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Conservation movement

Concrete conservation - Dave Parker opens NCE's special feature with a look at some of the issues confronting the concrete industry.

When important structures like the Öland Bridge in Sweden begin to decay long before the end of their design life (see page 24), those responsible for their maintenance and operation often face major dilemmas.

Demolition and replacement is rarely an option. Transport infrastructure is notoriously difficult to renew, given the scale of the disruption that would ensue.

Over the last 20 years or so, however, concrete repair and conservation specialists across the world have developed a range of advanced materials and technology capable of keeping deteriorating concrete structures safe and economic to operate for many more decades. The main challenge now is to make end users aware of the proven options, such as hydrodemolition.

Even the once feared spectre of 'concrete cancer' or alkali silica reactivity (ASR) has been diminished and put into perspective (see below).

Some may have panicked when cement manufacturer Lafarge admitted to supplying cement with a higher than declared alkali content for two years (NCE 20 January). But even if some structures in the south west of England are confirmed to be at risk from ASR, there are developed techniques to deal with the long term effects.

In future all strategically important concrete structures may be fitted with real time remote monitoring sensors.

Systems already exist which can report on the penetration of chlorides into foundations or listen for the ping of a corroded prestressing strand snapping.

Some structures already use one or more of these systems.

Construction research body CIRIA's forthcoming research into intelligent monitoring (page 33) should produce an authoritative evaluation of the individual systems. It should also give infrastructure operators the information they need to evaluate monitoring options and carry out a realistic cost/benefit analysis.

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