Physical and mineralogical changes of Hungarian monumental stones exposed to different conditions: stone-testing in-situ and under laboratory conditions
Creators: name: Theodoridou, Magdalini <1983>
Publisher: name: Alma Mater Studiorum - Università di Bologna
Year: 2009
Subjects: CHIM/12 Chimica dell'ambiente e dei beni culturali

description: The Székesfehérvár Ruin Garden is a unique assemblage of monuments belonging to the cultural
heritage of Hungary due to its important role in the Middle Ages as the coronation and burial
church of the Kings of the Hungarian Christian Kingdom. It has been nominated for “National
Monument” and as a consequence, its protection in the present and future is required. Moreover, it
was reconstructed and expanded several times throughout Hungarian history. By a quick overview
of the current state of the monument, the presence of several lithotypes can be found among the
remained building and decorative stones. Therefore, the research related to the materials is crucial
not only for the conservation of that specific monument but also for other historic structures in
Central Europe.
The current research is divided in three main parts: i) description of lithologies and their
provenance, ii) physical properties testing of historic material and iii) durability tests of analogous
stones obtained from active quarries. The survey of the National Monument of Székesfehérvár,
focuses on the historical importance and the architecture of the monument, the different
construction periods, the identification of the different building stones and their distribution in the
remaining parts of the monument and it also included provenance analyses. The second one was
the in situ and laboratory testing of physical properties of historic material. As a final phase
samples were taken from local quarries with similar physical and mineralogical characteristics to
the ones used in the monument. The three studied lithologies are: fine oolitic limestone, a coarse
oolitic limestone and a red compact limestone. These stones were used for rock mechanical and
durability tests under laboratory conditions.
The following techniques were used:
a) in-situ: Schmidt Hammer Values, moisture content measurements, DRMS, mapping
(construction ages, lithotypes, weathering forms)
b) laboratory: petrographic analysis, XRD, determination of real density by means of helium
pycnometer and bulk density by means of mercury pycnometer, pore size distribution by mercury
intrusion porosimetry and by nitrogen adsorption, water absorption, determination of open
porosity, DRMS, frost resistance, ultrasonic pulse velocity test, uniaxial compressive strength test
and dynamic modulus of elasticity.
The results show that initial uniaxial compressive strength is not necessarily a clear indicator of
the stone durability. Bedding and other lithological heterogeneities can influence the strength and
durability of individual specimens. In addition, long-term behaviour is influenced by exposure
conditions, fabric and, especially, the pore size distribution of each sample. Therefore, a statistic
evaluation of the results is highly recommended and they should be evaluated in combination with
other investigations on internal structure and micro-scale heterogeneities of the material, such as
petrographic observation, ultrasound pulse velocity and porosimetry. Laboratory tests used to
estimate the durability of natural stone may give a good guidance to its short-term performance
but they should not be taken as an ultimate indication of the long-term behaviour of the stone.
The interdisciplinary study of the results confirms that stones in the monument show deterioration
in terms of mineralogy, fabric and physical properties in comparison with quarried stones.
Moreover stone-testing proves compatibility between quarried and historical stones. Good
correlation is observed between the non-destructive-techniques and laboratory tests results which
allow us to minimize sampling and assessing the condition of the materials. Concluding, this
research can contribute to the diagnostic knowledge for further studies that are needed in order to
evaluate the effect of recent and future protective measures.