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Vol.2, No.1, January - March 2015
Company News.............................................................1,7Around the world.............................................................2Concrete Innovations & Trends..................................1,3,4Forum.......................................... .................................5,6Mail Box...........................................................................8
(Continued on page no.7)
Now-a-days, it is not uncommon to construct
foundations and other massive elements for tall
buildings, bridges and other structures requiring single 3concrete pour exceeding say 500 m . A designer always
prefers to have reduction in the number of joints as the
provision of joints involves delay in construction with
consequential increase in cost and also because of the
practical difficulties in forming fully-effective joints. Further,
from long-term durability perspective, less number of joints
(or for that matter no joints at all!) is certainly preferable.
The density of the conventional concrete generally varies 3from 2350 to 2600 kg/m . Concrete having an oven dry
3density in excess of 2600 kg/m is termed as heavy
weight concrete. Such concrete can be advantageously
used in two main applications. Firstly for radiation
shielding as the high density slows down and absorbs
the energy released. Secondly, the high mass to volume
ratio is useful as a ballasting and dead-weight
counterbalancing.
Mix proportioning, production and placement of
heavyweight concrete requires special expertise. RMC
Readymix (I) has developed a special product, named TMas Highdensecrete , catering to the needs of the
customers.
TMHighdensecrete for a hospital in Mumbai
(Continued on page no.3)
Company News
Concrete Innovations & Trends
Recently, this product was supplied to a reputed hospital in TMMumbai. The hospital authorities used Highdensecrete for
the construction of 375-mm thick walls for radiation
shielding.
TMUsing hematite aggregates, Highdensecrete was 3designed to achieve a density of 3500 kg/m and the 28-day
compressive strength of 30 MPa. Initial trials were done in the
laboratory and once the customer was satisfied with the TMproperties of concrete, Highdensecrete was transported in
a transit mix to the hospital and placed into the forms. A
slump of 150mm was achieved at the placement site and
there was no segregation in the mix. Before each delivery, the
density of concrete was measured to the satisfaction of the
customer.
Estimating Peak Temperature in Mass Concrete
PCA Study confirms higher solarreflectance of concrete
Concrete does a very good job of reflecting solar energy, confirms a study by the Portland Cement Association (PCA) which measured the solar reflectance index (SRI) of 45 concrete mixes.
Lighter coloured materials (such as concrete) generally have a higher solar reflectance. They reflect heat from the sun and do not warm the air very much. Darker surfaces such as black roofs and dark pavements generally have a low solar reflectance. They absorb heat from the sun and warm the air through convection, which is generally considered undesirable for its effect on the environment. This may have an immediate, local effect, like heat gain in urban areas, commonly known as 'heat island' effect.
The PCA SRI study measured the solar reflectance of 45 concrete mixes in accordance with ASTM C 1549, Standard Test Method for Determination of Solar Reflectance Near Ambient Temperature Using a Portable Solar Reflectometer. These concretes were selected because they represent the range of concrete and concrete constituents typically used in exterior flat work in the United States.
Solar reflectance (sometimes called albedo) is the ratio of solar energy that falls on a surface to the amount reflected. It is measured with a solar spectrum reflectometer on a scale of 0 (not reflective) to 1: (100 percent reflective). Generally, materials that appear light-coloured have high solar reflectance and those that appear dark-coloured have low solar reflectance. The study revealed that all 45 concretes tested according to ASTM C 1549 have a solar reflectance of at least 0.3 and an SRI of at least 29, and meet or exceed LEED requirements. Regardless of mix constituents, concrete in the United States reduce heat islands and qualify for points in the LEED Green Building Rating System.
Earlier study by the CTL Group, USA, on different concrete mixtures representing exterior concrete flatwork (published in Concrete International) showed that the solar reflectance of the cementitious materials has more effect on the solar reflectance of the concrete than the other constituents. While the solar reflectance of the fine aggregate has a small effect on the solar reflectance of the concrete, that of the coarse aggregate does not have a significant effect. With mixtures including fine aggregate consisting of crushed limestone, average solar reflectances of at least 0.64 (an SRI of at least 78) can be obtained using ordinary Portland cement and light-coloured slag cement or using white cement alone. Solar reflectances ranged from 0.34 to 0.48 for mixtures consisting of ordinary Portland cement and dark gray fly ash.
(Source: PCA News and Concrete International)
Haulage weight of transport vehicles
increased in Austria
Recently, Austrian Parliament has unanimously voted in favour of an increase of total weight of 4-axle vehicles circulating on the Austrian road network, from 32 to 36 tons.
This decision of the Austrian National Assembly will go a long way in reducing CO emissions on Austrian roads and will 2
also help in reducing traffic.
The Stone and Ceramics Industry Association and the Ready-Mixed Concrete Association of Austria welcomed the unanimous decision of the National Assembly.
The Austrian ready-mixed concrete producers are a deeply regionally-anchored and mostly owner-managed industry. These are primarily small and medium-sized companies and create jobs in often structurally weak regions.
"By strengthening these companies, it also strengthens the regions in a sustainable way and secures jobs", says Peter Neuhofer, President of the Austrian Ready-Mixed Concrete Association. "Moreover, this new regulation will lead to a reduction of up to 200,000 trips per year and a significant decrease of traffic."
Source: Fachverband der Stein- und keramischen Industrie
Regulatory issues in Quarrying in Australia
Cement Concrete & Aggregates Australia (CCAA) is the industry body for the heavy construction materials industry in Australia. CCAA recently commissioned a study by the Centre for International Minerals and Energy Law (CIMEL) at the University of Queensland Law School (internationally renowned as a leading centre of knowledge in resource law) into the legal and policy frameworks for the extractive industry in Australia. The study report concludes,
“the current regulatory framework for access to and the supply of aggregates in Australia is not optimal and that the regulatory system for the extractive industry is likely to struggle significantly in the future to meet increased demand for aggregate due to increases in population significant infrastructure projects.”
These conclusions are also similar to the 2014 Productivity Commission report on Public Infrastructure in Australia which noted the raft of social and environmental regulation affecting quarries, some of which may impose undue costs and restrict supply. It noted that a failure to allow new quarry developments or expansions, particularly close to cities,“could lead to future scarcity of some key inputs into many infrastructure projects”.
Sounds familiar? Are the Regulatory authorities in India listening?
Source: Policy Priorities for Australia's Extractive Industry, CCAA
Around the World
While these advantages of large volume concrete pours
are obvious, their successful execution demands
attention to specific technical requirements. The most
important technical requirement is to control the risk of
early-age thermal cracking. The risk mitigation exercise
generally includes a variety of provisions such as
appropriate selection of concrete mix ingredients and
their proportions, control on temperature profiles in fresh
and hardening states of concrete, insulation or cooling
of cast elements, etc.
Incidentally, it is observed that the risk of early-age
thermal cracking also exists in deep lift construction, for
example, in walls, deep beams and large-sized
columns. Neville reports that
mass concrete temperature
prof i les are observed in
concrete elements that are only 10.5-m thick ! Many of the deep
lift constructions that are being
done today are more than 0.5-m
thick. Thus, it is highly essential
to take proper precautions while
designing and constructing
concrete elements using large
concrete pours and deep lift
constructions.
With a view to control the risk of
thermal cracking, codes and
standards do not specify the
exact value of the lowest
p o s s i b l e p l a c e m e n t
temperature for mass concrete.
Some guidance on initial
c o n c r e t e p l a c e m e n t
temperature is available in the
standards on hot-weather
concrete. For example, ACI's guide on hot-weather
concrete (ACI 305R-10) recommends the initial concrete
placement temperature should be limited to 24-38°C,
depending on the placement conditions. The Indian
Standard on Extreme Weather Concreting, IS 7861,
suggests to maintain the placement temperature below 040 C.
For mass concreting some consultants and concrete
technologists specify much lower limits. Although there 0are cases in India where around 20 C placement
temperature was specified and achieved in actual
practice, a number of practical difficulties exist in
achieving lower temperatures. It is well known that
replacing ordinary Portland cement with supplementary
cementitious materials (SCMs) like fly ash, blast-furnace
slag, metakaolin, etc. reduces the heat of hydration.
However, there are code-specified restrictions on the level of
percentage replacement of ordinary Portland cement by
SCM and the mix designer also needs to take into account
the early-age strength requirements. The use of cold water
and ice flakes are effective in reducing the placement
temperature. In particular, use of ice flakes as a part
replacement of mixing water is quite effective in bringing
down the placement temperature.
However, storing and dispensing of ice involves certain
operational difficulties. RMC Readymix (India) is able to
overcome all such problems
and has been producing a
special product, named as TMThermocrete , catering to the
specific placement temperature
requirement of its client.
Here, it must be stated that
engineers and contractors need
to understand that there is cost
involved in reducing every
single degree of the placement
temperature. Restricting the use
of supplementary cementitious
materials or specifying the limit
on the percentage replacement
of OPC may not lead to cost-
effective and technically-sound
solution. Further, wherever
possible the minimum 28-day
compressive strength criteria
need to be replaced with say 56-
day or even 90-day criteria
(especially for foundations).
In addition to placement temperature requirement, two other
temperature-related parameters are equally important in
mass concrete and deep-lift applications. The first relates to
the maximum allowable temperature gradient and the
second to the permissible peak temperature within the
concrete mass. As regards the former parameter, there
seems to be a broad agreement amongst concrete
technologists that maximum temperature difference
between the hottest portion and the surface of the concrete 0should be limited to 20 C to avoid possible internal cracking.
Strict enforcement of this requirement becomes the
responsibility of the contractor who needs to devise a
suitable insulation regime. Further, the removal of insulation
(Continued on page no.4)
Concrete Innovations & Trends
(Continued from page no.1)
ThermocreteMix with the Best
Beat the Heat
(Continued from page no.3)
and formwork need to be based on temperature
monitoring with the help of thermo-couples inserted in
the concrete mass at suitable levels and locations. It is
heartening to note that a few leading contractors in India
have started adopting such practice.
The second important factor is to estimate the peak
temperature within the body of the concrete mass. ACI
310 on structural concrete limits the maximum 0temperature in concrete to 70 C to minimize concerns
due to a phenomenon known as Delayed Ettringite
Formation (DEF). It is observed that high temperatures
during hardening of concrete may inhibit the normal
formation of ettringite, resulting in both sulfate and
alumina being encapsulated in the rapidly forming inner
calcium-silicate-hydrate (C-S-H). Later, in the long run,
the sulphate and aluminate absorbed by the C-S-H are
released into the pore solution of the hardened cement
paste and form ettringite. This ettringite tends to grow in
small, confined spaces, and as it expands, it leads to
very significant pressures that cause the concrete to
expand and crack. Therefore it is essential to control the 0peak temperature of concrete below 70 C.
For arriving at the temperature profiles at different
intervals including the peak temperature, experts can
conduct a complicated thermal analysis with the help of
finite element analysis in combination with cement
hydration model. However, from practical perspective,
ready-mixed concrete producers need to have a rough
idea of the possible peak temperature when designing
their concrete mixes. With this in view, a researcher from
Europe has recently developed an innovative
Nomogram (Fig 1) which enables quick and reliable 2estimation of peak temperature in concrete .
The procedure of obtaining the estimate of peak
temperature from the nomograph is simple. The inputs
required for this purpose are: cement type, unit mass of
total binder content, effective percentage of SCM,
element thickness, initial concrete temperature, and
average ambient temperature. Amongst these inputs,
finding out the effective percentage of SCM requires the
use of equation which is included in the paper.
The nomogram is validated with field data and it was
observed that the prediction error was of the order of only 04 C. The nomogram was evolved for European cement
CEM I 42.5. The author has however developed graphs
to find out corrected values for CEM I 32.5 and CEM I
52.5 cements. Thus, the nomogram is indeed a good
tool for the ready-mixed concrete producers for quickly
Concrete Innovations & Trends
2Fig 1 Nomogram for estimating peak temperature in concrete
arriving at the desired peak temperature by making suitable
adjustments in the mix proportions.
Can we use this nomogram in India? The answer to this
question is – not in the present form! This is mainly because
the hydration kinetics of Indian cements may be different
from those of the European varieties. Secondly, we observe 0
that in India the ambient temperature Ta goes above 40 C 0reaching around 45 C or even more at some locations and
the specified initial concrete temperature Ti also exceeds 0 030 C, going up to 35 C. Therefore, the boundary conditions
in the current nomogram need to be accordingly extended.
We suggest that attempts should be made to develop a
nomogram suitable for Indian cements and the higher
ambient temperature prevailing in India. Possibly, the
academics in India can a take a lead in this direction and
develop nomogram suitable for indigenous materials and
conditions. RMC Readymix (India) would be pleased help
this process by participating in the authentication of the
developed nomogram.
References
1. Neville A. M., Properties of Concrete, fourth edition, John Wiley &
Sons Inc., London, UK, 1996.
2. Wilson Ricardo Leal da Silva and Vít Šmilauer, Nomogram for
Maximum Temperature of Mass Concrete, Concrete
International, May 2015, pp. 30-36.
Aggregates used in concrete are generally inert in
nature, in that they will neither react chemically with
cement in a harmful manner nor be affected chemically
by normal external influences. However, sometimes
certain naturally occurring aggregates contain some
active mineral component which can react with alkalis in
concrete, mainly derived from cement. The chemical
reaction between alkali hydroxides in concrete and
reactive component of aggregate is termed as Alkali-
Silica Reaction (ASR), resulting in the formation of an
alkali-silica gel which has a tendency to absorb moisture
and swell. This may result in abnormal expansion and
cracking.
The draft revision to IS 383 on aggregates from natural
sources, which was recently available for wide
circulation, includes separate clauses of ASR and also
specifies the accelerated mortar bar test. It would be
appropriate here to provide broad background
information on the subject and also acquaint readers
with the new IS draft provisions.
Worldwide, ASR is one of the major phenomena of
deterioration affecting concrete structures. Fortunately, it is
not as widespread as other deterioration phenomena, like for
example, corrosion of reinforcement in concrete. However,
when ASR occurs, the adverse effects of disruptive
deterioration of plain and reinforced concrete are quite
serious.
Generally ASR is caused by siliceous minerals like chert,
chalcedony, opal, etc. which could occur in quartzose,
opaline cherts or siliceous limestone and volcanic rock.
Presence of strained and microcrystalline quartz in some
aggregates may also be reactive leading to ASR.
With the rapid depletion of known “safe” clusters of
aggregate sources the concrete industry is now constrained
to exploit unknown sources of aggregates. Simultaneously,
in view of the constraints of energy savings in the production
of cement, it is quite likely that the total alkali content in
cement may sometimes cross the threshold limit. Thus, the
risk of ASR cannot be underestimated.
Forum
Assessment of Aggregates for Potential Alkali-Silica Reaction
(Continued on page no.6)
TM TM TM TMAquaresistcrete •Coastcrete • Dyecrete • FoundationcreteTM TM TM TMEasycrete • Enviroprotectcrete • Elitecrete • Portacrete
TM TM TM TM FRCcrete • Highdensecrete • Megacrete • XpresscreteTM ® TMPerviouscrete • Readyplast • Thermocrete
RMC Specials
Besides ASR, there is another kind of harmful reaction
known as alkali-carbonate reaction (ACR) which occurs
between alkalis and argillaceous dolomitic limestone.
ASR is more widespread than ACR. Both ASR and ACR
are classified under the broad category of alkali-
aggregate reaction (AAR).
It is widely recognised that damage due to AAR can
occur and be sustained only if three basic conditions are
satisfied - first, sufficient alkalis are present in concrete;
second, aggregates contain an alkali-reactive
component; and third, sufficient moisture level is
present within the concrete. The source of alkalis in
concrete could be either from the cement, from alkali-
bearing aggregates used in the concrete, or from
external sources. The moisture level required for the
reaction to occur needs to be of the order of over 80-85
percent of relative humidity. Under dry conditions, there
will be no scope for the reaction to get initiated. There are
examples where ASR-affected aggregates used in
outdoor exposure conditions have shown early signs of
deterioration, but the same aggregates when used in
indoor exposure conditions proved innocuous for a long
time. High ambient temperature is also one more
causative factor. Some aggregates which are relatively
not-so-reactive may show deleterious expansion at 0temperature above 40 C.
Testing for ASR
Past reliable field performance of the aggregates in
existing structures is considered a reliable yardstick in
selecting the source of aggregate for any new
construction. However, if such information is not readily
available laboratory testing of aggregate becomes
essential. IS 4926 on ready-mixed concrete specifies
that testing for potential alkali-aggregate reactivity
including petrography should be conducted at a 5-yearly
interval or when there is a change in the source. A
number of test methods including the conventional
mortar-bar test method are available to verify the
potential reactive aggregates. However, what is
important is to select test methods that are rapid,
reliable, simple and reproducible.
In this context, the revised draft IS 383 provides a good
guidance. The best initial practice would be to carry out
the petrography analysis of aggregates to identify
presence of reactive materials. The IS 2386 (Part 7)
specifies two more tests, namely the chemical method
and the mortar bar method. The chemical method is
quicker; however it is not found suitable for slowly reactive
aggregates or for aggregates containing carbonates or
magnesium silicates. The mortar bar method takes
excessively longer time to get results. The code suggests
that the length change measurements should be taken
periodically at the ages of 1, 2, 3, 6, 9 and 12 months, and if
necessary, at an interval of 6 months thereafter.
The revised draft of IS 383 therefore specifies an accelerated
mortar bar method which requires 16 days and which is
specially found suitable for slowly reacting aggregates. A
comprehensive criteria for qualifying the aggregates as
innocuous has been developed for this test.
One business vertical of RMC Readymix (I) is involved in the
aggregate mining, processing and supply of aggregates.
The Company has been taking care to ensure that the
aggregates supplied by it meet the specifications of various
tests (including the test on evaluating potential alkali-
aggregate reaction) specified by the Bureau of Indian
Standards. A typical third-party test report included in Fig 1
shows that aggregates samples from of the aggregate-
processing plants belonging to the Company was found to
be innocuous. In addition, the Company will be pleased to
share data on the new ASR test viz. accelerated. Mortar bar
test specified in draft IS 383, whenever demanded by the
customers.
6
(Continued from page no.5)
Fig 1 A typical test report showing that aggregates samples from one of the plants belonging to RMC
Readymix (I) was found to be innocuous
Forum
TMEasycrete at Raipur
A developer in Raipur wanted to construct the compound
wall of his housing project without any horizontal joint.
RMC Readymix (I) approached the developer with a TM
proposal to construct the wall with Easycrete and the
same was accepted.
(Continued from page no.1)
mpo aC ny NewsCompany News
does not get affected adversely. Also, the need of carrying
out prolonged curing was impressed upon the contractor .
Further, as against the 28-day compressive strength of 34
MPa specified by the designer, the actual value of strength
obtained was 42 MPa. Further the concrete has developed
and attained a compressive strength of 58 MPa at 56 days.
7
TMThe work involved designing M25 grade Easycrete . This
was done to the satisfaction of the customer. The
standard tests on the fresh concrete such as slump flow,
U box, L box etc. were conducted as a part of the initial
laboratory work.
The thickness of the wall is 230mm and height 2.4m.
Besides achieving a good jointless external finish, the use TM
of Easycrete also helped in completing work speedily.
TMFoundationcrete for a Residential Tower
in Chennai
It was pointed out in the TechBeat issue (Vol. 2, No 4) that
site engineers are required to face two major challenges
in the construction of massive rafts. Firstly, it is essential
to ensure that concrete fully encapsulates the congested
reinforcement and flows easily to all corners of the raft.
Secondly, effective measures are needed to mitigate the
adverse effects of high heat of hydration generated
within the large concrete mass. With a view to meet the
above challenges in a satisfactory manner, RMC
Readymix (India) has developed an innovative special TMproduct – Foundationcrete .
Recently, one of the leading builders in the country TMutilized Foundationcrete for the construction of a large
raft foundation in the central core area of his multi-3storeyed residential tower in Chennai. A total of 2,900 m
TMof Foundationcrete was supplied. While supplying this
concrete it was ensured that the fresh concrete
properties like slump-flow, density, temperature
matched with those specified. Proper precautions were
taken to ensure that the final setting time of concrete
Fig 1 Congested reinforcement in the raft foundation
TMFig 2 Foundationcrete after pouring in raft foundations
Students Visit Lab and RMC Plant
During the month of April a large section of students from
engineering colleges and polytechnic visited the NABL-
accredited laboratory of RMC Readymix (I) as well as the
Ghatkopar plant. Students from following colleges
participated in the industrial visit:
• K. J. Somaiya Polytechnic, Vidyavihar on April 6, 2015
• Sardar Patel College of Engineering, Andheri, Mumbai, on
April 10, 2015
• Saraswati College of Enigineering Kharaghar on April 14,
2015
Students were briefed by Mr. Uttam Bhandare and Ms. Aarati
Prabhu. A large number of students informed the company
officials that they were immensely benefited from the visit to
the plant and laboratory.
Q. : We are a Mumbai-based organization and have obtained concrete from your Company
in the past. We recently learnt that your Company's Laboratory at Ghatkopar received NABL
accreditation. While we congratulate you for this achievement, what are the advantages of
this accreditation for a customer like ours?
A.
accreditation recently under ISO/IEC 17025:2005 in the field of mechanical testing of aggregate, cement and concrete. In
fact, RMC Readymix (India) has the distinction of being the first ready-mixed concrete manufacturer in Mumbai region to
have acquired the NABL accreditation for its laboratory. The Company's incessant quest for technical superiority has
helped us in achieving this milestone. National Accreditation Board for Testing and Calibration Laboratories (NABL) is an autonomous body under the aegis of
Department of Science and Technology, Government of India, and is registered under the Societies Act 1860. NABL
accreditation provides formal recognition of competent laboratories, thus providing a ready means for customers to get
reliable testing and calibration services in order to meet their demands. The certification also means that systematic
procedures given in relevant standards are followed in the working of our laboratory and records are maintained properly.
The laboratory functioning and record keeping are subject to regular audit by the NABL authorities.
For a customer like you, buying concrete from a plant having NABL-accredited lab certainly means a higher level of quality
assurance. With NABL accreditation to our lab, we are of the opinion that there is no need to test samples of our concrete
either in your lab or in a third-party lab. While the slump testing and cube filling operations can be done by our
representative in the presence of your authorized site personnel, you are most welcome to send your representative to our
lab on the day of compressive strength testing to witness the test. Your representative can also witness the procedures of
different tests followed by our lab personnel and the efforts we pursue in maintaining the NABL accreditation.
We may also mention that our Ghatkopar plant is also certified by the Quality Council of India (QCI) under its Production
Control Scheme. Under this scheme we are required to conduct selected tests on concrete and its ingredients at regular
intervals as specified under various BIS Standards.
In addition, we are also required to get the
ingredient testing verified from a third-party lab
once in six months. Thus, stringent testing regimes
under the QCI and NABL certification provide you
double assurance about the quality of our
products.
Incidentally, a variety of testing services of our
NABL accreditated laboratory would be available
to you commercially, even when you are not
obtaining concrete from our Company.
It may be mentioned that the laboratory attached to our Whitefield Plant in Bangalore received NABL accreditation last year.
We have plans to undertake NABL accreditation for some more labs attached with our plants in near future – all this with the
objective of enhancing customer confidence.
We thank you for your compliments. Yes, our Company's central laboratory in Ghatkopar received the prestigious NABL
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Inside view of NABL accreditated lab at Ghatkopar
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