Ready-mix concrete (RMC) is a type of concrete which is manufactured in a cement factory, or specifically known as the batching plant, according to a given set of proportions, and then delivered to a work site, by truck mounted with mixers. This results in a precise mixture, allowing specialty concrete mixtures to be developed and implemented on construction sites. The fist factory which produced ready mix concrete was built in 1930s; however, the industry didn’t begin to expand until late 80s. Since then it has continued to grow significantly.
Ready mix concrete is sometimes preferred over on-site concrete mixing because of the volume it can produce with precision of proportion of mixtures and also due to reduced work site confusion. Using a pre-determined concrete mixture reduces flexibility, both in the supply chain and in the actual components of the concrete.
Ready-mix concrete is also termed as the customized concrete products for commercial purpose. Ready-mix concrete (RMC) refers to concrete that is specifically manufactured for delivery to the customer’s construction site in a freshly mixed and plastic or unhardened state. Concrete itself is a mixture of Portland cement, water and aggregates comprising sand and gravel or crushed stone. In traditional work sites, each of these materials is procured separately and mixed in specified proportions at site to make concrete. Ready-mix concrete is bought and sold by volume – usually expressed in cubic meters (cubic yards in the US).
Ready-mix concrete is manufactured under controlled operations and transported and placed at site using sophisticated equipment and methods. In 2011, there were 72,924 workers working in 2,223 companies that produced Ready Mix Concrete in the United States.
Process of Ready-mix concrete
Ready mix concrete has cement, aggregates, sand, water and other chemicals, which are weigh- batched at a centrally located plant for a premium quality. The concrete is then delivered to the construction site in transit mixers and can be used straight away without any further treatment. The automatic plant monitors weigh-batching, water-cement ratio, dosage of admixture, moisture content, with precision to produce quality concrete.
All ingredients used for the preparation of ready mix concrete are thoroughly tested for their quality and physical properties in a well equipped laboratory attached to the plant for conformity to relevant international standard codes. The moisture probe determines the water content in the sand and aggregates. This accordingly helps in fixing the proportion of water to be added for the preparation of the mix. Trial mixes are carried out and tested to ensure that each and every batch of concrete coming out of the plant meets various mix designs as per the client’s requirement with different grades of concrete.
Advantages of ready-mix concrete
Following are the advantages of ready-mix concrete:
- Ready Mix Concrete (RMC) allows speedy construction through programmed delivery at site, mechanized operation with consequent economy.
- RMC reduces the labour cost and site supervising cost.
- RMC comes with consistency in quality through accurate & computerized control of sand aggregates and water as per mix designs.
- Production of RMC helps in minimizing cement wastage due to bulk handling.
- Production of RMC is relatively pollution free.
- Reduced project time resulting in savings in all aspects.
- Proper control and economy in use of raw material resulting in saving of natural resources.
Disadvantages of ready-mix concrete
Following are the disadvantages of ready-mix concrete:
- The materials are batched at a central plant, and the mixing begins at that very plant. So the travelling time from the plant to the site is critical over longer distances. Some sites are just too far away, which can risk that ready mix concrete may become unusable due to setting.
- It will generate additional road traffic. Generally, Ready Mix Trucks are large in size and may cover lot of area in the road blocking other traffic. Furthermore, access roads and site access have to be able to carry the greater weight of the ready-mix truck plus load. (Green concrete is approx. 2.5 tonne per m³.) This problem can be overcome by utilizing so-called ‘mini mix’ companies which use smaller 4m³ capacity mixers able to reach more-restricted sites.
- Concrete’s limited time span between mixing and curing means that ready-mix should be placed within 210 minutes of batching at the plant. Modern admixtures can modify that time span precisely, however, the amount and type of admixture added to the mix is very important.
Volumetric mobile mixer
Volumetric mobile mixer can provide a good alternative to ready-mix concrete. This is a hybrid approach between ready-mix concrete and traditional on-site mixing. The volumetric mobile mixer is a truck that contains concrete ingredient materials and water to be mixed on the truck at the job site to make and deliver concrete according to the amount needed. The on-truck mixing at the job site eliminates the problems of ready-mix concrete such as delays that can cause the pre-mixed concrete to become unusable.