SPECIAL ISSUE
Moisture expansion associated to secondary porosity:
an example of the Loseros Tuff of Guanajuato, Mexico
Rube´n Lo´pez-Doncel • Wanja Wedekind •
Reiner Dohrmann • Siegfried Siegesmund
Received: 5 June 2012 / Accepted: 12 June 2012 / Published online: 1 July 2012
 The Author(s) 2012. This article is published with open access at Springerlink.com
Abstract The old mining city of Guanajuato in middle
Mexico preserves one of the most important historical
legacies in colonial buildings, the UNESCO declared the
city World Heritage Site in 1988. Practically all the colo-
nial constructions were built with natural stones from the
neighbourhood, of which stands a greenish to reddish
vulcanite, called Loseros Tuff. Although the Loseros Tuff
is widely used in historical buildings in the city. It shows
significant deterioration and weathering effects, principally
in the parts where the tuff shows a coarse grain size. The
petrographic, petrophysical, mineralogical and geochemi-
cal properties of the Loseros Tuff were analysed in order to
determine the causes, effects, behaviour and response to
deterioration of this volcanic rock. The results of the
investigations suggest that in addition to the parameters
like the grain size and the porosity properties, the pore radii
distribution is decisive for the effectiveness of porosity and
the water transport into the rock. It is recognized that once
the liquid water invades the rock the dissolution of the
matrix occurs, which is accompanied by a sudden moisture
expansion favoured by the newly formed secondary
porosity and the high content of expandable clay minerals.
Keywords Tuff  Moisture expansion  Porosity 
Guanajuato
Introduction
The old mining city of Guanajuato in middle Mexico belongs
to the most important historical cities of Latin America, which
preserves one of the most important historical legacies in
colonial buildings. The establishment of this city, which later
would become one of the most important cities of the New
Spain, was basically due to the discovery of the silver and gold
ore deposits that initiated the mining industry in 1548, which
resulted in the legal foundation of the town of Santa Fe de
Guanajuato in 1570. The result of the wealth spread around the
city was reflected in beautiful buildings that were constructed
with natural rocks. Mainly during the seventeenth, nineteenth
and early twentieth centuries a number of buildings were
erected that would play important roles during the battles for
independence of Mexico. Since Guanajuato had become an
important economic, cultural and religious centre in Mexico,
it has shown a remarkable growth during the twentieth cen-
tury, and thus increasing the preservation of old churches and
the construction of notable buildings such as the Teatro Juarez
and the building of the University Guanajuato (Fig. 1a, b);
the city was declared in 1988 World Heritage Site by the
UNESCO. Practically all the colonial constructions were
built with natural stones from the neighbourhood, of which
stands a greenish to reddish vulcanite, called Loseros Tuff.
Utilization and deterioration
The utilization of the Loseros Tuff as natural building
material includes filler rock for roads, walls, bridges and
R. Lo´pez-Doncel (&)
Geological Institute, Autonomous University of San Luis Potosı´,
San Luis Potosı´, Mexico
e-mail: rlopez@uaslp.mx
W. Wedekind  S. Siegesmund
Geoscience Centre of the University Go¨ttingen,
Go¨ttingen, Germany
R. Dohrmann
Bundesanstalt fu¨r Geowissenschaften und Rohstoffe,
Hannover, Germany
123
Environ Earth Sci (2013) 69:1189–1201
DOI 10.1007/s12665-012-1781-1
especially the construction of a complex system of under-
ground tunnels that cross the city of Guanajuato (Fig 1d).
When the Loseros Tuff is cut along the lamination (X-axis),
or it is finely reworked perpendicular to the lamination it is
used as fine masonry for the most important cultural,
religious and governmental buildings (Fig. 1c). In the
nineteenth century and early twentieth century the Loseros
Tuff found a widespread use as a popular material espe-
cially for tomb monuments in central Mexico. Examples
can be found in Guadalajara (Fig. 2c), as well as in Mexico
City.
Although the Loseros Tuff is widely used, it shows
significant deterioration and weathering effects, first of all
by scaling parallel to the bedding but also by the scaling
independently of the bedding (Fig. 2c), crumbling (Fig. 2b,
d) and flaking (Fig. 2a). These destructive phenomena
mostly are found in areas of the building where moisture
and water are permanently or temporarily present such as
columns, fountains, balconies or external staircases. A
detailed view of the deterioration of the rock directly in the
construction clearly shows that the horizons formed by
coarser grain sizes are more affected than those of finer
fractions. It is also evident, that the coarser horizons have
an apparent higher porosity, because the pores reach the
grain size of sand, or even bigger. Also the binding cement,
relocation processes and the concentration of this cement
near the surface seems to play a role especially in forming
of scales.
The aim of this study is to determine the petrographic,
petrophysical, mineralogical and geochemical properties of
the Loseros Tuff. The main goal is to provide information
about the influence of porosity, pore radii distribution,
grain size and chemical composition on the causes, effects,
behaviour and response to deterioration of this volcanic
rock.
Materials and methods
Based on the macroscopic observation a marked difference
in the type and form of damage was identified. The
hypothesis is that the integrity of the tuff is probably
Fig. 1 Historic buildings erected with the Loseros Tuff in the city of
Guanajuato. a Staircase and facade of the central building of the
University of Guanajuato. b Juarez Theater in the centre of the city,
the columns and the facade were built entirely with the studied tuff.
c Legislative Palace whose facade is built with cuts parallel to the
lamination (X-axis) of the Loseros Tuff. d Entrance to one of the
underground tunnels that cross the city
1190 Environ Earth Sci (2013) 69:1189–1201
123
affected by the particle (grain) size and by the apparent
porosity. In order to analyse these differences two different
varieties of the tuff were studied: (1) a coarse-grained
specimen, which has been separated into seven different
horizons appointed 1g–7g (Fig. 3). And (2) a fine-grained
specimen, that was separated into five horizons called 1f–5f
(Fig. 4). All the coarse-grained horizons have a grain size
that ranges from fine sand-size (1g and 2g), sand-size (3g
and 6g), coarse sand-size (5g and 7g) to very coarse sand-
size, and to very fine pebbles (granules) (4g). The horizons
of the fine-grained variety vary from very fine sand (4f and
5f) to silt grain size (1f and 3f), and locally even clay
fraction (2f).
The petrographic analyses were performed on oriented
thin sections of the coarser and finer species and studied
under a polarizing microscope. Mineralogical and geo-
chemical analyses were performed using XRD (whole rock
samples, and oriented slides of clay fractions \2 lm),
along with XRF, elemental carbon and sulphur analysis,
and CEC analyses (compare Ru¨drich et al. 2011a, b).
Hydrostatic weighing was carried out to acquire the
matrix and bulk density as well as the porosity of each
horizon. Water uptake coefficient (w value) was deter-
mined with help of the capillary suction in a closed cabinet
while weighing. The water vapour diffusion resistance
value (l) was measured using the wet-cup method. The
pore radii distribution was determined using mercury
injection porosimetry (Brakel et al. 1981, see also Sieges-
mund and Snethlage 2011).
The hydric and hygric expansion of each horizon was
measured on cylindrical samples (diameter 15 mm, length
100 mm). For hydric expansion measurements the cylin-
ders were completely immersed in distilled water (water
saturated). For hygric dilatation analysis an initial relative
humidity (RH value) of 20 % was used, which was
increased gradually to a RH value of 95 %. The
Fig. 2 Appearance of the different damage and deterioration types
observed in the Loseros Tuff. a Flaking in the lower parts of a
balcony. b Crumbling in the bars of the staircase of the university.
c Scaling perpendicular to lamination in a grave in the cemetery of
Guadalajara. d Crumbling in a filler rock into the tunnel wall
Environ Earth Sci (2013) 69:1189–1201 1191
123
temperature was kept constant at 30 C during the whole
experiment.
Cylindrical samples with co-planar end-faces of 50 mm
in diameter and 50 mm in length and 40 mm in diameter
and 20 mm in length, respectively, were used for the
compressive and tensile strength tests. The compressive
strength load was realized with the help of a servo-
hydraulic testing machine with a stiff testing frame
(3,000 kN/mm2) and a load range up to 300 kN. The ten-
sile strength measurements were determined by means of
the ‘‘Brazilian test’’.
Geological settings, petrography and mineralogy
The Loseros Formation belongs to the Cenozoic volcanic
rocks that form the Sierra de Guanajuato Area. This area is
divided in two main rock successions. A succession that
represents the basement composed principally of volcanic
sedimentary sequences of Jura to Upper Cretaceous ages.
These rocks are the oldest outcropped units in this region.
These Mesozoic rocks belong to the so-called ‘‘Mesozoic
Basement or Basement Complex of the Sierra de Guan-
ajuato’’ (Ortiz-Herna´ndez et al. 1992, also called ‘‘Guan-
ajuato volcanic arc’’ for Monod et al. 1990). A second
succession is overlying the Mesozoic sequence. Here more
than 2,500 m of Tertiary to Quaternary volcanic rocks are
outcropped, which show diverse chemical compositions,
varying from basaltic, andesitic to rhyolitic. The extrusions
of these Cenozoic volcanites are associated to the exten-
sional tectonic at the end of the Laramide Orogeny in west
and middle Mexico (Nieto-Samaniego et al. 1992).
The Loseros Tuff is a felsic vulcanoclastic rock that
consists of well-sorted, sand-sized crystals and detrital
rock fragments, which are embedded in an ash-rich
altered groundmass. The Loseros Tuff appears in a wide
variety of colour shades, which can range from reddish
brown, pink, green and even white, but undoubtedly the
green variety is the most requested and used. The grain
size can also locally vary from gravel (granule), up to the
clay fraction but the sand-grain size dominates. Loseros
Tuff is a volcanic pyroclastic rock (Fisher 1961; Fisher
and Schmincke 1984; Le Maitre et al. 2004) with a sig-
nificant amount of epiclastic detritic material protruding
pseudo-stratification with preferably normal gradation
composed of 5 to 40- to 50-cm-thick layers (locally
accretional lapilli layers thicker than 1 m). Together with
the lamination there are a series of very characteristic
sedimentary structures, as cross-lamination, ripples, flame
and cut-and-fill structures, etc.
Edwards (1956) noted that the majority of the grains are
quartz, plagioclase and volcanic lithic fragments. In the
thin section the Loseros Tuff shows a glassy matrix, which
Fig. 3 Appearance of the coarse variety of Loseros Tuff and its
separation in the different studied horizons
Fig. 4 Appearance of the finer variety of Loseros Tuff and its
separation in the different studied horizons
1192 Environ Earth Sci (2013) 69:1189–1201
123
in polarized light appears almost completely opaque and its
texture ranges from hypocrystalline to holohyaline. The
recognized crystals are altered angular to subhedral pla-
gioclase, angular quartz, and also altered biotite flakes
(Fig. 5) (see also Wedekind et al., this issue). Likewise
under the microscope it is possible to recognize ‘‘fissibility-
like’’ laminae, due to intercalations of fine sand and the
clay fraction.
XRD analysis showed a significant amount of CaCO3
(calcite) that under the microscope is recognized as cement
in the matrix. Observations on thin sections evidence that
the remarkable greenish coloration of the tuff comes from a
large number of small albite crystals with altered appear-
ance (initially stage of transformation to clay minerals,
Figs. 5 and 7a) and also recognizable is that the matrix is
made up also of volcanic glass, which shows different
stages of devitrification. This green colour was not recog-
nized in the matrix. Buchanan (1980) attributes the
greenish coloration of this tuff to alteration (chloritization)
of the lithic fragments, but our geochemical analyses do
not show the presence of chlorite in the Loseros Tuff.
Wedekind et al. (this issue) noted: ‘‘the matrix has more
than 20 % calcite and contains also kaolinite, however
most common are the dioctahedral clay minerals illite plus
R3 ordered illite(0.95)-smectite mixed layers which add up
to a CEC value of 7 meq/100 g’’.
Practically there is no mineralogical difference between
the finer and the coarser varieties of this tuff and the XRD
patterns of both show only a major amount of albite and
calcite in the coarser fraction (Fig. 6). SEM on the other
hand indicated that the tuff is relatively dense with
very fine-grained feldspar and illite–smectite particles
(Fig. 7a–c).
Petrophysical properties
Analyses of each of the studied horizons were performed,
in order to determine the density and porosity of both, the
fine (g1–g5) and the coarse fraction (g1–g7). The results of
the determination of the porosity, bulk density, particle
density and average pore radius are presented in Table 1.
As shown in the table, fine-grained horizons have a
greater particle density than the coarse-grained, with an
average of 2.63 and 2.37 g/cm3, respectively. The same
occurs with the bulk density. A very interesting result and
contrary to the expectations is, that the fine variety has a
higher porosity and in some horizons even a larger average
pore radius than the coarse one. Sedimentary rocks such as
siltstones and claystones (similar to the f1–f5 samples)
usually have much lower porosities than sandstones
(equivalent to g1–g7 samples) because decreasing grain
sizes typically correlate with decreasing pore sizes. Studied
Tuffs were deposited in principle in a similar way (as
pyroclastic and epiclastic rocks) as the above-mentioned
sediments, so they are supposed to have similar behaviour,
which in this case does not occur. This phenomenon is
securely related to the type and distribution of the porosity
(micro or capillary porosity), which will be discussed
below.
Compressive and tensile strength
The realized compressive strength tests show that the
coarser type of the Loseros Tuff has values that range from
74.3 to 58.0 N/mm2, where the largest value occurs in the
X-axis and the lowest value in the Z-axis. This condition is
certainly associated to the lamination of the tuff. The
anisotropy in the coarser Loseros is of 22 % and its mod-
ulus of elasticity ranges from 6.3 to 10.0 kN/mm2 with an
anisotropic behaviour of around 37 % (Table 2).
Fig. 5 Thin section photomicrographs of the studied tuff. Above the
green coloration of an altered albite crystal (centre of image, compare
with Fig. 7a) is recognizable in natural light. The matrix consists of
poorly recognizable calcite, volcanic glass and small quartz crystals.
Below the same sample under polarized light shows that the matrix is
made up of opaque components (volcanic glass) with small crystals of
calcite (crystals with third-order colours) and the altered plagioclase,
that show rare interference colour. 910, scale bar 0.2 mm
Environ Earth Sci (2013) 69:1189–1201 1193
123
Fig. 6 Diffractograms showing
the primary mineralogy of the
two varieties of tuffs. Down in
blue coarse Loseros, top in red
fine Loseros
Fig. 7 Typical large pore of relictic crystals in the tuff (a) embedded
in a dense matrix as observed by SEM. Tenfold magnification of the
central region (b) indicates presence of very fine-grained albite
crystals. Clay minerals (illite–smectite) are densely packed (c) and
identified under high magnification (d)
1194 Environ Earth Sci (2013) 69:1189–1201
123
The uniaxial compressive strength of the finer Loseros
Tuff ranges from 57.3 to 42.3 N/mm2, with an anisotropy
of 26 %. Contrary to the coarser variety here the greatest
value of compression occurs in the direction of the Z-axis
and the smallest value in the direction of the Y-axis
(Table 2), which can be explained by the much finer
lamination in the Loseros Tuff (presented as laminae), and
therefore the sample appears more homogeneous.
Measured tensile strength values follow the same trend
as the compression test, where the higher values occur in
the coarse variety. The tensile strength values of the
coarser Loseros Tuff range from 66.0 to 50.1 Mpa, with an
anisotropy of 24 %. The fine-grained Loseros show a
maximum value of 59.2 and a minimum value of 30.6 Mpa
with an anisotropy of 48 %.
The obtained data of the strength tests are represented in
the Table 2.
Porosity and pore size distribution
Grain sizes and pore size vary greatly from one horizon to
the other. Table 3 shows that the average pore radius is
larger in the fine-grained horizons, which influences the
effectivity of the porosity. In general the fine-grained
variety has a larger effective porosity (average of 16 %),
and even the horizon 5f (Table 4) reaches almost 20 %.
Moreover, the coarse variety shows a lower effective
porosity with an average of 14 %. The horizon 4f has the
lowest effective porosity with only 11 %; interestingly this
horizon is the one with the coarsest grain size of all sam-
ples (Table 4).
Table 1 Porosity and density properties of the investigated tuff
horizons
Name Porosity
(vol %)
Bulk density
(g/cm3)
Particle
density
(g/cm3)
Average
pore radius
(lm)
Loseros Formation fine-grained
1f 13.05 2.30 2.65 0.030
2f 12.02 2.30 2.62 0.017
3f 17.33 2.20 2.66 0.030
4f 15.12 2.22 2.62 0.020
5f 17.41 2.16 2.61 0.037
Loseros Formation coarse-grained
1g 10.05 2.17 2.42 0.009
2g 8.19 2.16 2.35 0.08
3g 6.79 2.20 2.36 0.008
4g 9.83 2.21 2.46 0.07
5g 7.70 2.13 2.30 0.006
6g 8.89 2.13 2.33 0.011
7g 10.50 2.17 2.42 0.05
Table 2 Tensile and compressive strength as well as the elastic
modulus of the studied tuffs
Loseros
Formation
tuff type
Tensile strength
(Mpa)
Compressive
strength
(N/mm2)
E-modulus
(kN/mm2)
Fine Coarse Fine Coarse Fine Coarse
X 59.19a 66a 50.30b 74.26 nd 10.00
Y 41.07a nd 42.26b 66.90 nd 9.86
Z 30.6a 50.13a 57.27b 57.98 nd 6.26
Anisotropy (%) 48.3 24.0 26.2 21.9 nd 37.4
nd not detectable
a Wedekind et al. (this issue)
b Sa´nchez Gonza´lez (2004), p 93
Table 3 Pore radii distribution of each of the studied horizons
Sample Pore radii distribution (%)
Micropores Capillary pores
0.001–0.01 0.01–0.1 0.1–1 1–10 [10
Fine-grained Loseros Tuff
1f 13.839 76.422 7.989 0.870 0.880
2f 21.168 73.168 3.349 0.930 1.430
3f 9.912 78.966 9.662 0.870 0.590
4f 10.771 63.076 23.842 1.240 1.070
5f 11.970 65.410 20.700 0.820 1.100
Coarse-grained Loseros Tuff
1g 32.13 59.42 5.20 1.34 1.90
2g 8.659 68.93 17.57 4.83 –
3g 54.46 35.87 5.100 1.54 3.030
4g 10.491 52.66 31.47 5.37 –
5g 48.09 43.47 5.88 1.09 1.47
6g 32.79 53.44 7.18 4.54 2.04
7g 7.56 54.70 30.89 4.82 2
Table 4 Effective porosity of each of the studied horizons
Effective porosity (%)
Fine-grained Loseros Tuff Coarse-grained Loseros Tuff
1f 13.27 1g 14.60
2f 15.53 2g 15.09
3f 18.35 3g 13.25
4f 16.28 4g 11.54
5f 19.37 5g 15.31
Average 16.56 6g 18.34
7g 14.22
Average 14.62
Environ Earth Sci (2013) 69:1189–1201 1195
123
The distribution of the pores in both varieties is preferably
unequal unimodal (Figs. 8, 9). Most of the studied horizons
are dominated by micropores with pore sizes ranging from
0.001 to 0.1 lm (Table 3; Figs. 8, 9). Horizons 1f and 2f
contain practically only microporosity (76.4 and 78.9 %,
respectively). These are also the horizons with the finest grain
sizes (Fig. 7). Moreover, in the horizons of the coarse-grained
variety (1g–7g) the microporosity also dominates; however,
absolute percentages are smaller. Horizons 4g and 7g reach
high values of about 30 % capillary porosity and as expected
these horizons have the coarsest grain size (Table 3; Fig. 9).
Horizon 3g has the widest pore size distribution, including
more than 3 % of pores[10 lm and the horizon 4g includes
more than 5 % of capillary pores in the size range of 1–10 lm.
Sa´nchez Gonza´lez (2004) reported water absorption values
of the fine-grained Loseros Tuff of around 0.8–2.4 % and for
the coarser type the values varies from 6.3 to 6.5 %. Wedekind
et al. (2012a, b), reported absorption values of 0.1 kg/m2
ffiffiffi
h
p
,
for the fine-grained tuff (see also Wesche 1996).
Water transport properties
The water transport mechanisms in porous materials are
important properties that influence dilatation, swelling, and
weathering. The capillary water absorption measured was
dependent on the three principal directions (X, Y, Z) on sample
cubes of 65 mm length. The cubes were set with the bottom
Fig. 8 Pore radii distribution of the different studied horizons of the fine Loseros variety
1196 Environ Earth Sci (2013) 69:1189–1201
123
plane into water and the weight increase over time was mea-
sured. On average both varieties have a low water uptake
coefficient of 0.04 kg/m2
ffiffiffi
h
p
for the coarse variety and
0.057 kg/m2
ffiffiffi
h
p
for the fine variety. The coarse variety shows
an anisotropy of 46 % and the fine variety of 43 %. Both
varieties have different vapour diffusion resistances. The
coarse variety has a resistance, which is more than a factor of
two larger than the fine one. The fine variety has an averaged
vapour diffusion resistance value of 26.3 with an anisotropy of
36 % while the l value with 57.3 and an anisotropy of 39 %
for the fine variety nearly is three times higher. The calcu-
lated water absorption coefficient (w value) and the water
vapour diffusion resistance value (l value) are given in
Table 5 for all directions.
Fig. 9 Pore radii distribution of the different studied horizons of the coarse Loseros variety
Environ Earth Sci (2013) 69:1189–1201 1197
123
Petrophysical studies conducted on the tuffs shown a
relationship between the parameters porosity, pore radius,
pore size and pore distribution. The finer variety has a
greater average pore radius, which remains very regular in
the different horizons and which is located practically
always in the area of microporosity (Table 3; Fig. 8) On
the other hand, the average value in the coarse-grained
variety is smaller (Table 3), but its distribution is wider and
includes horizons with an average pore radius greater than
any horizon of the fine variety (g2, g4, g7), but nevertheless
it has horizons with a very small average close to zero
(g3 and g5) (Fig. 9).
Moisture properties (hygric and hydric expansion)
In order to probe the response in presence of hygric
moisture (related to the relative humidity RH) and hydric
moisture (under water immersion) tests were performed
with both tuff varieties. In order to investigate each horizon
individually, the realized experiments were conduced only
in the X-axis (parallel to stratification), and after that tests
in the direction of the Z-axis of each variety were imple-
mented, which includes all studied horizons together.
The behaviour of the hygric dilatation in the X-axis
direction both in the finer as in the coarser variety was very
discrete and the values reach scarcely the expansions of
0.05 mm/m (finer Loseros) to up 0.1 mm/m (coarser
sample). The maximum values were reached at a relative
humidity of 95 %.
In order to study the moisture anisotropy, the direction
perpendicular to the Z-axis of the coarse-grained variety
was also measured (Fig. 10). Results indicate that the
hygric expansion in the direction of the Z-axis was slightly
higher than in the previously measured direction of the
X-axis. Hygric expansion values had a maximum of
0.54 mm/m through the lamination (Fig. 10).
The fine-grained horizons were then tested under water-
saturated conditions giving smaller values for the hydric
than for the hygric experiments (Fig. 11). In the direction
of the X-axis were recognized values between 0.17 mm/m
in the horizon 2f up to 0.42 mm/m in the 1f horizon.
Interestingly, the 1f horizon has the smallest effective
porosity with 13 % while the grain size (very fine sand)
was the coarsest of all horizons examined in this variety
(Fig. 11), but still the dilatation was not very pronounced.
The same experiment was performed in the axial
direction X of the horizons of the coarse-grained variety,
too. Six of the seven horizons show moderate responses to
water immersion, with expansion values ranging from
0.17 mm/m in horizon 5g to 0.35 mm/m in horizon 3g
(Fig. 12). The hydric expansion values of these six samples
were comparable to the fine variety except one particular
horizon (4g) with a much larger expansion and a dilatation
Table 5 Moisture transport properties of the investigated tuff
horizons
Fine variety Coarse variety
w value (kg/m2
ffiffiffi
h
p
)
X 0.077 0.026
Y 0.048 0.044
Z 0.050 0.045
Average [ 0.057 0.039
A (%) 43 46
l value
X 23.87 64.5
Y 21.48 40.93
Z 33.57 66.7
Average [ 26.30 57.37
A (%) 36 39
Anisotropy A = nmax - nmin/nmax 9 100
Fig. 10 Moisture expansion depending on relative humidity stages
(hygric)
Fig. 11 Moisture expansion under water-saturated conditions (hyd-
ric) of the fine Loseros parallel to the lamination (X-direction)
1198 Environ Earth Sci (2013) 69:1189–1201
123
value of 1.55 mm/m (Fig. 12). The pronounced hydric
expansion value of horizon 4g can be explained by (1) the
highest average pore radius value (Table 1); (2) the highest
absolute capillary porosity (Table 3); and (3) by the
coarsest grain size (Fig. 12), however, on the other hand
horizon 4g has the smallest effective porosity of all the
analysed horizons (Table 4).
The same kind of experiment was repeated, but this time
the hydric expansion of the coarse-grained variety was
measured along the direction of the Z-axis (perpendicular
to lamination). This analysis sums up the properties of the
horizons 2g, 3g, 4g, 5g and 6g together. The measured
hydric expansion along the Z-axis (Fig. 13) that results
from subjecting the sample under water-saturated condi-
tions shows very interesting aspects. Initially the sample
shows a very regular trend with expansion values up to
1.44 mm/m during the first 16 h of the experiment, but
immediately after this point an extremely quick expansion
with an increase of almost a factor of two in a span of about
2–3 h was detected. Measured values ranged from 1.5 to
3.5 mm/m and the slope of the curve was almost vertical
(Fig. 13).
This is again followed by a weaker increase, with
values ranging from 3.5 to 4.1 mm/m expansion in
approximately 6 h (Fig. 13). After 26 h of experiment, the
sample began to stabilize and eventually stop its expan-
sion (Fig. 13). Obtained hydric expansion values excee-
ded markedly the values of expansion of the horizons
studied individually and that represented probably the
addition of each expansion values of each horizon
together.
A fact that should be noted is that at the end of the
experiment a thin layer of sediment was deposited at the
bottom of the vessel where the sample was immersed for
carrying out the experiment. After the end of the experi-
ment crumbling was recognized and eventually the sample
started to break. The collapse phenomenon (scaling and
crumbling) was not observed in any other test used to
check the moisture properties of the Loseros Tuff, but it
was widely recognized during the fieldwork directly from
the constructions.
It must be noted the main damage in the sample,
including the collapse and breakup happened on the hori-
zon 4g, in which the lack of cementation between the
grains was clearly recognizable, which caused the forma-
tion of scaling and crumbling.
Discussion and conclusions
The observed differences in both varieties of the Loseros
Tuff allow drawing some conclusions about their weath-
ering and deterioration behaviour that affect them. The
causes of the deterioration cannot be attributed to a single
factor but it includes a number of causes including com-
position, texture and physical properties (see also Yavuz
2006; Klinkenberg et al. 2009).
It was initially recognized in the field that the most
problems do not occur in fine-grained layers but in areas
where the grains and crystals have sizes around the sand
fraction. The grain shapes are mostly angular to sub-angular
and the fabric varies between matrix supported and grain
supported, which depends on the content of matrix. The
matrix in this case was identified as a mixture of volcanic
glass, silt up to clay-sized particles and calcite. It is already
known that fine-grained rocks composed of particles in the
clay-silt fraction have better consolidation than rocks with
particles of the sand fraction (Hjulstro¨m 1935; Sundborg
1956). This obviously plays an important role during the
weathering of the Loseros Tuff, but another important
factor that must to be considered is the composition of the
Fig. 13 Moisture expansion under water-saturated conditions (hyd-
ric) of the coarse Loseros perpendicular to the lamination (Z-
direction)
Fig. 12 Moisture expansion under water-saturated conditions (hyd-
ric) of the coarse Loseros parallel to the lamination (X-direction)
Environ Earth Sci (2013) 69:1189–1201 1199
123
cement, which keeps the grains bonded to one another. As
seen, there is a high amount of calcium carbonate (calcite,
CaCO3) in the matrix and this mineral may be the reason for
the observed differences because calcite is relatively solu-
ble under weathering conditions, which can be probed even
with normal meteoric water.
Therefore, it is likely to assume that the matrix may
have been partially dissolved, which greatly reduced the
cohesion of the particles promoting flaking and crumbling
The petrographic study also showed a high content of glass
micro-shards and ash in the matrix and its consolidation
(collapsing) with the grain crystal rock fragments and other
lithic fragments depends of the grade of compaction
between them, but under the microscope it looks weakly
welded to the grains (Fig. 5).
Other important factors are the porosity and the average
radius of the different horizons, which are related to the
water transport in the rock. It is known that volcanic rocks,
especially tuff rocks show a large variability in the porosity
(Siegesmund and Du¨rrast 2011), and the effective porosity
in the Loseros Tuff varies from 11 to 20 % but almost
always with an average radius in the micropore size
(Klopfer 1985). The fact that the coarse-grained 4g horizon
has the largest pore radius and at the same time the lowest
effective porosity shows that the pores are not well inter-
connected between each other, which allow the water
uptake but restrict its transport (Kraus 1985; Graue et al.
2011). It seems that in the fine-grained horizons the simi-
larities between the pore sizes and grain sizes (well-sort-
ing) allow for a better interconnection between the pores.
The results of the moisture hygric dilatation in the fine-
grained variety show a normal trend related to its average
pore radius and effective porosity, mainly because the
water uptake and its transport occurs almost exclusively
across the micropores and restricts the contact between the
water vapour and the swellable clay minerals (Larsen and
Cady 1969; Siegesmund and Du¨rrast 2011). A very dif-
ferent behaviour was observed when the coarse-grained
tuff was saturated in water. On the one hand, an initial
moderate expansion can be seen, which means that mois-
ture is introduced slowly into the sample causing a gradual
and slow expansion. At the same time the water, which
now fills the low primary effective porosity, begins to
dissolve the carbonate matrix, causing a secondary poro-
sity, releasing new spaces (pores) where the water now
invaded the rock. This process of dissolution was clearly
identifiable in the hydric test. After the dissolution, mois-
ture and water contacted the clay minerals in the matrix
that previously had no interaction with it and this process
was accompanied by a sudden expansion. The hydric
dilatation values reached very high values, which also
caused disaggregation of crystals and fragments that were
cemented.
The dissolution of the matrix in this case was irrevers-
ible because the cement material dissolved out in the
infiltrating water flows, as happens with outcropped natural
rocks, even in buildings stones. The time required for the
expansion varies greatly according to the rock type and it
depends mainly on the pore space properties. Rocks with a
good connected pore network and higher porosities have
faster expansion and rocks with less connected pores and
lower porosity values show low expansion velocities
(Siegesmund and Du¨rrast 2011; Morales Demarco et al.
2007; Ruedrich et al. 2005). The Loseros Tuff shows both
behaviours (velocities), which can be only explained with a
change in the pore space properties.
Finally, hydric dilatation is another process that is not
necessarily irreversible, but when it happens, it contributes
to the separation of the crystals and rock fragments espe-
cially if the cement is partially dissolved, causing the
collapse of the rock, as happened during our experiments.
Acknowledgments The first author conducted the laboratory work
in the Department of Structural Geology and Geodynamics, Geosci-
ence Centre, University of Go¨ttingen, thanks to a grant from the
DAAD (German Academic Exchange Service). We are grateful to
Annette Su¨ssenberger, Gu¨nter Tondock, Harald Tonn and Sergio
Molina for the technical and laboratory support.
Open Access This article is distributed under the terms of the
Creative Commons Attribution License which permits any use, dis-
tribution, and reproduction in any medium, provided the original
author(s) and the source are credited.
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