Guest Column
The RMC Story
As the use of RMC can ensure better quality of structures,
its production should be promoted by the Indian government,
opines Jagvir Goyal.
Ready mix concrete is no more a stranger to the Indian construction
world. The construction scene has undergone a major change
during the last 10 years. During 1998, even an engineer needed
to be explained the full form of RMC. Now, RMC plants have
sprung up in all major cities of India, thanks to the cement
manufacturing companies who have taken initiative to
set up most of these plants and utilise part quantity of their
cement production for RMC. The venture has proved profitable
for them.
RMC equipment suppliers are also not left behind. Standard
equipment companies of the world have developed their
network of branches in India to supply RMC plant equipment.
Since long, it was being felt that RMC is one such item that
needs to be brought to the centre of Indian construction
scene if the desired parameters
of quality, progress and durability are to be achieved. The
dream is being realised now, though RMC, a house-hold term
abroad, is yet to see a six to seven fold increase in India.
What exactly is RMC?
To be precise, RMC is concrete that is prepared and supplied
to construction sites in a plastic, unhardened and ready to
use state. The consumer avoids all sorts of burden of procurement
of various aggregates, cement, plant and machinery. Above
all, a strict quality control can be ensured at the RMC station.
The batching and mixing of different ingredients is done at
a central batching and mixing plant. Final mixing is done
in the truck-mounted transit mixers which carry the concrete
to the site of its pouring. In a way, RMC is the concrete
produced as per specifications laid by the buyer and delivered
to him under strict quality controlled conditions.
RMC equipment
RMC plants are designed for different concrete production
capacities and batch sizes. Capacities of individual components
obviously depend upon total production capacity. In addition,
the batch size of concrete also matters. Components of a 30
cu m per hour plant with batch size of 1 cu m shall be different
from that of a
30 cu m per hour plant with batch size of 0.5 cu m. Therefore,
before choosing a RMC plant, concrete production required
per day, number of working hours and batch size should be
fixed.
For a requirement of 100 cu m concrete per day, with 10 working
hours per day, a RMC plant of 15 cu m per hour capacity with
batch size of 0.5 cu m per hour shall be sufficient. As it
can produce the required quantity in just 7 hours, it will
take care of any unforeseen stoppages of work.
An RMC plant can set up its own aggregate crushing plant
to save on the cost of readily available crusher if financial
resources for initial investment are available. Otherwise
it may buy ready aggregate from the market. If the RMC plant
is required to be at aggregate quarry, aggregate crushing
and screening plant with conveyors, crushers and screens shall
be required.
Features
Automatic batching of concrete ingredients is preferred for
better efficiency of the equipment and stricter quality control
of concrete. Aggregates, cement and water must be added by
weight and not by volume. In addition, an admixture dosing
system should inject required quantity of admixture if the
concrete mix design asks for it. All batching process should
preferably be controlled by PLC. Automatic batching system
should produce an alarm after every production. Bulkage of
sand should be accounted by it through a moisture correction.
Unit control board should have SCADA based controls, display
monitors, moisture control display, data printing arrangements,
computerised mix proportions and choices of both manual as
well as automatic controls. Number of batches produced, to
be produced; value of concrete produced, batch record output
should be given by the control systems. In fact, a host of
control parameters and data is generated by the control panel
and operator should be able to have a complete control of
the RMC equipment through the mouse and keyboard.
Mixing options
RMC is prepared by mixing the ingredients at the centrally
installed plant itself and later in the transit mixers while
being carried to the site. Revolving speed of transit mixers
is controlled to avoid segregation of concrete and to keep
the concrete in plastic and unhardened state. This mixing
option is exercised when the distance of site from the RMC
plant is smaller. Otherwise, when the transportation distances
large, concrete ingredients are are batched and added to transit
mixer for mixing them during transportation.
The batching and mixing plant of an RMC equipment has a number
of attachments such as loading and unloading screws,
inclined belts, extraction belt, load cells or scales for
weighing aggregates in batches – all provided to simplify
the operations. Mixers are lined with wearing plates or special
tiles to save them from wear and tear as the mixers keep running
constantly to meet the concrete demand.
Some desirable features
The capacity of RMC equipment may vary any where from 15 to
150 cu m of concrete per hour. Manufacturers are not sitting
silent and working on producing even higher capacity equipment.
A builder can choose one depending upon the demand of concrete.
A RMC station needs to be supported by a fleet of transit
mixers required to transport ready mixed concrete to
various sites. Again, the capacity of each of these mixers
may vary somewhere from 4 to 7 cu m per hour. Concrete can
be delivered to places as far as 40 km from the RMC station.
RMC equipment must provide the user with the following
results:
• Minimum breakdowns despite continuous use. Equipment
should be strong enough to produce concrete continuously.
• Least power and oil consumptions should be there.
• Least maintenance of parts of equipment should
be required.
• There should be no decrease in output of concrete
with the passage of time.
• Spares and service should be easily available.
• Computerised controls for maximum automation should
be available.
• Investment cost should be least or competitive.
• All components of the equipment should be easily accessible.
Basic needs of RMC equipment
Land: First requirement is availability of sufficient land.
Depending upon the capacity of the plant, especially the storage
capacity, area of land needs to be worked out and acquired.
A 30 cu m per hour plant may require around 500 sq m area
including that for bins. Only the plant structure may need
hardly 10 m X 10 m area i.e. only 100 sq m for setting up.
Foundation: The equipment supplier will ask for foundations
for the equipment components. And these need to be created
at site as per the drawings provided by the equipment supplier.
If a mobile RMC plant is to be used, no foundations shall
be required.
Assembly cranes: In order to erect the RMC plant equipment,
cranes shall be demanded by the equipment supplier. A manufacturer
of RMC equipment normally has his equipment production unit
at one place and transports the equipment components
to site where the user provides him with crane facilities
for erection of plant and commissioning it.
Water supply: The user has to create a source of water supply
at site of RMC station. For this, he has to make arrangements,
preferably by boring a tubewell or from other sources, if
available and reliable. Generally, an outside source may be
available but not reliable. Further, the user has to get the
water tested and check that it is potable and suitable for
concrete.
Electric power supply: Electric power supply shall also be
required for operation of RMC equipment. Necessary connection
of required load shall be required to be obtained from the
electricity department. In addition, standby diesel generator
set arrangements shall be required.
Earthing arrangement: RMC equipment essentially needs
to be earthed in view of abundant use of metal. Necessary
earthing facility needs to be created by the owner or buyer.
Air conditioning: Control unit of the RMC plant needs to
be kept air-conditioned for trouble free running of computer
systems and to provide good environment to the operators and
staff.
Plumbing and drainage work: Water supply network needs to
be laid at site for availability of water at different locations
including testing laboratory. This arrangement has to
be made by the user. Similarly, site drainage for rain water
or spillages need to be provided to keep it workable.
Fly ash connection: A highly promising advantage of
RMC is large scale utilisation of fly ash because of its best
blending with other materials in an RMC plant when fly ash
concrete is to be produced. Fly ash is increasingly becoming
an environmental hazard and its utilisation in concrete
is essential to maintain the ecological balance. Economy achieved
due to saving of cement is an additional advantage. The problem
that engineers have been facing earlier was that fly ash didn’t
get fully mixed up with concrete ingredients. At RMC stations,
dispersion of fly ash within concrete is not at all a problem
even in concrete with high slump values. To make this use,
RMC producer has to arrange his supply of fly ash from nearby
sources like thermal power stations and tell the RMC equipment
supplier that fly ash shall be used in concrete and some concrete
mix designs with fly ash as an ingredient should be available
in the mix options made available.
Different from batching plants
The concept of RMC plant is different from that of batching
plants used at
most of the project sites. The batching plants are established
at project sites on temporary basis in order to cater to the
needs of the project with respect to certain defined mix-designs.
Many times, these plants are manually operated or semi-mechanised.
A RMC station is established permanently in a city or town
where the consumers lodge their concrete requirements along-with
the required mix-designs and concrete is supplied to different
locations as per given requirement and mix. An RMC station
has a computerised and fully automatic arrangement for
batching and mixing of ingredients and as many as 100 mix-designs
can be stored in the RMC control panel to produce concrete
for any of them. The consumers – may be a Government
department, a private firm, a building contractor or
even an individual – can exercise their option among
the available mix designs or can handover the concrete mix
design evolved by them.
Cost factor
Reputed foreign companies have gauged the untapped potential
that India holds in RMC field and have established their set
ups here. A plant producing about 30 cu m /hour concrete costs
about Rs 35 to 40 lakh while a plant of 18 cu m per hour capacity
costs Rs 25 to 30 lakh. Taking all costs and taxes into account
including the cost of land, transit mixers, site facilities
like water supply, power supply, offices, stores, testing
laboratory, utilities, roads and approaches, lighting arrangements
etc., the cost of setting up a 30 cu m per hour capacity RMC
plant should be below Rs 40 million if land has been
allotted by the government in the industrial zone at low rates
to promote the industry. The concrete prepared at site and
supplied by RMC plant should be around Rs 2500 per cu m for
M20 concrete after taking in to account the present cost of
cement.
Promoting RMC in India
As the use of RMC can ensure better quality of structures,
its production should be promoted by the Indian government.
To promote its use in India, special tax concessions and holidays
should be announced by the government for RMC industry. Land
should be made available at concessional rates More emphasis
should be laid on setting up of RMC stations for its commercial
supply like any other commodity. Use of RMC can be made mandatory
by the Government departments for major power, irrigation
and other infrastructure projects. Though Indian construction
industry is highly labor-intensive, the scene is changing
now as most of the skilled labour has shifted to Middle-East,
looking for better avenues and labor is no longer cheaper
in India. Under the present scenario, an industrialist
can rest assured that the future belongs to RMC and can diversify
or invest in this field for rich gains.
Indian scene
Scores of RMC plants supplied by various players are presently
operating in India. A survey of construction scene across
the globe shows a complete transformation of concrete
production methods from conventionally followed manual and
semi-mechanised methods to fully automatic and computerised
ready-mixed concrete production. USA is using 75 per
cent of its annual cement production in ready-mixed concrete
through its 3700 RMC plants. Sri Lanka has shown real initiative
by making RMC mandatory for all high rise buildings. In India,
L&T and ACC are two major concerns that have planned installation
of RMC plants all over the country. These two firms have the
capacity to implement their decisions. Present infrastructure
and housing boom is going to augment their plans. At present,
L&T has more than 40 plants in India, producing about
2 million cu m of RMC and there is no stopping. ACC, Birla
and Ahlcon are also engaging themselves whole-heartedly in
production of RMC. Ahlcon has been planning to set up 10 to
12 more plants in Gurgaon, Noida, Ahmedabad and Kolkata.
Indian RMC scene is picking up and RMC equipment suppliers
can encash the opportunity by supplying the equipment at discounted
rates.
* Dy. Chief Engineer Civil, Author, Technical
books and columns, can be reached at
jagvirgoyal@yahoo.co.in
Components of an RMC plant
• Basic structure of the plant.
• Cement silos.
• Aggregate bins.
• Aggregate batching gates.
• Aggregate weighing system.
• Cement weighing system.
• Water weighing system.
• Compressor.
• Turbo mixers.
• Mixer discharge hopper.
• Conveyor for cement.
• Cement feeding hopper.
• Admixture weighing system (if required)
• Unit control board.
• Micro computer control system.
• Transit mixers.
• Water tank.
• Ladders for operator cabin and mixer platform.
RMC Advantages
• Total automation of material-batching and weighing
eliminates under/over-batching or weighing of materials.
• Water cement ratio, the most crucial factor gets maintained.
• Admixtures can be added to concrete with high accuracy.
• A cement saving of 15 to 25 kg per cum of concrete
is certain due to better control.
• Accurate measurements result in a reduction in standard
deviation thus reducing
cost factor.
• Pilferage of material, so much associated with construction
works, gets eliminated.
• There is a significant reduction in wastage of materials
and labor.
• Degree of quality control can be very high.
• Fly ash can be successfully used in production of
concrete.
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