Link between Durability Defects and Construction Failures

Abstract

Over thirty years ago enthusiastic and dedicated materials scientists and structural engineers initiated a series of research projects and draft International Standards which has now revolutionised the design approach to durability of concrete structures. Concrete mix design is dominated by the contractual requirement for the concrete supply not to exceed specified limiting values of the nationally favoured durability criteria. The specifying Authorities are striving to ensure that structures achieve their design service life (ideally 100 years+). Concrete research and development is their primary hope. During the 1990s, the concrete construction industry was also working hard to develop better specifications and contract management procedures to address the pressing problems of not only durability but also safety. Central to all the work of the construction industry was the principle that all concreting operations were ‘special processes’ (as universally acknowledged for welding processes), and therefore they had to be documented, trialled, verified and implemented in compliance with the process control requirements of ISO 9001:1987/1994. Procedures had to be prepared, approved and implemented for all processes which were identified as being potentially ‘adverse to quality’ (which included most processes involved in concreting and prestressing operations (including grouting)). The critical question to answer in preparing a procedure is HOW the process will be carried out and verified. However, equally critical questions may be WHEN, WHERE and BY WHOM. The Project Specification must ask these questions in the tender documents and the Owner and/or his Designer must satisfy themselves that all the identified problems have been resolved – both technical and administrative – before relevant design/construction commences. These questions must be answered by all subcontractors, including designers and checkers of falsework structures. Example are given, based on recent fatal bridge collapses largely caused by Owner and Designer failings to control subcontracting of temporary works design and checking.

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