Building materials and degradation phenomena of the Finale Emilia

Periodico di Mineralogia (2016) 85, 59-67
PERIODICO di MINERALOGIA
established in 1930
An International Journal of
Mineralogy, Crystallography, Geochemistry,
Ore Deposits, Petrology, Volcanology
and applied topics on Environment, Archaeometry and Cultural Heritage
Building materials and degradation phenomena of the
Finale Emilia Town Hall (Modena): an archaeometric study
for the restoration project after the 2012 earthquake
Stefano Lugli a, Marta Caroselli a,*, Simona Marchetti Dori a, Vincenzo Vandelli b,
Gaetano Marzani b, Roberto Segattini c, Clara Bianchi c, Johannes Weber d
a
Dipartimento di Scienze Chimiche e Geologiche, Università di Modena e Reggio Emilia, Italy
Progettisti Associati, Sassuolo, Modena, Italy
c Fondo Ambiente Italiano (FAI), Italy
d University of Applied Arts Vienna, Institute of Arts and Technology/Conservation Sciences, Austria
b Studio
ARTICLE INFO
Submitted: September 2014
Accepted: January 2016
Available on line: February 2016
* Corresponding author:
marta.caroselli@supsi.ch
DOI: 10.2451/2016PM371
How to cite this article:
Lugli S.. et al. (2016) Period. Mineral. 85, 59-67
ABSTRACT
The Town Hall of Finale Emilia (18th century; Modena) is one of the 1600 historical
buildings seriously damaged by the seismic crisis that affected the Emilia region of Northern
Italy in May 2012 (ML 5.9). FAI, Fondo Ambiente Italiano (Italian National Trust) selected
this important building for a complex restoration and structural strengthening project.
A nationwide fundraising campaign was immediately launched to bring back to life the
symbol of the community so badly struck by the earthquake. The restoration project is now
in its executive phase under the scientific supervision of Direzione Regionale per i Beni
Culturali e Paesaggistici. Among many other diagnostic tools that have been applied to
elaborate the restoration project, detailed surveys and petrographic analyses were performed
to characterize the ornamental stones, mortars and plasters and their alteration phenomena.
In particular, the study of more than 40 samples provided fundamental information to
distinguish different building phases. In the first construction phases all the raw materials
(lime rock and sand) were taken from the Panaro River, the closest source to the palace. The
more recent renovations saw the use of industrial materials coming from the Veneto area and
the Po River.
Keywords: mortars; plasters; ornamental stones; decay phenomena; petrographic analyses.
INTRODUCTION
On the 20th May 2012 a ML 5.9 earthquake struck
the eastern sector of the Po plain followed by several
aftershocks, up to ML 5.1 the 29th May (INGV; National
Institute of Geophysics and Volcanology). More than 1600
historical buildings were seriously damaged in the provinces
of Modena, Ferrara and Mantova. FAI (Fondo Ambiente
Italiano, Italian National Trust) selected the Town Hall of
Finale Emilia (Figure 1) for a comprehensive restoration
and structural strengthening project as the symbol of the
post-earthquake reconstruction for its double public and
historical value.
The “Direzione Regionale per i Beni Culturali e
Paesaggistici dell’Emilia Romagna” (Regional Board
for Emilia Romagna Cultural and Landscape Heritage),
the Municipality of Finale Emilia and FAI signed a
Memorandum of Understanding that states the cooperation
efforts. FAI committed to finance the consolidation
and repair project involving various professionals
and organizations that offered their expertise for this
philanthropic purpose. The aim of the project was to restore
the old town hall, Palazzo Pubblico, and the annexed
buildings, Palazzo Bortolazzi and Casa Galei, to create a
new public space for the community. After the first safety
measures, as the main building was declared not accessible,
the removal of the furniture started in October 2012. The
early surveys revealed that most damage was located close
the elevator, a reinforced concrete structure added in the
1970s. In February 2013 it was possible to proceed with the
diagnostic analyses.
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Figure 1. Map of the ornamental stones and map of selected alteration phenomena in the facade of the Town Hall.
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Archaeometric study of the Finale Emilia Town Hall building materials
This paper illustrates the results of our petrographic
investigations that were used to characterise the raw
materials (ornamental stones, mortars and plasters), their
alteration phenomena, the typological and structural
configuration of the various building elements and the
different construction phases. This characterisation was
used as the basic scientific information for the stratigraphic
interpretation of the building elements, for the restoration
project of the ornamental stones and the production of
repair mortars and plasters.
HISTORIC BACKGROUND
Palazzo Pubblico
The building was founded in 1744 and finished the
following year, probably replacing a previous community
building. The building underwent several modifications
trough time and consists of a typical courtyard structure,
with the main façade overlooking “Piazza Verdi”. The main
element of the façade was a central tower with a belfry
and an elegant onion-shaped roof that collapsed during the
seismic crisis. The palace features are typical of the Este
ducal family that ruled the area.
The ground floor was used for the administrative offices
and hosted the ancient “Caffè Commercio”. The main floor
consists of a system of connected rooms and shows wall and
ceiling decorations dating back to the nineteenth century.
Bortolazzi Palace
At the end of the 16th century, the palace area was still
occupied by gardens. The presence of residential storage
buildings is testified by documents of the 17th century. During
the 18th century the palace, original residence of the Trombi
family, was enlarged and modified by the Bortolazzi family.
In the 20th century the use of the palace changed many
times: as public building, as a bank (“Piccolo Credito
Romagnolo”), and, during the 1930s it was renovated to
host the “Casa del Fascio”. After the 2nd world war the
palace was separated in different functional areas, a school
(up to 1982) and a Cultural and Museographic circle and
was eventually abandoned.
Casa Galei
The Casa Galei was the connection building between the
two palaces, probably used to host the services of Palazzo
Bortolazzi.
MATERIALS AND METHODS
The ornamental stones of the façade have been recognized
mostly through macroscopic analysis, but a few were
sampled for petrographic investigations under the optical
microscope to clarify the rock typology, characteristics and
degradation phenomena.
The degradation phenomena have been mapped using as
reference the Document UNI- Normal 11182. A scale of
three intensity degrees was considered, where the degree 3
is the most intense recorded degradation level.
Mortars and plasters from the Town Hall Palace were
studied to understand their relative chronology depending
on composition and technology production. Whenever
possible, sampling has been made systematically from
every wall stratigraphic unit. Samples were taken also in
correspondence of flat jacks tests.
An empirical evaluation of the cohesion of samples was
made following the terminology proposed by Alessandrini
et al., 1986.
The 46 samples of mortars and plasters were vacuum
impregnated in epoxy resin (araldite) for the preparation
of thin sections. The samples were then analysed under the
polarizing microscope with transmitted and reflected light.
The main mortars features under the optical microscope
were qualitatively described using as a reference the
Document UNI-Normal 11176.
A qualitative evaluation of the aggregate composition
was made to identify the provenance of sands following the
methodology proposed by Lugli et al., 2007.
To identify the texture and the composition of binders and
of binder related particles, SEM/EDS analyses were also
performed.
RESULTS
Ornamental stones
Six different types of natural stones were identified in the
façade: Scaglia rossa, Pietra d’Istria, Rosso Ammonitico,
trachyte, Carrara marble and a black marly limestone.
The balcony and the decoration of the upper parts of the
façade are mostly made of “Pietra d’Istria” from Croatia
(Middle Jurassic - Early Cretaceous age). It consists of a
white fine-grained limestone containing intraclasts, peloids
and stylolites. This rock is relatively uncommon in the
Modena area, its first documented use dates back to the 15th
century (Lugli, 2010).
The Scaglia Rossa is a fine-graned limestone containing
Globotruncana planktonic foraminifera (Upper Cretaceous
- Eocene) (Figure 2a). The Rosso Ammonitico is a nodular
fine-grained limestone showing different shades of white,
pink, dark and red colour (Jurassic Middle-Upper, 146176 million years ago). The Rosso Ammonitico slabs are
located in the access paving of the three windows on either
side of the portal. The slabs from the balcony and the carved
slab over the balcony are in Scaglia Rossa.
The provenance of both rocks is from the Verona area.
These stones show the characteristic presence of ammonites
shells and became very popular in the Modena area starting
from the Estense ruling (Lugli, 2010).
Carved out from Carrara marble are the slabs carrying
inscription at both sides of the portal. The famous
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Figure 2. a) Photomicrograph, transmitted light, parallel polars. Scaglia rossa, note the presence of Globotruncana planctonic foraminifera,
b) Photomicrograph, transmitted light, crossed polars. Recrystallized marly limestone showing a crust of gypsum crystals (white needles)
at the top of the exposed surface (upper half of pictures).
Figure 3. Degradation phenomena. a) Black crust affecting sheltered areas below the balcony and the ashlar trachyte of the portal. b)
Differential degradation phenomena of the Pietra d’Istria, which is strongly enhanced by the structural damage (fractures) caused by the
earthquake. Note the strong fragmentation in correspondence of a metal anchor bolt induced by the earthquake movements. c) Columns of
Pietra d’Istria and upper elements in Scaglia rossa from the balcony affected by biological colonization and mild differential degradation.
d) Sulfation phenomenon on the exposed surface of the black marly limestone in the medallion above the balcony. The whitish decorated
frame has been carved out from Pietra d’Istria. e) Carrara marble slab affected by granular disintegration enhancing the accumulation of
dust and shoot.
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Archaeometric study of the Finale Emilia Town Hall building materials
marble from the Apuane Alps (Northern Apennines) was
extensively used in the Modena area starting from the
Estense ducal period (Lugli, 2010).
Blocks of trachyte, from the Euganei Hills (Padua), frame
the main entrance of the building. The trachyte is a greyish
Oligocene volcanic rock (about 32 million years ago)
with a porphyritic structure consisting of phenocrystals of
anorthoclase, plagioclase and biotite, in a homogeneous
background. It was imported extensively by the Romans,
re-used during the Middle Age and imported again in the
19th century (Lugli, 2010).
A black marly limestone from the Northern Apennines
was used to carve the medallion above the balcony. It is
recrystallized with some fossil relicts (shells of bivalves and
echinoids) and rich in opaque minerals giving the black colour
(Figure 2b). The recrystallization phenomena hampered the
possibility to identify the provenance of this rock.
Degradation phenomena
The alteration phenomena of the ornamental stones are
mostly related to various degrees of black crust, differential
degradation, exfoliation, granular disaggregation, weathering,
surficial deposits, biological colonization, soluble salts
efflorescence, rust staining and fractures (Figure 1).
Differential degradation affects mostly the Rosso
Ammonitico, the Scaglia Rossa and to some extent the
Pietra d’Istria, as it represents the deterioration phenomenon
typical of nodular limestones. The leaching of the matrix
of iron oxides and/or hydroxides and clay minerals located
along the stylolites causes the detachment of micritic
nodules. The balcony shows the most severe differential
degradation phenomena, strongly enhanced by the structural
damage (fractures) caused by the earthquake (Figure 3b).
The biological colonization occurs mainly in the balcony
and affects mostly the Rosso Ammonitico and the Pietra
d’Istria elements (Figure 3c).
The Carrara marble is affected by granular disintegration,
which consists in the fall of powdering material. The
surface roughness, due to this phenomenon, facilitates the
accumulation of dust and dirt (Figure 3e).
The typical degradation of trachyte is exfoliation with
detachment and fall of surface stone layers.
The black crust occurs in sheltered areas not directly
exposed to rainwater, especially below the balcony, in the
statue and the ashlar trachyte of the portal (Figure 3a).
The most intense sulfation phenomenon was observed
on the exposed surface of the black marly limestone in the
medallion above the balcony (Figures 2b and 3d).
Mortars and plasters
Composition of the binders
Three types of binder were recognized in mortars and
plasters: 1) lime with variable hydraulic properties produced
by burning impure limestone cobbles; 2) gypsum, used for
decoration plasters, in some cases without aggregate; and
3) Portland cement, which characterizes the later additions.
The lime binder is typical for the older mortars. It contains
frequent binder related particles, possibly related to simple
artisanal preparation techniques (Elsen, 2006; Rattazzi,
2007; Manicardi, 1993; Marinelli et al., 1992). Fragments
of partially burned marly carbonate rocks showing the
structure and texture of the original rocks are common in
these mortars (Figure 4a). Another type of binder related
particles are the lime lumps sensu strictu, which appear
extremely porous (Figure 5a).
In the external plaster of the collapsed tower was found
the addition of brick dust (cocciopesto) in the lime binder.
Gypsum is the binder of some plasters, commonly used
without aggregate (Figure 6b). In this case the binder
related particles are gypsum crystals not completely burned
that show deformation caused by grinding. Large gypsum
pseudomorphs crystals, consisting of microcrystalline
gypsum, are originated by the rehydration of hemihydrate.
The gypsum binder contains impurities such as iron oxides
and/or hydroxides nodules and micritic carbonate.
Only in a few cases a sand aggregate is mixed with the
gypsum binder (Figure 6a).
The third type of binder is Portland cement. It is
characterised by the presence of unhydrated remnants
of clinker minerals such as alite (tricalcium silicate),
belite (dicalcium silicate), tricalcium aluminate and alkali
aluminates. These aggregates were finely ground and the
cement powder mixed with water and sand for application.
The main component formed during the hydration of these
clinker minerals is portlandite (calcium hydroxide). Particles
of cement not fully hydrated remain as clinker nodules. The
size and quantity of such clinker residues, their mineral
composition (e.g. the ratio of belite vs. alite), and their
microstructure are characteristic of low burning temperature
of early Portland cement (end of 19th - beginning of 20th
cent.). This indicates the use of shaft kilns and not the more
advanced later technologies at higher temperature of the
rotary kilns developed since 1950s (Campbell, 1999; Pintér
et al., 2013) (Figures 7 a,b e 8a). Typical of the latest stage
of renovation of the building was the addition of fly ash
(particularly after the 1950s). Fly ash is a spherical vitreous
material originating from the waste of industrial production,
added to induce a pozzolanic reaction (Figure 8b).
Composition of the aggregate
We identified four sources of aggregate sand by
petrographic composition which correspond to different
construction phases:
a) Panaro River sand characterised by the predominance of
carbonate fragments over to the siliciclastic fraction (Lugli et
al., 2007). The Panaro River sand was identified in mortars
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Figure 4. Photomicrographs of different mortar types: a) Mortar with lime binder and an underburned binder-related particle (marly
limestone, at center left) with fine-grained sand from the Panaro River; b) Mortar with cement binder, the sand is from the Secchia River;
c) Mortar with cement binder, the sand aggregate is from the Po River; d) Cement mortar with sand aggregate from a Veneto area river
(peloidal Mesozoic limestone, lower right side). All samples are shown in transmitted light, crossed polars.
Figure 5. Photomicrographs, in transmitted light, crossed polars, of mortars with lime binder. a) At the centre of the image two porous lime
lumps sensu strictu. b) Mortar with a binder/aggregate ratio >1.
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Archaeometric study of the Finale Emilia Town Hall building materials
Figure 6. Photomicrographs in transmitted light, crossed polars, of plasters with gypsum binder. a) Medium-fine sand aggregate and some
of gypsum crystal relicts (grey and whitish crystals). b) Re-hydrated gypsum crystals (large fragment at the top) and micritic carbonate
(brownish fragments) that was originally present in the gypsum rock.
and plasters from the most ancient parts of the building (lime
and gypsum, Figure 4a);
b) Secchia River sand, which shows the predominance of
the siliciclastic components over the carbonate grains (Lugli
et al., 2007). A provenance from the Secchia River was
identified in the later plaster cement additions (Figure 4b);
c) Veneto river sand, probably from the Adige River,
showing abundant limestone fragments such as oolitic,
calpionellids, Scaglia rossa, Rosso Ammonitico and
abundant fragments of trachyte and porphyric rocks (porfido
atesino). This sand supply was active for recent renovation
works (Figure 4d);
d) Po River sand: characterised by frequent metamorphic
rock fragments, rare fragments of limestone rocks, amphibole,
pyroxene and epidote grains. The Po River sand was used for
the very late renovation of the building (Figure 4c).
Construction phases and degradation phenomena of mortars and plasters
The stratigraphy, composition and textural parameters of
mortars and plasters clearly distinguish different building
phases of the palace. All the bedding mortars of the palace
were made using raw materials taken from the Panaro River:
the limestone cobbles were used to produce the lime and the
sand used as aggregate.
The oldest lime mortars from the ground floor appear
strongly deteriorated. The high humidity and the capillary
Figure 7. a) Photomicrograph, reflected light of clinker minerals in the mortar, suggesting an early Portland cement production b) Back
scattered SEM image, the large grain at centre of the image is a quartz granule of the sand aggregate; the composite granule in the upper
part of the picture are clinker nodules.
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Figure 8. a) Photomicrograph of Portland cement, reflected light. Crystals of belite (at center) and alite showing angular shape and typical
lamellae; the light gray interstitial phase consist of aluminate and ferrite. b) Back scattered SEM image. Detail of clinker and a fly ash,
beneath the big one a smaller phase of hydrated reaction.
rise of dump caused disintegration and binder dissolution
phenomena followed by local secondary calcite precipitation
within pores, secondary gypsum formation and mould. For
these reasons, the plasters underwent several substitutions
through time. The interior rooms show at least two restoration
phases both with aggregate coming from the Veneto region:
one very recent with fly ash and acrylic painting with cement
additive. The last plaster addition was prepared with Portland
cement mixed with Po River sand and fly ashes. The plaster
ceiling is made by gypsum without aggregate.
The external masonries are characterized by bedding lime
mortars with cocciopesto and Panaro sand and are covered
by later cement plasters additions: at least two phases of low
temperatures cements (early cement), the first with Secchia
River sand and the second mixed with Po River sand. The
most recent renovation phase is characterized by the use of
modern high-temperature cement with the addition of fly ash.
The external plaster of the collapsed tower was probably
the original plaster, prepared with lime and brick dust
(cocciopesto). The surface was treated with “sagramatura”,
a typical local finishing consisting of very thin layers of lime
putty mixed with crushed bricks.
The bedding mortars of the main floor are well preserved.
We could recognise two different building phases due to
the modification of the main room. The decorations of the
prestigious rooms at this floor underwent many changes.
The first phase was finished using a gypsum plaster without
aggregate. The painted plasters made by lime and Panaro
River sand were probably added in the 19th century. In
very recent years the walls were repainted with a modern
acrylic paint. The ceiling plaster was made of gypsum with
aggregate coming from the Panaro River and two different
painted layers.
CONCLUSION
The Town Hall of Finale Emilia is a typical 18th building
of the Emilia Romagna Region constructed with local
materials: most of the stones were imported in the Modena
area during the 18th century or re-used from ancient Roman
buildings (Lugli, 2010). In the first construction phases all
the raw materials for the production of mortars and plasters
were taken from the Panaro River, which is the closest source
to the palace. The more recent renovations saw the use of
industrial materials coming from the Veneto area and the Po
River.
The decay phenomena are related to capillary dump rise,
black crusts, and differential degradation phenomena. The
damage produced by the 2012 earthquakes further enhanced
degradation by water infiltration along new cracks and
fractures. The recent transformation and the use of unfitting
new industrial materials acted as elements of discontinuity
amplifying the effects of the earthquake.
The result of this study will be used as the basic scientific
information to elaborate the restoration project of the
ornamental stones and the preparation of the repair mortar
and plasters. This work was an example of philanthropic
collaboration among institutions in charge for preservation
and protection of historical heritage and professionals,
cooperating for the preparation of a comprehensive
restoration project.
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