Mobile Batching Plants or Continuous Mixing – choices for Construction

As the name implies, batch mixing plants produce concrete one batch at a time, while continuous mixers produce concrete at a constant rate. Choosing the best mixing method for a construction site requires consideration of a variety of factors.

These factors include:

  1. location of the site
  2. the amount of material needed (concrete or asphalt)
  3. the construction schedule, as well as
  4. the cost implications.
  5. In addition, where quality is an issue, one of the measures is the homogeneity of the material after mixing, so the efficiency of the mixer must be taken into account.

Mobile batching plants

Batching of concrete can be done by either mobile or stationary plants, but in general, the mobile concrete batching plant can produce the same output of a stationary plant at almost any location.

Equipment can, therefore, be transported to a new site and quickly start to produce the required batch of material, as long as the machinery is washed after the last use, when a different mix is needed. This type of plant is perfect for temporary construction sites or projects where the equipment is only needed for specific and brief portions of the project.

The internal structure of the concrete batching unit keeps the raw (dry) materials in separate compartments until they are required and only then is a batch of concrete mixed.  The mix can be any volume or recipe as required by the customer.

The popularity of this type of plant is due to the chosen unit being easily fitted to a different truck or railcar or, additionally, be utilised in a stationary position. By contrast, standard stationary batch plants need to be transported on a flatbed truck and must be erected at the site using a crane or similar equipment.

High output plants are simply mobile batch mixing plants on a large scale, with individual dry materials being loaded into separate areas until the product is required. The benefit of these larger plants is that they can self-loaded onto a low bed with no craneage required.

A concrete batching plant usually consists of five major systems:

  1. Sand and stone: three or more feeding buckets used for the measurement and feeding of sand and stone.
  2. Powder: The powder system consists of a storage silo (horizontal silos are an excellent option here), and can come with a dust removal system.
  3. Water and admixture: This consists of an admixture box, water tank, pump plus the water and admixture weighing hopper and pipeline.
  4. Transmission/mixing/storage: This is really the “engine” of the plant, comprising a belt machine, mixer frame and mixer and is where all the components of the output mixture are churned together as required.
  5. Control: This is made up of low-voltage electrical and automatic control components, with sensors to manage the different processes.

What are the Benefits of Batching Plants?

  1. Portable and reliable
  2. Lower transportation cost due to manoeuvrability around sites over short distances.
  3. Minimal preparation or set-up before use.
  4. Easy to change mixes.
  5. Tolerant of poor aggregate control.
  6. Precision concrete production when used with reliable components.
  7. Uncomplicated maintenance and low operating costs.

Continuous Mixing Plants

As the name indicates, continuous concrete mixing plants are where materials are fed into the continuous mixer at the same rate as the concrete is discharged. They can have an hourly output of up to 120m³/h and are ideal for road basement foundations, as well as zero or low slump concrete, for example, pavements. 

The process used by Continuous Concrete Mixing Plants.

  1. Raw materials are gathered using automation in the relevant proportions and are channelled to the mouth of the mixing cylinder.
  2. The material is then drawn into the mixer in a uniform manner.
  3. The mixer swirls and stirs the bulk material to create a composite, whilst propelling the mixture towards the exit of the drum.
  4. Depending on the pre-determined volumetric amount, the final material is held ready for discharging onto waiting trucks which will distribute their load.
  5. This input, mixing, propelling, and discharging process takes place continuously to have a steady stream of ready product for use.

What are the benefits of Continuous Batching?

  • High productivity
  • Lower capital cost
  • Less maintenance
  • When used for specialised tasks, this type of unit is more practical for roller-compacted concrete, cement treated soil and so on.
  • Ideal for projects requiring a short working time, but long curing period.
  • Where equipment is needed on a remote site, not suitable for ready-mix. A new introduction by Blend Plants are their off-road mobile units for rural areas, where timing and accessibility to sites become critical for the completion of projects.

What choices are there on Asphalt?

Continuous and batch production methods are also relevant for asphalt, not only concrete. Here too, there is no ideal choice, as this depends on an analysis of all the factors at play, including the type of output required.

Batch plants are globally used most widely for asphalt production, as the process provides the best flexibility, as well as optimal quality of output product. In some countries, quarries are not regulated on control procedures, so batch plants tend to be used almost exclusively, due to earlier mentioned tolerance on aggregate quality.

In continuous plants where there is no interruption in the production cycle, the mixing of the material takes place inside the elongated dryer drum, in a simultaneous process. This means there is no separate mixing tower, providing an added bonus of lower maintenance costs. But there needs to be accurate control at the beginning of the product cycle, before the aggregates are fed in and asphalt is produced.

The benefit of using continuous mixing for asphalt, is more RAP (reclaimed asphalt pavement) utilisation for road making/repairs, as well as fewer escaping transmissions into the atmosphere.

Summary of choices for mobile plants.

In general terms, the following would apply:

  • Batch Plants are used where flexibility, a variety of client-specified requirements and distinct formulae or particular dry mix solutions are needed.
  • Continuous Plants should be considered for lower operational costs and a continual production of product, provided there is consistent quality in the aggregates.

Innovation is a fundamental feature of Blend Plants Africa, paying attention to all aspects of the construction industry. Their professional teams recognise customer challenges and needs, leading to the development of solutions that will beneficially impact such activities.  Blend Plants’ goal is to offer equipment that will improve the quality, the efficiency and, particularly, the profitability of all their customers’ projects.

Blend Plants’ E-Series mobile plants have one to three aggregators installed, while the A-Series has a maximum of four on their ground units. MMI’s BLEND Plant solutions can cater for a wide choice of applications whether it be stabilisation cement, bridge mix, laboratory specified mix, colour cement, backfill, cold asphalt or standard concrete. Contact Blend Plants for more information on your specific needs.