ABSTRACT

As individuals, and probably without thinking in a systematic way, we routinely take decisions in our everyday lives, which could be classified as management and maintenance. To repair and maintain, or to replace by new, this might relate to personal things like shoes, household furniture and fittings, or the family car. Mostly, these are items which have relatively short lives, and we are spoilt for choice, with upgraded or more attractive versions appearing on the market. Increasingly, here, the trend is to buy new – the culture of the so-called ‘throw-away society’. Even in our homes, attitudes are changing. The traditional activity of

regularly painting wooden windows and doors is being challenged by the advent of plastic, which apparently requires much less maintenance. Upgrading is becoming more common, either in the form of insulation or by building extensions, as family needs change, i.e. due to changes in our expectations or performance requirements. As we move out into the wider world of infrastructure, the picture, at

least so far, is rather different. Expectations are for longer lives (however ill-defined) but, initial design has not really taken service life or maintenance needs into account; design for the time factor has largely been via material and component specifications. It is not clear why this has been so in practice. Design lives for different types of structure have been given in Codes (in the UK) for over 50 years, but largely ignored. Over the same period, major attempts have been made to develop and rationalise maintenance regimes in a general way, the importance of which cannot be overemphasised, since maintenance work was estimated at 30 per cent of the construction industry budget 40 years ago, and this has now risen to over 50 per cent. For concrete structures in particular, the situation has been complicated

by durability issues. While some types of aggressive action have been known for some time, e.g. sulfate attack, new forms have appeared, e.g. thaumasite. Physically, abrasion and frost attack have also been known, and attempts

have been made to deal with these via specifications. We have also had the spectre of alkali-silica reaction (ASR), now well researched and understood. However, the major hazard has been corrosion, due either to carbonation of the concrete or to the effects of chlorides from various sources, and especially from the use of de-icing salts on roads. In research terms, durability has become a growth industry, aimed mainly

at understanding the mechanisms involved and the effects that they produce. The impact that these effects can have on structural performance and strength is less well defined; researchers in this area have tended to take a general approach, based on risk analysis and probabilistic methods. While striving to understand and use all the new scientific information,

owners have been faced with deteriorating structures and the need to manage these on a day to day basis, with function, safety and serviceability in mind. In general, the basis for rational decision-making has not always been clear. Is the priority to prevent, or at least slow down, the rate of deterioration or is it to repair, upgrade, strengthen, or rebuild? What is the most effective action, and, just as important, when should it be taken, in optimising the balance between whole life costing (WLC) and the maintenance of satisfactory technical performance? In response to this need, the development of repair and preventative

measures has also become a growth industry. Different categories of remedial action have evolved, based on different principles and with different objectives, and, within each category, a plethora of options are now available on the market. Based on development and laboratory testing programmes, there has been strong reliance on manufacturers’ literature in the past, and it is only very recently that Standards have started to appear, particularly through CEN and EN 1504 (see Chapter 7). While there is still a dearth of reliable data on the long-term performance of repairs in the field, feedback is beginning to appear, presenting a perspective of perceived expectations and actual reality. As a result, the repair industry itself is becoming much better organised on a more scientific basis. The importance of asset management and maintenance will become

greater in the future. The ancient myth that concrete lasts for ever has proven to be false, due to a combination of unforeseen or disregarded aggressive actions and less-than-perfect design and construction. The resulting need to maintain structural performance has to be seen alongside the issues of functional obsolescence, rising expectations in performance requirements and increases in loadings. Thus, asset management has to become more hands-on and proactive, with much less recourse to the crisis management tools. In addition, sustainability will dictate the need to maximise the use of existing infrastructure. In general, the need to think in terms of whole life performance (and

costs) has gained acceptance, but how best to achieve that is much less

clear. Owners of structures are having to cope as best they can, but progress has been made for certain types of structure at least; concrete bridges are a particular example, simply because they are the most threatened by de-icing salts. It is a dynamic period of change and evolution, and this book is targeted at providing an overall perspective – with the emphasis on a straightforward engineering approach.