Home generalMix concrete yourself - correct mixing ratios

Mix concrete yourself - correct mixing ratios

  • Make normal concrete
  • Different mixing ratios
    • Use the rule of thumb as the mixing ratio
  • Check consistency of concrete
    • The setting attempt
    • The propagation attempt
    • The compaction attempt
  • The production of smaller quantities
    • Step-by-Step Guide
  • The production of larger quantities

Concrete mixing yourself - this requires knowledge of the correct mixing ratio. This determines the later properties of the material and thus the strength, the durability and the resistance. Whether as a foundation for a garden shed, as a basis for the wall or the production of paths, only with the right guidance succeeds the construction project. You can stir small quantities by hand, for larger quantities, the use of a concrete mixer is recommended.

If you use a manual for the concrete mix, then you must pay attention to which areas of application the concrete should be used for. The consistency and mixing ratio affect not only the ease of processing but also the applications. Depending on the quantity required, you can also calculate the amount of ingredients using the three-rate set up or down. In this case, the instructions are only a guideline and form the basis for the finished mixture. Only when the right consistency is achieved, the concrete mixture can be used. You must decide on a specific density of your concrete (lightweight concrete, normal concrete or heavy concrete).

Make normal concrete

As a rule, normal concrete with a strength class C20 is selected for private construction projects. This corresponds to a mixing ratio of 4: 1, ie one part of cement and four parts of gravel. Here, the grain size should be a maximum of 32 millimeters. As the third ingredient, water is added. The amount of water here should be half the amount of cement, but can be varied here in practice to achieve the correct consistency. Depending on the required quantity this means:

  • 25 kg of cement
  • 100 kg of gravel
  • 12.5 liters of water
Mix concrete

Different mixing ratios

A universal mixture for fresh concrete is:

  • 1 kg of cement
  • 4 kg of gravel
  • 0.5 liters of water

The universal mixture is especially suitable for home improvement work such as steps and garden plates.

The foundation concrete mix :

  • 1 kg of cement
  • 5 kg of gravel
  • 0.5 liters of water

The foundation concrete mix is ​​used for concrete elements in the ground. These include, for example, the anchorages of fence posts.

A particularly robust mixture :

  • 1 kg of cement
  • 3 kg of gravel
  • 0.5 liters of water

If the components are particularly affected by environmental influences and the concrete mix must be resistant and resilient, then this mixture is the right choice. One possible area of ​​application is pavement.

Tip: The more fluid the fresh concrete, the easier the subsequent concreting. A higher water also means a longer drying time.

Use the rule of thumb as the mixing ratio

Do-it-yourselfers often resort to certain rules of thumb for mixing concrete. One possible variant and widespread variant is:

  • 300 kg of cement
  • 180 liters of water
  • 1900 kg surcharges

= 1 cubic meter of concrete with the strength class C25 / 30

However, you have to keep in mind that the concrete properties are strongly dependent on the selected cement and aggregate. Therefore, rigid formulas are only limited use and can only represent the basis for the mixing ratio. In individual cases adjustments must be made.

Calculate concrete weight

Check consistency of concrete

The consistency is an indication of whether you have chosen the correct mixing ratio. It depends on the chosen application and must be determined before the start of construction. Thus, in some cases, a tough consistency may be beneficial, in other cases, a liquid fresh concrete is needed. The nature of the concrete determines the processability, which is crucial for the further construction measures. To create a consistent definition, the different consistency ranges are standardized, ranging from very stiff to very fluid. To check the consistency, there are several methods that can be used with simple means. These include, among others:

  • setting test
  • slump
  • compaction test

The setting attempt

Material and tools:

  • frusto-conical shape of standardized size
  • trowel
  • tape measure

The procedure:

  1. Place the frusto-conical shape on a backing plate on the floor.
  1. Apply the fresh concrete to the mold in three equal thicknesses. Compact each layer with 25 bumps.
  1. Pull a supernatant flush.
  1. Now pull the mold off without lateral displacement or turning upwards. The movement should be completed in about 5 to 10 seconds.
  1. The concrete stump collapses. Immediately after removing the mold, measure the height of the stump at the highest point. The difference between the original and the new height is the slump. This now provides conclusions about the consistency:
  • 10 mm - 40 mm: plastic
  • 50 mm - 90 mm: soft
  • 100 mm - 150 mm: (very) soft
  • 160 mm - 210 mm very soft
  • greater 220: flowable

The propagation attempt

The spreading test is suitable for grain sizes of the aggregate of up to 63 millimeters. Self-compacting concretes can not be controlled by this method.

Tool:

  • table
  • trowel
  • Truncated cone shape
  • tape measure

The procedure:

  1. Moisten a tabletop with water and remove the resulting film of water with a trowel. The goal is a damp surface. It serves to ensure that the consistency is not changed by the table.
  1. Center the truncated cone and fill it with fresh concrete. The excess concrete is smoothed off at the opening.
  2. Pull up the mold now. The fresh concrete will spread on this.
  1. Lift one side of the table jerk-free 15 times, about 4 centimeters, and drop each one. Between sessions, a period of 1 to 3 seconds should elapse. The fresh concrete continues to spread through the vibrations.
  1. Now measure the diameter of the mass. To get the most accurate value, cross over twice and calculate the mean in millimeters. Round the value down to 10 millimeters.
  1. The following table now indicates the consistency of the mass:
  • stiff (F1): 340 mm
  • plastic (F2): 350 mm to 410 mm
  • soft (F3): 420 mm to 480 mm
  • very soft (F4): 490 mm to 550 mm
  • flowable (F5): 560 mm to 620 mm
  • very flowable (F6): 630 mm to 700 mm

The compaction attempt

The compression test will test stiff, plastic and soft concrete mixtures. To do this, take a cuboid container with a base of around 20 cm x 20 cm and a height of 40 cm. You also need a tape measure.

  1. Fill the bucket with fresh concrete. Pull the concrete smooth on the surface.
  1. Compact the concrete mixture on a vibrating table. This air escapes and the surface sinks down.
  1. Now measure the distance s between the concrete surface and the upper edge of the container. Since this does not have to be uniform on the four sides, calculate the mean.
  1. Now calculate the compression ratio v. Use the following formula:

v = 40 / (40 - s)

Calculate compaction

Tip: The 40 is created by the height of 40 centimeters of the bucket. According to the formula divide the 40 by the height of the concrete column after shaking.

Now read the consistency from the following table:

  • v is greater than 1.20: stiff
  • v is between 1.19 and 1.08: plastic
  • v is between 1.07 and 1.02: soft

When do I need what consistency?>> The production of smaller quantities

Step-by-Step Guide

Tool and equipment:

  • protective clothing
  • Wheelbarrow or bucket
  • Trowel or shovel
  • Mörtelrührer

Step 1: The preparation

Since it can easily come to the pollution of your own clothes during concrete mixing and in return all the necessary items must be quickly at hand, the utensils should be ready to hand. To avoid skin irritation, wear gloves and long-sleeved clothing. In addition, a protective goggles, which protects against splashes in the eyes.

Step 2: Mixing

If the work is done by hand, put the gravel and cement in a wheelbarrow or bucket. Mixing in the wheelbarrow is often chosen in order to be able to transport the fresh concrete lightly.

Step 3: The stirring

Mix the mixture with a trowel or a shovel.

Step 4: The water

Now carefully add the water. You must be careful not to make the mixture too fluid. Then mix the fresh concrete with a mortar stirrer.

Tip: Smaller amounts of fresh concrete are ready after about 5 minutes. If the fresh concrete used in the garden, then a porridge-like consistency is recommended.

The production of larger quantities

concrete mixer

Step 1: Turn on the concrete mixer. Put about two thirds of the required water in the concrete mixer.

Tip: Dosing is particularly easy with a bucket.

Step 2: Now put the gravel in the mixer. This is followed by the addition of the cement. The remaining water is added gradually to the mass.

Step 3: Let the concrete mixer run for a few minutes, so that water, cement and gravel can mix well with each other. The surface should shine easily. If the consistency is still too firm, then add some water carefully.

Step 4: When mixing fresh concrete, it is important to clean the tool as quickly as possible so that the mass can be easily removed. Every tool and all surfaces that have had contact with the concrete must be rinsed off immediately. Thoroughly clean the concrete mixer and blades. Dried concrete residues are almost insoluble and therefore remain permanently on the ground or on the tool. If unneeded concrete is left behind in the mixer, it can become unusable.

Tip: Caution is also required when the fresh concrete gets into the sewage system. To prevent clogging of the pipes, you must pour enough water to dilute them. This is true even for smaller quantities of fresh concrete. Larger concrete residues must be properly disposed of in accordance with the guidelines on construction waste.

Tips for quick readers:

  • Concrete consists of water, gravel and cement
  • the consistency determines the behavior
  • liquefy by adding water
  • Can be mixed with hand or concrete mixer
  • Check consistency with setting test, spreading test or compaction attempt
  • Normal concrete: 25 kg cement; 100 kg of gravel; 12.5 liters of water
  • Universal mixture: 1 kg cement; 4 kg of gravel; 0.5 liters of water
  • Foundation concrete mixture: 1 kg cement; 5 kg of gravel; 0.5 liters of water
  • robust mixture: 1 kg cement; 3 kg of gravel; 0.5 liters of water
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