MOULDS:-
There are three types of inner mould for casting of segments.
(a) Pier Segment Mould
(b) Intermediate Segment Mould for segment S2
(c) Intermediate Segment Mould for remaining segments
Each mould comprises 3 major components – Outer Shutter, Bottom shutter and Inner shutters. Bottom Shuttering is supported on casting bed pedestals. Outer shutters are supported on a Movable Trolley.
BOTTOM SHUTTERING
Bottom Shuttering is supported on 3 rows of concrete pedestals. Bottom shuttering is fabricated in the form of panels of 7.8m x 1.25m sizes.
Bottom Shutters shall be fixed for all segments on the Long Line casting bed.
SIDE SHUTTERS
Side shutters are mounted on a movable trolley. Each Long Line casting bed shall have two such moulds so that two intermediate segments are cast simultaneously, one from either side.
SEQUENCE OF CASTING
A long line bed shall be provided wherein width of bed shall be 7800mm. In a typical casting sequence two pier segments (which shall be cast separately on pier segment bed) shall be brought and placed on bottom shutter on either side of long line bed. Two intermediate segments are match cast simultaneously, starting from either end. Subsequent to casting of S2, S3 is match cast. This procedure is continued till 2 segments are balance. The last segment of the span is match cast between 2 segments. The other shutter is used to start the next span from the pier segment.
REBAR JIG
Three Rebar jigs for intermediate segments and one Rebar Jig for pier segments shall be fabricated to meet the requirement of 40mm clear cover from all sides of concrete surface.
REBAR CAGE
The rebar cage shall be cut & bent by using cutting & bending machine at the centralized reinforcement yard adjacent to the casting yard.
The cage shall be lifted with a structural frame holding the cage in a manner to prevent any distortion while lifting and placing in position inside the casting mould.
The cage shall be lifted and placed in the casting mould by the 20T capacity Goliath Crane
CONCRETING
The sequences of concrete shall be as follows:-
1) Soffit Slab
2) Half height of Web – 1
3) Half height of Web – 2
4) Half height of Web – 3
5) Remaining Portion of Web – 1
6) Remaining Portion of Web – 2
7) Remaining Portion of Web - 3
8) Deck Slab including Cantilevers on both sides
The concrete of M-45 grade with a slump of 80mm to 120mm shall be produced at the centralized Batching plant, and transported to location by transit mixers. The concrete shall be placed in sequence mentioned above by concrete pump. The concrete shall be vibrate by both shutter vibrators fitted to the web shutter as well as needle vibrators (60mm dia needles). Cubes in required number shall be cast from respective concrete pours. Roughing of deck slab of the segment shall be done in required locations were secondary pour is to be carried out.
For separation of match-cast segment a suitable bond breaking material (such as Concure WB from Forsroc) shall be used on the surface of previously cast segment.
FIXTURES IN SEGMENT
All other fixtures such as drainage spout etc. shall be provided at specified locations as detailed in the drawings.
CURING OF SEGMENTS
Curing of concrete shall be complete and continuous with water. Curing will be done for 14 days from date of casting. As an alternative, the segments can also be cured by applying curing compound duly approved for use. After casting the segment curing compound shall be applied on all exposed surface after initial set is achieved and the surface is moist and free surface water has disappeared from concrete surface.
DESHUTTERING
The shuttering shall be removed after the concrete has attained 20 Mpa crushing strength.
The internal forms shall be collapsed using the turn buckles provided for movement of shutter.