Ready Mix Concrete- Impotance and Impact on Quality of Concrete Work

RMC is a specialized material in which the cement aggregates and other ingredients are weigh-batched at a plant in a central mixer or truck mixer, before delivery to the construction site in a condition ready for placing by the builder. Thus, `fresh' concrete is manufactured in a plant away from the construction site and transported within the requisite journey time. 

The RMC supplier provides two services, firstly one of processing the materials for making fresh concrete and secondly, of transporting a product within a short time. Sometimes Materials such as water and some varieties of admixtures can be transit-mixed (also known as Transit Mixture), that is they can be added to the concrete at the jobsite after it has been batched to ensure that the specified properties are attained before placement.  

Here materials are batched at a central plant and are completely mixed in the Batching Plant or partially mixed in transit. Transit-mixing keeps the water separate from the cement and aggregates and allows the concrete to be mixed immediately before placement at the construction site (Dry Concrete). This method avoids the problems of premature hardening and slump loss that result from potential delays in transportation or placement of central-mixed concrete.

Additionally, transit-mixing allows concrete to be hauled to construction sites further away from the plant. There are several types of RMC plants varying in type of mixing and capacity of concrete production. These plants are generally available in capacities varying from 15 Cum/hour to 200 Cum/hour.

What is the need of RMC?

RMC is generally looked upon as a costly product rather than a facility to get an appropriate quality product on site as and when required. The first cost of RMC may seem higher. However, there are several hidden advantages which can cause considerable reduction in cost to the owner. Since they cannot be accurately determined, they are ignored while evaluating the cost of RMC over site mixed produced concrete.

The following points gives best answer the above question:

1. Generally speaking, the quality of concrete will be superior than site mixed concrete. However, it will greatly depend on the controls and checks exercised at site and at RMC producer's plant.

2. There is a considerable wastage of materials on site due to poor storage conditions and repeated shifting of the mixer location. This is prevented if RMC is used.

3. In most cities, the plot area is barely sufficient to store reinforcement steel, formwork, concrete and other construction materials. Using RMC can cause less  congestion and better housekeeping on the site resulting in efficient working environment.

4. Obtaining RMC at site can reduce supervision and labour costs which would otherwise be required for batching and mixing of concrete at site.

           

5. Many sites in cities, house their work force on the site itself to reduce the time and cost of daily travel. This creates unsafe and unhygienic conditions on the site as well as for the surrounding areas. This will reduce to a certain extent if RMC is utilized.

6. Fluctuation of raw material prices and their availability has always caused delays and problems of inventory and storage for site producers of concrete. This is totally avoided when RMC is used.

7. Availability of labour gangs intermittently has always posed problems to concrete producers on site. This can now be avoided. Besides these labour gangs are difficult to supervise and control as they are only interested in completing the concreting operations as fast as possible. This results in addition of excess water and inadequacies in batching/mixing.

8. A problem of inspection, checking and testing of all concrete materials on site is avoided. However, to a certain extent these checks and tests may be required to be done at RMC producers' plant.

9. Concrete mix design and its control due to variations of material properties is avoided as RMC producers are responsible for the same and supply concrete as specified by the purchaser as per the requirements of the construction site.

10. In public places it creates less nuisance. Congested roads and footpaths are often blocked by carelessly stored concrete materials. RMC allows a much better flow of road traffic as well as pedestrian movement.

11. It improves the environment and around the site. Nuisance due to stone dust and cement particles is reduced considerably. To a certain extent even noise pollution is reduced.

12. The modern RMC plants have an automatic arrangement to measure surface moisture on aggregates this greatly helps in controlling the water to cement ratio (w/c) which results In correct strength and durability.

13. RMC plants have proper facilities to store and accurately batch concrete admixtures (chemical and mineral). To improve properties of concrete both in plastic and in hardened stage this accuracy is useful.

14. In general, RMC plants have superior and accurate batching arrangements than the weigh batchers used on site.

15. RMC plants have superior mixers than the rotating drum mixers generally used for mixing concrete materials at site.

16. RMC plants have efficient batching and mixing, facilities which improve both quality and speed of concrete production.

17. Temperature control of concrete in extreme weather conditions can be exercised in a much better manner than done at site.

18. RMC helps encourage mechanization and new technologies like pumped concrete bulk transportation of cement production of self-compacting concrete and high strength high performance concrete.

19. New materials like micro silica and fibers can be safely used in RMC which in conventional concrete may pose problems.

20. Introduction of RMC improves the rate of supply of concrete in the formwork and thereby automatically improves quality of formwork, layout of reinforcement steel and its detailing and safety / strength of scaffolding and staging.

So this show that RMC concrete is much better option of concreting now a days not only because of cost but apart from that it also offer many benefits to us.

Drawbacks of Site Mix Concrete

Normally the concrete operation is carryout in India is of site mixed, which having some disadvantages which are listed as below:

1. Quality Assurance not guaranteed. 
2. Constant control on aggregates for size, shape & grading  

    not exercised on site.
3. Arbitrary batching and mixing by volume. Strict water-

    cement ratio not exercised.
4. Wastage of materials.
5. Retarded speed.
6. Possible break down of mixers.
7. Concreting operations prolonged beyond day light 

    without proper lighting.
8. Manual operation.
9. Speed restricted depending on mixers.
10. Restricted spaces.
11. Storage of aggregates and cement.
12. Blocking of roads / approaches
13. Dust pollution & Noise pollution