02-02-2013, 10:40 AM
Structural concrete repair – A durability based revised approach is needed
1Structural concrete repair.pdf (Size: 696.69 KB / Downloads: 171)
ABSTRACT
In recent years, durability problems, poor performance,
and, most of all, repair failures have tarnished the
public’s image of concrete. Repair failures and endless
“repair of repairs” make a substantial contribution to
the current perception of concrete. Concrete often gets
a bad name because premature repair failure is one of
the most visible manifestations of poor design decisions
and details, and inadequate field practice.
Concerned with the current state of concrete repair
technology, the author wrote this article in an attempt
to improve the performance of repaired structures. To
do so, the author has analysed some common problems
with structural repairs especially those in coastal regions,
explored issues that must be investigated further and
attempted to provide revised opinions on various
concrete repair issues.
Introduction
Various factors have impeded improvements in the
durability of concrete repairs, including: inadequate
condition evaluation and design; lack of quality
construction practices and quality control; and the choice
of repair materials (that may be incompatible with the
existing substrate). It is necessary to reconsider some
recent developments in structural repairs from the view
point of extending the service lives of structures under
repairs.
Repair materials – What are 'better'
materials?
As we have accelerated the pace of concrete construction,
we have required cement-based materials to become
stronger sooner and to set faster. At the same time,
we’ve increased concrete’s brittleness and reduced its
resistance to cracking. In this attempt, we have damaged
concrete’s “immune system.” Concrete that continues to
hydrate offers increased resistance to aggressive agents.
The “old-time” concrete used to gain strength, density,
and the ability to resist environmental attack over its
service life; “new” concrete does not.
There has been unquestionable progress made in the
field of repair materials. But the material that has the
required properties for a particular application is only
one part of the complex system that makes up a concrete
repair.
Design and field practice
The concrete industry could learn a lot from concrete
repair failures had adequate information been available.
Unfortunately, it seems that only catastrophic structural
failures (resulting from inferior design and poor
quality materials and workmanship) are publicized.
Information about other repair failures, although they
may be serious and extremely costly, is generally not
available. A better understanding of the initial factors
and properties affecting the performance of repaired
structures is critical to the longevity of a repair. Because
data on causes of concrete repair failures do not exist,
let us take a look at the results of various analyses of
damage in concrete construction.2 The British Cement
Association reviewed factors that contributed to the
failure of structures.
Research—problems and
opportunities
Research has substantially improved our knowledge of
cementitious materials, the fundamentals of concrete
deterioration from carbonation-induced corrosion,
chloride-induced corrosion, sulphate attack, alkaliaggregate
reaction, and frost. Several research studies
in the repair field have been concerned with the
improvement of properties of repair materials and
their dimensional behaviour relative to the existing
substrate. But these activities will lead to improvements
in repair durability only if the issues of electrochemical
compatibility are also addressed. Removing deteriorated
concrete (see Figure 2) and replacing it with a repair
material, even with the best one, may result in accelerated
reinforcing steel corrosion due to macrocell formation.
Suggested initiatives
As discussed earlier, a lack of attention to condition
evaluation, design objectives and details, and poor
construction practices cause the majority of faults and
problems in concrete repair field.8,9,10 Unless the designer
and the artisan are skilled at their jobs, the great part of
the money spent in developing improved performance
materials is wasted.
Therefore, it is necessary to approach the improvement
in rehabilitation/repair performance in two stages.
Stage 1 must address the most serious problem at hand
reduction of design and worker errors. The success in this
stage can only be achieved by improved education and
training of all involved in the concrete rehabilitation/
repair process. ACI, ICJ, IBC, ICI, universities, and others
must take the leadership position in achieving this.