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Indian Concrete Journal, 69, 3, p. 165, 1995-03
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Uncertainty in concrete repair and restoration
Mailvaganam, N. P.
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U nc e rt a int y in c onc re t e re pa ir a nd re st ora t ion
N R C C - 3 8 8 1 3
M a i l v a g a n a m , N . P .
M a r c h 1 9 9 5
A version of this document is published in / Une version de ce document se trouve dans:
Indian Concrete Journal, 69, (3), pp. p. 165, March, 1995
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Current techniques and practices for concrete rehabilitation are largely bor-rowed from those of new construction. Rehabilitation and new construction, however, differ from each other in sev-eral respects, including project scale, technology management and financing. The use of proper technical and admin-istrative procedures in repair and resto-ration are critical to success, yet these procedures are not well defined by cur-rent codes and standards.One of the challenges in repair and restoration work is to accomplish it safely and efficiently so that the facility can still be used. This operational reality may dominate technical, scheduling and logistic considerations. Further-more, the repair location is typically confined or cramped, and may be inac-cessible to work crews using standard construction equipment and technol-ogy. Ifthe work must be done during off-peak hours, scheduling and quality control are affected.
Designers can make the greatest con-tribution to minimise the cost and dis-ruption associated with maintenance and repair. However, at present, their contribution is not as effective as it
should be in this domain because of
their failure to appreciate the interre-lated causes of concrete degradation
and the complexity of the repair proc-ess. These causes of concrete degrada-tion include unsatisfactory detailing, incorrect selection or specification of materials, components and systems, and a lack of understanding of how a structure will be used and maintained.
Concrete repair requires a wide range of materials with different physi-cal and chemiphysi-cal properties, and appli-cation techniques. Compatibility with the original substrate, ease of use in a wide variety of situations, and struc-tural considerations are all crucial to effecting a successful repair. Despite these accepted principles, many archi-tects and engineers design repair pro-jects without sufficient knowledge of the materials they specify or without understanding the significance of com-patibility between repair materials and the substrate.
Surveys of existing conditions (for measuring the extent of deterioration) employ rudimentary diagnostic tools that do not yield the information re-qUired to carry out the repair effective-ly. With insufficient knowledge and inadequate analysis of the problem, the validity of the diagnosis would be doubtful, thus contributing to ambigu-ity and error in the design of the repair programme.
The design of concrete restoration is many times undertaken by the un-trained or poorly informed whose fears of liability are realistic. However, these fears, in combination with a lack of com-prehensive knowledge, can result in the specification of materials and proce-dures which create new problems in ad-dition to the initial ones which have not been adequately addressed.
As a result of the inadequacies in current concrete repair and rehabilita-tion practices (described above), many concrete restorations are required to be redone later at considerable cost This phenomena is reflected in the fact that much more money (100,000 times) is spent annually on damage awards from concrete-deterioration litigation than is spent on researching repair degrada-tion,
The development of performance standards for concrete repair has not kept pace with the development of ma-terials, primarily because of a lack of supporting scientific and field data. It seems clear that research must be un-dertaken to help find a more direct means for linking the properties of re-pair materials with the quality and per-formance of whatisactually produced in the field in order to reduce the uncer-tainties of the repair process.
Noel P. Mailvaganam, Manager, Sub·Program on Repair and Protection, Materials Laboratory, National Research Council, Ottawa, Canada, KIA OR6.
March 1995*The Indian Concrete Journal
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