Concrete mixers: All you need to know before buying

• Concrete mixers
• Batch mixer
• Drum mixer
• Non-tilting drum
• Reversing drum
• Tilting drum
• Pan mixers
• Continuous mixers
• Order of mixture (tilting drum)
• Order of mixture (non-tilting drum)
• Relations for a good mixture
• Concrete consistency
• Concrete analysis
• Transport concrete information
• Preserving drum mixers
• Preserving pam mixers
• Preserving mixers with explosion motors
• Blades
• Criteria for a mixer selection

Concrete mixers

Concrete mixer is a device that mixes homogeneously cement, water, gravel or sand to form concrete. There are a lot of choice on the market so you can find one that adapts better for your usage, this provide a less hard task then mixing it by hand.

The concrete mixers are largely used on civil construction, mostly to build houses, dams, bridges and infinity of others tasks. It has also other uses like mixing rations or manure, but on these cases it calls only mixer.

They normally measure the capacity of the mixer in liters that corresponds to the dum capacity. The best you can get is a concrete mixer that provides you homogeneity and does it quickly. The homogeneity is determined by the type of mixer, the order of introduction into the mixer, and duration and power of mixing.

Efficiency is the best way to achieve success on your daily work, don’t buy one just because is the best price you can find in market, always give preference to relation quality/price, you can save 10 bucks today and lose 1000dollars tomorrow, you have to measure the pros and cons of acquiring it, facing the idea that only a quality mixer will perform such task well, they are also more resistant to daily work, they need less repairing, and they are normally easy to repair, look also carefully the energy necessary to produce concrete, this could reveal a high bill at the end of the month.

For homeowners, for tasks like repairing, a concrete mixer between 140 liters and 300 liters should be the adequate, otherwise for industrial projects that need a large amount of concrete consider buying a concrete mixer between 350 liters and 1000 liters, but always depends on the project.

If you are going to choose the best concrete mixer for a specific application, you must consider these factors, location of the construction site, the amount of concrete needed, the construction schedule, and the amount of concrete that you will need.

There are two main types of mixer: batch mixers and continuous mixers

Batch mixer

In the batch mixer there are two main types: the drum mixers have orientation of the axis of rotation: horizontal or inclined, and pan mixer has orientation vertical.

Drum mixer

Drum mixers are composed by a drum, with fixed blades, rotating around its axis and a container with a cross section similar. The blades are attached to the inside of the movable drum. The purpose of the blades is to lift the materials as the drum rotates.

There are three main types of drum mixers:

• Non-tilting drum
• Reversing drum
• Tilting drum

Non-tilting drum

This type implies that the orientation of the drum is fixed, the materials are added at one end and discharged at the other. This working principle, is usually used by the biggest concrete mixers.

The reversing drum

All process is similar to non-tilting drum with the exception that the same opening is used to add constituents and to discharge concrete.

Tilting Drum

In tilting drum, the inclination of the drum can be varied. For a better mixture the drum axis should be at an angle of 15º from horizontal, increasing the angle to a more vertical position of the axis of rotation, the blades cannot lift concrete, and it will not be well mixed.

Pan mixers

The pan mixers work basically using a cylindrical pan that could be fixed or rotating, with the concrete to be mixed, while the sets of blades mix the materials.

Continuous mixers

Continuous mixers are used for applications that require a short working time and long unload time, as the name tells, the materials are continuously fed into the mixer at the same rate as the concrete is discharged.

Order of mixture (Tilting drum)

• Water +/- 3 liters
• Gravel
• Cement
• Sand
• The rest of water

Order of mixture (non-tilting drum)

• Almost all the water in the mixer
• 50% Gravel
• Sand
• Cement
• 50% Gravel
• Rest of water

Relations for a good mixture:

Relation water/cement (x) – Responsible for resistance and durability of concrete.

Relation water/dry materials (A%) – Responsible for workability

A% = (x/(1-m))*100 m=s+g (sand and gravel)

In function of consistency, the concrete is classified to:

· Dry or wet – when the relation water/dry materials is low, between 6 and 8%;

· Plastic – when relation water/dry materials is between 8 and 11%;

· Fluid – when relation water/dry materials is high, between 11% and 14%;

Concrete analysis

The performance of concrete is determine by its microstructure, that its determined by its curing conditions, by the mixing method, and the type of concrete mixer used to process concrete.

Transport concrete information

This task must be as fast as possible, to minimize the effects of drying concrete and loose workability.

In concrete trucks:

• Necessity of extra water;
• Adherence of concrete into the mixer;
• Pumping difficulties;
• Possibility of losing resistance, durability and other properties;

This could be caused by too much mixture time on transport, bad mixture or high temperatures that alter the concrete properties.

Preserving drum mixers

• You should watch the mixer after the usage, letting it approximately 30 minutes with gravel and water, for cleaning all the interior.
• Do not fulfill the concrete mixer with the motor stopped.

Preserving Pam mixers

• For a good equipment working, this could not work without a leveled base.
• Apply the same careful usages of drum mixers.

Preserving mixers with explosion motors

• Use only clean fuel, in ventilated environment.
• Always supply with cold motor, avoiding fire.
• Clean the air filter and fuel filter daily.
• Verify oil level in carter every 4 usage hours.

Blades

There a two types of blades in a concrete mixer, one set drags the concrete upwards and towards the center of the mixer when the drum rotates in one direction, the other set pushes the concrete toward the opening when the drum rotates in other direction, these blades are attached to the inner walls of the drum. With the usage blades will vary in shape and change the concrete, so you should consider changing blades regularly.

Criteria for a mixer selection

• Easy to clean;
• Cost and difficulty of replacing the blades or parts;
• Sensitivity of the blades to wear and tear;
• The size of dum;
• The energy of mixing;
• The efficiency of a mixer;
• Amount of time it needs to leave concrete homogeneity;

With all these tips and advices I hope that you can make the right choice.

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