ORIGINAL ARTICLE
The influence of building materials on salt formationin rural environments
Vesna Matovic • Suzana Eric • Danica Sreckovic-Batocanin •
Philippe Colomban • Aleksandar Kremenovic
Received: 26 August 2013 / Accepted: 25 January 2014
� Springer-Verlag Berlin Heidelberg 2014
Abstract Blocks of limestone and sandstone used in
walls of the Manasija Monastery complex showed damage
caused by the efflorescence and subflorescence of different
salts in a low-pollution rural environment. In addition to
common salts such as thenardite, thermonatrite, trona and
gypsum, a small amount of eugsterite and darapskite was
also present. Although these sodium and sodium–calcium
salts formed where cement mortar was used for repairs, the
lithological type and chemical composition of the substrate
also had an influence on the development of distinct salts.
The interaction between limestone and sandstone (sub-
strates) and a solution rich in sodium (without calcium)
was successfully simulated in the laboratory. The presence
of gypsum and sodium–calcium sulphate, as experimental
products, solely on the limestones indicated that, in addi-
tion to the cement-mortar solution, part of the calcium
required for the formation of calcium and double sodium–
calcium salts could occur from this substrate.
Keywords Soluble salts � Na–Ca sulphate � Limestone �Sandstone � Porosity
Introduction
Stone building and monument decay has been a subject of
scientific and official debate in recent decades. The causes
of such decay and scientifically supported hypotheses about
weathering mechanisms, including experimentally docu-
mented degradation phases, are already well known, but
the types of salt and their influence on building materials
are still the focus of numerous research projects. The
successful and appropriate protection of cultural heritage
objects requires good knowledge not only of building
materials, but also of the nature and development mecha-
nisms of various degradation products. Soluble salts are the
most dangerous and significant cause of decay (Winkler
and Singer 1972; Charola 2000; Doehne 2002; Cardell
et al. 2003; Flatt 2002; Scherer 2004).
Various soluble salts occur in cultural-historical monu-
ments built of porous stone (limestone or sandstone),
including sulphates, nitrates, carbonates and chlorides of
Na, K, Ca and Mg (Charola 2000; Arnold and Zehnder
1991; Steiger 2005; Benavente et al. 2004, 2007; Ruiz-
Agudo et al. 2007). The most common and destructive salts
are gypsum (CaSO4�2H2O), thenardite (Na2SO4), trona
Na3(CO3)(HCO3)�2(H2O) and mirabilite (Na2SO4�10H2O).
When these salts’ hydration/crystallisation pressure exceeds
the porous substrate’s resistance, the released stress dam-
ages the stone in the form of scaling, spalling, etc. (Doehne
2002; Lewin 1989; Gaudie 1987). The sources of these salts
vary (Doehne 2002; Cardell et al. 2003; Winkler and Singer
1972; Winkler 1997; Gauri and Bandyopadhyay 1999;
Kloppmann et al. 2011). Ions of a possible salt may occur
V. Matovic (&) � S. Eric � D. Sreckovic-Batocanin �A. Kremenovic
Department of Mineralogy, Crystallography, Petrology
and Geochemistry, Faculty of Mining and Geology,
University of Belgrade, Djusina 7, Belgrade, Serbia
e-mail: [email protected]
S. Eric
e-mail: [email protected]
D. Sreckovic-Batocanin
e-mail: [email protected]
A. Kremenovic
e-mail: [email protected]
P. Colomban
LADIR, UMR 7075 CNRS, Universite Pierre and Marie Curie,
C49, 4 Place Jussieu, 75252 Paris 05, France
e-mail: [email protected]
123
Environ Earth Sci
DOI 10.1007/s12665-014-3101-4
due to capillary forces brought on during building con-
struction (Rosch and Schwarz 1993), be derived during the
reaction of atmospheric factors with components of the
stone (Camuffo et al. 1983; Cardell et al. 2008; Chabas et al.
2000) or be of anthropogenic origin (Winkler 1978). Mor-
tar, common in modern building construction and an
obligatory component of cultural heritage restoration pro-
jects, is also significant and a common source of salts.
Mortar contains high concentrations of Ca, Na, K and SO4
ions whose permeability enables the easy migration of
water solutions, dissolution and subsequent release and
deposition of salts that will damage a stone (Duffy et al.
1993; Perry and Duffy 1997). For example, these ions can
affect the salt crystallisation resistance of built materials
(Klisinska-Kopacza and Tislova 2013).
Stone damage due to salts activity is a result of very
complex physical–chemical reactions (Charola 2000).
Identifying the interactions between a variety of factors is
commonly performed in laboratory simulations and ageing
tests (Goudie 1986; Goudie and Viles 1997; La Iglesia
et al. 1994; Benavente et al. 2001; Warke and Smith 2007).
The treatment of various stone types with salt solutions
(Goudie and Viles 1997; La Iglesia et al. 1994; Rothert
et al. 2007; Cultrone et al. 2008; Yu and Oguchi 2010),
most commonly with Na2SO4 solution (Rodriguez-Navarro
et al. 2000; Tsui et al. 2003; Espinosa Marzal and Scherer
2008; Steiger and Asmussen 2008), enables the comparison
of destructive activities caused by formed salts. Cardell
et al. (2008) have considered the reaction products and
decay forms of limestone weathering caused by certain
magnesium, calcium, sodium and potassium sulphate
solutions. Based on the mineralogical observation of
derived salts, the authors have concluded that the chemical
weathering of stone leads only to solutions of magnesium
sulphate. According to Ruiz-Agudo et al. (2007), differ-
ences in the damage created by Na-sulphate and Mg-sul-
phate have been due mainly to differences in their
crystallisation patterns, and they have experimentally
demonstrated that the mechanism of salt weathering by Na-
sulphate consists of the detaching of successive stone
layers, while Mg-sulphate induces crack formation and
propagation within the bulk of the stone.
The Manasija Monastery is a lithologically heteroge-
neous building in a non-polluted rural environment. It was
built between 1407 and 1418 and located in the central part
of Serbia, near Despotovac city. Some types of salts in
form of efflorescence and subflorescence were formed on
the surfaces of built blocks. It should be emphasised that
the formation of the above mentioned salts has generally
been linked to the utilisation of cement mortar, during
either the building or reparation of cultural monuments, but
the role of substrate on the type of formatted salts has not
yet been made clear. In the aim to examine possibilities of
Ca and double Na–Ca salts crystallisation in laboratory
conditions, lithotypes built in the Manasija monastery were
treated with sodium-rich solution. The premise for the
chemical treatment was: Is substrate source of the part of
calcium ions required for salt formation? The results
obtained on this way could enable a better understanding of
mechanism of salts formation in natural conditions, espe-
cially the double sodium–calcium salts in porous building
materials.
Site characteristics and historical background
The Manasija Monastery is located in a mountain-valley
region in the central part of Serbia, near Despotovac city
(Fig. 1a). The climate in this area is temperate continental
(average annual temperature is 11.4 �C) with moderately
warm summers (21.2 �C) and rather cold winters (0.7 �C;
data from the Republic Hydro-Meteorological Service of
Serbia). The average annual rainfall is 600–750 mm/year
and the relative humidity (RH) reaches maximum values in
winter (80–85 %), while the minimum values occur in July
and August (65 %). According to data from the Agency for
Environmental Protection, the average annual concentra-
tions of air pollutants in 2011 were SO2 11.7 lg/m3; NO2
26.7 lg/m3; and CO 0.78 lg/m3.
The Manasija Monastery is one of the most significant
monuments of medieval Serbian heritage. It was founded
by Despot Stefan Lazarevic between 1407 and 1418 and
consists of the Holy Trinity church, a refectory and forti-
fication with eleven towers connected by massive walls,
with an exterior guard wall and pedestrian path on the
rampart level (Janicijevic 1998) (Fig. 1a). The church
facades were made of sandstone blocks, while porous
limestone was used for the parapets and profiled elements
on the facades. The eastern and south-eastern church
facades are authentic, excluding the window stone frames,
while the west and narthex facades were rebuilt during
1960–1970 (Fig. 1b). In addition to massive walls built of
compact grey limestone blocks held together by mortar
courses, the fortification includes ten rectangular towers
built mainly of porous limestone and rare sandstone and
compact grey limestone blocks. All frontal parts of the
passages throughout the towers were built of tufa blocks.
Materials and methodology
Samples
Salt samples were taken from stone blocks built in the
Monastery towers and fortification walls in August 2011.
The main criteria for the sampling positions were: (1)
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123
significant quantities of salt in the form of efflorescence on
the stone surface (the facade of the church had no visible
salt) and (2) the originality of the blocks from the period of
Monastery construction. Salt samples were taken from the
interior walls and vaults of towers where only joints were
repaired 40 years ago. Beside the form of salt efflores-
cence, the subflorescence is evident on some sandstone
blocks (Fig. 2). Their surfaces are subject to scaling and
one salt sample was taken from the new opened surface.
The number of salt samples required for X-ray powder
diffraction (XRPD), SEM/EDS and Raman spectrometry
(*5 g) were mechanically removed from the substrate and
packed into vials. The locations of the collected salt sam-
ples are given in Table 1 and Fig. 1a.
Thirty-three stone samples were collected for charac-
terisation of their mineral compositions. These samples
were taken from labile zones in the stone blocks where
efflorescence was lacking. Samples used for the determi-
nation of pore size distribution were separated after their
petrographic observation.
Analytical methods
Petrographic analyses of the built stone were performed on
thin sections using a Leica DMLSP microscope for polar-
ised light that was connected to a Leica DC 300 digital
camera.
Determination of physical properties of stone (e.g.,
bulk and apparent density, total and open porosity, water
absorption, and hydric properties) was performed using
laboratory tests according to European Standards. Total
and open porosity values were calculated according to
values for real and bulk densities according to test EN
1936 (2006). Hydric behaviour of these stones was
characterised by the water absorption test EN 13755
(2008), and the capillary absorption test EN 1925 (1999).
All the tests performed for each lithological type were
carried out on 5 9 5 9 5 cm samples taken from Ma-
nasija Monastery.
Pore size distribution was determined using a mercury
intrusion porosimeter (Carlo Erba Porosimeter 2000) and
using the Milestone 100 Software System on stone samples
taken from the towers. This high-pressure mercury intru-
sion porosimeter operates within the 0.1–200 MPa inter-
val and enables the estimation of pores within the
0.005–100 lm interval.
X-ray diffraction analyses were used to determine the
phase compositions of powdered salts and powdered and
chemically treated limestone and sandstone. The XRPD
was performed using a Philips PW-1710 diffractometer.
The diffraction patterns were obtained from 5� to 60� 2Husing CuKa1,2 radiation with a step scan of 0.02� 2H and a
0.5 s step time.
Fig. 1 a Panoramic view of the Monastery Manasija with 11 towers (http://pes2011.elfak.ni.ac.rs/?page_id=873); b The Despot tower and
rebuilt facade of Church narthex (photo: V. Matovic)
Fig. 2 Sandstone scaling caused by subflorescence (stone block in
vault of the tower no. 11); salt sample 8 was taken from interior
surface of detachment scale
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123
SEM–EDS was performed using a JEOL JSM-6610LV
scanning electron microscope connected to an X-Max
energy dispersive spectrometer to identify the morpholo-
gies and chemical compositions of the mineral phases
present in the salts and chemically treated limestone and
sandstone. The samples were covered with gold and carbon
using a BALTEC-SCD-005 sputter coating device, and the
results were recorded under high vacuum conditions.
Raman spectrometry was performed on the samples
using multichannel notch filtered, high-sensitivity Senterra
(Bruker Optics) and HR (Horiba Jobin–Yvon) microspec-
trometers equipped with a Peltier-cooled CCD matrix. An
Olympus microscope (950 objective) was used to produce
an analysed volume of a few lm3. The same spot was
illuminated alternately with different laser lines [532 (both
instruments) and 780 (Senterra) nm]. The step times ranged
from 3 9 100 to 5 9 100 s.
Chemical treatment of built stone
Stone samples including (1) porous limestone, (2) grey
limestone and (3) sandstone were cut into cubes approxi-
mately 1 cm3 in size and put in 50 cm3 glasses with pre-
viously prepared solution of 0.1 M Na2SO4. Each cube was
soaked up to halfway in a solution of 0.1 M Na2SO4. The
samples were kept in the solutions for 15 days and then air-
dried for 15 days (18–25 �C air temperature and 42–55 %
humidity). The treated samples (where salts were formed)
were analysed by SEM/EDS and XRPD with the goal of
determining the formation of salts containing calcium.
Results and discussion
Petrophysical characteristics of built stone
The optical study of the samples and thin sections showed
that the rocks could be characterised as porous limestone
(PL), grey limestone (GL) or sandstone (S). This order
represents the sequence of representation in the towers
and walls. Porous limestones dominated the towers and
sandstone occurred sporadically, while the fortification
walls were built of grey limestone. Tufa was used in the arc
elements of towers. However, this rock was not a subject of
this study because salts did not appear on it. The stone
samples estimated porosimetric parameter values are pre-
sented in Fig. 3.
Porous limestone (PL) was Miocene in age and light
brown in colour (Fig. 3a). The rock consisted of microcrys-
talline calcite and variable amounts of a terrigenous com-
ponent (commonly 5–10 % quartz clasts; Fig. 3a). The
micrite and microsparite groundmass was frequently reddish
in colour due to the presence of iron oxides. The results
of physical properties show that value of bulk density is
2.18 g/cm3 and real density is 2.66 g/cm3. Total porosity is
18.1 and open porosity is 13.6 %. Values for water absorption
6.1 % is in agreement with open porosity and the absorption
coefficient by capillarity (11.22 g/m2 s1/2; Fig. 3d). The pore
size distribution was unimodal, with an average pore radius of
7.9 lm. The percentage of pores with a radius between 10 and
100 lm hardly approaching 10 % and those with a radius
of \10 lm dominating (*85 %; Fig. 3e, f).
Grey limestone (GL) was Jurassic in age and the dom-
inant stone in the fortification wall facade, but rare in the
towers. The rock was dark grey, fine-grained rock cut with
numerous veins of secondary calcite (Fig. 3b) and con-
sisted of carbonates (95–98 % CaCO3) and insignificant
amounts of clayey minerals. It contained rare skeletal
remains of marine organisms bound by a micrite matrix
(Fig. 3b) and was very hard and compact rock (bulk den-
sity is 2.69 g/cm3 and real density is 2.70 g/cm3 with a
total porosity of 0.59 % and open porosity is 0.2 %). The
average pore radius of 22 lm (probably microcracks),
displaying a bimodal capillary pressure saturation curve
(two maxima in the ranges of 0.1–1 lm and 10–100 lm;
Fig. 3f). Water absorption is 0.13 % and the capillary
absorption coefficient (0.064 g/m2 s1/2; Fig. 3d).
Sandstone (S) was Lower Miocene in age and consisted
of quartz, feldspar, rock fragments, rare micas, cement and
a matrix (Fig. 3c). Quartz, as the dominant mineral,
occurred in angular or subangular, rarely isometric grains
that varied in size from 0.25 to 0.5 mm in well-sorted
Table 1 List of salt samples
with their locations and
substrate and extent of their
appearance
Number of samples Location Substrate Surface/thickness
1 Entrance in the tower 3 Porous limestone 1.2 9 0.7 m2/0.5–1 cm
2 Tower 2 Porous limestone 1 9 0.7 m2/0.5–1.2 cm
3 Tower 2 Porous limestone 0.6 9 0.5 m2/0.5–0.8 cm
4 Tower 2 Porous limestone 1.2 9 1 m2/0.5–1 cm
5 Main stairways Grey limestone 0.5 9 0.6 m2/0.1–0.5 cm
6 Fortification walls Porous limestone 0.3 9 0.5 m2/0.3–0.7 cm
7 Entrance in the tower 10 Sandstone 1.4 9 1.2 m2/0.5–1.2 cm
8 Vault of tower 11 Sandstone 0.3 9 0.2 m2/0.3–0.6 cm
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123
sandstone. The quartz grains were either homogenous or
built mosaic aggregates. Feldspar also occurred in the form
of orthoclase, microcline and plagioclase. Orthoclase and
microcline occurred in subrounded, commonly fresh, very
rare kaolinitised grains measuring 0.4–0.8 mm across,
while plagioclase occurred as lamellar, fresh grains mea-
suring 0.4–0.7 mm in size. Mica occurred as orientated
muscovite flakes, while rock fragments were determined to
be cherts, quartzites and volcanic rocks. Cement (carbona-
ceous to siliceous-calcitic) occurred as a contact-pore
Fig. 3 Images and photomicrographs of stones from the Monastery
Manasija, a Porous limestone; b Grey limestone; c Sandstone.
d Capillary absorption curves of sandstone (S) and limestone (PL,
GL), e, f Distribution of pore size and relative volume of pores in
different rocks (S sandstone, GL grey limestone, PL porous limestone)
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123
filling. The sandstone (S) was characterised by a relatively
high total porosity of 17.8 % and open porosity is 13.0 % (a
bulk density is 2.34 g/cm3 and real density is 2.84 g/cm3). It
showed a unimodal pore size distribution with an average
pore radius of 13.9 lm and the majority of pores have
radius over 1 lm (* 70 % vol. of rock; Fig. 3e, f). Value
for water absorption is 6.2 % and the absorption coefficient
by capillarity is 12.47 g/m2 s1/2 (Fig. 3d).
XRPD, SEM–EDS and Raman analyses of salts
collected from the monument
The X-ray powder diffraction analyses conducted on the
collected salt samples (samples no. 1–4) revealed the pre-
sence of different salt types in addition to the commonest
calcite (obtained from limestone). Thenardite (Na2SO4)
prevailed in the majority of samples and eugsterite
Fig. 4 XRPD diagrams of the salts (samples 1–8) from walls of the Monastery complex (Da darapskite, Td thenardite, Eu eugsterite, T trona,
Th thermonatrite, Cc calcite, Q quartz)
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(Na4Ca(SO4)3�2H2O) was another identified sulphate salt
(Fig. 4). Nitrate-sulphate salt (darapskite (Na3(SO4)
(NO3)�H2O)) was found in the samples dominated by the-
nardite. Carbonate salts were identified in the fifth salt
sample that developed on the limestone: trona
(Na3(CO3)(HCO3)�2(H2O) and thermonatrite Na2CO3�(H2O) (Fig. 4). Only calcite and quartz were identified in
sample 6. XRPD analyses of the salts that formed on the
sandstone in samples 7 and 8 suggested that the major
phase was thenardite (Fig. 4).
Fig. 5 SEI images with EDS spectrums, a eugsterite and thenar-
dite—sample 1; b thermonatrite—sample 5; c thenardite—sample 8;
Representative Raman spectra, d sulphates: main phase thenardite
plus eventually eugsterite; e–f main phases trona, darapskite and
bassanite (see Table 2; samples 1–5)
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The morphologies of the mineral phases were deter-
mined using SEM and their semi-quantitative chemical
composition determined using EDS analyses. Eugsterite
occurred in elongate, prismatic, pseudorhombic forms
approximately 2–10 lm in size. Thenardite occurred in
bipyramidal shapes approximately 6–10 lm in size (sam-
ple 1, Fig. 5a). The thermonatrite from sample 5 developed
in prismatic or tabular aggregates ranging in size from 5 to
20 lm (Fig. 5b), while only thenardite was observed in salt
sample 8 that occurred in the form of tabular and irregular
grains ranging from 2 to 20 lm in size (Fig. 5c). Due to its
low sensitivity to nitrogen, the SEM–EDS analysis did not
identify darapskite.
The representative Raman spectra collected on salt
samples 1–5 (Table 1) are shown in Fig. 5d–f. The spectra
are grouped as a function of the main fingerprints, sul-
phates (strong 990 cm-1 symmetric stretching mode of a
SO4 tetrahedron) and (hydroxyl) carbonates (strong
ca1090 cm-1 peak of the symmetric stretching mode of a
CO3 unit). Characteristic Raman signatures from the lit-
erature are listed in the Table 2 for the presence of all
potential minerals. It should be noted that the efficiency of
Raman spectroscopy to identify the different sulphate and
carbonate phases is obviously limited in the lack of accu-
rate references covering the low wavenumber region.
However, XRPD and SEM/EDS results are more efficient
in regard to mineral composition of investigated samples.
The sulphate fingerprint was the characteristic signature
of the XO4-based structure, with a strong and narrow
symmetric A1 X–O stretching mode, degenerated F
asymmetric stretching (1060–1150 cm-1) and bending
(617–645 cm-1) triplets with a degenerated E symmetric
bending doublet (450–465 cm-1). The modes at lower
wavenumbers included libration XO4 (280 cm-1). As evi-
denced by the sulphate signatures, the peak relative
intensity varied widely. However, the Raman peak inten-
sity depends heavily on the orientation of the crystal axis
vs. the electric vector of the laser beam. Orientation varied
based on the spot under analysis (see further figures) and
was not characteristic of phase allotropy. The thenardite
and darapskite signatures, as listed in Table 2, agreed with
Fig. 5d spectra. Bands at 1365 and 1455 cm-1 did not
belong to sulphate compounds and may have corresponded
to weddellite (CaC2O4�2H2O), carbonates (see below) or
even nitrates. Traces of gypsum (1008 cm-1) were also
observed, and no other bands were observed at higher
Table 2 Characteristic Raman signatures of formed phases as well as phases that could be in paragenesis or mismatched in Raman spectra
Name Composition Raman signature/cm-1 Observed References
aQuartz SiO2 464 X Tournie et al. (2011)
Calcite CaCO3 1437, 1086, 712 X Culka and Jehlicka (2010)
Dolomite CaMg(CO3)2 1443, 1098, 725 – Kramar et al. (2010)
Anhydrite CaSO4 1018 – Tournie et al. (2011)
Bassanite CaSO4�0.5H2O 1008, 1026 X Prasad (1999)
Darapskite Na3(SO4)(NO3)�H2O 1123, 1059, 993, 640, 456 X Jentzsch et al. (2012)
Eugsterite Na4Ca(SO4)3�H2O 1084, 1125 X This work
Kalicinite (aq. sol.) KHCO3 1364, 1312, 1016, 640 – Rudolph et al. (2008)
Glauberite Na2Ca(SO4)2 1002 X? Clark et al. (2010)
Yusupov et al. (1983)
Gypsum CaSO4�2H2O 1137, 1007, 673, 621, 416 X Maguregui et al. (2010)
Prasad (1999)
Natron Na2CO3�10H2O 1071, 716 ? Sarmiento et al. (2008)
Mirabilite Na2SO4�10H2O 1086, 989.3, 615, 446 ? Hamilton and Menzies (2010)
Metastable-Mirabilite Na2SO4�7H2O 1106, 987.6, 464, 592 ? Hamilton and Menzies (2010)
Pirsonite Na2Ca2(CO3)3�2H2O 1070, 710 ? Zaitsev and Keller (2006)
Shortite Na2Ca(CO3)3 1399, 1088, 1069, 730, 709, 695 – Mernagh et al. (2011)
Thenardite Na2SO4 1258, 1149, 992, 626, 432 ? Agayo et al. (2011)
Maguregui et al. (2012)
Sarmiento et al. (2008)
Morillas et al. (2012)
Thermonatrite Na2CO3�H2O 956, 579 ? Gomez-Laserna et al. (2013)
Trona Na3(CO3)(HCO3)�2H2O 1061, 225, 186 X Gomez-Laserna et al. (2013)
Witherite BaSO4 1424, 1061, 693 – Bucca et al. (2009)
Notably peaks wavenumber in bold
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wavenumbers. A second group of Raman signatures
exhibited a strong narrow peak at 1062 cm-1 and a well-
defined doublet at *1310–1430 cm-1 (Fig. 5e, f), the
latter of which is characteristic of carbonate ion. Strong
differences were observed in the low wavenumber range
(\300 cm-1) according to the presence of different phases.
One spectrum exhibited a 995–1062 narrow doublet, but
other spectra showed an additional broader band at
1028 cm-1. Witherite exhibits a strong 1061 cm-1 peak,
but the rareness of this phase allowed us to rule out this
assignment. Darapskite, a mixed sulphate-nitrate, has a
strong 1059–993 cm-1 doublet (Table 2) that fits well with
the observed spectrum. A broad band before a strong nar-
row peak is characteristic of H–XOn vibration units: the X–
O–H stretching mode is decoupled and its wavenumber is
lower due to the H-bond. Accordingly, features appear in
the O–H stretching region (2500–4000 cm-1), although the
995–1062 cm-1 doublet compound does not exhibit bands
above 2000 cm-1. The low wavenumber signature of the
doublet compound was also very different from that of the
other. A natron Raman spectrum exhibits a strong
1071 cm-1 peak and the stronger peak of the glauberite
spectrum is observed at 1002 cm-1. The observed spec-
trum was thus consistent with a mixture of the later two
phases.
The spectra with medium broad 1028 cm-1 (H–O–
C = O) stretching mode and narrow 3438 cm-1 (O–H
stretching mode) bands could be assigned to trona.
Accordingly, the broad band centred at 3075 cm-1 was the
H2O stretching massif.
Generally, thenardite was the main phase in samples 1–3
and trona the dominant phase in sample 5, while a mixture
of sulphate phases with calcite and darapskite was most
likely in sample 4.
SEM–EDS and XRPD analyses of salts obtained
in the laboratory
The chemical treatment of limestone with a solution of
sodium sulphate caused some chemical reactions between
the solution and substrate. In addition to thenardite, small
amounts of tabular, pseudo-hexagonal gypsum crystals
were formed on the grey limestone. A radial and fan-
shaped aggregate of sodium-calcium sulphate occurred on
the gypsum crystals (Fig. 6a, b).
Double Na–Ca sulphate in the form of a fan-shaped
aggregate was also identified after chemical treatment of a
porous limestone sample using EDS analyses (Fig. 6c, d).
The crystallisation of thenardite was observed on all sub-
strates. XRPD performed on the treated samples identified
only thenardite, while other mineral phases (gypsum and
Na–Ca sulphate) occurred in insignificant amounts below
the applied method’s detection limit. However, it was clear
that the solution of Na2SO4 led to a partial dissolution of
Fig. 6 a SEI images of salts on limestone after chemical treatment with Na2SO4 of (a) gypsum, thenardite and Na–Ca sulphate—grey limestone,
b detail of Na–Ca sulphates—grey limestone, c, d Na–Ca sulphate—porous limestone
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123
limestone because the formed phases contained calcium.
Glauberite is only stable anhydrous phase in nature, but
several phases contain hydroxyl groups or molecules of
water: hydroglauberite (Na4Ca(SO4)3�2(H2O)), eugsterite
(Na4Ca(SO4)3�2(H2O)), cesanite (Ca2Na3[(OH)(SO4)3])
and omongwaite (Na2Ca5(SO4)6�3H2O) (Mees et al. 2008;
Cavarretta et al. 1981). The identified sodium–calcium
sulphate was probably glauberite or hydroglauberite/
eugsterite. Hydroglauberite and eugsterite are rhombic and
monoclinic polymorphic modifications with the same
chemical composition, but omongwaite and cesanite have a
higher calcium content compared to their sodium content,
which is not the case with the identified Na–Ca sulphate
(Table 3).
The chemical treatment of sandstone with the sodium
sulphate solution did not cause chemical reactions between
the solution and substrate because only thenardite was
formed.
Mechanism of Ca and double Na–Ca salt formation
The majority of sodium salts occurred due to the utilisation
of cement mortar and the influence of atmospheric water.
The permanent influence of atmospheric water (rain,
moisture and snow) led to the disintegration of the cement
mortar and its partial dissolution and enriched it with
various ions, such as Ca2?, Na?, K?, Mg2? OH-, HCO3-,
SO42-, etc., enabling the precipitation of diverse salts
under certain temperature conditions and saturations. Pro-
cesses of salt formation, their repeated dissolution and re-
precipitation were common. The occurrence of salt on the
stone blocks was largely the result of the transport of
solutions formed in the cement mortar.
The role of the rock type was also important to salt
formation (chemical composition and solubility of mineral
phases, such as constituents, porosity, etc.). Chemical
treatments of stone block samples were performed to
examine the possibility that part of the calcium ions
required for salt formation originated from the substrate.
The simulated conditions of salt formation included solu-
tion enriched by sodium and sulphate ions (related to the
cement solution, but without calcium and carbonate ions).
According to the results of the conducted experiments, the
influence of chemical composition and porosity of the
substrate on the type of salt formation were considered.
The influence of 0.1 M sodium sulphate on limestone was
seen in the release of Ca2? ions from the substrate and the
formation of small quantities of gypsum and Na–Ca sul-
phate (Fig. 6a, b). The sodium–calcium sulphate (such as
glauberite) that occurred with gypsum under this chemical
treatment could have been formed by:
(a) The direct influence of the sodium sulphate solution
on limestone:
CaCO3ðsÞ þ 2Na2SO4ðaqÞ
! Na2Ca SO4ð Þ2ðsÞþ Na2CO3ðaqÞð1Þ
(b) The influence of sodium sulphate solution on already-
formed gypsum (glauberite developed at the expense
of gypsum as a precursor under the influence of
sodium-rich solutions (Orti et al. 2002):
CaSO4 � 2H2OðsÞ þ Na2SO4ðaqÞ! Na2Ca SO4ð Þ2ðsÞþ 2H2O ð2Þ
and/or
(c) The synchronous formation of gypsum and glauberite:
2CaCO3ðsÞ þ 3Na2SO4ðaqÞ þ 2H2O
! 2Ca2þ þ 3SO2�4 þ 6Naþ þ 2CO2�
3 þ 2Hþ þ 2OH�
! CaSO4 � 2H2OðsÞ þ Na2Ca SO4ð Þ2ðsÞþ 2Na2CO3ðaqÞ
ð3Þ
In a similar way hydroglauberite or eugsterite could be
formed. On the other hand, under natural conditions, there
are a number of other factors (amount of water and its
circulation, changing the pH of the microenvironment, etc.)
that can significantly influence the mechanism of formation
of these salts.
According to a comparison of the experimentally
obtained results with those obtained through the study
of natural samples, certain facts should not be excluded.
At first, the experiments were partially controlled (without
the additional dilution that always occurs in natural con-
ditions under precipitation, and without rapid changes
in temperature and humidity) and significantly invasive
(a high concentration of sodium sulphate similar to its
Table 3 EDS analyses of salts formed in laboratory (Fig. 6)
Weight %
1 2 3 4 5 6 7 8 9
Na – 18.56 34.25 17.55 19.22 33.28 32.54 20.05 19.86
Ca 25.02 9.42 – 8.91 8.75 – 0.05 9.12 8.94
S 20.30 20.19 21.30 21.34 21.26 23.47 22.38 19.53 20.39
O 54.68 51.83 44.45 52.20 50.77 43.25 45.03 51.30 50.81
Environ Earth Sci
123
concentration in natural conditions). Second, the source of
calcium was not only limestone itself. Certainly, Ca2? ions
originated partly from the cement mortar. The sulphates
were mostly related to the cement mortar, and to a lesser
extent to the sulphuric acid that formed due to the oxida-
tion and dissolution of SO2 present in the air. Sulphur oxide
(SO2) from the atmosphere can be oxidised to sulphate ions
on the surfaces of stone blocks, which is one of the reasons
for the occurrence of gypsum on limestone monuments
(without the use of cement mortar) in urban areas (Camuffo
et al. 1983; Garcia-Valles et al. 1998; Siegesmund et al.
2007). According to data from the Agency for Environ-
mental Protection, the average annual content of SO2 in the
air in this rural environment has been low in the last few
years (\30 lg/m3). However, these values were estimated
in a city (Paracin) approximately 20 km from the Monas-
tery. The heating of the Monastery for hundreds of years by
wood and coal have significantly contributed to the amount
of smoke, soot and SO2 in close vicinity to the Monastery
complex.
The formation of glauberite as Na–Ca sulphate in
experimental conditions was compared with the occurrence
of eugsterite (also Na–Ca sulphate) in natural conditions
(the salts on porous limestone in samples 1 and 4).
According to past studies, eugsterite has been determined
as a meta-stabile phase in the system CaSO4–Na2SO4–H2O
(Vergouwen 1981; Freyer et al. 1997). The precipitation of
eugsterite is possible if the Na/Ca ratio exceeds four
(Vergouwen 1981). Nonetheless, Li et al. (2010) have
studied mineral assemblages in evaporates such as halite–
gypsum–eugsterite, halite–gypsum–eugsterite–glauberite
and gypsum–thenardite–eugsterite, and concluded that
eugsterite may develop either under the influence of
sodium and sulphate ion- enriched solutions on gypsum:
CaSO4 � 2H2OðsÞ þ 4Naþaqð Þ þ 2SO2�4 aqð Þ
! Na4Ca SO4ð Þ3�2H2OðsÞ ð4Þ
or under the influence of calcium and sulphate ion-enriched
solutions on thenardite:
2Na2SO4ðsÞ þ Ca2þaqð Þ þ SO2�
4 aqð Þ ! Na4Ca SO4ð Þ3�2H2OðsÞ
ð5Þ
The sandstone does not have a direct influence on the
formation of calcium and sodium-calcium salts because
only thenardite was formed after chemical treatment.
It should be noted that the formation of distinctive salts
and the deterioration of stone depends on the porosity, and
the distribution of pores, such as the content of pores with
diameters ranging from 0.1–10 lm (Benavente 2011).
Although the total porosity (which includes closed pores) is
significant, the open porosity is of greater importance, as it
has a direct impact on the likelihood that undesired fluids
will penetrate the stone. The flow mechanism is quantified
by the capillary absorption coefficient because it is linked
to the characteristics of the pore interconnectivity, the
migration of fluid and the stone permeability (Benavente
et al. 2002). The porous limestone has a homogeneous pore
system with the domination of capillary pores that are
responsible for a high value of capillary coefficient and
water uptake. The porosity in this stone is characterised by
microcracks and ink-bottle pores (pores with diameter
below 10 lm). Similar values of total and open porosity
accompanied with the high capillary coefficient, suggest on
interconnected pores that enable a high absorption, but
slow evaporation of solution. The porous structure is
responsible for the easy entrance of salt solution in porous
limestone, where they remain long enough to enable the
dissolution of substrates and the interaction and subsequent
deposition of glauberite, eugsterite and other salts in a form
of subflorescence. The pore spaces in grey limestone allow
only for the efflorescence of thenardite, gypsum crystals
and double Na–Ca salts, but in smaller amounts than in
porous limestone. The grey limestone is very resistant to
weathering processes related to fluid circulation into and
within a stone. It can be explain by the characteristics of its
porous system. The pore space in grey limestone includes
only open pores, which not allow retain of solution in the
stone, so subflorescence cannot develop. The low value of
open porosity and water uptake correspond to very low
capillary absorption coefficient. However, the rapid
chemical reaction solution in grey limestone occurred only
at the stone surface, probably due to the dominant presence
of micrite carbonate particles. The composition of sand-
stone does not have a direct influence on the formation of
calcium and sodium–calcium salts, but the porosity and
hydric properties of this stone enables solution to be
retained inside it. The sandstone shows a homogeneous
pore system (more than 90 % of pore radius [ 0.1 lm)
with high pore connectivity that allows internal movement
of salt solution through stone. This statement is in agree-
ment with its high absorption coefficient and very fast
capillary water uptake (Fig. 3d). The deposition of salts
beneath the stone surface occurs during periods when
evaporation is slower than capillary movement (Benavente
2011). Such a process leads to thenardite deposition, whose
crystallisation pressure is responsible for sandstone scaling
and spalling.
Conclusion
The main salts contributing to efflorescence and subflo-
rescence that occurred on limestone in the Manasija
Monastery complex were thenardite, thermonatrite, trona,
eugsterite, darapskite and gypsum, while only thenardite
Environ Earth Sci
123
was detected on sandstones in the complex. The source of
Na and Ca for the formation of these salts was definitely
the cement mortar used during repairs made to the Mon-
astery. However, the concentration of Ca ions was con-
siderably increased by dissolving substrate such as
limestone, thereby increasing the possibility of the forma-
tion of Ca and Na–Ca double salts. This phenomenon was
confirmed by the interaction between the limestone and
sandstone in the Manasija Monastery (substrates) and a
solution rich in sodium (but without calcium) in laboratory
conditions. The presence of small amounts of gypsum and
sodium–calcium sulphate as experimental products indi-
cated that, in addition to a solution of cement–mortar,
limestone could be an important source of calcium for the
formation of these salts. Sodium–calcium sulphate could
have been formed by the direct influence of a solution rich
in sodium sulphate on limestone or already-formed gyp-
sum. The simultaneous formation of gypsum and Na–Ca
sulphate was also possible.
Acknowledgments The authors would like to thank Jugoslav Krstic
for performing the mercury porosimetry measurements. The Serbian
Ministry of Science has financially supported this work under contract
No. 176016. This work is partly supported from EGIDE Pavle Savic
cooperation also. We are also very grateful to architects from the
Republic Institute of Heritage Protection who helped us during
observation and recognition of the stone conditions within the
Monastery.
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