This document describes the slipform construction method for building reinforced concrete chimneys. The slipform method involves using hydraulic jacks to continuously lift steel formwork panels, allowing wet concrete to be poured without stopping to form continuous cylindrical shells. As the jacks lift the formwork by 1.5 to 3 meters per day, workers are able to place reinforcement, pour and finish the concrete, and cure the shell in a continuous, 24-hour process. Once the shell is complete, internal platforms and flues are installed along with other finishing work.

2. The purpose of this work is to provide uniform, pre-defined and well
defined
method for the construction of RCC shell in chimney.
Slip formwork system is a system in which the formwork is continuously
raised by
hydraulic equipment namely jacks by 1.5 to 3 Mtrs per day depending on
the rate
of concrete setting. This act of slipping is a continuous process and thus
the name
“SLIPFORM”.

3.  The system uses steel panels of 1M height, which are fixed to working
carcass consisting of steel frames (yokes), the yokes in turn are fixed
to the trusses through spindles. A set of spindles connect the outer
and the inner yokes and a set of spindles connect the yokes to the
shutters.
 Carcass / structural framework provide stability and is a reliable base
for the wooden flooring (consisting of 2”X6”X6’ wooden planks made
from hard wood) used as a working platform for placement of
concrete, movement of reinforcement, etc.
 One hydraulic jack is placed on the lower head beam connecting the
outer and the inner yokes. The jack climbs onto the jack rods that are
fitted through the jack. The jack rods are embedded in the concrete of
the shell through sleeves. The sleeves are fixed to the jacks. After a
certain height the jack rods are recovered by Recovery jacks and the
cylindrical openings left in the shell are grouted.
 The jack consists of a cylinder and a pair of upper and lower clamp
mechanisms gripping the rod and working in cycles.

4.  The principle is that the jack works against the lower clamp to lift
the frame.
 When the pressure is released the upper clamp grips the rod and
the lower clamp is released and come up by spring action.
 Large capacity jacks are usually used with steel tubes of big
diameters and greater stiffness.
 Concreting with slip formwork can be carried out on a continuous
basis, 24 hours a day, or with intervals.
 The slipform has three decks/ working platforms. They are :
i. Upper Deck : Mainly to deliver concrete and fixing
reinforcement
ii. Intermediate Deck : Used for vibration of concrete, adjustment of
spindles and operation and maintenance of
jacks
iii. Lower Deck : Finishing and Curing

5.  Once the shell is completed by the slipforming process, the structural
steel beams and platforms are erected at various levels within the
chimney.
 The flue cans are rolled & fabricated in segments of 2M – 2.5M width
which are brought separately to the inside of chimney on rail tracks.
Three such segments (incase the width of each is 2M) or two such
segments (incase the width of each is 2.5M) are assembled for
installation. They are assembled at the vertical location of their
installation, welded and erected with hydraulic jacks which are
installed on the roof of the chimney.
 After both the flue cans are erected, the mini shell is casted at the top.
The mini shell can be either of RCC with acid resistant lining or of
stainless steel construction with insulation on the outside.
 External platforms, generally, at the rate of 40M intervals of RCC
construction are constructed by workers supported by hanging
platforms through winches.
 All other miscellaneous works like painting, fixing of elevators and
electrical are completed.

12. 24 HRS – ROUND THE CLOCK

14. SHELL CONSTRUCTION(CURING PROCESS)