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Preliminary study of 19th century mortars from railway engineering structures abandoned since 1950

Authors:
PRELIMINARY STUDY OF 19TH CENTURY MORTARS FROM RAILWAY
ENGINEERING STRUCTURES ABANDONED SINCE 1950
V.Thiéry1,2, T.Katayama3, Y.Ando3, G. Link4, M.Bouichou5, E. Marie-Victoire5
1 IMT Lille Douai, Civil & Environmental Department, F-59508 Douai, France,
2 Université de Lille, F-59000 Lille, France,3 Taiheiyo Consultant Co.Ltd. Sakura, Japan, 4 UMR
5563 Géosciences Environnement Toulouse (GET) 31400 Toulouse, France, 5Laboratoire de
recherche des Monuments Historiques, Ministère de la culture et de la communication, CRC-
LRMH, CNRS-USR 3224, Champs-sur-Marne, France
Introduction
Portland cement-based binders from the second half of the eighteenth century are known as “early age
Portland cements” [1] or “meso-Portland cement” [2]. They cover a compositional range broader than
modern Portland cement, especially concerning a richer Al content [3].
The present study investigates mortars from masonry structure on a 19th century railway line from the
French Massif Central, built around 1880, which was subsequently totally abandoned in 1950 due to the
flooding of the valley by a dam lake.The studied railway runs through the Chavanon valley located ca. a
hundred kilometers to the west of Clermont-Ferrand (Figure 1), mainly constituted of various acidic
metamorphic rocks (migmatites, gneisses and micaschists). The incision of the valley ranges from 180 to 250
meters in the area of interest, with locally cliffs and mainly steep slopes as well as a narrow river. The
altitude of the present section ranges from 600 to 550 meters above sea level.
Fig. 1: location of the studied railway in France and detail of the itinerary along the Chavanon valley. The
locations of the two structures on which sampling have been carried out have a light grey frame.
In the ca. 8,5 km long in the more incised part of the valley (figure 2), the railway crosses six tunnels for
a total amount of 1100 meters and two bridges for a total of ca. 85 meters. All structures are in masonry and
were built around 1880 since the railway line has opened in 1882.The present study documents two
structures from the southern part of the line.
Fig. 2: a steam train on the Randonnière bridge, getting outside the Randonnière tunnel. Picture from [4]
The Confolent tunnel (figure 3) is a 388 m long, curved tunnel. Its northeastern entrance is partly
collapsed, the southeastern one still stands. Moss and calcite deposits are abundant on exposed surfaces;
from time to time the southern entrance is partly flooded, depending on the level of the dam lake.
The Pont Biais bridge (figure 3) cuts across the Chavanon river at an angle, hence its name (biais, in
French, means “not orthogonal”). This masonry bridge is ca. 40 meters long. The intrados of the arch as well
as the abutment are covered by calcite deposits forming locally some stalactites.
Southern entrance of the Confolent tunnel
(April 2007)
Northern entrance of the Confolent tunnel
(May 2015)
Interior of the Confolent tunnel (May 2015)
The Pont Biais bridge (May 2015)
Fig. 3: structures from which the mortars have been sampled
The goal of this study is to give a preliminary insight of the type of binders used since there is currently
no data on those specific structures, as well as to give new descriptions to early Portland cement.
Materials and methods
Sampling for this preliminary study was done on two structures, one bridge (Pont Biais) and one tunnel
(Confolent tunnel) at its two (northern and southern) entrances in May 2015. Since the study of historic
mortars is greatly enhanced by the use of microscopy and microanalysis techniques [5], especially
concerning early Portland cements [1], this preliminary study was based only on optical microscopy (OM)
and scanning electron microscopy (SEM).
Thin sections were produced firstly at the conventional thickness (30 micrometers) to study the sand from
the mortars, another sequence of thinner ones (15 micrometers) was done subsequently to study the binder.
Optical microscopy was carried out on a Zeiss Axiozoom macroscope (stereomicroscope observations
under white and UV light), a Leica DMRXP microscope and a Nikon Eclipse polarizing/reflecting
microscope. SEM-EDS, qualitative standardless analysis were done on a Hitachi S-4300SE/N SEM working
in high vacuum mode, coupled to a ThermoscientificUltradryEDX detector. Semi-quantitative, standard-
bases SEM-EDS analysis were obtained on a JEOL JSM-7001F operating at 15 kV, 0,3 nA with a working
distance of 10 mm, coupled with an Oxford Penta FETx3 detector. Data acquisition was 60s with a dead time
of 20%.
Results
The sand of the mortars is rounded and consists of quartz grains, feldspars and various metamorphic
rocks as well as volcanic ones. It corresponds most probably to sand dredged from the Chavanon river close
to the works during the construction of the structures.
Hand samples are characterized by a clear, light-grey color, with a local darker patina (figure 4).
Fig. 4: ground slab of mortar from the southern entrance of the Confolent tunnel.
Left: white light, right: UV light.
The microscopical investigation of the binder has revealed that it consists of Portland cement. Hydraulic
lime was not observed in the samples. The mineralogy is variable (figure 5). It is dominated by
pseudowollastonite (CS), belite (C2S) and alite (C3S), as well as rankinite (C3S2) and local ye’elimite
(C4A3S
̅).
a
b
c
e
Fig.5: Features observed in binders as seen in optical microscopy, transmitted light and crossed polars
except when indicated. a: cement particle composed of pseudowollastonite and potassium silicate (confirmed
by EDS) from the Pont Biais Bridge, b: pseudowollastonite dominated assemblage, Confolent tunnel
(southern entrance), c: SEM (BSE) image of a cement particle composed of hydrated alite (dark), hydrated
belite (dark) and interstitial ferrite (bright), d: coal ash (reflected light), e: limestone filler, Confolent tunnel
Carbonation is conspicuous in cross sections of the surface of exposed mortars. Ettringite is quite
abundant, both in voids and in cracks. The main features observed microscopically in the mortars and are
summarized in table 1.
Constituent
Biais
Bridge
Confolent tunnel
Northern entrance
Southern
entrance
P1
P2
N1
N2
S1
S2
Binder
Portland
cement
Isolated particle
x
x
x
x
x
x
Lump
x
Limestone powder
-
-
x
x
xx
xx
Coal ash
x
x
x
x
x
x
Cement hydrates
Portlandite
Void
-
-
-
x
-
-
Cement paste matrix
-
-
x
x
-
-
Ettringite
Void
-
-
-
-
x
x
Crack
Fresh
-
-
-
-
xx
xx
Carbonated
-
-
-
-
xx
xx
Carbonation
Calcite
Void
-
-
x
x
-
x
Cement paste matrix
x
x
x
x
x
x
Crack
-
-
x
-
xx
xx
Table 1: summary of microscopical investigations in mortars from 2 structures built around 1880. -: not
observed, x: minor, xx: abundant
Discussion and conclusions
This railway line has been opened the very year during which the famous French chemist Henry le
Chatelier published the first description of Portland cement phases under the microscope [6]. At that time,
cement was heterogeneous due to both the heterogeneity of the raw meal and the ill-defined calcination
conditions [3]. The present study is in good agreement with such conclusions since several mineral
assemblages, hydraulic or not, has been observed.
An excess of sulfur can be emphasized by the presence of C4A3S
̅ (ye’elimite) in unhydrated cement
particles relics; its source is to find in the coal used for cement production, from which ash has been
observed in all of the samples. Ettringite, present in both voids and cracks, is also a manifestation of the
excess of sulfur.
REFERENCES:
[1] C. Gosselin, F. Pintér, Examples of early age Portland cements applied in historical masonries,
in: 4th Hist. Mortars Conf., 2016: pp. 211219.
[2] D.L. Rayment, The electron microprobe analysis of the CSH phases in a 136 year old cement
paste, Cem. Concr. Res. 16 (1986) 341344. doi:10.1016/0008-8846(86)90109-2.
[3] P. Dariz, J. Neubauer, F. Goetz-Neunhoeffer, T. Schmid, Calcium aluminates in clinker
remnants as marker phases for various types of 19th-century cement studied by Raman
microspectroscopy, Eur. J. Mineral. 28 (2017) 907 LP-914.
[4] L.M. Vilain, Vapeur en montagne, Tardy Lengellé, 1982.
[5] J. Elsen, Microscopy of historic mortars-a review, Cem. Concr. Res. 36 (2006) 14161424.
doi:10.1016/j.cemconres.2005.12.006.
[6] H. Le Chatelier, Recherches expérimentales sur la constitution des ciments et la théorie de leur
prise, Comptes Rendus Hebd. lAcadémie Des Sci. 94 (1882) 867869.
... Similarly to C 5 S 2 $-bearing residues, cement grains that contained C 4 A 3 $ were also free of C 3 S suggesting the above mentioned lower temperature regime of formation. A recent study mentions the presence of C 4 A 3 $ traces in 1880 PC cement mortar samples [37]. Finally, CaS verified in the samples has been reported as a minor component in blast furnace slag [38,39], but it may also form in OPCs when during burning reducing atmosphere develops [28,40]. ...
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