Select a Suitable Repair Mortar for Concrete Segments Damaged...
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AASCIT Journal of Materials
2018; 4(1): 6-13
http://www.aascit.org/journal/materials
ISSN: 2472-9736 (Print); ISSN: 2472-9752 (Online)
Keywords Repair Mortar,
Acid Attack,
Pozzolan,
Bond Strength
Received: December 27, 2017
Accepted: January 16, 2018
Published: January 29, 2018
Select a Suitable Repair Mortar for Concrete Segments Damaged by Acidic Attack
Erfan Riahi1, Alireza Joshaghani
2
1Civil Engineering Department, Amirkabir University of Technology, Tehran, Iran 2Zachry Department of Civil Engineering, Texas A&M University, College Station, Texas, USA
Email address [email protected] (A. Joshaghani)
Citation Erfan Riahi, Alireza Joshaghani. Select a Suitable Repair Mortar for Concrete Segments Damaged
by Acidic Attack. AASCIT Journal of Materials. Vol. 4, No. 1, 2018, pp. 6-13.
Abstract The existence of hydrogen sulfide gas in the natural environment produces sulfuric acid,
which causes rapid destruction in concrete. The aim of this study is to propose potential
resistant repair mortars to protect against the sulfuric acid attack. Three types of cement
(Type 1-Delijan, Sepahan slag and Kurdistan) with three types of pozzolan (micro silica,
trass and pumice) were used to make ten mix designs. Capillary and water absorption,
strength reduction and weight loss tests in an acidic environment were also conducted.
Finally, the most resistant mix was selected based on the parameters of the repair
materials, adhesive shear strength and pull-off tests. The sample that contained micro
silica and trass performed better and was proposed as a repair mortar against sulfuric
acid attack.
1. Introduction
Chemical attacks affect the durability of concrete significantly, which determines the
expected service life of concrete members [1]. Structures degraded by acid attacks have
caused excessive maintenance costs. The existence of a suitable repair mortar can
increase the life of the structure and reduce the amount of acid attack [2]. Hydrogen
sulfide, which is oxidized to sulfuric acid on the concrete surface, is formed under
anaerobic conditions. The sulfuric acid reacts with the alkaline components of the
concrete to form gypsum that has a little structural strength [3]. The increasing
temperature results in increased rates of oxygen consumption, which leads to anaerobic
conditions and enhances the rate of hydrogen sulfide formation [4]. Ying-fang et al. [5]
reported that the acid solution creates a more porous concrete microstructure, and the
average porosity in the concrete specimen increased with the conditioning age linearly.
Bemdt et al. [6] believed that replacing cement with 5-10% micro silica increased
concrete resistance against acidic attack. Idriss et al. [7] subjected mortar specimens to a
H2S solution for a year and concluded that 8% cement replacement by micro silica and
water to cement reduction led to suitable resistance against H2S. However, Kawai et al. [8]
reported that an increase in water to cement ratio improved the resistance against sulfuric
acid. Sersale et al. [9] also reached the same results against acidic rain. Bakharev et al. [10]
investigated the acidic resistance of concrete made by alkali-activated slag. Cylinder
specimens were subjected to acetic acid (pH=4) for a year, and meanwhile compressive
strength and pH variations were monitored. Results indicated the satisfactory performance
of alkali-activated slag specimens against the acidic solution.
AASCIT Journal of Materials 2018; 4(1): 6-13 7
Momayez et al. [11] tested both repair mortars composed
of the different percentages of micro silica and mixes with
10% cement replacement with K100 polymer glue and 20%
SBR polymer. They observed that micro silica improved the
bond strength by 25%; however, this strength was lower
compared to the main sample. The optimum cement
replacements for K100 and SBR were 7%. Parhizgar et al.
[12] also reported that adding micro silica and SBR polymer
to cement based repair mortars improved the moment
resistance and the modulus of elasticity, and it also reduced
water permeability. Abbasnia et al. [13] used the slant shear
test and reported that SBR polymer admixture reduced
compressive and tensile strength, and it generally reduced the
bond strength. They reported that micro silica led to a little
shrinkage in a repair mortar, but had better performance than
the control and SBR samples. Sadeghi et al. [14] prepared
seventeen mixture designs as repair mortars. They reported
that adding nano silica by 4.5% cement replacement led to
increased compressive strength and bond strength. On the
other hand, adding zeolite by 9% replacement generally
indicated more compressive strength and more bond strength
than the control sample. Moodi et al. [15] investigated the
probability of an acid attack on the inner walls of the water
transfer tunnel. They prepared a sulfate ion profile for cores
excavated and confirmed that an acid attack occurred due to
the conversion of H2S to H2SO4. In this research, mortars
were prepared, and the experiment was carried out to select
the appropriate repair mortar to use in the destructive area,
such as Nosoud tunnel.
2. Materials and Methods
In order to repair damaged segments with the acidic attack,
repair mortars were prepared with three types of cement:
Type I-Delijan cement (D), Sepahan slag cement (S) and
Type II- Kurdistan cement (K). Also, micro silica (MS), trass
(T) and pumice (P) were used as cement replacement
materials. Cement material properties are shown in Table 1.
The physical properties of aggregates were displayed in
Table 2.
Table 1. Material properties.
Delijan Kurdistan Sepahan slag cement Micro silica Trass Pumice
Oxide
SiO2 23.12 22.28 27.32 87.5 67.82 64.9
Al2O3 3.56 4.72 6.08 0.5 14.14 12.1
Fe2O3 3.29 2.75 2.12 1.53 2.96 5.2
CaO 63.07 64.12 55.34 1.27 3.36 7.4
Na2O 0.19 0.28 0.36 0.36 4.3 2.49
K2O 0.66 0.76 0.76 1.14 2.5 1.88
MgO 1.31 1.23 4.21 1.01 1.6 1.98
TiO2 0.146 0.156 0.58 0.02 - 0.79
MnO 0.091 0.112 0.512 0.086 - 0.123
P2O5 0.224 0.263 0.201 0.13 - 0.2
SO3 1.638 1.973 2.355 0.46 - -
L.O.I (%) 2.37 1.12 0.02 5.92 7.18 2.5
Density (gr/cm3) 3.06 3.02 3.07 2.14 2.34 2.54
Fineness (cm2/gr) 2908 3035 3120 650000 4100 5074
Table 2. Aggregates properties.
Fineness modules Density (Kg/m3) Water absorption (%SSD)
3.36 2550 2.67
Ten mix designs were prepared with three types of cement
and three cement replacement materials as shown in Table 3.
The cement was made with Delijan cement as a control
sample with which to compare the other mixture designs’
performance. The replacement content of MS was 5% with a
fixed ratio. However, 10% and 8% were employed as
replacement percentages for trass and pumice, respectively.
The water-to-binder ratio was 0.36, and workability was
fixed between 120-130 mm by adding water reducer
admixture in the flow table test. For evaluation of the bond
strength, designed mortars were implemented in the concrete
with a mix design as shown in Table 4.
Table 3. Mix designs.
Mix designs Sand Cement Water Micro silica Trass Pumice
1 OPC 1781 400 144 0 0 0
2 M.D.5%MS 1774 380 144 20 0 0
3 M.K.5%MS 1774 380 144 20 0 0
4 M.S.5%MS 1774 380 144 20 0 0
5 M.D.5%MS.8%T 1767 348 144 20 32 0
6 M.K.5%MS.8%T 1767 348 144 20 32 0
7 M.S.5%MS.8%T 1767 348 144 20 32 0
8 M.D.5%MS.10%P 1768 340 144 20 0 40
9 M.K.5%MS.10%P 1768 340 144 20 0 40
10 M.S.5%MS.10%P 1768 340 144 20 0 40
8 Erfan Riahi and Alireza Joshaghani: Select a Suitable Repair Mortar for Concrete Segments Damaged by Acidic Attack
Table 4. Mix design of based concrete (kg/m3).
Material content (Kg) Coarse aggregates Fine aggregates Cement Water Water Reducer
Based concrete 693 1073 450 137.4 2.7
In preparation of samples for the bond strength test, a
piece of polystyrene was embedded into the molds, and then
based concrete was cast. In order to have better bonding, the
surface of the based concrete was ridged until aggregates
appeared. In this research, durability tests were carried out on
repair mortars to determine what the optimal mix designs
were (phase 1). Then, bond tests were conducted on selected
samples to distinguish the mixtures that performed better
than others (phase 2). In the first section of the experimental
plan, the compressive strength, the water absorption, the
capillary absorption, the shrinkage, the weight loss and the
strength reduction were conducted. In the next phase, pull-
off, slant shear and bi-surface shear tests were carried out.
A capillary absorption test was performed based on ASTM
C1585. Cubic specimens were kept in the oven with 50°C
heat for 14 days. After that, specimens were weighed and
then were put into 5 mm of water. After 3, 6, 24 and 72
hours, the weight of specimens was measured again to
determine the water content. 10cm cubic water absorption
specimens were also kept in the oven with 105°C heat for 72
hours. After that, specimens were weighted and then
submerged in water for 30 minutes. Weight loss in an acidic
solution was used to determine the resistance of 10 cm cubic
specimens against sulfuric acid (pH=1). The acid solution
was circulated due to the pH being constant all around the
tank.
The 10 cm cubic specimens for the strength reduction test
were submerged in an acidic solution (pH=1). In order to
evaluate the strength reduction in the presence of an acid
attack, the compressive strength was measured and compared
with results before subjecting to an acidic solution (28 days
results). According to BS6319, In 10cm×10cm×20cm
specimens for the slant shear test, a failure surface (at an
angle of 30 degrees) between old and new material was
subjected to both compressive and shear stress (see Figure 1
(a)). For the bi-surface shear test, initially,
15cm×15cm×10cm specimens were made as old concrete.
Then 15cm×15cm×5cm a repair mortar was inserted near the
old concrete. Compressive loading was carried out as Figure
1 (b) shows.
Figure 1. (a) The Slant shear test specimen, (b) Bi-surface test specimen.
On the Pull-off test, a core excavated from a 15 cm cubic
sample consisted of repair mortar and old concrete. As shown
in Figure 2, the bond strength was assessed based on the level
of the failed surface.
Figure 2. (a) Schematic of the Pull-off test, (b) Cut from boundary surface, (c) Cut from based concrete.
The difference between shrinkage of old concrete and
repair mortar led to a shrinkage strain on the boundary
surface. Therefore, 2.5cm×2.5cm×28.5cm specimens were
used for measurement of repair mortar shrinkage.
AASCIT Journal of Materials 2018; 4(1): 6-13 9
3. Results and Discussion
3.1. Compressive Strength
Results were obtained for an average of three samples after
7, 28, 90, 180 and 210 days of curing in lime water, as shown
in Figure 3. According to Figure 3, using MS increased the
compressive strength. Regarding trass and pumice, these two
pozzolans reduced the compressive strength at the earlier
time; however, the later time reduction was negligible. The
slag cement (S) indicated weaker results in comparison to
other mixes due to pozzolanic reactions.
Figure 3. Compressive strength test results.
3.2. Capillary Absorption
Results for an average of three samples at the ages of 28, 90,
180 and 210 days are shown in Figure 4. Specimens that
contained pozzolan had less capillary absorption in comparison
to the control sample, and this might be due to pozzolanic
reactions and making secondary silicate gels that converted little
spaces to capillary voids and created a discontinuity between
them. Results showed that MS individually reduced capillary
absorption in earlier times. However, the rate of this reduction in
Delijan/Kurdistan cement mixes reduced gradually. The
composition of trass/pumice and MS in slag cement mixes
performed better in later times. This performance was for a
higher reaction rate of MS in earlier times, which decreased
significantly with time and in the following was continued by
the next pozzolan (trass/pumice) in later times and finally
reduced capillary absorption.
Figure 4. Capillary absorption test results.
3.3. Water Absorption
Results at ages of 28, 90, 180 and 210 days were obtained
as shown in Figure 5. Pozzolanic specimens had less
absorption, like the previous section. Less water absorption
indicated that specimens containing pozzolan would perform
well against corrosive ions in the aspect of durability. Here,
MS reduced water absorption in earlier/later times. Slag
cement mixes like the previous section, devoted less
absorption in later times in comparison to other mixes.
10 Erfan Riahi and Alireza Joshaghani: Select a Suitable Repair Mortar for Concrete Segments Damaged by Acidic Attack
Figure 5. Water absorption test results.
3.4. Weight Loss
Results were obtained at 7, 14, 28, 56, 90, 120, 180, 210
and 240 days of submerging to acid exposure after 28 days
curing. The weights of specimens after submerging were
compared with their weight before subjecting to acid attack
in order to get the weight loss, as shown in Figure 6. Most of
the specimens had the same weight loss until 56 days of
submerging. After that, slag cement specimens had less
weight loss, and the reason was attributed to the high
resistance of slag against loss of cement bonding in the
presence of an acid attack. In slag cement specimens, the
composition of MS- trass/pumice pozzolans performed better
than using MS singly. The slope of the diagram up to a
month exposure was approximately equal to the slope for
more than three months, and the slope between the ages of
one to three months exposure was greater than other ages.
Figure 6. Weight loss test results caused by acid attack.
3.5. Strength Reduction
Results were obtained at 7, 28, 90, 180 and 210 days of
subjecting to acid attack after 28 days curing (see Figure 7).
For better comparison, the compressive strength of
specimens was divided on primary compressive strength
before subjecting to acid attack and strength reduction
measured. The strength reduction in MS samples was more
than the control. After 180 days submerging, pumice
specimens experienced less strength reduction in earlier
times in comparison to other specimens. Slag cement
specimens generally experienced less strength reduction over
time. The composition of MS and pumice in slag cement
performed better than other samples.
AASCIT Journal of Materials 2018; 4(1): 6-13 11
Figure 7. Compressive strength test results caused by acid attack.
3.6. Slant Shear
According to experiments conducted for the evaluation of
mortar performance against acid attack, as slag cement
specimens generally performed better than other specimens,
these mixes made to investigate the phase 2 of experiments.
Table 5 displays the 28 days compressive strength of new
slag cement specimens and concrete. These results were not
much different from the results of the first phase.
Table 5. The 28 days compressive strength of selected specimens.
Selected mixes Compressive strength (MPa)
1 RM.S.5%MS 52
2 RM.S.5%MS.8%T 61
3 RM.S.5%MS.10%P 47
4 Based concrete 67
Results were obtained for an average of three samples at
the age of 7, 28 and 90 days by dividing failure load on a
boundary surface. According to Figure 8, usage of MS and
the composition of micro silica-trass performed better than
micro silica-pumice specimens. Trends showed that more
than 90% of final strength was obtained after 28 days.
Figure 8. Slant shear test results of selected specimens.
3.7. Bi-surface Shear
The bi-surface shear test was conducted at the ages of 7,
28 and 90 days by dividing failure load on a boundary
surface. According to Figure 9, adding trass/pumice to MS
slag cement specimens reduced bond strength in the earlier
ages. This reduction was compensated in the later ages in
samples containing trass.
Figure 9. Bi-surface shear test results of selected specimens.
3.8. Pull-off
Results were obtained at the ages of 7, 28 and 90 days by
dividing failure load on connecting the surface of repair
mortar to based concrete (circle with a diameter of 6.9 cm).
As shown in Figure 10, specimens containing MS
individually and consisted of MS- trass, performed better
than micro silica-pumice specimens in the whole of the time.
Usage of trass leads to increase the tensile bond strength.
Figure 10. Pull-off test results of selected specimens.
12 Erfan Riahi and Alireza Joshaghani: Select a Suitable Repair Mortar for Concrete Segments Damaged by Acidic Attack
3.9. Shrinkage
Shrinkage results were obtained every 7 days until the age
of 56 days (see Figure 11). Specimens containing micro
silica-pumice had more shrinkage in comparison to other
specimens. Here, the composition of micro silica-trass
performed better than MS.
Figure 11. Shrinkage test results of selected specimens.
4. Discussion
Adding pozzolans to cement paste decreased C3A content
and produced secondary silicate gel with consumption of
Ca(OH)2. Although the rate of hydration development in
trass/pumice pozzolan specimens was generally lower than
the control samples, in the later ages, the development of this
reaction and promoted interfacial transition zone,
compensated strength reduction and other durability
parameters were observed. However, it should be noted that
the performance of specimens is important in both earlier and
later times; failure to meet minimum mechanical and
durability specifications in earlier times causes a bad
performance in the whole service life of repaired concrete. In
this research, almost all specimens’ results were acceptable
in earlier times. MS was used in all mixes except for OPC, so
specimens containing MS were used as a control to
investigate the effect of adding trass or pumice to mixes.
In this investigation, the compressive strength was
important in three aspects; at first, the inherent mechanical
properties of specimens were studied by compressive
strength test, but the performance of specimens against acid
attack would be different. Consequently, a compressive
strength test was carried out on the specimens subjected to
the acid solution. Eventually, the ratio of strength reduction
was selected to evaluate the specimens’ performance. This
parameter could be useful in the evaluation of specimens’
performance with time against the corrosive environment, but
compressive strength content of every specimen shouldn’t be
forgotten. A specimen had high strength reduction would be
excluded in the evaluation, while its primary compressive
strength was high enough that could be compensated a large
percentage of compressive reduction against acid attack. For
example, MS specimens singly devoted high compressive
strength before being subjected to acid attack; these
specimens also had a high strength reduction. Therefore, this
high primary compressive strength could be relatively
enough for the resistance against acid attack, so both primary
compressive strength and strength reduction should be
considered in the evaluation.
In phase 1 tests, pumice in slag cement generally
performed better than the other samples. On the other hand,
trass generally reduced workability of mortar that needed
water reducer to supply workability. Trass also needed time
to react, so results in earlier times usually were slightly lower
than the control sample. In later times, the performance of
specimens containing trass would be better than the control
sample or the same as its performance. Slag cement
specimens performed well in comparison to other cement
types. The C3A reduction in slag cement was more than other
samples. As repair mortars should have sufficient bond
strength, determination of this parameter is important. Slant
shear and bi-surface tests results were very similar to each
other. These two bond tests with pull-off test ensured that
composition of trass and MS in slag cement would be
appropriate as a repair mortar.
5. Conclusion
From the results of this investigation, the following
conclusions can be drawn:
MS led to promote the performance of mortar generally in
all aspects of durability and mechanical properties. Since MS
generally had a high rate of reaction in earlier times,
pozzolanic reaction continued at a lower rate over time.
Adding another pozzolan to MS samples could promote the
performance in later times. Trass and pumice were generally
effective in this respect.
Usage of pozzolans reduced mortar permeability and
gradually improved mortar performance against acid attack.
Producing secondary silicate gel and making discontinuity
between capillary voids might be the causes.
AASCIT Journal of Materials 2018; 4(1): 6-13 13
Slag cement mixes generally performed better than other
cement types, especially in later times. High capability of
slag pozzolan could be beneficial to filling the pores and
making discontinuity between them. Acceptable compressive
strength, low absorption, low strength reduction and low
weight loss led to select these mixes as alternatives to repair
mortar.
Phase 2 experiments indicated that composition of slag
cement with MS and trass performed better than other slag
cement mixes. More bond strength in slant shear, bi-surface,
and pull-off tests and also less shrinkage show that this
composition will be an appropriate repair mortar against
acidic environments.
References
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