Coordenação de Apoio Tecnológico à Micro e Pequena Empresa - CATE
Centro de Tecnologia Mineral
Ministério da Ciência , Tecnologia e Inovação
WEATHERING OF SOAPSTONE THAT COVERS THE “CHRIST
REDEEMER” STATUE, RIO DE JANEIRO, BRAZIL
Roberto Carlos da Conceição Ribeiro
Pesquisador - Eng° Químico
Núria Fernández Castro
Pesquisadora – Eng° de Minas
Rio de Janeiro
Julho/2012
CAC-004-00-12 – Contribuição técnica realizada para o Global Stone Congress, realizado
em Borba – Portugal, de 16 a 20 de julho de 2012.
WEATHERING OF SOAPSTONE THAT COVERS THE “CHRIST
REDEEMER” STATUE, RIO DE JANEIRO, BRAZIL
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Ribeiro, R. C.C. & 1Castro, N. F.
1
. Coordenação de Apoio Tecnológico a Micro e Pequenas Empresas – CATE, Centro de
Tecnologia Mineral – Cetem, Av. Pedro Calmon, 900, Ilha da Cidade Universitária, Rio de Janeiro
– RJ, [email protected] e [email protected]
Keywords: Christ Redeemer, alterability of rocks, soapstone.
Abstract
The “Christ Redeemer” monument, built between 1926 and 1931 at the top of the Corcovado Hill,
South of the Rio de Janeiro city is one of the New Seven Wonders of the World. However, years of
exposure to the environment results in severe damages and loss of parts. It is located at 710 meters
above sea level, surrounded by the Tijuca Forest National Park, the world’s largest urban forest,
close to the sea and exposed to strong winds, rain, rays and sun, typical of tropical climate. In
addition, helicopters and airplanes use to pass by to offer a good view of the monument to the
tourists. The statue is made of concrete and covered by a steatite (soapstone) mosaic, chosen by its
durability and easy use, and largely used in monuments and buildings of Minas Gerais historical
cities. Several restoration works have been undertaken on the monument and many original tesserae
of the mosaic had been already replaced by new ones from the same or other quarries. In order to
assess the last restoration of the statue, in 2010, this study was done to evaluate the conservation
product selected by the restoration technicians and to verify the similarity of the tesserae selected to
substitute old pieces. So, several characterization and weathering tests and analyses, colorimetric
determinations and some water behavior tests were carried out on new and old tesserae, with and
without protective. Even though it should deserve a much deeper study, the need for a quick
restoration, as it is the most visited tour istic place of Brazil, didn’t allow doing so. However results
showed that the soapstone is extremely damaged and many tesserae had to be replaced. It’s believed
that wind and water acted as transport means for microorganisms, probably from the forest, which
generate acids that deteriorate the soapstone, so it was concluded the real need to protect the
monument from water. The conservation product chosen performed successfully in laboratory tests
and didn’t alter the color or superficial texture of the soapstone, even in aging tests.
Introduction
Rocks Restoration
The restoration of architectural monuments and art arises from the need to preserve records that
mark not only moments in the history of a society, as well as styles of bygone eras, religious beliefs
and rituals, therefore, a work of vital importance both within cultural and scientific [1].
Technological Characterization
The technological characterization of rocks is done through testing and analysis, whose main
objective is to obtain parame ters petrographic, chemical, physical and mechanical properties of the
material, allowing the characterization of rock for use in the coating of buildings [2].
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Monument of Christ Redeemer
The monument of Christ Redeemer to fit these previously mentioned aspects, and its
construction was suggested in the late nineteenth century by the priest Pedro Maria Boss
recommending to Princess Isabel to build such a monument. The statue is covered with a mosaic of
soapstone or steatite, in which each piece that composes it is designated as tesserae (Figure 1).
Figure 1: Aspect of tesserae.
Soap-Stone
The soapstone is a metamorphic mafic rock or carbonate source consisting essentially of talc is a
mineral of secondary origin, formed by the alteration of magnesium-rich silicate minerals such as
olivine-type fosterita, and constitutes almost the entire rock mass. This rock is characterized by not
very porous, have silky shine and be greasy to the touch [3].
Objectives
The present work aims at characterizing technologically rocks of soapstone covering the Christ
the Redeemer, to determine inherent pathologies, check problems imposed by the environment and,
from the set of data obtained through laboratory tests, to compare the behavior of the rock face of
weathering conditions in its natural state and application of protective water repellent and thus
identify the agents that cause the greatest degradation in the monument and thus provide technical
support for the restoration and preservation of the monument, making the restoration work is more
efficient and lasting.
Methodology
Sampling
The selection of tesserae removed was carried out jointly by the Center of Mineral Technology
(Cetem) and representatives of the Institute of Historical and Artistic Heritage (IPHAN). Were
taken for laboratory tests nine (9) tesserae sides of North, South, East and West.
Colorimetry
The evaluation was conducted in standard color tesserae. For the determination of the chromatic
pattern was used colorimeter whose brand is Technidyne Color Touch 2 Model ISO. The reading of
the result is based on the values represented by the axes a *, b * and L * as shown in Figure 2,
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where the a * axis indicates the change in color from green to red, blue b * axis and the axis yellow
L * white to black.
Figure 2: Graphic of colorimetric distribution.
Mineralogical Characterization
The mineralogical analysis were determined by the powder method using a Bruker equipment of the
mark-D4 Endeavor qualitative and interpretations of these mineral phases was performed by
comparison with standards contained in the database.
Petrographic Characterization
The petrographic analysis, according to ABNT. NBR 12.768/92 [4] was performed through the
interpretation of thin sections of the original samples, with the aim of observing texture, mineral
composition, state microfissural, nature of rock and mineral changes.
Physical Indices
By this test it was possible to determine the specific mass, dried and saturated, porosity and
absorption by means of water according to the formulas specified ABNT. NBR 12.766/92 [5]. In
this test the specimens were weighed dry after 24 hours in an oven at 70ºC providing the equivalent
of dry weight. Subsequently, they were immersed in distilled water for 24 hours so obtaining the
weights saturated and immersed using a precision balance.
Alterability Tests
a) Salt spray attach
This trial aims to reproduce the effects caused by exposure to salt spray so that the bodies are
subjected to vapor concentrations of sodium chloride. According to the ABNT. NBR 8094/83 [6],
the samples were rinsed with distilled water so that the surface residues were removed, after been
dried at an average temperature of 75 ° C and then weighed. Later, the bodies were placed in the
chamber of salinity and subjected to 30 cycles, equivalent to 360 hours. Upon completion of test,
the samples were immersed in deionized water so that the deposited salts were removed. Then they
were again dried and weighed in greenhouses. Finally, we determined the pattern color and have
been visual inspection.
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b) Water Attack
According to ABNT. NBR 8095/83 [7], the bodies were initially weighed and had their initial color
observed after drying at 70 ° C. The bodies were hung by a nylon thread for 10 cycles within the
humidity chamber. With the conclusion of the test bodies were dried, weighed and had their color
rechecked.
c) SO2 Attack
According to the ABNT. NBR 8096/83 [8], the specimens were washed and dried. Then taken to
the chamber, whose main feature is to simulate the effect of acid rain, where the SO2 is injected and
the atmosphere inside the chamber. After eight hours, the chamber was opened for ventilation 16
hours characterizing the completion of a cycle. Performed a total of 30 cycles totaling 720 hours. At
the end, the bodies were washed, dried, weighed and had their color index measured.
d) Water repellency
The hydrophobic polymers are generally based on silicone which in turn are formed by an inorganic
matrix with non-polar radical responsible for water repellency. Therefore, have a surface tension
less than water and therefore hydrophobic characteristics [9]. The water exerts an important
influence on the characteristics of stone monuments reducing its thermal performance, causing
efflorescence and accelerating the growth of microorganisms. Their affinity to the surface of these
materials is due to surface tension that varies with the medium in which is in contact and, therefore,
the use of resin causes this voltage is reduced. For the tests we used the water repellent brand
Wacker-Chemical of Brazil in a 1:9 ratio being 14 days of healing, as was stated by the
manufacturer.
Results and Discussion
Colorimetry
The results of the colorimetric assay show that there is a tendency to light yellowish-green
coloration, due to the average values for the axes a *, b * and L *, respectively, -0.11 (green), 5.3
(yellow) and 53 (white).
Petrographic Characterization
The tesserae which looks massive and with a high degree of degradatio n due to stains,
discoloration, dark spots and loss of material causing rounding the edges of tesserae. Under the
microscope (Figure 3) shows no microcracks, the average level of change is observed and minerals
are: talc, chlorite, calcite, tremolite, actnolita.
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Figure 3: Photomicrographs of petrographic evaluation.
Mineralogical Characterization
The mineralogical analysis was evaluated for interpreting the diffractogram as shown in Figure 4,
where, in general, the peaks of greater intensity can be represented by the following minerals: talc,
tremolite,
calcite,
chlorite,
thus
confirming
the
analysis
Petrographic.
Figure 4: Difratogramas of original tesserae.
Physical Contents
The results of this test (Table 1) showed that, before use of the water repellent resin, the values for
absorption and porosity was too high for normal standards of the bedrock in that generates throne,
indicating a high degree of alteration.
Testing Changeable
a) Salt spray attach
The salt spray was a major contrib utor to the change in the tone of the pieces, this indicates that it is
likely that sea air is one of the causes of color variation in different sectors of the mosaic.
b) Moisture Attack / Attack of SO2
The results of these tests were not significant changes in the samples studied with regard to weight
loss and color change.
c) Microorganisms
Were observed and collected micro-organisms (fungi, mosses, etc..) That proliferate in the presence
of water in a short time at various points of the monument. They are: Penicilliumm sp, Fusarium sp,
Cladosporium and Aspergillus. The action of the metabolism of these results beings acids, such as
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mevalonic acid produced by Penicilliumm sp, which, combined with the action of rain, wind, salt
spray, can in turn accelerate the degradation of the rock concerned.
d) Waterproofing
The use of resin water repellent played a major role, because it showed that undoubtedly acts by
reducing the effects of porosity, possibly due to the interaction between water repellent and mineral
assemblage that constitute the original tesserae, or because of the absorption caused the high degree
of fracturing. It is possible that such tesserae have a high degradation in its structure so that they
may have many "empty", resulting in a smaller value of specific gravity, which may reflect the
higher values of absorption and porosity, and thus the most absorption of water repellent. The
predominant color (yellow-green) were not affected after applying the water repellent, there was
only a slight darkening has been reduced in a short time (Table 1). The salt spray attack was
responsible for changing the tone of the pieces, both natural and waterproofing (Table 1).
Furthermore, the use of such repellent also reduces the chances of formation of colonies of fungi, as
it prevents the water to remain on the surface.
Table 1: Results of tesserae
Without Resin
With Resin
Reduction %
Porosity
4,07 %
0,49 %
88 %
Absorption
2,32 %
0,17 %
93 %
Variation
Colorimetric
a*
-0,11
-1,49
-
b*
5,3
8,45
-
L*
53
37
Before test
Salt spray
Without Resin
With Resin
black
after test
7,84g
7,78g
2%
10,37g
10,26g
3%
Conclusions
Given the analyzes generated throughout the research process, it was concluded that the state
change of tesserae that cover the Christ the Redeemer is due to several factors, where the main
water penetration, and in this respect, the application of repellent an important procedure as their
role, as could be proved, is to reduce the vulnerability experienced by these materials. Therefore,
proving the importance of technological characterization as a tool that can applied in studies of
restoration, not only of that monument, as well as numerous other stone monuments.
References
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Paulo, v.1, n.1, p. 16-40, nov. 2005/ abr. 2006.
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por meio de ensaios e análises e das patologias associadas ao uso. No: III SIMPÓSIO DE ROCHAS
ORNAMENTAIS DO NORDESTE, 2002. Recife, Brasil. p. 1-7.
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[7] _______. NBR 8095/83: material metálico revestido e não revestido – Corrosão por exposição à
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[8] _______. NBR 8096/83: material metálico revestido e não revestido – Corrosão por exposição ao SO 2 .
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