ABSTRACT
The need to repair concrete structures is not new. Much of the early work involved making good via patch repairs and crack filling, for aesthetic and serviceability reasons [7.1]. As the concrete infrastructure of the mid-20th century matured, there was also a demand to strengthen or upgrade to meet changes in use or increases in loadings. The need to treat cases of corrosion emerged in the 1950s with post-war prefabricated reinforced concrete housing, and many of the references to Chapter 2 detail examples of corrosion in highway structures as the use of de-icing salts increased rapidly in the early 1960s. Reference [7.2] gives some details of this, and reference [7.3] is a detailed review of the situation in the UK and France with regard to post-tensioned concrete bridges. As durability concerns became more widespread, and the consequences
of failure more critical, repair became a growth industry, and the options available on the market increased significantly in terms of principles and approaches, and the individual solutions within each basic approach. This process continues apace as witnessed via a recent publication [7.14] containing over 200 short papers on all aspects of the problem. The literature is full of individual case studies, describing what has been
physically done and giving some reasons for selecting a particular option; it is often difficult to draw general conclusions from these. Such articles, which are also helpful since they provide website addresses, appear most frequently in concrete-related journals such as Concrete from the Concrete Society in the UK. In North America, the various journals of the American Concrete Institute (ACI) do a similar job, and focus on repair is provided by the International Concrete Repair Institute (ICRI), which publishes a bi-monthly Bulletin, and whose website (www.icri.org) gives details of available publications in the USA; generally, these are either guidance documents, or compilations of articles on particular topics. There are also guidance documents available on individual repair, pro-
tection and upgrading methods, which explain the principles involved and
are strong on the ‘how to ’ aspects of the problem. Some examples of these can be obtained from the ICRI website for North America, and references [7.4-7.9] are similar publications available from the Concrete Society in the UK. The Concrete Society portfolio is augmented by other reports on test methods and diagnosis, and on how to enhance durability in new construction; Technical Report 61 [7.10] is an example of the latter, where much of the detailed information is transferable to the repair and renovation situation. The Concrete Repair Association in the UK also has a website (www.cra.org.uk). The above brief review is intended to show that there is quite a lot of infor-
mation available on repair and renovation methods and also to indicate the nature of that information. It can become dated quite quickly however, as the technology is improved and new techniques are introduced. Moreover, the nature and format of the information make it difficult to compare the technical and economic merits of alternative approaches – essential information to the owner when making a choice. This situation is now changing, with serious attempts being made to develop a systematic scientific basis for classifying repair and renovation methods, supported by sound specifications and test methods. The emergence of EN 1504 is a prime example of that, and will be referred to strongly in later sections of this chapter. The final major missing link from the data bases is the lack of in-depth
feedback on real performance in the field over relevant periods of time. How does this compare with claims and expectations? Again, this is changing, as typified by Figures 2.13-2.16, taken from the paper by Tilly [7.11]. Tilly’s paper comes from the activities of a European network CONREPNET, which has examined well over 100 case studies in some detail and, apart from providing field data, has focused on developing criteria to permit alternative options to be evaluated to a common base. This information will also be used extensively later in this chapter. Repair and renovation is a huge subject, deserving several books in its
own right. This book is about assessment, management and maintenance, and repair is an integral part of that. The emphasis in this chapter is on how it fits into the overall scheme of things, in moving forward from the assessment phase to taking effective action in selecting optimum solutions. This approach leads to the following sequence of sub-sections.
