The diagnosis of the condition state of a reinforced concrete work, makes it possible to characterise the origin and the extent of possible damages. As a rule, this diagnosis is carried out after some damages have appeared, but it is also asked within various frameworks, such as rehabilitation works or regular inspections.

In addition, a diagnosis has several objectives:

    to identify the origin of reinforcement corrosions,
    to evaluate their extent, in the structure,
    to predict their probable change, with time and space,
    to estimate their consequences on the safety concerning the structure and people
    to define the further actions to make.

A preliminary visit of the structure makes it possible to put forth assumptions on the possible causes of the damages, and thus to specify the operations to be carried out, by taking account of the functioning of this structure. The mechanical behaviour of the various structure parts, is a point very significant to examine. However, it is not developed here.

A diagnosis concerning the reinforced concrete relates to the concrete of coating, on the one hand, and them reinforcements, on the other hand. It is done within the framework of an inspection.

Protective qualities of a concrete cover and its ageing conditions are assessed by various tests, which are carried out on site and which are not (or are not too much) destructive. Here are the tests and measurements:
    on site measurements of the concrete permeability to the air and water,
    on site measurements of the electrical resistance of concrete, in particular to locate wet or salted       areas,
    possibly, on site measurements of the concrete surface cohesion,
    determination of carbonation depth on small cores taken from concrete,
    determination of content chloride profile, on cores taken from concrete.

The reinforcement state of the is characterised by its geometry and its corrosion condition.

The reinforcement geometry concerns its cross section (diameter), its arrangement in concrete (number of mats) and especially the cover thickness above reinforcement close to the facing. This thickness is determined by various non-destructive methods.

The condition state of reinforcement is characterised by measuring half-cell potential with using various equipments This method makes it possible to locate the corroding areas.

A reinforcement starts to corrode, when it is in contact with aggressive agents which are with contents higher than some critical values. The progressive deteriorations of the concrete cover, which lead to reinforcement corrosion are especially carbonation and chlorides penetration.

The penetration of the aggressive agents is characterised by tests and calculations, which are:

    on site measurements of concrete permeability to air or water,
    determination of the time when carbonation will reach reinforcement,
    determination of the time when, chloride concentration at the reinforcement level, will reach a critical       value (critical chloride content).

The reinforcement corrosion results in a loss of cross section and a formation of corrosion products, which can expand and deteriorate the concrete cover.

The corrosion rate is determined on site, at a given time, by measuring polarisation resistance or with validated similar methods.

To calculate the dissolution change, a mean rate, characterising corrosion either is calculated by using instantaneous corrosion rate, or by using the experimental correlation between corrosion rate of reinforcement and concrete cover resistivity.

Books and documents to be consulted on the diagnosis and the prediction of steel corrosion in    concrete :

   
   
   

Institutions to be contacted for the diagnosis and the prediction of steel corrosion in concrete :