Environ Geol (2008) 54:283–289
DOI 10.1007/s00254-007-0816-5
ORIGINAL ARTICLE
Evaluation of weathering-resistance classes in clastic rocks
on the example of Polish sandstones
Malgorzata Labus
Received: 23 February 2007 / Accepted: 14 May 2007 / Published online: 1 June 2007
Springer-Verlag 2007
Abstract The scope of the paper is an attempt at the
identification of the weathering-resistance classes within
clastic rocks by means of analysis of capillary pressure
saturation curves. The porosimetric parameters corresponding to the cementing character and the grains’ mineralogical content are very important features of stone
building materials, because of the weathering processes.
The analysed rocks were Polish sandstones and muddy
sandstones used for building purposes, collected from different geological units of Poland (i.e. Sudety Mts. Carpathian Mts. and Holy Cross Mts.) The results indicate the
usefulness of sandstone materials for building purposes.
They could also be used in conservation procedures and for
the reconstruction of existing buildings and monuments.
Basing on the parameterisation, with the van Genuchten
function, of cumulative capillary pressure saturation
curves, it was possible to distinguish four groups of the
sampled rocks. The lithological features and weathering
sustainability within the groups are quite uniform, what
allow identifying the weathering resistance classes. Taking
into account the complicated nature of all the factors
influencing weathering processes, it is supposed that the
presented parameterisation could be a useful tool for
weathering-resistance classification of clastic rocks. The
classification could be useful in building industry and in
conservation of historical stone monuments.
Keywords Porosity Sandstones van Genuchten
function Weathering resistance
M. Labus (&)
Institute of Applied Geology,
Silesian Technical University,
Akademicka 2, 44-100 Gliwice, Poland
e-mail: [email protected]
Introduction
Porosity parameters are essential for rocks weathering;
hence the objective of this paper is to evaluate rocks
weathering resistance classes, on the bases of the analysis
of pore diameters distribution curves. Water is the main
weathering agent, whereas pores and microcracks are a
natural way for rock penetration. The importance of microcracks is especially observed in low porosity granites
(Sousa et al. 2005).
Fitzner and Kownatzki (1991) conclude that the porosity
distribution and the total amount of pores are the main
factors contributing to decay, because of the maximum
pressure of ice crystallisation in larger pores. Also, salt
crystallisation starts in large pores and the supply is
strengthened by smaller pores connected to them. On the
other hand, Honeyborn and Harris (1958) defined microporosity (where the diameter of open pores £ 5 lm),
stating that smaller pores generally participate to decay
mechanisms faster than coarser ones. Temporal permeability, porosity and reactive surface area evolve during the
dissolution of rock, subjected to new environmental conditions (Cólon et al. 2004; Andriani and Walsh 2003; He
et al. 2002), which is a specific problem concerning
building stones deterioration.
This study was undertaken to relate the porosity
parameters to the weathering resistance, in connection to
the cement character and grains mineralogical content. The
above-mentioned features are very important parameters
characterising stone building materials, because of the
weathering processes (Grassegger 1999).
The analysed rocks were Polish sandstones (derived
from different geological units of Poland), used for building purposes. The results enable the usefulness of sandstone materials to building purposes. They could also be
123
284
used for conservation procedures and for the reconstruction
of existing buildings and monuments.
Characteristic of the sampled sandstones
In the study 35 rock samples representing different sandstones from Poland were analysed (regarding geological
region or stratigraphical position). Samples numbered 1–16
are Cretaceous sandstones from the Sudety Mountains,
samples 17–24 represent the Cretaceous or Older Tertiary
System of the Beskidy region (the Carpathian Mts.), and
the rest (25–35) are the Paleosoic or Mesosoic rocks of the
Holy Cross Mountains. Figure 1 shows the deposits from
which the samples were collected.
The sampled sandstones are used for building purposes.
Especially the cretaceous Sudetan cut sandstones are
valuable dimension stones, slab facings and building
stones. The history of their exploitation goes back to the
thirteenth century.
Mineral composition of the rocks was analysed with the
use of polarising microscope Axioscope by Carl Zeiss.
Data for the sandstones were collected by means of the
point-counting methods; i.e: grains and cement mineralogical content and grain sizes.
The sandstones from the first group (the Sudetan rocks)
are built mainly of quartz (79–98%); other components are
feldspars and muscovite. They are usually not well cemented, which is caused by a big content of clay minerals
(mainly kaolinite and illite) within matrix. In some parts of
sandstone beds (in Czaple and Radkow) there are trails of
the rock coloured with ferruginous compounds.
The Carpathian sandstones are mainly fine-grained and
hard (with the exception of rocks from the Ciezkowice
Fig. 1 Sampling places—sandstone quarries: 1 Zeliszów, 2 Czaple, 3
Jerzmanice, 4 Radków, 5 Szczytna, 6 Dlugopole, 7 Kozy, 8 Kleczany,
9 Ciezkowice, 10 Tumlin, 11 Suchedniów, 12 Wachock, 13 Smilów
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Environ Geol (2008) 54:283–289
locality). The quartz content oscillates from 49 to 71%. The
other components are, first of all, lithic fragments (mudstones), as well as muscovite and feldspars. Cement is
generally clay-siliceous or siliceous-clay-carbonate.
The sandstones of the Holy Cross Mountains are differentiated, and this for distinguishing several types, the
names of which are usually derived from their place of
origin. The samples were collected from two general types:
the Triassic red sandstones from Tumlin, Suchedniów and
Wachock, as well as the Jurassic white sandstones from
Smilów. In the analysed rocks, the quartz content oscillates
from 76 to 96%. Other components are: feldspars, lithic
fragments and muscovite. The clay-ferruginous cement is
most frequent; in some cases the siliceous- ferruginous
cement is present.
Porosimetric measurements
Porosimetric measurements were carried out using the
mercury injection capillary pressure method, at the Oil and
Gas Institute in Kraków (Poland). Capillary pressure
curves were obtained by means of AutoPore 9220 Micrometrics Injection Porosimeter. Density of the samples was
measured with use of helium AccuPyc 1330 picnometer.
During the porosity measurements, as pressure is increased, the volume of the invading mercury in a series of
steps is recorded. As a result, the cumulative or differential
intrusion volume curve is plotted (Fig. 2). The analysis of
the differential saturation curve makes it possible to display
the modal peak (or two peaks when the distribution is bimodal). This is an important correlation parameter, characterising the pore area.
The fractional pore volume at each pressure step can be
calculated using the total intruded volume. The equivalent
Fig. 2 Example of the cumulative and differential saturation curves
Environ Geol (2008) 54:283–289
pore-throat radius D at each pressure step is given by the
Washburne equation (Washburne 1921).
The apparatus makes it possible to obtain imbibition and
drainage capillary pressure curves for increasing and,
decreasing capillary pressures, respectively. The obtained
cumulative intrusion curves of pore volumes versus
diameter enable the determination of the pore class percentage. The porosimeter penetrates the pores of the volume from 0.01 to 100 lm.
In a semilog mercury injection plot the pore-throat size
[lm] on the logarithmic axis (x), is presented against the
percent pore space saturated with mercury on y-axis. The
total amount of injected mercury indicates the effective
porosity of the sample. With a given mass of the sample (it
is weighed before the procedure) the sample volume and
skeletal volume are obtained. After calculating the results
on the ground of Washburne equation, the pore size distribution, porosity, and apparent (skeletal) density are
evaluated. The additional parameters, which could be calculated are: median pore diameter and total pore area. The
parameters obtained for the analysed samples are presented
in Table 1. The results show a large scale of differentiation
of the sandstones, regarding effective porosity (ranged
from 0.44% to 27%) and average pore diameter (0.07–
29.5 lm).
Parameterisation of cumulative intrusion volume
curves
The correlation between the pore area character of the
examined samples as well as their lithology and the observed weathering resistance was conducted basing on the
parameterisation of the cumulative intrusion volume
curves. In petroleum geology there are used large range of
models parametering real pore area (Schowalter 1979;
Pittman 1992; Such 2002). Basing on the modified KatzThompson formula, Such (1996) presented the definition of
similarity classes of pore area of the reservoir rocks. The
study presented in this paper was undertaken in order to
distinguish the lithofacial classes of weathering sustainability for the analysed psammitic rocks.
The curves obtained from mercury injection tests were
fitted to van Genuchten’s empirical capillary pressure-saturation function (1980). The most frequently used functions providing the empirical descriptions of the shape of
the mercury injection curves are van Genuchten’s and
Brooks-Corey’s functions (1966). They were developed to
describe capillary-pressure phenomena in structured soils,
but their application extended to a range of materials.
The experiments, performed by Bloomfield et al. (2001)
and Gooddy et al. (2002), proved a better fitting relation of
the van Genuchten function for the Permo-Triassic sand-
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stones from the United Kingdom. The van Genuchten
function will generally provide better means of systematic
classification of the sandstones, than the Brooks-Corey
function. This is probably due to relative sensitivity of the
Brooks-Corey function at small pore-throat sizes (Bloomfield et al. 2001).
The van Genuchten function is expressed as:
P ¼ Po ðS1=m
1Þ1m
e
where:
P
Po
m
Se
-
macroscopic capillary pressure,
characteristic pressure for the medium,
pore-size distribution index,
normalised wetting fluid saturation, defined as:
Se ¼
Sw Sr
Sm Sr
where:
Sw - wetting phase saturation
Sr - residual saturation of non-wetting phase,
Sm - fluid content at natural saturation.
Bloomfield et al. (2001) take the characteristic pressure Po
to be equivalent to the breakthrough pressure of the
sandstones, where percolation first takes place. The capillary pressure-saturation curves were fitted to the van
Genuchten equation using the standard least squares
minimisation routine.
The above-mentioned function provides a good fit to the
data. The examples of the fitted curves are presented in
Figs. 3 and 4. For the unimodal curves (i.e. for sample 15)
the fit to the experimental data is quite good (R2 = 0,99),
whereas for the bimodal curves the fit is lower (for example
for sample 1 R2 = 0,95). For the samples of bimodal curves
the final intrusion volume is slightly underestimated by the
van Genuchten function (Fig. 4).
As a result of the fitting routine, for each sample three
parameters are calculated: DPo, m, Sr and Sm. The most
essential are: DPo—the equivalent pore-throat sizes for
characteristic pressure Po; and m—pore-size distribution
index.
Index m is ranged between 0.23 and 0.87, and the
equivalent pore-throat size DPo is strongly diversified between 0.2 and 22.6 lm.
By plotting the fitted parameter m versus DPo (Fig. 5)
the points representing samples can be grouped into some
classes. In the plot sample 29 is omitted because of the
extremely low value of index m (0.027). Out of the
remaining 34 samples four classes are distinguished. In
each class the samples collected form different geological
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Environ Geol (2008) 54:283–289
Table 1 Porosimetric parameters for sandstone samples
Region
Sample
no.
Total
porosity
(%)
Skeletal
density
(g/cm3)
Bulk
density
(g/cm3)
Effective
porosity
(%)
Average pore
diameter
(lm)
Total pore
area (m2/g)
Pores
>1 lm
(%)
Threshold
pore diameter
(lm)
Hysteresis
(%)
Sudetan Mts.
1
16.62
2.6
2.18
16.15
1.43
0.21
80
50
20
2
15.27
2.74
2.27
17.04
0.34
0.9
57
6
86
3
14.44
2.57
2.22
13.52
1.11
0.22
70
8
71
4
14.56
2.6
2.23
13.94
0.67
0.37
62
5
76
5
14.06
2.56
2.22
13.1
0.83
0.28
77
10
74
6
12.69
2.6
2.29
12.19
0.4
0.54
60
4
78
7
8
16.87
14.76
2.44
2.6
2.1
2.23
14.06
14.15
1.47
2.21
0.18
0.12
75
77
35; 4
25
34
39
9
16.27
2.61
2.19
15.99
3.52
0.08
84
50
50
10
26.66
2.65
1.94
26.98
0.68
0.82
65
70
26
11
23.8
2.59
2.02
22.06
1.14
0.38
72
70
22
12
23.04
2.65
2.04
22.99
1.04
0.36
77
90
19
13
21.97
2.61
2.06
21.32
0.34
1.23
73
80
22
14
25.26
2.43
1.93
20.74
1.7
0.25
83
60
18
15
15.08
2.6
2.23
14.36
0.39
0.66
45
8
61
16
19.79
2.61
2.11
19.08
0.33
1.08
32
20; 5
46
17
4.56
2.66
2.54
4.42
0.17
0.42
16
0.8
57
18
4.19
2.64
2.54
3.97
0.1
0.65
21
0.6
65
19
2.39
2.63
2.57
2.24
0.07
0.48
32
0.2
66
20
2.94
2.62
2.55
2.73
0.24
0.18
36
0.5
56
21
18.47
2.56
2.12
16.97
2.31
0.14
93
30
44
22
23
10.49
18.87
2.59
2.66
2.34
2.16
9.62
18.81
0.21
1.2
0.8
0.29
53
86
5
20
77
62
Carpathian Mts.
Holy Cross Mts.
24
9.94
2.57
2.34
9.11
0.82
0.19
77
30
54
25
0.45
2.61
2.59
0.44
29.52
0
ND
ND
ND
26
8.17
2.56
2.37
7.37
0.31
0.4
18
2
69
27
8.76
2.4
2.23
6.94
0.38
0.32
30
2
60
28
3.28
2.62
2.54
3.19
0.74
0.07
43
3
36
29
17.43
2.58
2.16
16.26
2.76
0.11
85
50
25
30
18.98
2.44
2.06
15.59
2.58
0.12
83
50
30
31
12.88
2.54
2.25
11.46
0.83
0.25
68
18
68
32
23.57
2.6
2.01
22.64
9.48
0.05
91
30
9
33
17.28
2.62
2.19
16.58
0.9
0.34
71
30
31
34
26.68
2.57
1.94
24.78
20.18
0.03
90
35
1
35
5.98
2.57
2.43
5.42
0.14
0.62
16
0.6
42
ND not determined
region of Poland are found. The common features of the
rocks belonging to one class are: similar shape of the
capillary pressure saturation curve (Fig. 6), and also some
lithological features—influencing the weathering resistance
of the rocks (Table 2).
The cumulative capillary pressure saturation curves of
all the samples are concentrated in a graph (Fig. 6), where
the distinguished classes are differentiated as symbols. The
lowest curve (belonging to class II) seems to be untypical
123
cumulative curve, because of its nearly horizontal shape. In
fact, this is the curve for sample 25, the porosity of which is
extremely low (0.44%). However, when the scale of axis y
is properly fitted, the shape of the plotted curve is uniform
to the other sample curves in this group.
As it can be noticed in the cross-plot m/DPo (Fig. 5),
group IV seems to be the most evidently distinguished one.
In spite of the biggest size of the group, the sample points
are concentrated on a relatively small area. The shape of
Environ Geol (2008) 54:283–289
287
Fig. 3 Fitting the capillary pressure saturation curve for sample 15
Fig. 6 The cumulative capillary pressure saturation curves of all the
samples
Fig. 4 Fitting the capillary pressure saturation curve for sample 1
Fig. 5 Grouping the sandstone samples into classes basing on m and
DPo parameters cross-plot. Sample numbers: 1 Radków, 2–6
Dlugopole, 7–8 Szczytna, 9 Jerzmanice, 10–15 Czaple, 16 Zeliszów,
17–20 Kleczany, 21 Ciezkowice, 22–24 Kozy, 25–28 Tumlin, 29–31
Suchedniów, 32–33 Smilów, 24–25 Wachock
the cumulative curves indicates the uniform pore sizes
distribution in the samples. The features selected in Table 2 indicate that the total porosity in this group is the
most differentiated, as well as the cement content. In spite
of these differences the lithological features and weathering sustainability are quite uniform. The most important
feature, common for the samples belonging to group IV is
very low weathering resistance—granular disintegration.
The petrographic analysis shows that in the case of some
samples from this group, the disintegration is connected to
a high content of cement. In other cases (e.g. in samples 26,
27, 28 and 35) the cement content is low (1–6%), but it is
clay-ferruginous, which accelerates deterioration. The
dominating clay mineral in the cement is kaolinite.
Group I is separated due to low values of pore-size
distribution index m (0.22–0.46) and low values of porethroat diameter DPo (0.22–4.0). Just as in the case of Group
IV, there is visible that total porosity, as well as cement
content are quite differentiated. The cumulative capillary
pressure saturation curves indicate that the pore distribution is bimodal. Basing on the lithological observations it is
visible that the high compacity and weathering resistivity
are main features of Group I samples.
The most difficult to precise characterising seems to be
the Group II. This group area on the plot (Fig. 5) is
localised in the centre of diagram. The lithological features are not uniform, and they are not sufficient for
distinguishing the weathering-resistance class. It is worth
mentioning that belonging to one of the distinguished
groups in the diagram, is not influenced by the porosity
value. This is obvious on the example of sample 25, the
porosity of which, as was mentioned above, is extremely
low.
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Environ Geol (2008) 54:283–289
Table 2 Characteristic of the distinguished classes
Group
Samples
m
I
7, 8, 15, 16, 22, 24, 31
0.22–0.46
DPo
0.22–4.0
Total
porosity (%)
9.11–19.08
a
II
9, 21, 23, 25, 30, 33
0.35–0.76
5.0–10.86
15.59–18.81
III
1, 32, 34
0.67–0.88
17.86–22.6
16.15–24.78
IV
2–6, 10–14, 17–20, 26–28, 35
0.67–0.8
0.05–1.94
2.24–26.98
a
Cement
content (%)
Selected lithological features
1–16
Fine-grained, compact
2–10
Different grain sizes and lithological features
1.5–4.5
Fine-grained, mainly quartz sandstones
1–23
Fine- and medium-grained, disintegrated
With the exception of sample 25, because of its extremely low porosity 0.44%
Group III is distinguished by means of its position on the
diagram (Fig. 5), which is connected to relatively high
values of m and DPo. Nevertheless only three samples are
found in this group, rendering the classification more difficult. The common features of the samples are: great
content of quartz, and minor content of cement (1.5–4.5%).
The sandstones are fine-grained, placed between the
psephite and aleurite.
Regarding the weathering-resistance, the most differentiated are Groups I and IV. The parameter which enables
the distinguishing is the pore-size distribution index m. For
Group I. m < 0.5; for Group IV. m > 0.5.
distribution or cement content. The weathering-resistance
is connected with the following factors:
•
•
•
Composition of the above-mentioned features, as well
as
Mineral composition, and
Pore area characteristic.
Taking into account a complicated nature of all the
factors, the above-presented parameterisation could be a
simple and useful device for the weathering-resistance
classification of clastic rocks.
References
Conclusions
The analysed rocks represent the sandstones and muddy
sandstones from several geological and stratigraphical
units of Poland. The parametrisation of the cumulative
capillary pressure saturation curves makes it possible to
distinguish a few groups of the sampled rocks. It is a
hypothesis that basing on the performed lithological and
porosimetric analysis, it is possible to extract the weathering-resistance classes. The porosimetric parameters are
essential for the class identification.
The most evident are the two groups of sampled rocks:
•
•
Very high weathering-resistive class, where the porethroat diameter DPo is between 0.2 and 4 lm, and the
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class could be identified. For this class the above-mentioned parameters are as follows: DPo > 17, m > 0.6.
The identification of weathering-resistance classes is not
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(lithostratigraphical position), total porosity, grain-size
123
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