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PREFACE:

Concrete, when it first came into use, was hailed as being long-lasting and largely maintenance free. The need for extensive repairs to concrete structures was hardly considered. 

And, with appropriate design of the concrete, with due recognition of the exposure conditions and a few simple rules in designing the mix and some simple pre-service testing, there is no reason why extended lifetimes for RC structures cannot be enjoyed. However, experience tells us that reinforced concrete is often not the maintenance-free material that some people expect and early failure sometimes ensues.

 It is worth exploring the reasons for this before proceeding. Far too often, the basic design of the concrete and attention to detail in its placement are lacking. In the author’s experience, many concrete mixes are not correctly designed and suffer a tendency to bleed and segregate, all of which renders the protection that should be afforded to the steel reinforcement compromised from the start. 

Add to that incorrect placement of the steel, with inadequate cover and you have a recipe for early failure, whatever the exposure conditions. In severe conditions, with exposure to marine or de-icing salt, for example, failure can be very rapid indeed. Concrete Society Advice Note 17 (Roberts, 2006) lists some simple rules for good-quality surface finishes for cast-insitu concrete (see next section).

 Not surprisingly, those same rules will help to provide durable structures when combined with due attention to selection of an appropriate concrete and cover for the exposure conditions it will experience. 

The author once worked on the old Severn crossing, now replaced by the new bridge. The concrete in this bridge was of such high quality that it had not carbonated at all in 35 years and attempts to demonstrate a Windsor Probe device for strength estimation, caused the pin to simply bounce off, as the concrete was so hard.