Multiscale characterization of limestone used on
monuments of cultural heritage
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2013 MRS Fall Meeting
Draft
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Saheb, Mandana; LISA,
Mertz, Jean-Didier; LRMH,
Colas, Estel; LRMH,
Rozenbaum, Olivier; ISTO,
Chabas, Anne; LISA,
Michelin, Anne; LISA,
Verney-Carron, Aurelie; LISA,
Sizun, Jean-Pierre; LCE,
porosity, chemical composition, porosimetry
Page 1 of 6
Multiscale characterization of limestone used on monuments of cultural heritage
Saheb M. 1, Mertz J.-D. 2, Colas E. 2, Rozenbaum O. 3, Chabas A. 1, Michelin A. 1, Verney-Carron
A. 1, Sizun J.P 4
1
LISA, UMR CNRS 7583, Université Paris-Est Créteil and Université Paris-Diderot, 61 avenue
du Général de Gaulle, 94010 Créteil Cedex France
2
LRMH, USR 3224, 29 rue de Paris, 77420 Champs-sur-Marne, France
3
ISTO, UMR 7327, 1A rue de la Férollerie, 45100 Orléans, France
4
LCE, UMR 6249, 16 route de Gray, 25030 Besançon, France
ABSTRACT
In the context of the preservation of the cultural heritage, it is of importance to
understand the alteration mechanisms of the materials constitutive historical constructions.
Especially limestone is widely used in many French monuments exposed to an urban aggressive
atmosphere affecting their durability. To better understand the alteration mechanisms, the first
step is to characterize at different scales the stone material properties. In one hand, the pore
network that allows the fluids transfer inside the materials is characterized. And on the other
hand, the alteration layer formed on several decades aged materials is studied. Results on this
fine characterization are presented here.
INTRODUCTION
The preservation of the built heritage constitutes an environmental, economic, and
cultural challenge. In France, 52% of the stone buildings are made out of limestone, so that their
preservation is of primary importance. The climate plays a role on the natural ageing of the
building constructions. Moreover atmospheric pollution directly affects the evolution of the
materials due to the chemical reactions induced by dry and wet deposition and their alteration
kinetics. For over 200 years, the energy production increasing has caused high atmospheric
emissions under the form of gases (SO2, CO2, NOx) and particulate matter. The gases cause an
acidic deposit that could accelerate the materials dissolution and/or the crusts formation. The
particulate matter blackening of the surface of building materials often increases the water
sorption mechanism or catalyses the sulphation reaction. The present work belongs to an ongoing
study aiming at understanding the alteration processes on limestone exposed to an urban polluted
area. The first step is the ability of characterizing the relevant parameters of the stones that could
influence the further alteration processes and/or evolve with the alteration. Thus the pore
network needs to be characterized because it allows the water transfer (that is the main alteration
factor) inside the materials and because it can be modified by dissolution, pressure solution or
crystallization processes. The alteration zones need also to be characterized by a multiscale
approach (macro- to micrometric) as they could play a significant role in the further alteration
(changes of the kinetics) and in order to evaluate their evolution as a function of time. To this
purpose, non-destructive methods are favoured.
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EXPERIMENT
Materials:
The selected calcareous material is the so called “Saint-Maximin roche fine” limestone
widely used for the restoration of historical monuments in France, especially in the Parisian
basin. This limestone from the Lutetian period (45 My) is relatively homogeneous from a
chemical point of view and heterogeneous regarding its physical properties, linked to the fluid
transfer parameters. Materials at different alteration types and stages are studied: pristine
materials from quarries (Q) and samples from various monuments in Paris and Paris suburbs.
Three stones from the ‘Basilique of Saint-Denis’ (SD, 12th c.), and pre-Haussmannian
monuments such as the ‘Tribunal Administratif’ (TA, 17th c.) and the ‘Comédie Française’ (C,
17th c.) have been selected. These stones are part of restoration stone blocks of the 2nd part of the
20th century and no surface treatment has been applied since the replacement.
Pore network characterization:
All samples are characterized at different scales (from micrometric to nanometric) using
complementary analytical tools.
Classical petrophysical measurements allow determining several parameters linked to
storage and fluid transfer properties of the stones, such as the total porosity (Nt) and the water
capillary coefficient (A).
Qualitative visualization of the porosity is investigated using an original staining method
of pore network in thin section. The method is based on the imbibition of the stone by two
different stained resins. The first one, a red stained resin plays the role of a wetting fluid and fills
the ‘free’ or porosity accessible to wetting fluid by capillary imbibition [1, 2]. The fraction of the
porosity which is not accessible to water during rainwater absorption represents the trapped
porosity; this pore volume is blue stained in thin sections.
Quantification of the porosity is performed by mercury intrusion porosimetry (MIP)
using a Micromeritics® Autopore IV system in standard conditions [3]. Because mercury is a
non-wetting liquid, progressive saturation of the pore network within the mercury is obtained by
applying a controlled pressure on the mercury in the range of 0.035 to 206 MPa. MIP technique
allows determining the opened pore access corresponding to the pore size distribution of the
limestone in the range from 0.005 µm to 180 µm in radius.
Non destructive microtomography analyses are performed using an industrial CT device
Nanotom 180NF (GE Phoenix X-Ray, Wunstorf, Germany). The 6 mm diameter rods samples
used enable to obtain 3 µm voxel size images. Multiple scans allow imaging the rod on a large
depth: from the top surface down to 16 mm under this surface.
Alteration characterization:
To identify the mineralogical composition of the alteration phases, macroscopic X-ray
diffraction is performed using an Empyrean diffractometer from Panalytical equipped with a
copper anode. The Highscore software allows providing semi-quantitative data.
Micro-Raman measurements are performed on an Invia reflex spectrometer from the
Renishaw Company equipped with a frequency-doubled Nd YAG emitting at 532 nm. A 50×
optical microscope LEICA objective is employed to focus the laser beam and to collect the
Page 3 of 6
scattered light, providing a laser spot size on the samples less than 2 µm. A 2400 l/mm grating
induces a spectral resolution of about 1 cm-1. The laser power on the sample is about 100 µW to
avoid any phase transformation due to the heat.
RESULTS AND DISCUSSION
Pore network characterization:
Microscopic observations on thin sections (see figures 1 and 2) shows that the limestone
is mainly composed of miliole tests and crinoid fragments, quartz grains and micritic shell clasts
in different proportions. The main petrographic difference between the stones is the lowest
proportion of quartz grain in the quarry stone (Q) than in the SD, C and TA types.
Figure 1. General free and trapped pores Figure 2. (SD limestone) External surface = left
distribution (Quarry limestone)
side. Sulphation zone mainly contains trapped
porosity sometimes associated to emerging cracks.
The high porosity of the stones (27-40%) is induced by diagenetic conditions and most of
the pore spaces are accessible to capillary water (see table 1). Pore network is composed by most
of the macropores (mode 1) and all the micropores (mode 2) (<7µm). The trapped porosity
corresponds to spherical macropores located in the central part of the largest pore spaces of the
network and the macropores sheltered inside the foraminifera tests (figures 1 and 2). In addition,
epigenetic phenomena resulting from weathering can locally create a new porosity.
In the altered samples from monuments, the exposed stone surface is modified. For TA
and C limestone, alteration of the exposed surface leads to a moderate increasing of the original
roughness due to dissolution. Considering the SD limestone type (figure 2), the upper partlocated at few millimeters from the surface is heterogeneous because it has been modified during
the weathering. This alteration zone leads to a significant reduction of the initial porosity of the
limestone. The residual pores are mainly trapped pores (figure 2) and could reduce or inhibit the
fluid transfers. Such structural modification and pore blocking resulting in a gypsum enriched
layer at around 2 mm under the outer surface is related to the sulphation mechanism.
Mercury intrusion porosimetry reveals a bimodal pore size distribution (table 1). The
main mode is in the range 10-15 µm in radius and a secondary mode is present in the range 0.1-8
µm. The first one is clearly in close relation with the size of the macropore network. The
difference between the stones concerns the amount of microporosity and the position of the
secondary mode. It probably means that the modification of the structural parameters of the
samples occur at this micrometric to sub-micrometric scale.
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The well-connected pore network results of the main mode and explains the high
capillary properties of the stones. Nevertheless, local porosity and additional transfer parameters
as water capillary kinetic coefficient confirm the effect of the sulphation layer on the fluid
transfer properties, especially for the SD samples (table 1).
Table 1. Petrophysical parameters of the materials (*: measurements on 3 samples; Nt: total
porosity (EN1936); A: water capillary coefficient (EN1925); PHg: porosity opened to mercury;
D: bulk density; SSA: surface specific area)
TA
Nt*
(%)
38.1±0.4
41.7±2.1
43.0±0.2
SD
30.7±1.0
Limestone type
Quarry Q
C
A*
(g.cm-².h-1)
3.7±0.1
1.9±0.7
4.7±0.5
0.5±0.1 to
2.4±0.4
PHg
(%)
36.2
40.4
39.8
27.6 to 33.9
D
(g.cm-3)
2.174
1.903
2.019
2.120 to
2.140
SSA
(m².g-1)
0.59
0.24
0.22
0.31 to
0.49
Mode 1
r1 (µm)
20
10
15
Mode 2
r2 (µm)
0.15
3
0.1
10
3.5
As expected, X-ray tomography shows that the porosity of the pristine stone (not shown
here) is homogeneous and the average porosity is 24 % for this resolution (i.e. 3 µm). On the
altered samples, decrease of porosity is observed due to recrystallization processes (see figure 3).
The porosity of the C sample gradually decreases from 20 % on the surface to 15 % between 6
and 9 mm under the surface. After this range, the porosity slightly increases to a stable value
around 21 % at 11 mm up to 16 mm. The porosity of the SD sample rapidly decreases from 21 %
on the surface to 4 % between 1.8 and 3.5 mm under the surface. After this range, the porosity
increases and reaches a stable value (around 21 %) at 11 mm up to 16 mm. This observation on
the SD stone is in good agreement with the ones based on the other (destructive) characterization
methods. On the opposite, for the TA sample, porosity increases in the 1.5-3 mm under the
surface and decreases in the 0-1.5 mm range. Images (not shown here) show that recrystallisation
phases close the pore spaces and replace some missing grains.
Figure 3. Images obtained using X-ray tomography at different depths on limestones (SD and C)
Page 5 of 6
Alteration layer characterization:
X-ray diffraction has been performed on a black crust of a sample located on sheltered
from rainfall part of monuments. The comparison with JCPDS files shows that it is mainly
composed of carbon (graphite-60%), gypsum (CaSO4.2H2O-25%) and calcite (CaCO3-15%)
(figure 4).
2000
S: Soot 59.5%
G: Gypsum 25.3%
C: Calcite 15.2%
S
Counts
1500
C
1000
G
S
G
G
G
500
S
C
G S SS
S
SS
C
S
S S
0
10
20
30
40
50
60
70
80
Position (2Θ) Copper anode
Figure 4. Diffractogram of a black crust formed on the limestone (SD) (copper anode)
This composition is in good agreement with literature data on such stone samples exposed to a
polluted atmosphere [4]. The presence of graphite corresponds to the crystalline core of the soot
emitted from diesel exhaust and adsorbed on limestone. The presence of gypsum has also been
evidenced using optical observations on thin sections. Its formation is due to the interaction
between the atmospheric SO2 and the calcite. SO2 is oxidized in SO3 and condensation water at
the surface of the calcite dissolves it and forms H2SO4. This acidic attack reacts with the Ca2+
(from the dissolution of the calcite) and leads to the gypsum formation. The presence of calcite
inside the crust could originate from the substrate itself (during sampling) or correspond to the
dissolution/ re-crystallization processes happening during the water cycles. Actually, water
transiting inside the pore network can dissolve part of the calcite of the materials and then reprecipitate somewhere else during the drying. That leads to modification of the porous network
and consequently to the modification of the further alteration.
On some localized zones, Raman microspectrometry has allowed identifying scytonemin
(see figure 5). The high luminescence of the Raman spectrum is linked to the organic carbon.
This aromatic organic molecule has been detected in other studies on limestone and is linked to a
biological activity exposed to UV radiation or a polluted environment [5]. The urban area of
Paris suburb is a suitable environment for the activity of such bio-organisms.
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Figure 5. Optical micrograph on the limestone from Saint-Denis and associated Raman spectrum
(λ=532 nm)
CONCLUSIONS
This study is part of an ongoing work aiming at understanding the alteration processes
occurring on limestone exposed to an urban area. The fine characterization of the pore network
shows a macroporous limestone where the water can transit. Moreover open micropores could
also play a role in the alteration processes. The alteration layer is mainly composed of gypsum
and soot which is coherent in a polluted atmosphere, and markers from a microbiological activity
have also been detected.
In parallel, another part of the project aims at reproducing in laboratory the alteration of
limestone exposed to an urban area in controlled and realistic environments. Associated with the
characterization of the stone, it will allow determining the modifications of its properties. This
will help studying specific questions on the alteration processes (identification of the reaction
zones), the kinetics of the alteration (quantification of the modified zones) and the role of the
alteration layer (evaluation of the kinetics).
ACKNOWLEDGMENTS
The authors would like to thank the French Ministry for Culture and Communication for
the financial support. Special thanks to Mr Chauvelier from Lanfry Company and Mr Debray
from Dubocq Company for their decisive help during the sampling on the monuments. For the
characterization measurements, the authors thank Sophie Nowak from the ITODYS for the XRD
and the SIS2M/LAPA for the Raman analyses.
REFERENCES
1. B. Zinszner and C. Meynot, Rev. Inst. Fr. Pétrole, 37, 337-361 (1982).
2. F.-M Pellerin and B. Zinsner, A Geoscientist's Guide to Petrophysics, Technip Eds, 384 p.
(2007)
3. ASTM D4404-10, 2010 - Standard Test Method for Determination of Pore Volume and Pore
Volume Distribution of Soil and Rock by Mercury Intrusion Porosimetry, 7p. (2010).
4. C. Sabbioni, Air Pol. Rev., 2, 63-106 (2003).
5. N. Prieto-Taboada I. Ibarrondo, O. Gómez-Laserna, I. Martinez-Arkarazo, M.A. Olazabal
and J.M. Madariaga, Jour. Hazard. Mat., 248–249, 451-460 (2013).