84 CE&CR March 2018
High Performance, High Grade Concrete For Extreme Tall
Structures
TALL STRUCTURE
As the economic capital of India and a megapolis of more than 20
million people, it comes as no surprise that one of Mumbai’s
biggest problems is scarcity of land. As a solution, builders have
opted to build upwards with skyscrapers. A prime example of this is
the
Lodha World One tower in Lower Parel. The tower is slated to be
the
world’s tallest residential skyscraper and will stand at 442
metres in
height, housing over 300 apartments, the structure will use @
800,000
m3 of High Performance Concrete (HPC).
Not just with the World Tower, ever since the 1980s, both the
use
and quality of HPC has increased drastically, which now not only
provides
compressive strengths above 100 MPa but also imparts structures
with
higher tensile strength and better durability, including
resistance to wear
and tear. Additionally, HPC is aimed at efficient use of
resources and its
columns are much smaller than those made using conventional
concrete.
This has been useful in reducing cost of construction,
environmental
impact and achieving increased floor space.
Advantages aside, there are fair share of challenges involved
in
designing extremely tall structures and therefore the HPC
required
for the same. For tall structures the forces generated by wind
and its
behaviour are significant challenges, thus more slender the
structure
greater wind resistant it is. Extreme tall buildings are a
combination of
massive sub structure and elegant slender complex super
structures.
In the case of ‘World One Tower’, Mumbai with a proposed 117
floors
and approximate height of 440 metres to the sky the project
requires
specialised HPC through dedicated RMX plants.
In a never seen before feat in India, World One Tower used a
super structure - a shear wall design based on a grade C95 –M125
of
concrete with a MOE (Modulus of Elasticity) of 48-52 Gpa with
minimal
shrinkage, creep and with vertical pumping above 400 metres.
The
designer had to employ the use of HPC with the above
requirements
because if he were to use standard concrete, the usable space
would be
less and the wind resistance compromised. The big question faced
by all
was whether this kind of a HPC as per the structural design
would have
been possible with the available materials locally. Nuvoco’s
Construction
CE&CR March 2018 85
TALL STRUCTURE
Development and Innovation Centre (CDIC), which specialises
in
search and development activities to develop innovative
solutions
that are specific to the unique requirements of the Indian
construction
industry took on this challenge and conducted a significant
amount of
R & D beginning from raw material characterisation within
economical
ranges, design mixed methodology, which was beyond IS Codes
and
came up with a desired solution as per the client expectations.
The
entire process of development took close to six months, which
involved
very specific tests like Creep, which measures inelastic
deformation
and is conducted only by a few agencies like National Council
for
Cement and Building Materials (NCCBM), IIT’s etc. After
achieving all
the technical details in the lab the big question now was how to
mass
produce and use it in the site to arrive at the desired results.
In house
RMX plant with well articulated and followed QA/QC procedures
and
a motivated staff helped to produce and supply consistent HPC
during
the last five years.
As the floors started rising, the team found that
conventional
pumping systems were not addressing the need. This is where
high
productive static pumps were introduced. But the peculiar
problem of
very high rise pumping still persisted with respect to the
jellification
of concrete in long pumping lines. So, this is when the Nuvoco
team
went back to their drawing board and redesigned the HPC with
lower
viscosity and thixotropic stability, which performed well with
respect
to end productivity and low pump pressure.
The sub structure was massive with a raft measuring five
metres
in height and 13,600m3 of concrete consumed, which was done
in
two layers of M40 and one layer of M60 with concreting
spread
over three days to achieve the desired results. The specially
designed
High Performance Self Compacting Concrete ensured filling of
every
corner of the congested reinforced raft. The main concern with a
big
raft is thermal cracks as concrete is a poor conductor of heat.
The
setting of concrete is a heat generating exothermic process,
which
results in extreme heat in the middle section of the raft. The
use of
pozzolonic (GGBS and Fly Ash) materials, substituting mixing
water
with ice to maintain low concrete temperature, monitoring
every
minute of concrete hydration and proper insulation ensured a
thermal
crack free raft.
While maintaining the plastic and mechanical performance of
concrete it was of utmost importance to look into the durability
aspect
as the project is located in Mumbai, which is under a severe
exposure
condition due to its proximity to coastal belt. A detailed
study with carbonation, chloride attack, and sulphate
attack was undertaken and concrete was designed with
high resistance to the same. To ensure quality assurance
for The World One Tower Project, a stringent continuous
test plan was set up in our laboratories. More than 100
cylinders of C95 are being tested for strength and
modulus of elasticity and so are the regular test for
shrinkage and durability being carried out thus providing
end-to-end solutions.
Mr. Pranav DesaiHead CDIC and Product Development
Mr. Amith KalathingalProduct Development Manager, CDIC
Nuvoco Vistas Corp Ltd. T: + 022 67692595 W: www.nuvoco.in
Grades: M95, M70, M60, M40
Raft: M40, M60
HPC: M95
Core Wall: M95
MOE: 48-52 Gpa
