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