Frequentlye Asked Questions (FAQs)
Q. What are the advantages of using ready-mixed concrete over site-mixed concrete?
How much is the difference between the cost of ready-mixed and site-mixed concrete?
A detailed answer to the first part of the question is enumerated in the write-up
on “What is ready-mixed concrete?” under the heading Customer Support. Briefly,
the two main advantages of ready-mixed concrete are: vast improvement in the quality
and uniformity of concrete and enhanced speed of construction. Besides, there are
many other advantages which include savings in labour, reduction in wastage, elimination
of material procurement requirements and storage hassles, etc. All these advantages
clearly establish the technical superiority of ready-mixed concrete over site-mixed
concrete. As regards cost, ready-mixed is slightly costlier than site-mixed concrete.
This increased cost is mainly on account of government taxation. It is indeed unfortunate
that a quality product like ready-mixed concrete is taxed in our country, whereas
there is no tax on site-mixed concrete! If tax component is removed, the cost of
ready-mixed would be quite close to that of the site-mixed concrete. However, if
due consideration is given to the higher speed of construction (which is possible
due to use of ready-mixed concrete) the savings on account of early completion of
the project would far outweigh the increased cost of ready-mixed concrete. Further,
the improved quality of RMC would go a long way in enhancing the long-term durability,
thus reducing the maintenance and repair expenses and hence the life-cycle cost
of your structures. In addition, the savings in labour and wastage would also be
available to you. Thus, if you look at the overall advantages and savings, the increased
cost of ready-mixed concrete would appear to be a paltry sum.
Q. Is ready mixed concrete a well established technology?
How long this technology is being used in practice in
Yes, ready-mixed concrete is a well-established technology. It was first patented
in
Compared to the advanced countries,
Q. How do we arrive at the exact quantity of concrete
required at our site?
Your architect/engineers need to work out the grade-wise concrete requirements and
communicate the same to our plant. They are the right people and are in a better
position to decide the quantities required. Concrete is generally specified in terms
of the 28-day compressive strength and workability (usually slump) at placement
point. These two are basic minimum requirements for us to design concrete mixes
for you. We will ensure that concretes in accurate quantity and appropriate quality
are delivered to your satisfaction.
Q. Can we base the measurements of concrete on the simple
L (length) x B (breadth) x H (height) multiplication?
All over the world, the basis of purchase and hence measurement of ready-mixed concrete
is the volume of freshly mixed concrete. The Indian Standard on ready-mixed concrete,
IS 4926:2003 states, “All concrete will be supplied and invoiced in terms of cubic
meters (full or part) of compacted fresh concrete”.
If the measurement is based on the simple L x D x H multiplication, it would be
unfair to the RMC producer as it would not include the wastage and spillage of concrete,
miscalculations in form volume, deflection or distortions of forms, settlement of
wet mixes, over excavation, loss of entrained air, etc. In most of these cases,
the responsibility does not lie with the RMC producer.
Improper excavation is a common site problem. Deflection or distortion of forms
is also quite common. It is observed that if the centre of 150-mm thick formwork
of a slab gets deflected by 5 mm, an increased volume of 3 % would be required at
the centre, decreasing towards the edges. Therefore ready-mixed concrete should
only be measured based on the actual volume of fresh concrete supplied through transit
mixers.
Q. How can we ensure that your transit mixer actually
carries the correct quantity as claimed in your delivery docket?
We are a professionally managed ready-mixed concrete company, operating a fully
automated and computerized batching system with the help of highly motivated personnel
trained to control all process parameters carefully. Production data is automatically
recorded and stored electronically in plant-based computers and can be retrieved
and verified whenever you wish to do so.
Our plant has a weighbridge and all incoming materials are accurately weighed before
being stored. Similarly, transit mixers carrying concrete are weighed from time
to time to verify the accuracy of the material being supplied to various sites.
You may visit our plant with prior appointment and verify the weights of the outgoing
trucks on random basis.
Further, we measure the plastic density of fresh concrete from time to time and
match the same with the theoretical density. In case of any noticeable discrepancy
in the two values, immediate action is taken to rectify errors, if any. Last, but
not the least, our Company has an unblemished reputation of adhering to ethical
practices. Hence, you may safely trust us for your quantities.
Q. How do you guarantee the quality of your concrete delivered
at site?
Our Company attaches immense importance to provide highest level of quality assurance
to our customers. The basic features of the quality systems practiced by the Company
are summarized as below:
Strict control on the quality of all input materials through rigorous in-house or
third-party testing
Stringent process control measures involving thorough inspection, good upkeep of
equipment, monthly scale calibration of weighing devices, etc.
Continuous monitoring of the key properties of concrete in the fresh and hardened
states, including their statistical analysis
Continuous monitoring on all stages of production and supply i.e. order processing,
purchase/control on input materials, concrete mix design, process control, sales,
delivery and statistical quality control.
Modern in-house central laboratory at different locations for testing of concrete
and its ingredients
Active involvement of well-qualified and experienced technical team trained in QA
& QC practices.
Another key feature of the QA system practiced by the Company includes the use of
CUSUM (cumulative summation) technique. The system assists in quick detection of
changes in the properties, and indicates when action should be taken to increase
the probability of meeting the specifications. This early-warning system has helped
us meeting clients’ requirements meticulously.
Q. How can you assure us about the long-term durability
of our structures with your concrete?
Long-term durability of your structures is dependent upon a variety of factors.
Important amongst them are the exposure conditions to which the structure will be
subjected to during service life, structural design and detailing, quality of concrete
and precautions taken during placement, compaction and curing of concrete. A plethora
of research conducted on the topic of durability indicates that permeability of
concrete is the crux of durability and that it is governed by numerous factors such
as water-to-cementitious ratio, mix proportions, properties and replacement levels
of supplementary cementitious materials such as fly ash, silica fume, ground granulated
blast-furnace slag, and the levels of controls exercised during placement, compaction
and curing.
Our strict QA & QC practices will ensure good quality concrete, which will provide
some assurance to you about its long-term durability. In addition, with the consent
of owner/architect/consultant, we do incorporate supplementary cementitious cementitious
material in our concretes to improve long-term durability. However, it well known
that durability is also governed by field practices, and you would appreciate that
these are beyond our control. Correct placement of concrete, its proper compaction
and adequate curing go a long way in ensuring the long-term durability. However,
the responsibilities on these accounts lie within the scope of the contractor.
Q. How the use of fly ash enhances quality of concrete?
How to ensure good quality fly ash?
Fly ash, obtained from thermal power plant in itself does not possess cementitious
properties. However, in its fine form, its particles react with the calcium hydroxide
produced in the hydration process of cement, leading to generation of beneficial
products of hydration. Voluminous research work done throughout the world on the
use of fly ash clearly reveals a number of advantages, leading to multi-level improvements
in the properties of concrete, both in its fresh and hardened states. These mainly
include improvement in workability and pumpability, reduction in bleeding, improved
later-age strength gain and enhancement in long-term durability of structures.
These improvements would happen, provided fly ash used in concrete possesses specific
physical properties and adequate curing is carried out by the contractor. On our
part, we take utmost care to ensure that only good quality of fly ash is used in
production. The physical properties of fly ash as well as its uniformity requirements
are checked from time to time to ensure compliance with the requirements of IS 3812:2003.
As a quick and reliable check, each consignment of fly ash is checked by us for
the % retained on 45 micron sieve. If the requirements are not satisfactory, we
reject the consignment. You would thus observe that on our part, we take utmost
care to provide you a better quality fly ash concrete that is better in terms of
later-age strengths and long-term durability.
Q. During concrete placement operation, how detrimental
it is to detain a transit mixer beyond 30-45 minutes after arrival at site? Why?
One of the important hallmarks of ready-mixed concrete is higher speed of construction.
If this objective is to be realized, it is essential for your contractor to align
his operations to the mutually-agreed schedule of concrete placement. If speedy
production and bulk transportation are not matched by equally speedy placement,
the basic advantage of using RMC would be lost. Placing concrete with the help of
pump would be an ideal solution. In fact, we also provide this service and you can
surely entrust this responsibility on us.
However, pumping is not suitable for all applications. You may have to use other
means of placement. While doing so, kindly ensure that there is least involvement
of manual labour and that our transit mixers are emptied within a span ranging between
30-45 minutes. The IS 4926: 2003 clearly states, “The purchaser should plan his
arrangements so as to enable a full load of concrete to be discharged within 30
minutes of arrival on site”.
Q. How much batch-to-batch variation is allowed in the
slump of concrete that we receive from your plant?
We carry out sufficient number of lab and field trials for various concrete mixes,
which are designed for client-specified slump and compressive strengths. On approval
of the mixes the recipes are finalized and incorporated in the computer-controlled
automated production systems of our plants. Once this is done, there is less likelihood
of any manual error on our part. However, slight variation in slump occurs due to
a host of factors such as variation in the ambient temperature and humidity, possible
delay in transport due to traffic jams, variation in aggregate grading, errors in
sampling and in carrying out slump test, etc. With a view to account for these factors,
the
Q. How much strength do you guarantee in 7 days?
When the 28-day strength is specified, we are responsible and would provide guarantee
for the same. As far as 7-day strength is concerned, we can provide you only the
indicative range of strengths. However, contractually speaking you would appreciate
that we cannot provide guarantee for the 7-day strength. In case you specify early-age
strength, (say strength at 3 or 7 days), we have the capability to satisfy your
requirements; however our quotation for the early-age strength would usually be
higher than that for the 28-day strength.
Q. What is the normal frequency of sampling of fresh concrete?
The IS 4926:2003 recommends that one sample should be taken for every 50 m3 of production
or every 50 batches, whichever is the greater frequency. For an automated production
process having computerized controls, established in all our plants, manual errors
are drastically minimized leading to reduction in batch-to-batch variations; hence
it is not essential to take samples frequently. Many specifications in other countries
specify a much larger frequency of sampling; e.g. the
In addition to having automated and computer-controlled production facility, we
also practice a meticulous QA and QC practice. As a result, variations in properties
of concrete are further minimized. We feel that once you are able to develop certain
level of confidence within our systems, it may be possible for you to specify larger
frequency of sampling. We would welcome this step and extend the necessary co-operation
to you.
Q. Why is it essential to employ trained personnel for
sampling and preparation of test cubes?
Although sampling and test cube preparation are simple methods, the procedures are
operator-sensitive; hence it is essential to employ trained personnel. Take for
example, extraction of a “representative” sample. You know that correct procedure
involves taking four incremental samples from the middle 80% of the load, ignoring
the first and the last 10% portion coming out from the truck mixer and then thoroughly
mixing the incremental samples. Unless workmen are trained in this operation, they
tend to violate the correct procedures. Similarly, standard procedures for making
cube test specimens (filling cubes in layers, tamping each layer 25 times, adequate
protection and curing of test specimens, etc.) tend to get violated on many occasions.
This is mainly because the workmen at site are not trained adequately to do these
jobs. If sampling and cube preparation work are done incorrectly, test results could
be erroneous and the producer may get punished for no fault his own. Therefore,
it is our considered opinion that sampling and cube preparation should be done only
by the trained and experienced personnel.
Q. Do we have to start curing earlier for ready-mixed
concrete after placement?
Irrespective of the type of concrete being used, the curing process for concrete
should commence immediately once the concrete surface looses its sheen, which is
normally within 2 hours after finishing compaction of concrete. Else, it will lead
to plastic shrinkage cracks.
