UK Highways Agency Research Articles

A review of the experience of thaumasite sulfate attack by the UK Highways Agency

Abstract The paper summarises and reviews the UK Highways Agency experience of thaumasite sulfate attack. Thaumasite sulfate attack was found in February 1998 in a number of bridge foundations and buried columns on the M5 Motorway in Gloucestershire. The paper will highlight the investigation of these structures, and assess the implications of the results of the extensive testing undertaken at these sites, for other structures. Subsequent to the discovery of thaumasite in Gloucestershire the Highways Agency participated in the Thaumasite Expert Group set up by the Minister for Construction. The report produced by the group influenced the development of the Agencies own guidance. Investigations were undertaken nationally using risk based criteria, to determine whether the occurrence of thaumasite was a local phenomenon, or of more widespread concern. Concurrently guidance was also issued for managing and minimising the risks of thaumasite in new construction, and this culminated in the development of a new specification for buried concrete. There are also implications for ground investigations, and these will be discussed. The paper will also highlight the case study of the A1 Mally Gill Bridge in County Durham, where a markedly different set of circumstances gave rise to thaumasite sulfate attack in a foundation. The Highways Agency has been involved with the development of improved guidance, as a result of the Expert Group Report, to ensure that that there is a consistency of approach across the construction industry. The paper will acknowledge that there are still many unknowns, particularly the mechanism governing the occurrence of thaumasite and the speed of thaumasite production. A particular aspect of concern to the Highways Agency is the ongoing management of structures that are known to be or may be affected by thaumasite. What are the methods for investigation and testing and are there suitable methods for remote detection? Do we need to introduce new inspection regimes? What are the requirements for the repair of thaumasite affected structures? Mention will be made of some of the research in this area, particularly the trial of repaired concrete at Moreton Valence. The paper will summarise the lessons learnt so far from the thaumasite experience, the implications for the future management of structures in potentially higher risk areas, and identify research needs.

New Developments in Bridge Management Methodology

Currently available bridge management systems (BMSs) are broadly based on two principles: firstly, the bridge maintenance needs are directly related to the condition states of the structures and, secondly, the justification for any proposed work is that it will cost more later if the work is not carried out now. However, contrary to the first assumption, experience gained from the UK Highways Agency’s bridge maintenance activities shows that the major part of the work depends on the load carrying capacity (or structural adequacy) of the structures rather than on their conditions alone. This paper describes the principles and basic steps of a new bridge maintenance bidding and bid prioritisation procedure being developed by the Highways Agency for implementing in the near future.

The Rankine Lecture

Application of soil mechanics principles to the design of pavement foundations, tbe design of complete pavements and to their structural evaluation 'in-service' has lagged some way behind knowledge accumulated through research. Present design methods are generally empirical and often based on use of the California Bearing Ratio test, which was abandoned in California some fifty years ago. The soil mechanics problem is one of understanding how soils and granular materials respond to repeated loading and applying this knowledge to pavement design with the aid of appropriate theoretical analysis and an understanding of failure mechanisms. Non-linear stress-strain characteristics are a particular feature of the problem and have to be catered for in design and evaluation. Various 'tools' are available to assist the pavement engineer. These include theoretical analysis, laboratory testing apparatus, field testing and full-scale trials with appropriate instrumentation. The resilient and permanent strain response of clays and granular materials is reviewed in the context of the requirements for design. The essentially empirical UK Highways Agency method of design and its evolution are discussed in the light of current soil mechanics knowledge. By contrast, the development of mechanistically based approaches is outlined, together with suggestions for the implementation of present knowledge in a practical method of design for pavement foundations. Parallels are drawn between road and rail track design and developments relating to the latter are also reviewed. A forward look suggests that further research to improve understanding of the effective stress state below pavements and the application of recent theoretical work on partially saturated soils could form the basis for improved pavement engineering in the future.