VISHAKHAPATNAM STEEL PROJECT
"CICO *Plast AP &
"CICO"
The ideal Admixtures for Chimney
Construction by SLIPFORM METHOD
Project Work requirement
The Chimney for coke oven and by-products
plant of Vizag Steel Plant was to be constructed using SLIPFORM method.
Compressive Strength of
Concrete
The drawings and specifications for this
Chimney called for 28 days compressive strength of concrete as 300 kg./sq.cm.
Exhaustive Tests
Undertaken
To achieve the above specifications
exhaustive tests were carried out by Indian and imported, having seven days compressive
strength of 400 kg./sq.cm.
The High Compressive Strength of Concrete
Meant Use of Low Water Cement Ratio.
The concrete mix ultimately used has been
with a water cement ratio varying from 0.38 to 0.40.
The Placement Conditions
Laid Down
The concrete at the time of placement had to
be plastic and had to have a good workability. The placement conditions required that the
concrete should have a slump varying from 80 mm to 130 mm.
CICO
Mix-Design Achieves Required Specifications
The mix-design finalised provided for 120
mm/150 mm slump using "CICO *PLAST-N" Concrete Plasticiser and Water Reducing
Admixture and "CICO PLAST-R" Retarding Water Reducing Admixture and Concrete
Placticiser.
CICO Got Involved To
Obtain The Result
The high compressive strength of concrete,
its homogeneity, plasticity and workability to the extent of 150 mm slump was achieved by
use of CICO *PLAST AP water reducing admixture @1% by weight of cement. This gave the
desired workability at low water cement ratio due to its water reducing properties.
Addition of CICO *PLAST AP made the placement and compaction of concrete easier.
CICO *CN_PLAST Was Used
For Construction Work Upto 16 Metres Height From Ground Level
The Exposure Time i.e. the time by which the
concrete surface of the chimney shell could be exposed was based on the time, the concrete
took was based on the time, the concrete took to attain a strength of about 10 kg. to 35
kig. per sq. cm. Addition of CICO *CN-PLAST admixture provided 16 to 18 kg. per sq.cm.
strength after 5 to 6 hours. Accordingly the exposure time of the concreted surface of the
chimney was designed to be 5 to 6 hours. Any delay beyond this time limit would have
resulted in DRAG in the concrete shell while the slipform was being raised.
Limitation Of Concrete
Transportation Units Poses A Problem
There was just one concrete transporting unit
available for the chimney construction work. Using this unit it was available to maintain
6 hours exposure time for a height upto 16 metres from the ground level. But for height
above 16 metres greater time was required from mixing point. Exposure time gradually
started increasing.
The Solution
The solution out of this problem was to use a
Retarding Plasticiser Admixture, which would not only retard the setting time of the
concrete, but would also give the concrete mix the required homogeneity, plasticity and
workability, at the time of placement. The admixtures had to help maintain high slump for
a longer period of time, with low water cement ratio.
CICO PLAST-R - THE PROBLEM
SOLVER
To solve the problem faced during
construction work of chimney for height above 16 metres from ground level, CICO
RETARDPLAST retarding Water Reducing Admixtures and Concrete Plasticiser @ 1% by weight of
cement was used which gave the desired results. due to the retardation property of CICO
RETARDPLAST, the concrete strength of 16 to 18 kgs. per cm2 i.e. the required strength at
which concrete could be exposed was achieved after 10 to 12 hours. This increased time
availability between mixing and placement of the concrete, the construction work of the
chimney for heights above 16 mts was so organised that the exposure was done atleast
within 12 hrs of the mixing.
*CICO PLAST AP
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