Problems / Pathologies
Common problems found in concrete monuments
Reinforced concrete was the material of choice for many architects of the modern era, and they exploited the material in a multitude of creative and innovative ways. Many of the modern era's most extraordinary structures demonstrate the potential of reinforced concrete and illustrate the material's rapid evolution over the twentieth century. Like many modern materials, reinforced concrete has raised new and distinct conservation challenges. These issues relate to the lack of appropriate techniques and materials to meet conservation needs, the current lack of knowledge on the efficacy and durability of existing repair solutions, the shortage of training opportunities, and the lack of technical and guidance resources available to professionals.
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Shrinkage
Concrete may suffer from decay due to uncontrolled restrained shrinkage. Shrinkage is a chemical-physical phenomenon that always exist in cement based material and start from early age (actually some sort of shrinkage occurs when the cement has not yet hardened) until very late in the age of the structure.
Shrinkage
Main visual effect due to the shrinkage is cracks formation. These cracks may appear either very early after casting the concrete e.g. settlement cracks, immediately after removing the formworks or few days, weeks or month later due to long term shrinkage.
Freeze and thaw
This is mainly occurring in countries or areas subjected to harsh winter conditions and it is very often accentuated by the presence of de-icing salts used in the bridge to reduce incidence due the frost formation on the road. This is due to improper design of the concrete that does not contain enough properly dispersed air network that provide enough space for the water to expand when freezing.
Freeze and thaw
Main symptoms are the scaling present at the surface of the concrete and swelling of all or part of the structure together with cracking behaviour. When to the extreme, the structure may completely get destroyed as shown in the enclosed picture.
As example, a survey carried out in UK in 1997 has shown that in average 10% of the reinforced concrete structure were affected by incidences of freeze-thaw cycles.
Decay due to other origins
Many other origins may be the causes of concrete decay such as for a bridge structure, accidental chock from a vehicle, abrasion, erosion in bridges over rivers, etc…
Decay due to other origins
Other important sources not detailed in this article but amounting for many failures, are fault of execution during the construction works, e.g. design error, improper spacing, honeycomb due to insufficient vibration or too stiff concrete, damages resulting from fire, etc…