Process of Mixing Concrete for Building Construction

The process of mixing concrete for building construction is done in tow different ways. It is either mixing on the job site or by ready mix concrete.

The ACI Building Code on mixing concrete states that:

For a job-mixed concrete, mixing shall be done in a batch mixer of approved type. The mixer shall be rotated at a speed recommended by the manufacturer and mixing shall be continued for at least 1-1/2after all materials are in drum, unless a shorter time is shown to be satisfactory by the criteria of specifications for Ready-Mixed Concrete for central mixers.

Mixing Concrete should be done only after uniform distribution of materials has been attained and that mixture shall be discharged completely before recharging the mixer.

Centralized Ready-Mix Plant

Concrete of any desirable proportions and quality for numerous special purposes can be ordered directly from ready mix concrete dealers. The desired type and quality of concrete is delivered to the project site very rapidly.

In a modern ready mix concrete plant, the production of various concrete mixtures are programmed by electronic computer. The batches of concrete for any desired size and strength is proportioned automatically by electronic control. all aggregates are measured by weights. Mixing at the batching plant provides more accurate control of the consistecy and other properties f fresh concrete.

There two ways on how to mix concrete by either:

In mobile mixers.

In Stationary Mixers

Mobile Mixing. Cement and aggregates are loaded in mobile mixer at the batching plant and then mixing operation is done on its way to the job site.

Stationary Mixer, refers to the mixer installed on site where batches of cement and aggregates are mixed and delivered to the forms, and It also refers to the concrete is mixed before it is loaded inside the truck mixer where the concrete is only agitated.

Hand Mixing. A good concrete can be produced also by hand mixing, provided that the fine and course aggregates are clean and well graded. If about one half as much as water as cement by weight is used and mixing is done properly. the results will be a good quality concrete.

A good concrete-mix proportion are as follows:

• 1/2 kgs of water
• 1 kgs of cement
• 2 kgs of sand
• 2-1/2 -3 kgs of gravel

Under that proportion by weight, laboratory tests showed that the weight of gravel is not necessarily double that of the sand. On the other hand, the volume of gravel is more or less double that of the sand if measured by volume using a measuring box.

source:

Simplified Methods on Bldg Construction by Max Fajardo jr.