Ready mix concrete: Types, advantages and disadvantages

Concrete prepared in a batch factory specifically for each task requirement and then delivered to the job site “ready to use” is known as ready mix concrete (RMC).

There are two variants, with the first type of barrel truck or in-transit mixers. This kind of truck transports plasticised concrete to the job site. The volumetric concrete mixer is the second type. This method mixes the concrete on site after delivering the ready mix in a dry form.

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See also: What is prestressed concrete?

Ready mix concrete: Types

According to how the different elements are mixed, ready mix concrete (RMC) comes in three different varieties, as listed below:

1. Transit mixed concrete
2. Shrink mixed concrete
3. Central mixed concrete

Transit mixed concrete

It is also known as dry-batched concrete since all essential components, including water, are loaded directly into the truck mixer. The mixer drum rotates quickly at charging speed while the material is being loaded, and then it continues to rotate at a regular agitation pace. Moreover, three different varieties can be made with this type of ready-mix concrete, which are as follows:

Concrete mixed at the job site

The drum is rotated at a slow, agitating speed of 2 rpm while transported to the destination. Still, when it arrives at the location shortly before the material is discharged, it is rotated for roughly 70 to 100 revolutions at a maximum speed of 12 to 15 rpm to ensure homogenous mixing.

Concrete mixed in transit

The drum speed is maintained at a medium level throughout the transit period, or around 8 rpm for roughly 70 rotations. It slows to an agitation speed of 2 rpm after 70 rotations before discharging the concrete.

Concrete mixed in the yard

In the field, the drum is rotated for 50 revolutions at a high speed of 12 to 15 rpm. The concrete is then gently stirred as it is transported.

Shrink mixed concrete

The drum mixer mounted on the truck completes the rest of the mixing of the concrete after it has been partially mixed in the plant mixer. The amount of mixing done in the central mixing plant determines how much mixing is done in the transit mixer. Tests should be carried out to determine whether mixing the drum mixer is necessary.

Central-mixed concrete

The place where the concrete is properly mixed before being loaded into the truck mixer is also known as a central batching plant. The facility is sometimes called a premix or wet batch plant. The truck mixer solely serves as an agitator when moving the concrete. Occasionally non-agitating units or dump trucks can also be employed when the load is less or the workability requirements are lower.

Ready mix concrete: Process of making it

To produce ready-mix concrete of the highest quality, cement, aggregates, sand, water, and other chemicals are weighed-batch-ed at a centrally located plant. After being treated, the concrete is transported in transit mixers to the construction site and ready for use without further preparation. The autonomous machine precisely measures weight, water-cement ratio, the dosage of admixtures, and moisture content to prepare high-quality concrete.

All ingredients used to prepare ready-mix concrete are extensively examined for their quality and physical characteristics following the international standard codes at a well-equipped laboratory attached to the factory. The moisture probe quantifies the water content of the aggregates and sand. It subsequently helps determine the quantity of water to be added while preparing the mix. Trial mixes are made and tested to verify that every batch of concrete leaving the plant complies with varied mix designs according to the client’s requirements with different grades of concrete.

Ready mix concrete: Advantages

1. A ready-mix concrete plant that uses advanced technology and reliable procedures produces concrete of the highest quality. It is strictly regulated how materials are tested, processes are run, and crucial manufacturing procedures are continuously monitored. In the case of site-mix concrete, poor control over the input materials, batching, and mixing procedures are resolved by a ready-mix concrete method.

2. Mechanised operations are regularly used to maintain the speed of construction techniques used in ready-mix concrete factories. A site mix concrete factory with an 8/12 mixer may produce 4 to 5 metric cubes per hour, compared to 30 to 60 metric cubes per hour in a ready mix plant.

3. If RMC is used, construction can move along quite quickly. Cement consumption can be decreased by 10–12% with better handling and suitable mixing techniques. If mineral admixtures or cementitious materials are used, there is potential for further reduction.

4. The adaptability of the concrete mix is very high and has a very flexible range of uses. The best concrete setting techniques are used to set it in place.

5. Because ready-mix concrete uses bulk concrete rather than cement bags, less cement is required, and less dust is produced.

6. Energy and resources will be saved by using less cement.

7. Reduced consumption means less cement is produced, which reduces environmental pollution.

8. Obtaining a more durable construction extends the service life, reducing life cycle expenses.

9. The production of ready-mix concrete relies less on human labour, which lowers the possibility of human error. Also, this will lessen the need for strenuous effort.

10. According to the specifications, concrete in any quantity is timely supplied on site.

11. The raw materials can be stored on-site without taking up any space. There is no delay brought on by installing or disassembling a site-based batching plant.

12. Less petrol and diesel is consumed, which lowers air pollution and noise levels.

Ready mix concrete: Disadvantages

1. The workability of the concrete will be lost during the transit from the preparation time to the delivery site. Adding more water or admixtures will be necessary to maintain the workability following the specification. Before using it for construction, the QA/QC engineers must perform slump tests on the site to ensure it is viable.

2. Concrete may be set if it is subjected to traffic while being transported. Admixtures will therefore need to be added to delay the setting period. Nonetheless, unexpected traffic is a major issue.

3. Since concrete may be purchased in larger quantities, the formwork and placement arrangement must be prepared in advance in a broad area.

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