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.