Protection of repaired concrete structures results in greatly extended service life

Like any other building material, concrete is subject to wear and tear or damage. The causes vary widely. Sometimes conception or construction defects are at the root. Often, however, they find their origin in external factors such as weathering, chemical attack, water seepage or use-related damage due to load or vibration. While deterioration or corrosion of the reinforcement by carbonation or chlorides are the most common causes of concrete damage, this does not have to mean the end of the concrete structure! FEREB, in cooperation with its members, promotes and advocates sustainable and quality concrete repairs and developed a step-by-step plan that leads to sustainable concrete repair.

Sustainable concrete repair begins with a preliminary study or diagnosis that identifies the cause and extent of the damage. Then, when the specifications are drawn up, the repair method with the appropriate products will be determined. To carry out the work, it is best to hire an experienced contractor who has the necessary knowledge to complete the work successfully. If necessary, he calls on specialists to prepare the subsoil by means of hydrodemolition; a technology in which the damaged concrete is shot away under high water pressure. Regarding the use of hydraulic hammers, they will spare the reinforcement and avoid the formation of micro-cracks in the unaffected concrete.

During and after the execution of the works, the necessary inspections must be carried out by the contractor himself and/or by an independent inspection body. In order to guarantee the service life of the concrete structure, the necessary protection must be applied according to the pathology.

A Life Cycle Cost model created from project information and product characteristics provides a cost comparison between concrete repair combined with protection versus concrete repair without protection. This report states that every dollar invested in protection saves $3 to $5 in recurring repair costs and that appropriate protection eliminates an average of three repair cycles within the life of the structure. 

Thus, once the concrete repair has been carried out, protection must be applied to prevent new damage in the long run. First of all, the protection must be in accordance with the environmental conditions described in EN 206-1 (concrete standard). NBN EN 1504-2 in turn specifies the different types of protection products. Here we distinguish between carbonation-inhibiting coatings, hydrophobic coatings, chemically protective coatings, fire protection, abrasion-resistant coatings, etc. In specific cases, where damage occurred due to a combination of chlorides and carbonation, we apply the technique of cathodic protection. Cathodic protection extends the life of concrete exposed to chlorides.

If concrete damage due to the presence of chlorides was detected at diagnosis, specific instructions regarding the repair technique and additional protection techniques should be included in the specifications. Here the density of the chlorides present must be taken into account. As additional protection, the technology of cathodic protection is applied here. Here one has a choice of two technologies: sacrificial anodes or impressed current.

A first possibility is the incorporation of sacrificial anodes in the concrete cover In this process, several sacrificial anodes are attached to the steel of the reinforcement. These anodes consist of zinc. This metal is corroded faster than the steel and thus will be sacrificed. As a result, the anodes must be replaced after a foreseeable time.

Another technique is to send a metered current from outside to the rebar, This imposed current starts an electrochemical process, which stops the corroding of the rebar. Regular monitoring is required for optimal operation. This involves checking whether the current is still sufficiently distributed throughout the rebar. 

The choice between the two systems is determined, on the one hand, by price and desired lifetime. Both methods are effective but sacrificial anodes are cheaper, while imposed current will last longer and more efficiently. Cathodic protection remains a very good solution in both cases. It protects the concrete structure long-term, even up to more than 25 years while minimizing the cost of interim repairs.

In most cases, concrete damage certainly does not mean the end of the structure. Thanks to a durable repair according to the FEREB step-by-step plan, protection of the structure and periodic inspection and maintenance, the service life can be greatly extended. In this respect, sustainable concrete repair contributes to the climate and environment.