Concrete is one of the most demanding materials used for the purpose of construction which is made of cement, aggregates (gravel, sand or rock), water and admixtures. In order to get the best quality of concrete, ingredients of concrete are pre-designed. If the ingredients of concrete are not as per the pre-designed proportion or if they are not properly mixed with each other then there is chance of getting very poor quality of concrete. Concrete mixers are the machines which help in mixing the ingredients of concrete and make the concrete paste in a workable condition. In other words, the machine used for mixing concrete is known as the mechanical concrete mixer, or in simple words, the concrete mixer.
Concrete mixer is used to mix cement with aggregates including sand or gravel, and water to form concrete. The concrete mixers must not only achieve the uniformity of the mix, but they should also discharge the mix without disturbing that uniformity.
When in absence of concrete mixers or while working on small jobs, concrete is sometimes mixed manually. But, due to the carelessness of the labour sometimes, the concrete is either mixed poorly or is frequently over-mixed. Hence, it is advisable to use concrete mixers for proper mixing of the concrete. Whatever may be the method of mixing the materials for the preparation of concrete, it should be done thoroughly to ensure the uniform distribution of materials in concrete mass and this can be judged by uniform colour and consistency of concrete. Remember mixing is the heart of concrete and poor mixing means it is not qualified to be called as concrete.
Also Read:
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Importance of Water-Cement Ratio in Concrete
What is Concrete Admixtures?
Types of Concrete Mixers
There are two main types of concrete mixers which are as under:
01. Continuous Mixer
Continuous mixers are used in massive constructions sites such as, for construction of dams, bridges, etc., which involves the use of large masses of concrete and also requires continuous flow of concrete. In continuous mixer, the weighing, loading and mixing of concrete ingredients as well as discharge of the concrete mixture is done continuously. It mixes ingredients continuously and in a single pass.
02. Batch Mixers or Drum Mixer
Batch mixer is one of the most common types of mixer and it is widely used to mix the concrete ingredients. It consists of a revolving drum with blades or baffles fitted within it. In this type of mixer, all the materials of the desired proportion are mixed and fed into the hopper of the revolving drum. Then the drum, on being rotated at a certain speed, mixes the materials with the help of a series of blades fitted inside. The resultant mixture is finally discharged from the drum and is ready for use.
As stated by Dr. Chiara F. Ferrari’s physicist, in the Building material division of the National Institute of Standards and Technology (NIST- U. S. Department of Commerce), ‘it is very important to control the rotation speed of the drum and in certain mixers, the angle of inclination of the rotation axis to get the good concrete or mortar’.
Types of Batch Mixers
The batch mixers are further classified in to drum types mixer and pan types mixers:
01. Concrete Drum Mixers
(a) Tilting Mixers
- Tilting mixers have a conical or bowl-shaped drum with vanes inside. These types of mixers are preferable for mixes of low workability and for those containing large sized aggregates. The mixing chamber which is known as drum is tilted for discharging the mixture.
(b) Non-Tilting Mixers
- In non-tilting mixers, the mixer is not allowed to tilt and the axis of the mixer is always horizontal. The discharge is done either by inserting a chute into the drum or by reversing the direction of rotation of the drum or sometimes by splitting of the drum (which is done rarely).
(c) Reversing Drum Mixers
- In Non-tilting mixers, mechanism of drum also comes with reversing arrangement which is known as Reversing drum mixers. In a reversing drum mixer, the ingredients of concrete rotate in one direction and are discharged from the opposite direction.
(d) Pan Types Mixers
- Pan type mixer consists of cylindrical pan that contains set of blades which mix the concrete ingredients. Generally, the mixture of concrete is discharged from the bottom of the pan.
Final Words: For mixing the ingredients of concrete, the manufacturers use batch mixer or continuous mixer depending upon the quantity of concrete and cost of the work/project. Mixing of concrete is a wide topic and this issue has not been fully discussed here. There are many parameters like mixing time, mixing speed, air pressure in the mixing pan; temperature, etc. which have an influence on the properties of concrete.
Dils, G. De Schutter, V. Boel stated regarding the Influence of mixing procedure and mixer type on fresh and hardened properties of concrete, in the journal of Materials and Structures, ‘in same composition of concrete, the properties of the concrete or mortar can differ due to the change in the mixing procedure and the mixer type’.
Hence, it is very important to select the proper mixing procedure and mixer type to mix the concrete.
Must Read:
Why Batching of Concrete is Important?
Various Excavation Equipments Use on Construction Site
