THE TUNNEL LINING - The Westerschelde Tunnel: Approaching Limits - page 112

Production process

Carrousel system
The production of the segments took place in a so-called carrousel system, in
which the segment 'in the making' went round and passed through various
stages before the segment was labelled 'finished product'. Broadly speak-
ing, the segments passed the following 'stations':
- the production process started with cleaning the formwork and removing
bits of hard concrete and other matter. Points requiring special attention
were the positions of the joints and the protection of the formwork in the
corners and at the bottom of the mould.
- the personnel fitted the mould with built-in parts such as anchors, plastic
screw casings and suchlike and put the mould faces in mould oil. After
this, the reinforcement cage was mounted in the formwork, including
special spacer blocks which would ensure the required covering of con-
crete on the reinforcement.
- at the next station, the concrete was cast in layers. Due to the curved sur-
face of the segments, a special scribe (upper formwork) was required,
which in view of the large surface area of the segments consisted of two
parts which were closed separately.
- after the concrete had been cast, the segment was taken to the heated
'hardening room'. The segment stayed there for at least 8 hours until it
had reached a compressive strength force of 19 N/mm 2 required for the

demoulding.
- after demoulding, the segment, which was covered with a protective foil,
went into storage for a period of at least 48 hours.The foil was necessary
to prevent effects from the outside as much as possible: the development
of the concrete strength had to take place under the most favourable pos-
sible conditions and the foil protected the surface from drying out.

The segment subsequently came on to the finishing line. This was where it
was looked at to see whether there were any holes, damage or air bubbles

Fig. 9.11
The concrete factory