The corrosion problem  
 One of the most important and worrying reasons of decay of the reinforced concrete structures is the corrosion of the iron due to the loss of the characteristics of protection of the concrete. 
The main reasons are: - the phenomena of carbonatation, from the external layers to the internal, reducing the alcalinity of the concrete and destroying the passive film of the reinforce and triggering the corrosion 
-  the use of the antifreeze salts which cause the penetration of the chloride ions until the reinforce where the corrosive localized attack start. 
- the atmospheric pollution 
Although such phenomena are often confined in small areas of the structures, their consequences are considerable and regard: 
- the structural aspects and therefor the safety conditions 
- the functional aspects and the outward state of the works 
- the corrosive attacks by vacant currents in the case of structures interested by electrical fields. 
Kind of intervention   
At the moment the main Companies engaged in the maintenance of the motorway structures plan their activities and fix the priorities o the interventions considering the results of  visual inspections and non-destructive tests elaborated in accordance with Markovís process. This kind of approach is due to the big number of bridges and viaducts to test.  
Itís clear that the process is in an advanced state in the moment where itís visible the effects due to the corrosion of the reinforcements (delamination, spalling). 
In the life of the reinforced concrete structures itís possible to individuate two perfectly distinguishable phases: 
- a phase of trigger of the corrosion when the phenomena leading to the local or generalized destruction of the protective film of the reinforcements start; 
- a phase of propagation of the attack starting from the moment when the protective film is destroyed. 
To develop rational and economical strategies to repair and to restore the structures itís necessary to acquire reliable information about the level and the speed of advancement of  the corrosive decay. 
Measurung before the risk of corrosion and considering the residual life of the work, the decay can be avoid or strongly reduced scheduling simple and cheap restoring interventions. 

The solution 
Aetech staff have designed and realized the DECOMETERS to test the conservative state of the reinforced concrete works. 
Using DECOMETER 2M or DECOMETER 4M itís possible to realize: 
- The systematic monitoring of the corrosive state of the new constructions. 
- The planning of the repair interventions 
- A save in the maintenance of the efficiency and safety 
- The objective verify of the designed choices and of the good realization of the works 
- The maximum reduction of the consequences of the interventions on the traffic