READY-MIX CONCRETE (RMC)

Ready-mix concrete is manufactured in a factory or batching plant to specified mix proportions and then delivered to site by lorry-mounted transit mixers. This results in precise mix proportions being delivered in pre-ordered quantities (measured by volume in m3), which can be custom-made to suit many different construction applications. Ready-mix concrete is manufactured under computer-controlled operations and transported and placed at site using sophisticated equipment and methods. Ready-mix concrete provides customers with numerous benefits but a few disadvantages.

Подпись: Fig. 13 Ready-mix concrete lorries.
Подпись: Cleaning Mixing Areas On completion of mixing operations, the mixing area should be thoroughly cleaned and tidied. If tools and equipment are not cleaned thoroughly after use, cement paste will harden on them and will be difficult to remove later. This is particularly important if pigments have been used in the mix.

The advantages of ready-mix over site-mixed concrete are

as follows:

• a better and more consistent quality concrete is produced;

• there is no need for storage space for basic materials on site;

• the elimination of procurement/hiring of mixing plant and machinery;

• wastage of basic materials is avoided;

• the labour associated with site production of concrete is eliminated;

• the time required is greatly reduced;

• noise and dust pollution on site are reduced.

However, ready-mix concrete does have a number of disadvantages:

• The materials are batched and mixed at a central plant, so the travelling time from the plant to the site is critical over longer distances. Some sites are just too far away!

• Concrete’s limited lifespan between mixing and ‘going off’ means that ready-mix should be placed within 2 hours of batching at the plant. Concrete is still usable after this point but may not conform to relevant specifications.

• It generates additional road traffic. Furthermore, access roads and site access have to be able to accommodate the weight and size of the truck and load.

• Any shortfall in quantity, due to a miscalculation, could result in work already done being wasted. Conversely, over-ordering will result in costly wastage of unused concrete.