Theodoridou and Török Progress in Earth and Planetary Science
https://doi.org/10.1186/s40645-019-0268-z(2019) 6:15

RESEARCH ARTICLE

Progress in Earth andPlanetary Science

Open AccessIn situ investigation of stone heritage sites
for conservation purposes: a case study of
the Székesfehérvár Ruin Garden in Hungary
Magdalini Theodoridou1*

and Ákos Török2

Abstract
This paper demonstrates the application of in situ diagnostic tools to document stone heritage sites prior toconservation interventions using a Medieval ruin of Central Europe (Székesfehérvár, Hungary). The applied methods
included lithological mapping and characterisation and mapping of decay forms as well as in situ measurements ofphysical parameters such as Schmidt hammer rebound, moisture content and micro-drilling resistance. The
combination of these methods allowed the condition assessment of different lithotypes and demonstrated the roleof micro-fabric, mineralogical composition and climatic conditions in stone durability. Differences were found in theproperties and in the weathering forms of fine-grained and medium-grained porous oolitic limestone andtravertine. The black crust observed in porous limestone is less prone to detachment on medium-grained oolitic
limestone ashlars, while scaling was observed on fine-grained oolitic limestone blocks. The micro-drilling resistanceof exposed porous limestone showed higher drilling resistance at the crust zone (upper 1–2 mm) than below,
marking the upper cemented zone, while the drilling resistance of porous limestone under shelter showed an
opposite trend. The shelly limestone, the sandy calcarenite and red compact limestone also showed an increase indrilling resistance at the topmost app. 2 mm zone. The applied in situ, non-invasive and micro-destructive
techniques helped in the identification of endangered zones at Székesfehérvár, thus, they can provide key
information on condition assessment of stones at heritage sites, where sampling is limited and preventive
conservation is important.
Keywords: Conservation science, Built heritage, Stone damage assessment, In situ evaluation, Non-destructive
techniques, Mapping, Micro-drilling

Introduction
Tangible cultural heritage such as ruins or stone buildings needs special attention in terms of preservation anddocumentation (Jokilehto 1999). It has been noted previously that prior to any intervention and conservation, adetailed survey is needed to record architectural elements and materials used at the site (Török and Přikryl
2010; Přikryl 2013, 2017). Additional studies are needed
to understand the behaviour of materials and their compatibility with any replacement stone, render or othercompounds that are planned to be used (Beck andAl-Mukhtar 2008; Modestou et al. 2016; De Kock et al.
* Correspondence: THEODORIDOUM2@CARDIFF.AC.UK
1
Cardiff School of Engineering, Cardiff University, Queen’s Buildings, The
Parade, Cardiff, Wales CF24 3AA, UK
Full list of author information is available at the end of the article

2017). On the other hand, materials that form part ofthe structure suffer from deterioration over time (Schaffer 1932). The natural processes can be enhanced byvarious intrinsic and extrinsic factors such as (i) mineralogical and textural characteristic of rocks and materials(Přikryl 2007; Fort et al. 2010; Török and Přikryl 2010;
Pappalardo et al. 2016; Pozo-Antonio et al. 2017), (ii) exposure conditions (Amoroso and Fassina 1983, Török etal. 2007a, 2007b, Graue et al. 2013), (iii) microclimate(Camuffo 1998), changes in climate (Brimblecombe and
Grossi 2009; Gibeaux et al. 2018) or in natural processes
and unexpected disasters (e.g. flood Kusar 2008, Siedel2010); (iv) anthropogenic pollutants (Maravelaki-Kalaitzaki and Biscontin 1999; Bonazza et al. 2005; McAlister
et al. 2008; Török et al. 2011; Calparsoro et al. 2017; La© The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made.

Theodoridou and Török Progress in Earth and Planetary Science(2019) 6:15

Russa et al. 2017) and (v) human activities, e.g. vandalism, or war (Mahgoub 2008).
The present study focuses on the diagnostics of amedieval ruin garden located in Hungary. It focuses on
the geological composition of materials, exposure and air
pollutants, as well as previous construction activities. The
main line is related to the fact that, before any intervention, a detailed survey of stone conditions is necessary(Drury 2006). The monument, which is comprised of different construction materials (e.g. various stones and mortars), needs a complex diagnostic approach. In this case,the role of earth scientists is crucial (Přikryl 2007). The
diagnostic survey can have a very broad context referring
to geotechnical studies concerning the ground support
and groundwater table; geomaterials characterisation fromlithological description to detection of weathering forms
and finally to measuring on site physico-mechanical properties and mineralogical and chemical composition. This
paper focuses on the latter two aspects, namely the description of lithotypes and weathering forms and also themeasurements of the physico-mechanical properties ofstones found at the Székesfehérvár Ruin Garden. The

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Garden is an exceptional assemblage of monuments and aprotected cultural heritage site of Hungary documenting
long history from the Roman period to the present. The
methodology presented here can also be applied in otherparts of the world for documenting and describing cultural heritage sites prior to any conservation measuresand also for planning restoration.
History and site description

The Ruin Garden is located in the historical centre of
the city of Székesfehérvár (65 km southwest of Budapest
in Hungary) (Fig. 1). In the Middle Ages (eleventh andtwelfth centuries), the city was a Royal residence and,
until the Turkish occupation in 1543, one of the mostimportant cities of Hungary. This is also supported by
the etymology of the city’s name which translates into
English as “white castle with the seat” with the word
“seat” referring to the throne of the king. The Ruin Garden of Székesfehérvár (Fig. 2) served in the Middle Agesas the coronation church for the kings of the Hungarian
Christian Kingdom and the burial place for fifteen kings,
several members of the royal families and, later on, ofFig. 1 a Map of Hungary with the location of Székesfehérvár. b–d Different aspects of the Székesfehérvár Ruin Garden, open air andcovered walls

Theodoridou and Török Progress in Earth and Planetary Science(2019) 6:15

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Fig. 2 Map of excavated ruins of the Székesfehérvár Ruin Garden depicting their different periods of construction and the main sampling points(modified after Bartos et al. 2004)

the high nobility. It was also the home of the royal treasury and relics. It is comprised of a provostal church dedicated to Virgin Mary, called today “Royal Basilica”, royal
tombs and related ecclesial and lay buildings. Since it
has been nominated for “National Memorial Place”, itspresent and future protection is required.
Between the eleventh and the fifteenth centuries, it
was reconstructed several times. The first phase of construction took place during the eleventh to twelfth centuries, under the Arpad Dynasty. During the ArpadianAge, in the twelfth century, the first rebuilding took
place. Damage from several fires necessitated the firstgothic reconstruction work that started in 1318, during
the Anjou Dynasty. Another fire in 1327 led to the second Gothic reconstruction (fourteenth to fifteenth centuries). The last expansion of the temple was
implemented by King Matthias in the second half on thefifteenth century, in a Late-Gothic style (Biczó 2005).
Its several reconstructions and expansions throughout
Hungarian history introduce another aspect of the importance of the historical site. A quick overview of thecurrent state of the monument reveals the presence ofseveral lithotypes that can be found among theremaining buildings and decorative stones. The research
related to the materials in order to understand theircomposition, structure, origin and behaviour is therefore

crucial not only for the conservation of that specificmonument but also for a series of other historic structures in Hungary.
In the nineteenth century, the excavation by Imre
Henszlmann revealed the size of the main parts of thechurch which was followed by several additional excavations (Theodoridou 2009). The total site of the excavatedruins is approximately 4700 m2. The palace of the bishop
borders the excavation area on the northwest part of theRuin Garden.
For the 900th anniversary of St. Stephen’s death, after
the excavation between 1936 and 1938, the Ruin Garden
was open to the public and the ruins were shown to thevisitors in their original condition before any intervention(Altmann et al. 1999). In the eastern part of the remainsof the Monostorbástya, a museum of stone carvings andthe mausoleum were erected. The stone tomb, which has
been called St. Stephen’s sarcophagus after the publishedstudy by Varjú in 1930, is placed in the aforementioned
mausoleum. The place is open to the public and a highnumber of tourists are visiting the site.

Methods/Experimental
Mapping

A series of maps were created based on investigations.
Five representative wall sections were selected based on

Theodoridou and Török Progress in Earth and Planetary Science(2019) 6:15

the distribution of the different lithotypes and the different construction periods to which the ruins belong(Fig. 2). Their location in the site, i.e. sheltered (walls 1,
3 and 4) or unsheltered areas (walls 2 and 5), was also
taken into account. The investigated side of wall 1 faces
southeast, wall 2 north, wall 3 northwest, and wall 4 and5 northeast. The total mapped area covered about 30 m2of the existing wall surfaces (Theodoridou 2009). Threedifferent kinds of maps were designed for each wall section: (i) the first series of maps depicts the different construction periods of the selected section of the walls, (ii)the second shows the distribution of the different lithotypes over the wall sections, and (iii) the visible weathering forms on the building materials. For the last
category of mapping, the first classification was developed by the working group “Natural stones and weathering” (Fitzner et al. 1995) with several publications that
followed, e.g. Fitzner and Heinrichs 2002, Fitzner et al.
1997, 2002, Viles et al. 1997 and the lately publishedglossary by ICOMOS-ISCS (2008).
Non-destructive techniques
Schmidt hammer

The Schmidt hammer is a non-destructive test methodthat has been applied in situ for estimating strength. The
working principle is a spring-loaded mass impacts thematerial and the rebound value is displayed at the
Schmidt hammer. The rebound measurements are on anarbitrary scale ranging from 10 to 100. Schmidt hammer
is also used for detecting of weathering of stone monuments (Török 2003; Viles et al. 2011). For this study, aDigi 2 Schmidt hammer was applied. Measurements
were made on the blocks of the five selected wall sections of the monument (Fig. 2). Ten values were acquired for each tested block and the extreme and meanvalues, in addition, to the standard deviation, wererecorded.
The Schmidt hammer was originally developed formeasuring the strength of hardened concrete (Schmidt
1951). Nevertheless, several studies have correlated its
results to predict several stone properties (Török 2008).
The correlation of the rebound values with the rockcompressive strength is the most commonly studied, e.g.
Miller 1965, Barton and Choubey 1977, Sachpazis 1990,
Kahraman 2001. The use of the rebound values in thecalculation of other mechanical properties has been alsostudied (Katz et al. 2000). Their state of weathering has
also been estimated by evaluating the hammer reboundvalues (e.g. limestones: Bell 1993, Christaras 1996, Török
2003, Viles et al. 2011).
Gann Hydromette

An estimation of the structural moisture of the tested
blocks can be very informative for the impact of climatic

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conditions. As a consequence, a correlation of the resultswith the materials weathering state may be possible. Furthermore, the obtained values, even in the case of numerical and not absolute ones, can be used incomparison with other measuring points and a profile ofrelative moisture content can be drawn (Török 2009).
For this study, a Gann Hydromette Uni was used for an
in situ and non-destructive estimation of the structural
moisture. The moisture content values that can be obtained by the Gann Hydromette are given in ‘digits’ andthey may range from 0 to 199 digits. When the measured relative values are more than a hundred units, thematerial is considered wet. Ten measurements were carried out on each tested block and the average value wascalculated. The blocks that were measured belonged to
the five selected wall sections of the monument (Fig. 2).
Micro-destructive techniques
Drilling Resistance Measurement System

The DRMS cordless (Drilling Resistance Measurement
System) by SINT Technology is a portablemicro-destructive cutting technique that was developed
for laboratory and in situ studies in heritage conservation (e.g. Exadaktylos et al. 2000; Singer et al. 2000;
Tiano 2001; Delgado Rodrigues et al. 2002; Cnudde etal. 2008; Theodoridou and Ioannou 2015; Modestou etal. 2015). It has been proven that the results of this testing method correlate well with various laboratory measured physical and mechanical properties of weak tovery strong limestones (Theodoridou et al. 2015). During
the measurements, the necessary force for penetrating acertain depth in time was measured continually, while
the penetration rate and rotational speed were kept constant. The outputs of the measurements were given in
x-y plots of the drilling force along the depth, and thedata was registered in numeric values. The operating
conditions were 600 rpm for the rotational speed, 10
mm/min for the penetration rate and 10 mm the total
depth of penetration. The diameter of the diamond drill
bits was 5 mm. A total of 20 blocks of building stone(Fig. 2) was subjected to the measurement system. Different lithotypes, such as various kinds of limestone,
marble and rhyolite were tested aiming at relating theresults with their state of weathering, avoiding further
invasive sampling.

Results
Mapping

The several construction periods of five selected wall
sections were mapped, along with the distribution of thedifferent lithotypes, highlighting the complexity of themonument (Theodoridou 2009). The properties of theidentified lithotypes are summarised in Table 1, whereTheodoridou and Török Progress in Earth and Planetary Science(2019) 6:15

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Table 1 Identified lithotypes and their major characteristics
Lithology

Code Description (mean open porosity %)Ooidal peloidal limestoneOL

Creamy, coarse-grained highly porous (28%)

Ooidal-peloidal packstone

Shelly limestoneSL

Creamy yellowish, fine-grained porous (23%)

Shelly packstone

Polimict sandy calcarenite

SC

Brownish creamy, coarse-grained, porous (13%)

Quartz-rich wackestone

Red biomicritic limestone

RL

Red nodular limestone with very low porosity (< 1%)

Wackestone

Foraminifera-bearing
limestone

FL

Light yellowish creamy, very porous (19%)

Peloid-microoncoid packstone

Travertine

T

Yellowish creamy, moderately porous (11%)

Boundstone

Quartz-porphyry (rhyolite)

Rh

Light brownish-purple brown with small phenocrysts of quartz and Kfeldspar (4%)

Micro-crystalline porphyritic

GraniteGr

Light red, fine-grained phaneritic (1%)

Hypidiomorphic crystalline

MarbleM

Light greyish white coarse crystalline (< 1%)

Inequigranular with serrated crystal
boundaries

the abbreviations (codes) of each lithology used in the
text can be found.
Figures 3 and 4 show the maps of construction phases
and lithotypes respectively of a representative wall section (wall section 1).
Based on the results of lithological mapping of the selected wall sections, several types of limestones such as
ooidal peloidal (i.e. oolitic), travertine and bioclastic ones
were the most widely used lithotypes in the different
construction phases of the monument. Besides Figs. 3
and 4 that represent different types of limestone on the
different construction phases of wall 1, oolitic, red compact, sandy, marly sandy, bioclastic limestones and travertine were identified in walls 4 and 5 as well, belonging
to the middle—second half of fourteenth century/second
Gothic reconstruction, the eleventh century/ÁRPÁD reconstruction and the intervention that took place in

Fig. 3 Wall 1—Map of construction phases

Microscopic characteristics

2005. Rhyolite was also widely used in some construction phases (e.g. wall 2—end of fifteenth century/King
Matthias expansion, and wall 3—twelfth century/ÁRPÁD reconstruction). The use of granite in the last
construction phase was also remarkable (wall 2—end of
fifteenth century/King Matthias expansion).
Several weathering forms were observed on the various lithotypes of the monument and they mapped forthe case of the five selected wall sections (Theodoridou2009). The most severe weathering processes occurredon the oolitic limestone when compared to the otherlithotypes of the monument. Individual fissures visible
by naked eye were observed (e.g. wall 1 (Fig. 5) and wall2). Detachment of grains also occurred, such as crumbling and granular disintegration (e.g. wall 1 (Fig. 5),
walls 2 and 3). Further detachment of thin layers of, ingeneral, a millimetric scale (multiple scaling) could be

Theodoridou and Török Progress in Earth and Planetary Science(2019) 6:15

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Fig. 4 Wall 1—Map of lithotypes

seen, for instance on the blocks of oolitic limestone ofwall 4. Exogenic deposits in combination with materials
derived from the stone created black and white crust indifferent blocks of the aforementioned lithotype (e.g.
wall 1 (Fig. 5) and wall 4). Detachment of the black crust
was observed in the case of fine-grained oolitic limestone (e.g. wall 1 (Fig. 5)).
In the case of bioclastic limestone, minor cracks werenoted with a dimension smaller than 0.1 mm, theso-called hair-line cracks, crumbling and erosion that
leads to smoother shapes due to loss of material such as

Fig. 5 Wall 1—Map of weathering forms

rounding and roughening of the surfaces (e.g. wall 3). In
the case of blocks of bioclastic limestone totally exposedto the exterior environment (e.g. wall 2), black crust andbiological colonisation (moss, lichens and plants) werealso observed.
The same forms of biological colonisation were observed on the blocks of travertine which were exposedto the outdoor environmental conditions, as well as
crack formation (e.g. wall 5). Besides the pre-existing
pore system networks of small interconnected depressions of millimetre to centimetre scale, dissolution

Theodoridou and Török Progress in Earth and Planetary Science(2019) 6:15

features were also observed on the exposed travertine.
The latter decay form was a result of surface dissolution
from exposure to water run-off.
The red limestone appeared to be the most durable
among the different types of limestones. Only minor alterations were observed on these blocks, such as decolourization of the surface (e.g. wall 3) and a few cracks.
In some cases of granitic blocks exposed to the environmental conditions (e.g. wall 2), major cracks and multiple flaking (scaling in thin scales of millimetricthickness) occurred. Rhyolite seemed to be relatively resistant to weathering processes besides a few hair-line
cracks observed in relatively small blocks (e.g. wall 3).
Additionally, salt efflorescence (e.g. wall 1 (Fig. 5)) andbiological colonisation were observed on the historicalmortar of the ruins. Especially the latter one was intensein the areas that were close to the ground level (e.g. wall
1 (Fig. 5), walls 3 and 4). In a few cases, the presence ofalgae expanded to the adjacent blocks of rhyolite (e.g.
wall 2) and travertine (e.g. wall 4).
Schmidt hammer and Gann Hydromette

The Schmidt hammer values and the moisture content
measured on the blocks of the selected walls weredepicted on the maps of lithotypes. Figure 6 shows therepresentative example of wall 1. The Schmidt hammer
values were recorded higher for the more compact
stones, such as rhyolite and granite, with the red limestone performing also relatively high rebound values.
Most types of limestones performed relatively low
values, with the oolitic showing generally lower values
than the travertine.

Fig. 6 Wall 1—Schmidt hammer and moisture content values

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The moisture content values were also presented on
the same maps (e.g. Fig. 6). The fluctuation of the values
for the same lithotype was related to the influence of thedifferent environmental conditions on the stone materials; blocks of the same lithotype showed higher moisture values where they were located in shadow areas,
especially in the covered parts of the monument. For instance, in the case of wall 1 (Fig. 6), the blocks whichwere on the right part of the wall, where the sunlightpasses through a transparent glass located on the right
top of the ceiling, were associated with lower moisture
content values than the blocks that had constantly been
under shadow. Moreover, in all cases, the blocks locatedcloser to the ground had higher moisture content thanblocks of the same lithotype which were located at ahigher distance from the ground level.
Drilling resistanceThree drilling measurements were carried out on eachblock with an exception of the quartz-porphyry rhyolite,
where the measurement could not be completed due toits higher drilling resistance than the potential of themeasuring system. Profiles showing the average values ofthe demanded drilling forces versus the drilled depth
from the surface to the interior of the material are given
in Figs. 7 and 8. Looking at the profiles of different
blocks of oolitic limestone (Fig. 7) and in particular tothe one belonging to the block that was exposed to theexterior environmental conditions (block 27), the highest
drilling resistance was observed at approximately the
first 1.5 mm of the drilling depth which was followed bylower values measured in the interior part of theTheodoridou and Török Progress in Earth and Planetary Science(2019) 6:15

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Fig. 7 Profiles of the average values of demanded drilling forces versus the drilled depth from the surface to the interior of the material for
representative blocks of oolitic limestones tested in situ; block 27 was located in the unprotected area of the monument and it was exposed tothe exterior environmental conditions, while blocks 8 and 10 were located in the sheltered areas of the site

Fig. 8 Profiles of the different lithotypes measured in situ showing the average values of the demanded drilling forces versus the drilled depth
from the surface to the interior of the material: oolitic limestone (OL), shelly limestone (SL), sandy calcarenite (SC), red limestone (RL), foraminiferabearing limestone (FL), travertine (T), rhyolite (Rh) and marble (M)Theodoridou and Török Progress in Earth and Planetary Science(2019) 6:15

material. This was not the same for the oolitic limestone
located in the protected areas of the monument (blocks
8 and 10). The profiles of the shelly limestone, sandy calcarenite and red limestone (Fig. 8) showed an increasein the drilling resistance during the approximately topmost 2 mm.

Discussion
Limestone was the most common building stone foundin the historic structures at the Székesfehérvár Ruin Garden. From a variety of limestone lithotypes, the oolitic
limestone (OL) was the prevailing one, while the use ofother types, such as shelly limestone (SL) and red compact limestone (RL), was also remarkable (Table 1). Additionally, several blocks of other lithologies, such as
sandy calcarenite (SC), rhyolite (Rh), marble (M), travertine (T) and other types of fossiliferous limestones (FL)were identified (Table 1). Regarding the use of different
stone types, there was a clear distinction between theseveral construction phases. OL was used throughout
the entire history of the construction (wall 1 (Figs. 3 and4), walls 2–5), while RL appeared only in the reconstruction period, that took place in the twelfth century (wall3). This observation is in good correlation with the previous findings (Kertész and Szabó-Balog 1988), since theuse of RL in Hungarian monuments dating back to
twelfth to eighteenth centuries was relatively common(Pintér et al. 2004; Török 2007a). The RL, which isanalogous to the Italian Rosso di Ammonitico, was a
popular dimension stone not only in Hungary, but
throughout the Mediterranean Basin (Lazzarini 2004). In
Central Europe, quarries of red limestones are known
not only from Hungary, but also from Austria (e.g.
Adnet) and from Romania (Pintér et al. 2004). The oolitic limestone (OL), or better defined as porous limestone, is also widespread in other monuments in
Hungary (Kertész 1982) but it includes varieties of lithologies (Török 2004a). The so-called Leitha Limestone,
which is a Miocene porous limestone type, is known
from Austria, Czech Republic and Hungary (Török
2004a). In Hungary, several porous limestone lithotypes
are known and historic quarries that could have provided the stone for Székesfehérvár can be found in thevicinity (Öskü) or at a distance of few tens of kilometresfrom the Ruin Garden (Budapest, or Fertırákos) (Török
2004a). Based on micro-fabric analyses, it is very probable that oolitic limestone (OL), which was used at Székesfehérvár, was quarried in Budapest region (probablyat Sóskút area) (Török 2002), while shelly limestone (SL)and sandy calcarenite (SC) came from Öskü area (Török
2004a). At the latter locality, no more active quarries
exist and the former ones are abandoned and often difficult to identify, which hampers the provenance analyses.
The provenance of the other stones used atPage 9 of 14

Székesfehérvár is very likely to be found in the present
territory of Hungary, except for the case of marble. The
travertine was from the North, from Süttő area (see Kertész 1982; Török 2007a) and the red limestone from Tardos (Kertész 1982; Pintér et al. 2004). The rhyolite (RH)
was most likely from the nearby igneous area of Velence
Mountains, but at present, no similar volcanic stones are
exposed in quarries. The marble (M) most probably
came from other territories than the current territory of
the modern Hungarian state, but further studies, such asgeochemical analyses, would be needed to identify theexact provenance.
The long-term behaviour of stone structures depends
on the durability of the stone materials (Macmillan
1967; Kieslinger 1968; Richardson 1991; Ordóñez et al.
1997; Vázquez et al. 2016; Přikryl et al. 2016; Přikryl2017), vegetation cover (Coombes et al. 2018) and theenvironmental conditions (Amoroso and Fassina 1983;
Siegesmund et al. 2007). When the various lithotypes ofthe studied Ruin Garden were compared it seemed thatoolitic limestone (OL), which was the most common
one, was less durable than other lithologies found at thesite. Based on the in situ observation, OL displayed various forms of decay such as cracks, crumbling, granulardisintegration, multiple scaling and flaking, black andwhite crust and biological colonisation (wall 1 (Fig. 5),
walls 2–5). The bioclastic limestone also showed several
decay forms, such as micro-cracks, crumbling, roundedsurface, black crust and, in the case of blocks totally exposed to the exterior environment (wall 2), biologicalcolonisation was also observed. The same forms of biological colonisation were observed on the blocks of travertine, which were exposed to the outdoor
environmental conditions, in addition to cracks andmicro-karstification (wall 4). Biological colonisation was
not restricted to outdoor environments. At the covered
parts of the ruin, green patches of microbial mats wereobserved (wall 1 (Fig. 5), walls 3–4). This was especiallyintense at low-lying blocks and in the joints, suggestingthat capillary water rise of groundwater provided moisture for biological activity. A clear dependence on thesubstrate was also noticed, since porous stone types,
such as OL, were preferentially covered, while lower
porosity stones, such as travertine (T) or rhyolite (Rh),showed far less intense biological colonisation (walls 3–4). Among the different types of limestones, the red
limestone appeared to be the most durable one, since
only minor alterations were observed, such as decolourization of the surface (wall 3). Stylolitic planes were also
observed in the red limestone and, as was shown previously (Aly et al. 2018), these clay-containing zones wereprone to weathering. In some cases, cracks and multiple
flaking developed even on blocks of relatively durable
stone types, such as granitic blocks in the uncovered

Theodoridou and Török Progress in Earth and Planetary Science(2019) 6:15

parts of the monument, which were exposed to the environmental conditions (wall 2).
Rhyolite (Rh) also seemed to be relatively resistant todecay; besides a few micro-cracks, no major decay forms
were observed on the relevant blocks (wall 3). Former
studies showed similar behaviour when those materials
were used in historical structures in other locations of
the country (Kertész 1988; Török 2003, 2006, 2007b;
Török et al. 2007a, 2007b; Török et al. 2011; Bögöly
et al. 2015).
The stone decay and especially the deterioration oflimestone monuments is a commonly reported
phenomenon from other countries, too. It is caused either by environmental conditions, such as freeze-thawor thermal stresses or by pollution plumes. The air
pollution-related soiling have been reported from cities
with heavy traffic load such as Athens (Moropoulou etal. 1998), London (Trudgill et al. 1991; Bonazza et al.
2007) or Budapest (Török 2002, 2004b). Exposed limestone facades located in smaller urban areas with heavy
pollution fluxes also show intense blackening in cities
such as Venice (Amoroso and Fassina 1983; Sabbioni1995), Oxford (Viles 1993; Smith and Viles 2006) or inother cities (La Russa et al. 2017; Pozo-Antonio et al.
2017; Gibeaux et al. 2018). At Székesfehérvár, the local
transport related pollution is less intense and the Ruin
Garden is located in a pedestrian area; therefore,
gypsum-rich black crust formation was subordinate. The
major decay processes were related to climatic conditions. The annual 70–75 freeze-thaw cycles were responsible for the granular disintegration of porous limestones(OL), as well as for scaling and flaking. Similar processesof porous limestone decay and frost damages were also
reported from Budapest (Török 2002, 2003, Török andRozgonyi 2004, Török et al. 2007b). Porous limestones
that are found in other parts of the world are also prone
to weathering (Cassar 2002; Vázquez et al. 2016), and it
has been documented that water absorption and frost(Al-Omari et al. 2015; Hassine et al. 2018) can lead to
rapid decay. Micro-cracks and micro-fractures observed
on other lithologies were also related to freeze-thaw.
Therefore, the new roof could be beneficial in terms ofregulating climatic conditions and reducing frost damage
at the Ruin Garden. Salt-related decay, which is common
in maritime environments, was not observed under thecontinental climate of Székesfehérvár. The use ofde-icing salts has not been a common practice at themonument; therefore, minor salt efflorescence observed
at some blocks is very probably related to the use of cement mortar as repair materials in the 1960s.
Non- and micro-destructive techniques were selected
for the estimation of the materials’ strength in situ, as they
are more suitable for heritage structures where samplingis limited. More specifically, micro-drilling resistance andPage 10 of 14

Schmidt hammer tests were performed at the Székesfehérvár Ruin Garden.
In the current research, the average demanded drilling
forces gave a good estimation of the strength parameters of
the tested materials, which agree well with the literature (e.g.
Theodoridou et al. 2015, Exadaktylos et al. 2000, Tiano et al.
2000, Delgado Rodrigues et al. 2002, Pamplona et al. 2008,
Vázquez et al. 2016). The drilling profiles corresponded tothe microfabric of the materials close to the surface, e.g.
higher heterogeneity for the sandy calcarenite due to thepresence of quartz grains in comparison with the compact
red limestone (Fig. 8). Moreover, the results achieved by insitu measurements depicted the occurring weathering phenomena, such as the presence of crust on the surface of oolitic limestone by showing higher drilling resistance on the
topmost millimetre (Fig. 7, block 27). At greater depth, thesamples showed lower values (Figs. 7 and 8).
Drawbacks of the micro-drilling technique have been
already mentioned along with relevant suggested solutions, such as the influence of using different drill bits insitu (Tiano et al. 2000; Pamplona et al. 2007), the dust accumulation during drilling (Mimoso and Costa 2006), thevirtual increase of drilling resistance in case of abrasivestones (Pfefferkorn 2000, Singer et al. 2000, Delgado Rodrigues and Costa 2004) and the problem in drilling hardmaterials due to the limitation of the drilling system (maximum measurable drilling force equal to 100 N). The latter
was the reason in this study micro-drilling could not be
performed on rhyolite (Fig. 8). However, possible solutions
to this issue have been already published (e.g. Mimoso
and Costa 2008; Pamplona et al. 2008).
Regarding the Schmidt hammer application (e.g. Fig. 6),
the results contributed to a quick and non-destructive
estimation of the materials strength properties. Furthermore, weathering of the materials surfaces could be detected by the changes in surface strengths measured by
the method as, for instance, the increase in surface
strength due to the formation of weathering crusts. This
decay pattern of oolitic limestone was also recorded inprevious studies (Török 2003). It should be also clarified
that despite the fact that the technique is considered a
non-destructive one, small impound marks are producedon the surface of tested stones. Hence, the application of
the test was avoided on deeply weathered stone blocks.
The moisture content of the stone blocks in situ is oneof the most crucial factors for the long-term behaviourof stones (Török 2009). Several methods are known formeasuring this value, such as conductometry andthermographic imagery (Meinhardt-Degen et al. 2008),
field dielectometry and unilateral nuclear magnetic resonance (Olmi et al. 2008). However, the high costs of applying some of the aforementioned techniques in situ
might be an obstacle. In our case, the Gann Hydromette
Uni was used, which, despite the fact that it gives only

Theodoridou and Török Progress in Earth and Planetary Science(2019) 6:15

relative and not absolute values, can give a profile of thedifferent values in different measured points. The
achieved measurements (e.g. Fig. 6) presented a good indicator of the influence of climatic conditions for eachblock, e.g. higher moisture content values for the samelithotype in case of blocks located closer to the groundor in areas that were constantly in shadow. It has been
documented that water uptake can influence the durability of porous limestones (Török et al. 2007a; Vázquez etal. 2016; Hassine et al. 2018), and thus, it is also linked
with the intensity of frost damage (Al-Omari et al.
2015). Water and moisture content controls the durability of travertine, too (Török and Vásárhelyi 2010). Manyof the measured points with higher moisture content
values had already presented salt efflorescence and/or
biological colonisation. Therefore, the use of thislow-cost technique could contribute significantly to theidentification of endangered zones.

Conclusions
The mapping method presented in this paper proved tobe very useful for the identification of the site, such as
the documentation of the different lithotypes used overthe different construction periods, the record of the insitu measured values and their ensuing interpretation in
relation with the existing climatic conditions and thecorrelation of the identified weathering forms with thedifferent lithotypes.
The use of several lithotypes, such as different kinds oflimestone, rhyolite and granite, was identified in the
Ruin Garden of Székesfehérvár throughout its several
construction periods between the eleventh and the fifteenth century. Few blocks of marble whose origin was
most probably out of the borders of the CarpathianBasin were also found. Oolitic limestone was found theprevailing type among the different types of limestones
used in the several construction periods of the monument, which is in accordance with its generally wide use
in historic constructions in the region. Moreover, thered limestone, which was found in the part that wasconstructed in the twelfth century and is very similar to
the Italian Rosso di Ammonitico, is another popular dimension stone in monumental constructions. Both of
the aforementioned materials could be found in Hungarian quarries, which are very close to the location of thestudied site such as the quarry in Sóskút which provides
oolitic limestone and the quarry in Tardos for the red
limestone.
In situ observations suggest that oolitic limestone suffered the most in terms of weathering since several
decay patterns were identified, such as black crust, scaling, crumbling, flaking, granular disintegration, roundedsurfaces and biological colonisation. This weathering
susceptibility is related to the micro-fabric, i.e. highPage 11 of 14

porosity of the lithotype. Red limestone seemed to berelatively durable with decolourization of the surface being its main observed weathering form together with
dissolution along stylolites. Those results were in accordance with the results of the in situ measurements bymeans of Schmidt hammer and micro-drilling. Moisture
content measurements proved the influence of
micro-environmental conditions on the stones seeingthat higher values coincided with more intense decay
forms, as for instance in the case of biologicalcolonisation.
All in situ test results were found consistent with thephysical state of the stone materials and the identified
decay forms on their surface. Thus, those non- or
micro-destructive tests could contribute significantly tothe characterisation of the materials and the identification of endangered zones at heritage sites, where sampling is limited, preventing or delaying further decay.
Regarding the importance of the presented research inrelation with the conservation of the studied site, the insitu investigation provided an overview of the state ofconservation of the stones of the Ruin Garden prior tothe construction of a new roof system. Also, the results
will keep serving as a database in the long term for the
future comparison of the stones’ behaviour before andafter the reconstruction of the site.
Acknowledgements
Dr. Biczó Piroska from the Hungarian National Museum is very muchappreciated for her help in accessing the heritage site and the
documentation of its construction history. Dr. Piero Tiano, Dr. Susanna Bracci
and Dr. Barbara Sacci from the ICVBC in Florence are thanked for
representing MOLAB in Hungary and supporting the performance of DRMS
in situ. MT would like to thank Dr. Sándor Józsa for his support from the sideof Eötvös Loránd University during the EPISCON project, as well as Dr.
Szakmány György for his assistance.
The authors gratefully acknowledge the travel grant from Japan Geoscience
Union to attend the Japan Geosciences Union Meeting 2017 that took placein Tokyo, Japan.
Funding
This project was part of the EPISCON project and financially supported by
the Marie Curie Actions (6th Framework Programme’s Human Resources andMobility - HRM, European Union). The application of the DRMS in situ waspart of the Mobile LABoratory-MOLAB of the Eu-Artech project funded underthe 6th Framework Programme’ s Infractures-1.
The financial support of National Research, Development and Innovation(NKFI) Fund (ref. no. K 116532) and BME FIKP-VÍZ by EMMI to ÁT are
appreciated.
Availability of data and materials
This work contains data of an ongoing project. Please contact authors fordata requests.
Authors’ contributions
Both authors contributed equally to the paper. Both authors read andapproved the final manuscript.
Competing interests
The authors declare that they have no competing interest.

Theodoridou and Török Progress in Earth and Planetary Science(2019) 6:15

Publisher’s NoteSpringer Nature remains neutral with regard to jurisdictional claims inpublished maps and institutional affiliations.
Author details
1
Cardiff School of Engineering, Cardiff University, Queen’s Buildings, The
Parade, Cardiff, Wales CF24 3AA, UK. 2Department of Engineering Geology
and Geotechnics, Budapest University of Technology and Economics,
Müegyetem rkp. 3, Building K, Budapest H-1111, Hungary.
Received: 23 April 2018 Accepted: 27 January 2019

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