Civil Engineering Reference
In-Depth Information
If a mobile crane is used to handle the segments, the storage yard may be organised
more fl exibly as the crane can negotiate less than absolutely fl at ground. Another
fl exible arrangement is to use a self-loading low loader, which can put down and
recover segments from any spare land around the site, Figure 14.18.
However the storage is organised, it is essential to avoid warping of the segments
which must each rest on a three-point support.
14.3.15 Joints with resin fi ller
When counter-casting was fi rst introduced, all prestressing tendons were housed in
ducts within the concrete section. To avoid the risk of corrosion to the tendons, it was
essential for the joints between segments to be made waterproof. This was achieved
by fi lling them with a suitably specifi ed epoxy resin. This resin offered the additional
advantages of lubricating the joint during the assembly of the segments, avoiding
the risk of points of hard bearing between segments in the event of less than perfect
match casting and eliminating the inconvenience of rainwater dripping through the
top slab or side cantilevers in service. However, in parallel to its advantages, this resin
introduced an additional element of cost and risk into the construction; the integrity
of the deck depends on the correct specifi cation and use of the resin.
The end faces of the segments are lightly sand-blasted to remove surface laitance to
optimise the bond of the resin. However this sand-blasting must be carefully controlled,
as if it is overdone, the perfect match of the two surfaces will be lost.
The two-part resin requires mixing immediately prior to its application. Generally,
the two parts have different colours so that it is clear when mixing is complete. It
Figure 14.18
East Moors Viaduct: segment transport by low loader (Photo: Benaim)
