Civil Engineering Reference
In-Depth Information
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Cost effectiveness, including minimising disruption costs to the users of
the structure
•
Delighting the eye, either restoring to match the original concrete or
providing an overall configuration and finishes to suit the continuing
use.
Cutting out and recasting concrete to be structurally effective is difficult,
time consuming and expensive. Sometimes it is simpler to provide a 'belt and
braces' structural bypass, minimising the cutting out and leaving the original
material to continue to deteriorate. In other circumstances, the complete
removal of the element and recasting of the whole will be simpler, cheaper
and structurally more effective then patching. There can be no standard
rules: the remedial strategy and the detailing must be developed on a case-
by-case basis.
3.2 Why is a full structural concrete repair difficult?
It has been reported by CONREPNET (Tilly and Jacobs, 2007, see also
Chapter 14)
that about 50% of concrete repairs fail within 10 years, but the
fundamental causes of these failures are not fully clarified. These 'repairs',
at considerable expense, have only served to recreate the risk of spalling.
Structural repairs that fail are doubly bad as the cutting out to repair will
have reduced strength, so that when they fail the structure is more seriously
weakened.
When specific repair failures are analysed and related to the properties
of available materials, it becomes clear that a reliable full structural repair
requires:
•
Cutting out to a sound substrate
•
Removal of carbonated or chloride-contaminated concrete from around
reinforcement, unless CP is viable
•
Incorporating additional reinforcement or replacing it internally and/
or externally
•
Supporting the structure while the repair is placed and gains its strength
and stiffness, so that the repair carries a sufficient share of dead and live
load
•
Matching the physical and chemical properties of the repair mix to the
original concrete
•
Placing the repair mix to fully fill the cavity and key and bond to back
and edges
•
Finishing it in a way appropriate to the use of the structure.
