A. DUFKA, T. MELICHAR: COMPOSITES BASED ON INORGANIC MATRICES FOR EXTREME EXPOSURE CONDITIONS
147–151
COMPOSITES BASED ON INORGANIC MATRICES FOR
EXTREME EXPOSURE CONDITIONS
KOMPOZITI Z ANORGANSKO OSNOVO ZA IZPOSTAVITEV
EKSTREMNIM RAZMERAM
Amos Dufka, Tomá{ Melichar
Brno University of Technology, Faculty of Civil Engineering, Institute of Building Materials and Components, Veveøí 95, 602 00 Brno, Czech
Republic
dufka.a@fce.vutbr.cz, melichar.t@fce.vutbr.cz
Prejem rokopisa – received: 2014-08-18; sprejem za objavo – accepted for publication: 2015-01-06
doi:10.17222/mit.2014.205
The vast majority of reinforced-concrete structures are exposed to aggressive substances from the environment during their
exploitation. The consequence is the degradation of the materials and reduction in the lifetime of the structures. Therefore, it is
natural to make an effort to develop and apply the materials that are maximally resistant to such conditions. Materials based on
alkali-activated matrices show a high resistance against chemically aggressive environments. The article is focused on the use of
the materials based on alkali-activated substances as repair materials for the structures exposed to aggressive groundwater.
Keywords: alkali-activated substances, aggressive surrounding, durability of structures
Velika ve~ina betonskih konstrukcij je med uporabo izpostavljena agresivnim snovem iz okolja. Posledica je razpadanje mate-
riala in skraj{anje trajnostne dobe konstrukcije. Zato je naravno, da si prizadevamo razviti in uporabiti materiale, ki so najbolj
zdr`ljivi v danih razmerah. Materiali, ki imajo z alkalijami aktivirano osnovo, izkazujejo veliko odpornost pri izpostavitvi
kemijsko agresivnemu okolju. ^lanek obravnava uporabo materialov, ki temeljijo na snoveh, aktiviranih z alkalijami, kot mate-
rialih za popravilo konstrukcij, ki so izpostavljene agresivni talni vodi.
Klju~ne besede: z alkalijami aktivirane snovi, agresivno okolje, zdr`ljivost konstrukcij
1 INTRODUCTION
A lot of structures are exposed to the environments
that are, due to their chemistry, quite aggressive to rein-
forced concrete. The material’s resistance against the
aggressive substances from the external environment is
mainly determined by the features of its matrix.1 Com-
pared to concrete stone, the materials with the matrices
based on alkali-activated substances have a significantly
higher resistance to chemical substances. The article
deals with the development and, especially, the applica-
tion of the repair materials based on alkali-activated
materials used for the repair of the reinforced-concrete
lining of an underground collector used in a chemically
aggressive environment.
2 SPECIFICATIONS OF THE COLLECTOR AND
THE CONDITIONS OF ITS EXPLOITATION
The excavation of the underground collector was
done using the machine-excavation technology, while the
final scraping of the excavation area was carried out with
the classical, manual excavation method. The excavation
area is from 13 m2 to 14 m2 (by stationing). The length of
the underground part of the collector is 7.87 km; the
lining and casing of the tunnels are made of shotcrete,
whose strength within this project is determined to be 20
MPa. The lining of the tunnels is reinforced with welded
mesh panels (Ø 6–100/100 mm) and a rigid mine casing.
The thickness of the shotcrete is 100 mm. Dry shotcrete
was applied.
Already one year after the construction, significant
defects began to occur. These were mainly the penetra-
tion of water through the lining, new formations of solid
carbonate on the surface of the lining, the formation of
waste products associated with the reinforcement
corrosion, etc. A typical state of the damaged lining after
one year of operation is shown in Figures 1 and 2.
Materiali in tehnologije / Materials and technology 50 (2016) 1, 147–151 147
UDK 691.32:620.193:624.012.4 ISSN 1580-2949
Professional article/Strokovni ~lanek MTAEC9, 50(1)147(2016)
Figure 1: View of the location, in which a massive penetration of
moisture occurred: new solid-carbonate formations are visible on the
surface of the lining
Slika 1: Prikaz podro~ja, kjer se je pojavila mo~na penetracija vlage;
viden je nastanek trdnega karbonata na povr{ini podlage
The state of the structure continued to deteriorate
very quickly and, therefore, it was necessary to take cor-
rective measures. It was found that before the construc-
tion of the collector no hydrogeological survey was per-
formed, or it was performed unprofessionally and
insufficiently.
To properly assess the causes of the failures, a
detailed construction and technical investigation was
carried out in the places where the state of the concrete
was being evaluated, and an analysis of the chemical
composition of the groundwater in various locations of
the collector was performed. The results of the chemical
analysis of the groundwater are given in Table 1.
The foregoing shows that in terms of the durability of
the concrete the amount of sulphate ions in the water is
essential. The aggressiveness of the environment in diffe-
rent parts of the collector can be classified as relevant in
accordance with EN 206-1 (Table 2).
Table 1: Results of the chemical analysis of groundwater
Tabela 1: Kemijska analiza talnice
Chemical
composition
Stationing
0.57 km –
tertiary
sediments
Stationing
1.56 km –
quaternary
sediments
Stationing
2.68 km –
tertiary
sediments
Alkalinity 7.68 7.50 7.70
Sulphates 3450 mg L–1 148 mg L–1 1369 mg L–1
Chlorides 170 mg L–1 152 mg L–1 260 mg L–1
Nitrates 146 mg L–1 124 mg L–1 180 mg L–1
Ammonia ions 0.17 mg L–1 0.13 mg L–1 0.08 mg L–1
Chemical
composition
Stationing
4.42 km –
tertiary
sediments
Stationing
5.93 km –
tertiary
sediments
Stationing
6.67 km –
quaternary
sediments
Alkalinity 7.15 7.25 7.38
Sulphates 3825 mg L–1 1740 mg L–1 193 mg L–1
Chlorides 156 mg L–1 78 mg L–1 178 mg L–1
Nitrates 160 mg L–1 112 mg L–1 134 mg L–1
Ammonia ions 4.12 mg L–1 0.17 mg L–1 16. mg L–1
Table 2: Evaluation of groundwater aggression
Tabela 2: Ocena po{kodb zaradi talne vode
Stationing
0.57 km – tertiary sediments
Highly aggressive
environment
Stationing
1.56 km – quaternary sediments No aggression
Stationing
2.68 km – tertiary sediments
Moderately aggressive
chemical environment
Stationing
4.42 km – tertiary sediments
Highly aggressive
environment
Stationing
5.93 km – tertiary sediments
Moderately aggressive
chemical environment
Stationing
6.67 km – quaternary sediments No aggression
On the basis of the results of the chemical analysis of
the water samples it was possible to conclude that the
water that passes through quaternary sediments does not
cause the sulphate corrosion of the concrete. A com-
pletely different situation occurs when the water passes
through tertiary sediments. These waters show moderate
and, in some areas, even high sulphate aggressiveness.
The results of the chemical analysis clearly demonstrated
a high level of aggressiveness of the groundwater affect-
ing the collector. Underestimating this fact or failing to
carry out a hydrogeological research before the construc-
tion of a collector is, therefore, shown to be a serious
deficiency.
To assess the actual state after two years of the ope-
ration of the collector, a construction and technical
research was performed, aimed especially to:
• assess the state of the concrete, in terms of both
physical and mechanical parameters (i.e., particularly
in terms of compressive strength) and in terms of its
chemical and mineralogical compositions;
• assess the state of the reinforcement and the degree
of its corrosion, especially in connection to the
concrete’s ability to passivate the reinforcement
corrosion with its natural alkalinity.
The process of the construction and technical re-
search was carried out in accordance with the provisions
of the Technical Conditions for Reinforced Concrete
Structure Reinstalment1 and the relevant technical stan-
A. DUFKA, T. MELICHAR: COMPOSITES BASED ON INORGANIC MATRICES FOR EXTREME EXPOSURE CONDITIONS
148 Materiali in tehnologije / Materials and technology 50 (2016) 1, 147–151
Figure 2: Collection of core bores from the lining. Significant car-
bonate efflorescence is visible on the surface of the wall.
Slika 2: Zbiranje jeder iz izvrtine v podlagi. Na povr{ini stene je vi-
den mo~an razcvet karbonatov.
Table 3: Concrete’s compressive strength depending on the aggres-
siveness of groundwater in different parts of the collector
Tabela 3: Trdnost betona v odvisnosti od po{kodb zaradi talne vode
na razli~nih pozicijah kolektorja
Stationing
0.57 km – tertiary sediments 8 MPa
Stationing
1.56 km – quaternary sediments 25 MPa
Stationing
2.68 km – tertiary sediments 14 MPa
Stationing
4.42 km – tertiary sediments 10 MPa
Stationing
5.93 km – tertiary sediments 16 MPa
Stationing
6.67 km – quaternary sediments 27 MPa
dards. The sampling for testing the compressive strength
and for the physico-chemical analysis was carried out
with core bores.
Within the project, the strength class of the concrete
was defined as 20 MPa. The results for the compressive
strength determined on the samples and collected within
the research are summarized in Table 3.
The mineralogical composition of the concrete was
evaluated with an X-ray diffraction analysis, its results
are presented in Table 4.
Table 4: Results of the mineralogical analysis of the concrete
Tabela 4: Rezultati mineralo{ke sestave betona
Sampling point Identified minerals
Stationing
0.57 km – tertiary sediments
Calcite, ettringite, gypsum,
quartz, feldspar
Stationing
1.56 km – quaternary
sediments
Calcite, portlandite, calcium
silicate hydrate II, mono-
sulphate, quartz, feldspar
Stationing
2.68 km – tertiary sediments
Calcite, portlandite,
monosulphate, quartz, feldspar
Stationing
4.42 km – tertiary sediments
Calcite, ettringite, gypsum,
monosulphate, quartz, feldspar
Stationing
5.93 km – tertiary sediments
Calcite, portlandite, calcium
silicate hydrate II, mono-
sulphate, quartz, feldspar
Stationing
6.67 km –quaternary
sediments
Calcite, portlandite, calcium
silicate hydrate II, carbonate
complex, monosulphate,
quartz, feldspar
It is clear that in certain locations, already after two
years of the groundwater penetration, a massive degra-
dation of the concrete occurred. The concrete’s compres-
sive strength in the affected areas is only about half of its
original value. This finding corresponds completely with
the results of the physical and chemical analyses show-
ing massive corrosion formations (gypsum, secondary
ettringite) in the microstructure of the affected concrete.
In addition, the physical and chemical analyses showed
that in some areas the water penetrating the lining caused
quite an intense decomposition ("a washout") of the
cement matrix. This, of course, resulted in a decrease in
the strength of the concrete.
So, massive and negative symptoms occurred after
two years of the operation of the collector. On the basis
of the experience with similar types of structures, sup-
ported by a mathematical simulation, an assumption was
formulated, according to which in approximately two
years, in some parts of the collector the rate of degra-
dation of the lining will be so high that the static load of
the collector will be affected.
Therefore, it was necessary to repair the structure.
The first phase of the repair work related to the most
affected areas. In these locations, the entire layer of the
concrete along the lining was removed and the reinforce-
ment affected by extreme corrosion was replaced. The
removed concrete was then replaced with the repair ma-
terial. Due to the highly aggressive environment, a mate-
rial with a matrix based on alkali-activated substances
was used.
3 REPAIR MATERIAL BASED ON
ALKALI-ACTIVATED MATERIALS
When developing a formula based on alkali-activated
materials, we used the results from earlier researches.2–7
In terms of the properties of the resulting mixture, the
compositions of individual components are important.
The basic characteristics of the materials used for pro-
ducing the mixtures with alkali-activated matrices are
summarized in the following tables (Tables 5 to 7).
Table 5: Chemical composition of metakaolin
Tabela 5: Kemijska sestava metakaolina
Component Representation (%)
Al2O3 41.90
SiO2 52.90
K2O 0.77
Fe2O3 1.08
TiO2 1.80
MgO 0.18
CaO 0.13
Table 6: Chemical composition of slag
Tabela 6: Kemijska sestava `lindre
Component Representation (%)
Al2O3 7.42
SiO2 38.51
CaO 36.26
MgO 10.11
K2O 0.43
Fe2O3 0.74
TiO2 0.026
Table 7: Chemical composition of sodium-silica water glass
Tabela 7: Kemijska sestava vodnega stekla Na-Si
Component Representation (%)
SiO2 50.82
Na2O 26.25
Water 22.12
Silicate module 1.92
Table 8: Formula of the repair mixture based on alkali-activated mate-
rials
Tabela 8: Sestava reparaturne me{anice na osnovi z alkalijo aktivi-
ranega materiala
Ingredient Ingredient dosage of concrete,kg/m3
Slag 430
Sodium-silica glass 95
Metakaolin 50
Water 180
Aggregates 1750
Aggregates with fractions of 0–4 mm and 4–8 mm
were used as the filler. The particle-size distribution
A. DUFKA, T. MELICHAR: COMPOSITES BASED ON INORGANIC MATRICES FOR EXTREME EXPOSURE CONDITIONS
Materiali in tehnologije / Materials and technology 50 (2016) 1, 147–151 149
curve was optimized according to the Empa II proce-
dure.5
The mixture composition is given in Table 8.
This mixture was applied in the locations of the
lining, where it was necessary to remove the original
concrete. The effectiveness of this measure was then
evaluated using the procedure described in the following
section.
4 PERFORMANCE ANALYSIS OF THE NEW
MATERIAL
The efficiency, or durability, of the repair material
was evaluated as follows: One year after the repairs,
control samples were taken from the localities in which
the repair mixture in question was applied. A set of
physico-mechanical and physico-chemical parameters of
these samples was determined. Attention was focused
especially on the following parameters:
• the tensile strength of the surface layers;
• the compressive strength;
• the microstructure, analysed with physico-chemical
methods. The X-ray diffraction analysis and the
scanning electron microscopy were used.
The tensile-strength test of the surface layers was
made "in situ", the sampling for testing the compressive
strength and for the physico-chemical analysis was
carried out with core bores.
These analyses were performed with the procedures
that are in accordance with the provisions of the relevant
technical standards. The samples representing the repair
material were then subjected to the same set of experi-
ments after being stored for about 28 d and 360 d in
standard laboratory conditions (i.e., t = (20 ± 2) °C,  =
(60 ± 5) %). These values were considered as the refe-
rences. The comparison of the values recorded on the
reference bodies and the samples of the repair materials
exposed to the environment of the collector for one year
was the essential criterion in the evaluation of the
effectiveness of the repairs carried out. The data found
with the set of experiments are shown below (Tables 9
and 10).
Table 9: Results of the strength-parameter tests of the repair material
Tabela 9: Rezultati preizkusa trdnosti reparaturnega materiala
sample identification
Bulk
density
(kg/m3)
Tensile
strength of
surface
layers
(MPa)
Compres-
sive
strength
(MPa)
Reference set – stored for
28 d in standard
laboratory conditions
2450 2.1 35.6
Reference set – stored for
one year in standard
laboratory conditions
2400 2.3 36.2
Stationing 0.57 km –
significant sulphate
aggressiveness, annual
exposure
2420 1.9 34.3
Stationing 4.42 km –
tertiary sediments, annual
exposure
2380 2.0 34.0
Table 10: Results for the mineralogical composition of the repair
material
Tabela 10: Mineralo{ka sestava reparaturnega materiala
Sample identification Identified minerals
Reference set – stored for
28 d in standard laboratory
conditions
Calcium silicate hydrate II,
goethit, quartz, feldspar
Reference set – stored for one
year in standard laboratory
conditions
Calcium silicate hydrate II,
goethit, quartz, feldspar
Stationing 0.57 km – signi-
ficant sulphate aggressiveness,
annual exposure
Calcium silicate hydrate II,
goethit, quartz, feldspar
Stationing 4.42 km – tertiary
sediments, annual exposure
Calcium silicate hydrate II,
goethit, quartz, feldspar
The microstructure of the material was also analysed
using the scanning electron microscopy (Figure 3).
On the basis of the above findings we can say that in
terms of both the strength parameters and mineralogy,
the parameters of the repair material exposed to the
highly corrosive environment are quite comparable with
the reference parameters.
A. DUFKA, T. MELICHAR: COMPOSITES BASED ON INORGANIC MATRICES FOR EXTREME EXPOSURE CONDITIONS
150 Materiali in tehnologije / Materials and technology 50 (2016) 1, 147–151
Figure 3: Detailed analysis of the microstructure showed a: a)
de-facto amorphous phase of the matrix for both the reference material
and b) the exposed material of the collector
Slika 3: Podrobnej{a analiza mikrostrukture poka`e: a) amorfno
osnovo tako v primerjalnem materialu kot tudi v b) izpostavljenem
materialu v kolektorju
(a)
(b)
5 CONCLUSIONS
The article deals with the way of repairing an under-
ground collector affected, in some areas, by underground
waters with a highly aggressive chemical effect. Already
in one or two years of the collector’s operation these wa-
ters caused distinct disorders. In the affected areas there
was a significant reduction in the mechanical properties
of the concrete, and its ability to protect the reinforce-
ment against the corrosion was significantly reduced.
Thus, local repairs were carried out, whereby a material
with its matrix based on alkali-activated materials was
used as the repair material.
The matrix of the repair material was composed of a
mixture of blast-furnace slag and metakaolin. Water
glass was used as the activator. The matakaolin added to
the mixture was to reduce the negative effects associated
with the autogenous shrinkage that usually accompanies
the aging of the materials with pure-slag matrices.3,6
The control tests that were conducted one year after
the repair work demonstrated that the aggressive effects
of the water did not result in a decrease in the strength of
the repair material. Neither were negative changes found
in its microstructure. It was also established that the rein-
forcement was very well protected against the corrosion
due to the repair material.
It is clear that the period (one year of application) is
short in terms of the durability of the structures, and for a
precise verification of our findings, we will need to con-
tinue with the monitoring of the concerned construction.
However, despite this fact, it can be noted that so far the
results have indicated a high potential of the material
with a matrix based on alkali-activated materials in the
repair of the reinforced concrete structures exposed to
chemically aggressive environments.
Acknowledgements
This research was done with the financial help of
project GA^R 14-25504S, Research of Behaviour of
Inorganic Matrix Composites Exposed to Extreme Con-
ditions, and EU project The Research and Development
for Innovation, reg. number CZ.1.05/2.1.00/03.0097,
through the activities of regional centre AdMaS –
Advanced Materials, Structures and Technologies.
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Materiali in tehnologije / Materials and technology 50 (2016) 1, 147–151 151