Batching is a Process of Measuring concrete mix ingredients either by Volume or by Mass introducing them into the mixture. Traditionally batching done by volume but most specification require that batching done by mass rather than volume.
Accuracy of Material During Batching in Concrete Mix: –
Cement: When the quantity of cement to be batched exceeds 30% of scale capacity, the measuring accuracy should be within 1% of required mass. If measuring quantity is less than 30% i.e., for smaller batches then the measuring accuracy should be within 4% of the required quantity.
Aggregates: If the measurement is more than 30% of the scale capacity then the measuring accuracy should be within 1%. If measurement is less than 30% then the measuring accuracy should be within less than 3%.
Water: Water is measured in volumetric quantity as 1 litre = 1kg. In case of water, the measuring accuracy should be within 1%.
Admixtures: For mineral admixtures same accuracy as that required for cement. For chemical admixtures same accuracy as that required for water. Mineral admixtures accuracy is same as that of cement because it is used as partial replacement of cement. As chemical admixtures are liquid or added to water therefore its accuracy is same as that of water.
Types Of Batching of Concrete: –
Concrete Batching can be Obtain By two methods
- Batching by Volume
- Batching by Weight
- Batching By Volume: – This method is generally adopted for small jobs. It is accomplished with the Measurement Box, also called Farmas, or Gauge Box. Concrete components Like Cement, and Aggregates are weighed properly by using this box. Precaution taken during the weighing process.
- Batching By Weight: – Batching by weight is more preferable to volume batching, as it is more accurate and leads to more uniform proportioning. It does not have uncertainties associated with bulking.
- Batching by weight equipment falls into 3 general categories: –
- Manual: batching of concrete is done manually and it is used for small jobs.
- Semi-automatic: the aggregate bin gates are opened by manually operated switches and are closed automatically when the material has been delivered. This system also contains interlock which prevents charging and discharging.
- Fully automatic: the materials are weighted automatically – Ready mixed Plant
Mixing Of Concrete: – It is an Operation of Which consist Rotation or Stirring for concrete mixing.
Objective – To coat the surface the all-aggregate particles with cement paste, and to blind all the ingredients of the concrete into a uniform mass.
Different Process of Mixing
The usual type of mixer is a batch mixer, which means that one batch of concrete is mixed and discharged before any more materials are put into the mixer. There are four types of batch mixer.
Tilting drum mixer
A tilting drum mixer is one whose drum in which mixing take place is tilted for discharging. The drum is conical or bowl shaped with internal vanes, and the discharge is rapid and unsegregated so that these mixers are suitable for mixes of low workability and for those containing large size aggregate.
Non tilting drum mixer
A non-tilting drum is one in which the axis of the mixer is always horizontal, and discharge take place by inserting a chute into the drum or by reversing the direction or rotation of drum. Because of slow rate of discharge, some segregation may occur.
Pan type mixer
A pan type mixer is a forced–action mixer, as distinct from drum mixer which relies on the free fall of the concrete inside the drum. The pan mixer consists of a circular pan rotating about its axis with one- or two-stars paddles rotating about vertical axis of pan.
Dual drum mixer
A dual drum is sometimes used in highway construction. Here there are two drums in series, concrete being mixed part of the time in one and then transferred to the other for the remainder of the mixing time before discharging.
These are fed automatically by a continuous weigh-batching system.