READY MIX CONCRETE (RMC)
Ready mix concrete refers to a concrete manufactured from a batching plant according to customer/clients requirements & approved Design Mix and conveyed to the site in a ready to use condition. The concrete is conveyed through transit mixers of capacity ranging from 3 cum to 10 cum and more. 6 cum trucks are most commonly used. Batching plants are available in a wide range of capacities and types. ranging from 10 cum per hour to 125 cum/hr and some manufactures have much higher capacity plants.Most commonly used capacities are 30 cum, and 60 cum.
MAJOR CONSUMERS OF READY MIX CONCRETE
a) BIG CONSTRUCTION COMPANIES
b) COMMERCIAL RMC SUPPLIERS
They setup there own plant in a specified location with all arrangements for stocking raw materials and commercially manufacture the materials as per customer/ client requirements.
COMMON METHODS USED FOR CONVEYING RMC
a) Transit mixed or truck mixed concrete
b) Shrink mixed concrete
c) Central mixed concrete.
a) Transit mixed concrete
The materials are batched at a central plant and are thoroughly mixed in the truck in transition. Transit-mixing separate water from the cement and aggregates and allows the concrete to be mixed instantly before using at the job site, Frequently partial mixing happens in transit and remaining mixing shall be done at site just before casting. This avoids slump loss, segregation, premature hardening, delays due to traffic jams, pouring delays due to equipment failure etc. The main disadvantage is the truck capacity is less compared to the one carrying fully mixed RMC.
b) Shrink mixed concrete
In shrink-mixed concrete, concrete is partially mixed at the plant to reduce or shrink the volume of the mixture and mixing is completed in transit or at the jobsite. The disadvantage is that concrete that has been remixed tends to set more rapidly than concrete mixed only once.
c) Central mixed concrete
The concrete is batched and completely mixed in a stationary mixer at the plant site before discharging it into the truck mixers. This can enhance the quality of concrete and cater higher production requirements.
HOW RMC IS MANUFACTURED
Ready mix concrete is manufactured from a centralised plant having facilities for storage of raw materials, Lab for inspection of raw material quality and concrete quality, having a series of batching plant/plants of different capacities etc.
The raw materials are checked to ensure compliance with relevant Indian standards so that there shall no be any quality issues to the end product. The raw materials are stored in separate areas on a firm ground. The RMC plant uses there In house design mixes most to the time. Customisation can also be done with the help of quality engineers. The design mixes are done in a way to give maximum quality with economy.
The running time, distance covered, initial settling time, slump etc are controlled using addition of special admixtures(mineral and chemical) etc without hampering the concrete strength. RMC is a totally controlled concrete having high work efficiency.
The raw materials stored shall be conveyed to the mixing drum using conveyor belts or bucket elevator. Cement is stored in silos also are conveyed using screw conveyors attached to the batching plants.
Once the weight of all material types meets the needs of specific amounts, the door of the weighing hopper is opened automatically. The materials will then be mixed by a concrete mixer. Once the setting time is over, the loading door of the concrete mixer opens and the concrete flows into a transit mixer.
WHAT ARE THE ADVANTAGES OF READ MIX CONCRETE
a) Uses the updated technology in proportioning, mixing and conveying and hence RMC plants can maintain excellent quality.
b) Transportation and placing is very easy. Once the concrete transit mixers reaches site concrete placing can commence immediately through concrete pumps, concrete buckets or boom placers.
c) As the concrete production and mixing is done in another place the site will be free form noise and dust pollution and free from raw material and cement trucks.
d) By using RMC the construction speed can be enhanced and schedule delays can be avoided upto an extent.
c) The concrete produced from RMC plants can be customised as per the client/ customer requirements.
d) RMC plants are a great relief when the site do not have sufficient spaces for stocking of raw materials and locating a batching plant with its raw material bins. RMC plants can cater any quantity of concrete starting from small residences to big construction sites.
e) Onsite wastage of raw materials and concrete can be eliminated by using Ready mix concrete.
d) Labour required for production of concrete and manpower for operation and running of batching plant & its associated machinery can be eliminated .
WHAT ARE THE DISADVANTAGES OF RMC
a) Requires huge investment to set an RMC plant.
b) Labour force shall be ready to place the concrete as and when it comes
c) Unforeseen delays and traffic jam leads to concrete rejection.
d) A very efficient and effective transporting system has to be maintained.
e) Quality has to be checked at site as per is standards on fresh concrete and also on hardened specimen.
f) Very effective quality system to be maintained for adjusting the setting time and slump according to the time of transit.
g) For residential construction the customer may not get a better idea of the quality of concrete due to lack of site testing facilities.
h) There are problems due to discrepancies in quantities which cant be convinced properly to the RMC vendors.