The Parthenon in Athens could serve to symbolise
most problems of conservation of the European cultural heritage.
For about 2500 years its white marble stones have weathered the
ravages of time, aggravated by numerous earth tremors that have
hit the regions over the century. This degradation has accelerated
in recent years due to the effect of chemical pollutants generated
by human activity. More than ever before, this masterpiece is under
threat and dozens of scientists have come to its aid, searching
for remedies but also for powerful diagnostic tools.
There have been various restoration projects carried out with varying
success, but none have ever provided a satisfactory solution to
the many maladies this unique monument has suffered. The fact is
that these projects have been managed in a particularly confusing
context as the results could diverge considerably from one laboratory
to another and according to the various methods of analysis used.
Some options have even proved harmful to the structure due to a
lack of proper knowledge of the physical and chemical properties
of the marble used in antiquity. Georges Exadactylos, coordinator
of the project funded under the European Standard, Measurements
and Testing Programme, explains that shortly after the war iron
was used, for instance, to repair some of the cracks, but the metal
quickly rusted which led to further damage inside the stone.
The first task of the European researchers was to make as objective
an assessment as possible of the damage suffered by the monument,
resulting from highly complex mechanical and chemical processes.
Traditional computerised analysis provides only limited remedies
as these "destructive" methods (involving the removal
of samples) are prohibited on such monuments. Georges Exadactylos
explains that a non-destructive acoustic technique was therefore
tested and standardised. It consists of applying in situ ultrasound
to the stone and analysing the waves reflected. These waves provide
valuable information on the state of the material surface. Damage
that is invisible to the naked eye can thus be detected and (especially)
The question is therefore how to go about restoring the damaged
stones. Traditionally, there have been two options: where possible
using the original material or finding a substitute with very similar
physical, chemical and aesthetic properties.
The project coordinator points out that in the case of the Parthenon
there is no real choice as the original quarry, located in the Athens
region, can no longer be used for environmental reasons. The stone
should therefore be sought in other white marble strata.
It is also necessary to have a thorough knowledge of the properties
of the materials to be combined for this purpose and compare them.
If the stone used in restoration work deteriorates, for instance,
at a different rate from that of the old marble, this phenomenon
may cause detrimental mechanical and aesthetic distortion.
One of the six tests studied and standardised under the Monuments
project is a "fatigue" test on the natural building stones.
In this type of test, samples are not exposed to sudden stress involving
immediate fractures but on the contrary undergo very progressive
stress. In this way the stone cracks slowly, which corresponds to
normal degradation conditions of monuments, apart from the special
case of earthquakes.
From the past to the present
These different tests have also been applied to and standardised
for a material widely used by Italian architects and artists of
the renaissance: Serena sandstone. The greenish colour, characteristic
of the city of Florence, results from the use of this material in
most edifices erected between the 15th and 17th centuries whose
restoration involves difficulties comparable to those of the Athenian
The researchers have also studied white Carrara marble, one of
the materials preferred by Michelangelo both as an architect and
as a sculptor. The quarries in western Italy are in fact still among
the major sources worldwide for the production of white marble,
which explains the presence in the Monuments project of the
international Marmi e Macchine Carrara company.
Paolo Salieri, scientific officer at the Directorate-General for
Research at the European Commission, explains that this industrial
partner is involved in the characterisation of properties and damage
of natural building stones. Certain contemporary structures in which
marble is used have serious faults due to a poor use of the stone.
The results of the Monuments project, which has led to the
standardisation and harmonisation of six different testing methods
- three of which entirely new - of the mechanical properties of
natural building stones, will serve as a basis for discussion within
the European Standardisation Committee. These results could help
to establish common ground for expert reports in the preservation
and restoration of historical monuments and help contemporary natural
building stone industries to establish new European quality standards
in this domain.
Characterisation of Mechanical Properties and Damage of Natural
Building Stones in Historical Monuments
Standards, Measurements and Testing Programme
Technical University of Crete
Department of Mineral Resources
Eleftheriou Venizelou 128BIS
72132 Chania, Greece
Fax: +3082 169554
E-mail : email@example.com
- Technical University of Crete, Chania, Greece (coordinator)
- National Technical University of Athens, Athens, Greece
- Politechnico di Milano, Milan, Italy
- Internazionale Marmi e Macchine Carrara SpA, Marina di Carrara,
- Università degli Studi di Pisa, Pisa, Italy
- SINTEF Petroleumsforskning AS, Trondheim, Norway