Executive summary

This project was undertaken to examine the current state of knowledge with respect to the implementation of patch repair, particularly in relation to the need or not of propping during excavation of the concrete. The project was prompted by the seeming disagreements between different research results.

It was discovered that most of the recommendations currently available have been based upon a small subset of structures: simply supported beams. They are not generally applicable to other structures, especially continuous beams and plate or shell structures.

Supporting evidence for the above observation was obtained through nonlinear finite element analyses of the repair process of a continuous beam.

It is individual aspects of the multi-aspect repair–structure system that are usually dealt with in the available literature. Conclusions derived from a single aspect of behaviour or a limited number of aspects of behaviour are inadequate for developing general rules.

There is a need to examine the conclusions and recommendations available in the literature to test their general applicability to conditions other than those considered by the original researchers.

Even where researchers studied the same aspect, differences are sometimes to be seen in their conclusions. This may be attributed mainly to a lack of a system approach.

In the 1990s there had been a call for a system approach for implementation of patch repair, although more from a materials point of view. To date there seems to be no publication that presents the development of such an approach, where the structural consequences and the possible of loss of durability are considered simultaneously in a rational manner.

The lack of a system approach may be attributed to a perceived lack of a common denominator that may be used in assessing various alternate options. A risk-based approach offers this common denominator needed to implement a system approach for patch repair of concrete. A risk-based approach would also offer a means of evaluating different patch repair techniques and defining performance requirements of repair.