, and not in one fell swoop, pour all the cement into the tank and wait a little until everything is mixed.
7. Sprinkle out the other half sand, and then the remaining rubble.
8. Finally, pour out the remaining water and let the concrete mix thoroughly. You can also add water little by little during the process, visually monitoring the batch. The main thing is not to pour in excess of the volume determined by the proportions. If the concrete is thick and you cannot do without additional water, add the same amount of cement to maintain the water-cement ratio and the quality of the concrete.
9. Turn off the mixer and pour the concrete into a container prepared for it, moistened with water. Clean off any residue stuck to the walls.
10. Start the concrete mixer and slowly pour water into the bowl to wash the inside of its walls. Make a note of how much water you poured so you can take it into account the next time you mix.

How to make concrete with your own hands in a trough

What you will need

• Trough, basin or other container;
• cement;
• sand;
• crushed stone;
• water;
• buckets;
• shovel.

How to do

1. Take a trough, basin, bath or other container. If nothing suitable is available, use a sheet of tin, a concrete pad, or any solid base that does not absorb water and allows you to easily pick up materials with a shovel.
2. Fill a bucket of sand and spread it evenly. It is advisable to take sand dry, otherwise lumps will form.
3. Sprinkle cement on top. Let's say ¼ of the required amount.
4. Next, pour out the sand bucket again and level it, and add another portion of cement on top.
5. So, alternating layers, add all the sand and cement, and then thoroughly mix the components dry with a shovel, without adding water.
6. Level the cement-sand mixture, evenly scatter all the crushed stone on top in accordance with the selected proportions. Then mix everything thoroughly with a shovel again.
7. Make a furrow in the middle (or a hole if you are mixing not in a container, but on the base) and pour half or a little more of the required amount of water into it.
8. Rest for a few minutes and wait for the materials to soak. Then gradually move the mixture into the water and mix everything until smooth, adding the rest of the water.
9. Mix the solution thoroughly so that there are no dry fragments or lumps left, and the entire mixture is as homogeneous as possible.