ABSTRACT

In the last few years a bigger consciousness for the preservation of the cultural heritage has been developed. However, if problems associated with corrosion are not considered, during the necessary interventions on related works, by avoiding the use of materials and resources that make this phenomenon possible, problems associated with the durability of those materials, structure and safety for the citizens will appear.

The aim of the present work is to identify, through various examples detected in several historical structures, certain corrosion problems that some of its components present, to establish the origin of the damages and to suggest guidelines for their refurbishment. The last point is the most important one, in order that the specialists in restoration leave rigid and unfounded intervention patterns that cause, in most of the cases, serious damages and put the own restoration in danger, as a consequence of a lack of knowledge about the mechanisms that proceed and which will act in a future if qualified personal on both basic and applied principles of corrosion not be requested.

INTRODUCTION

Most of the corrosion literature ~3 only highlights the aspects related to economics, preservation of the natural resources, contamination and security, when the corrosion phenomenon is analysed. Some authors mention social aspects 4, although without making reference to the conservation of the historical heritage, and in very few cases the action of raininess on the degradation of the materials is mentioned 5.

In the last years consciousness toward the care of the cultural heritage has been stimulated and the protection of both historical monuments as modem artistic works encouraged. At present it is evident that man's great concern to maintain the signs of his existence in each lived time exist. However, in many cases the absence of an appropriate social behaviour toward such preservation is still appreciated which threatens the survival of the heritage. In fact, a great number of structures, those which have remained during centuries, are now liable to suffer a strong degradation mainly as a consequence of mainly the changes in the environment due to an irrational industrial development. For both conservation and restoration, it must be kept in mind the incidence of corrosion. Otherwise, its destructive results will seriously affect the durability of the pieces to protect. In this sense it is necessary to highlight the interaction between materials and the environmental factors (particularly the effect of the average raininess of the region) which promote or facilitate the degradation of this type of structures 5. Within the different materials that conform these structures they emphasize the following: reinforced concrete, stone, bricks, concrete, mortar, lime, plaster and wood. Among them, concrete is one of the most abundant components in the majority of historically interesting structures.

Concrete, whose application goes back to several thousands of years, is basically a mixture of an agglomerant, aggregates and water. It is a porous material in which a solid phase exists, made up of hydrated minerals, and a liquid phase contained inside the pores (pore solution). Different searches 6 have shown that when the pore solution contains high quantities of sodium and potassium salts, its pH value remains high. The composition of the solution pore is critical in the case of reinforced concrete. A very alkaline surrounding round the steel armor promotes the formation of a protective passive layer on it, at the time that neutralizes the action of chlorides. The size, distribution and interconnection of the pores fit both the oxygen availability and necessary h

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