Civil Engineering Reference
In-Depth Information
coating towards the end of the project, it was imperative that a good bond
was achieved between the coating and the fabric.
Various methods are available to achieve this: simply scattering a suitable
fine aggregate onto the wet resin to form a mechanical key, or alternatively
using peel ply. Peel ply is a relatively inexpensive material that is placed
onto the wet resin prior to curing. When the contractor is ready to apply
the coating system he simply removes the peel ply. The advantage of using
the peel ply in this situation is that it keeps the area clean; there is no need
to wash the surface down if it has been left for a number of weeks. The
mechanical key is already formed by the peel ply being pushed into the wet
resin.
As already mentioned the Kevlar was coated with a cementitious flexible
coating. The reason for this, apart from aesthetic reasons, was the protection
it afforded to the installation as well as the structure. All the resins used in
the wet lay-up system were based on 100% solid epoxy components. Epoxy
resins are, however, susceptible to eventual degradation if not protected.
The advantages of using Kevlar on this particular project were: speed of
application; toughness and durability - Kevlar is very resilient to abrasion
whereas carbon is a very brittle material that would wear very quickly in this
environment; finally, the drapeability of the material in the way it adapted
itself to the shape of the structure.
The structure has now been in operation for several years and there have
been no problems reported as to the functionality of the materials.
16.6 Rhuddlan Castle, North Wales
This is a good example of where newer technology has been used. Rhuddlan
Castle is an ancient listed structure (
Figure 16.6).
The requirements for this
project were for the stabilisation and stitching of the masonry back together.
Owing to the strengths required by the designer, a high modulus carbon
fibre bar was used. To help with the adhesion properties of the carbon fibre
bar, it was coated at the time of manufacture with a peel ply finish, which,
when removed prior to application, gave a very good mechanical bond. The
mortar beds were raked out and the carbon bar inserted into the formed
channels.
16.7 Trenchard Street multi-storey car park, Bristol
The adhesive used to fix the bars in place was based on 100% solid epoxy
resin; although this resin is more of a putty-like consistency than the resins
used in the wet lay-up systems such as the projects at West Burton Power
Station and Harbour City MSCP.
BASF Construction Chemicals have had similar success in Europe
using carbon bar. Examples of NSM (near-surface mounted) bars are now
commonplace. This application tends to be in areas where seismic problems
