Evaluation of Pozzolanic Activity for Effective Utilization of Dredged Sea Soil
International Journal of Concrete Structures and Materials
Evaluation of Pozzolanic Activity for Effective Utilization of Dredged Sea Soil
In this work, pozzolanic activities of dredged sea soil from two different sources (South Harbor at Busan and Jangsaengpo Harbor at Ulsan) in Republic of Korea were investigated. Dredged sea soil used for this work has passed through a patented purification process, and particle size distribution, X-ray fluorescence, X-ray diffraction, and thermogravimetry/differential thermal analysis (TG/DTA) were utilized to understand its chemical and mineralogical characteristics. Temperature for heat treatment of dredged sea soil were determined using data obtained from TG/DTA, and pozzolanic activities of dredged sea soil samples were investigated by tracking the amount of calcium hydroxide spent for pozzolanic reaction as well as by monitoring the enhancement on 28 day compressive strength. According to the results, dredged sea soil samples from Jangsaengpo Harbor, which contains some amount of silt sized minerals, showed clear pozzolanic activity after heat treatment at 500 C. However, dredged sea soil samples from South Harbor did not exhibit strong pozzolanic reaction due to its larger particle size. At least, it was found that dredged sea soil samples have possibility to be used as a pozzolanic material after proper heat treatment if the size distribution of the particle contains certain amount of silt.
dredged sea soil; pozzolanic activity; recycling; calcium hydroxide; compressive strength
The amount of dredged sea soil has been increasing due to
the increase in maintenance and construction projects of
harbors. The dredging project is a continuous work in nature
due to importance of proper water depth maintenance for
ships to safely move and anchor at harbors. However, the
dredging project produces a large amount of dredged sea soil
as a form of environmental waste. It is known that dredged
sea soil includes a variety of contaminants, organic
substances and heavy metals such as cadmium, arsenic, lead,
(Bae and Yoon 2011; Kim 2012)
. It was reported that
only about 10% of dredged sea soil has been recycled due to
the presence of organic matters and hazardous chemicals.
Also, most of such wastes, approximately up to 90%, had
been dumped into the coastal and offshore area
(Kim et al.
Recently, disposal of dredged sea soil in such a traditional
manner has become impossible due to the enforced
environmental regulations, also in addition to the agreement by
‘‘London Convention on the Prevention of Marine Pollution
by Dumping Wastes and Other Matters (adopted in 1996)’’.
For this reason, currently in Republic of Korea, dredged sea
soil that was produced during various dredging works was
simply sent to a storage site and buried. However, it was
found that dredged sea soil has caused environmental
problems at disposal site during storage period, such as bad
odor and contamination of surrounding environment. Mostly
these are related to contamination by organics matters and
hazardous chemicals in dredged sea soil. Therefore, a strong
drive was placed on dredging companies to develop a
purification process to remove all organic matters as well as
hazardous chemicals before storing it to the disposal site.
The purification process, developed by Sindaeyang Co.
Ltd., was found to remove most of the organic matters,
hazardous chemicals, and chlorides
(Choi et al. 2014;
Sindaeyang Co. Ltd 2014)
. Dredged sea soil, which was
processed through such purification system, has various
possibilities for recycling it as a construction material.
Larger size dredged sea soil (often referred to as dredged sea
sand) can be recycled as fine aggregates or be used for land
(Tsuchida and Kang 2003; Watabe et al. 2004)
Whereas, finer size dredged sea soil (particle sizes similar to
those of silt or clay) is difficult to be used for such purposes
because finer dredged sea soil can cause higher water
demand in case of using it as a source of aggregate, and can
cause ground subsidence if used for land reclamation
et al. 2009)
. There is one way to effectively utilize finer
dredged sea soil, which is to use it as a pozzolanic material
with certain amount of heat treatment.
Various studies are being conducted for the recycling of
dredged soil. As representative example clay bricks were
produced using dredged soil by high temperature heat
treatment above 1100 C
(Im et al. 2013)
Wang et al. (2009)
studied the possibility of utilizing silt-sized dredged soil
obtained from reservoirs as lightweight aggregate by making
it in the form of pellets. However, these studies did not
mention about purification process of the dredged sea soil,
and thus might cause potential environmental issue with the
leakage of hazardous chemicals from dredged sea soil. In
addition, these works
(Im et al. 2013; Wang 2009)
temperature process that is not economical and
environmentally friendly. It was noted that Samara et al. (2009) have
utilized purification process and their purified dredged soil
obtained from the industrial complex was used for partial
replacement (up to 15%) of fine aggregate in cement brick. It
is understood that most of the work related to the dredged
sea soil focused on utilizing it as a source of fine aggregate.
There was almost no literature that extensively studied the
application of dredged sea soil as a pozzolanic material.
In this research, the pozzolanic activity of dredged sea soil
was investigated in order to utilize it as a partial replacement
material for cement. Utilizing dredged sea soil as a
pozzolanic material is a possible approach because dredged sea
soil may exhibit the structure that is similar to clay minerals,
and thus proper heat treatment of dredged sea soil can
develop pozzolanic activity. The properties of pretreated
(purified) dredged sea soil will be first investigated, proper
temperature range for heat treatment will be determined, and
the pozzolanic activity of heat-treated dredged sea soil was
evaluated using X-ray diffraction (XRD) and differential
thermal analysis (DTA)/thermogravimetric analysis (TGA).
Using dredged sea soil as a pozzolanic material can
contribute to the environment issue by (1) reducing the amount
of environmental waste and (2) reducing the use of cement
that is responsible for the global warming.
2. Experimental Procedures
In this study, pozzolanic activities of dredged sea soil
samples collected from South Harbor at Busan (SH) and
Jangsaengpo Harbor at Ulsan (JH), both in Republic of
Korea, were investigated. The dredged sea soil samples used
in this work have passed through purification system
patented by Sindaeyang Co. Ltd.
(Choi et al. 2014;
Sindaeyang Co. Ltd. 2014)
because dredged sea soil without
purification process cannot be used because of the secondary
environmental pollution caused by heavy metals and organic
substances. Details of the purification process can be found
in earlier literatures
(Choi et al. 2014; Sindaeyang Co. Ltd.
Chemical compositions of collected dredged sea soil
samples from South Harbor of Busan (SH) and Jangsaengpo
Harbor of Ulsan (JH) were analyzed by XRF 1700, X-Ray
Fluorescence spectroscope (Shimadzu, Japan). Particle size
distribution of dredged sea soil was also measured using LS
13320 laser diffraction particle size analyzer (Beckman
Coulter, USA). Type I Portland cement, manufactured by
Ssangyong Cement Industrial Co. Ltd., was used for
preparation of cement paste and mortar samples. Chemical
composition of type I Portland cement is shown in Table 1.
2.2 Heat Treatment of Dredged Sea Soil
Thermogravimetric analysis/differential thermal analysis
(TG/DTA) was performed using Bruker ASX TG–DTA
2020 model (Germany) to select proper temperature for heat
treatment of dredged sea soil samples. Since the inflection
points at DTA curve, as well as the weight loss associated
with this thermal event, can be an indicative of dehydration
in clay structure that can possibly bring pozzolanic activity
from dredged sea soil, those points were selected as
temperatures for heat treatment of dredged sea soil. Heat
treatment of dredged sea soil was performed using SH-SK-MF
MoSi2 box furnace (Samheung energy, Republic of Korea).
Mineralogical analysis and crystal structure changes of
dredged sea soil before and after heat treatment at specific
temperatures were analyzed using Ultima IV X-ray
diffractometer (Rigaku, Japan).
2.3 Pozzolanic Activity
Pozzolanic materials do not directly react with water. With
the presence of calcium hydroxide, or with other alkali
hydroxides, it reacts to form silicate or aluminosilicate
(Le et al. 2014)
. Pozzolanic activity can be assessed
by determining the amount of calcium hydroxide consumed
by the pozzolanic reaction. However, in atmospheric
condition, calcium hydroxide can also be consumed by
carbonation process. To eliminate such problem, degassed
nano-pure deionized (18.30 MX cm) water was used, and
mixing and curing process were carried out in a glove box
filled with N2 gas. For comparison of pozzolanic activity of
heat treated dredged sea soil, metakaolin, a very well-known
pozzolanic clay mineral, was used
(Dinakar et al. 2013)
Water to binder ratio was set at 0.5, and replacement ratio of
heat treated dredged sea soil (or metakaolin) to cement was
10 wt%. The blended cement paste sample was poured into
a 10 by 20 mm cylinder mold. After curing for 1 day in a
glove box filled with N2, it was demolded and further cured
in a lime saturated solution for 27 days, in a glove box filled
with N2 gas. XRD analyses were performed to understand
the mineralogical compositions of 28 day old cement paste
samples with heat treated dredged sea soil.
Pozzolanic activity of dredged sea soil was evaluated
using electrical conductivity method suggested by Luxa´n
(Luxa´n et al. 1989)
. This method uses 200 ml of
40 ± 1 C saturated lime solution and 5 g of test material,
and drop in electrical conductivity after 2 min of material
addition can be used to evaluate pozzolanic activity of a
material. When the pozzolanic material is exposed to an
aqueous calcium hydroxide solution, a portion of silicate or
aluminosilicate that dissolves from pozzolanic material and
silica reacts with the calcium component in the aqueous
solution to form an insoluble calcium silicate hydrate,
thereby reducing electric conductivity. Therefore, it can be
inferred that the pozzolanic reactivity is higher when a
material shows lower electrical conductivity. The evaluation
criteria provided by Luxa´n et al.
(Luxa´n et al. 1989)
presented in Table 2, and this criteria was used for
evaluation of pozzolanic activity. To obtain time dependent
changes in electrical conductivity, the measurements were
extended up to 240 min
(Choi et al. 2016)
In order to verify the results obtained from electrical
conductivity measurement, TG/DTA analyses of 28 day old
cement paste specimens were also performed to measure the
amount of calcium hydroxide present in cement paste
samples. Using the amount of calcium hydroxide present in each
specimen, the pozzolanic activity of heat treated dredged sea
soil was quantitatively evaluated.
2.4 Compressive Strength
The 28 day compressive strengths of mortar specimens
were measured in order to verify beneficial effect on
mechanical property by the pozzolanic reaction. Fine
aggregate used for this experiment is standard sand that
conforms to ISO-679. Water to binder ratio (w/b) was 0.5,
and cement to fine aggregate ratio was 1:3, as specified in
ISO-679. The amount of dredged sea soil in the mortar was
10% by weight of the cement. Metakaolin was also used as a
reference pozzolanic material for dredged sea soil. The
substitution rate of metakaolin was also 10% by the weight
The compressive strength was measured according to
ASTM C 109 ‘‘Standard test method for compressive
strength of hydraulic cement mortars (using 2-in or [50-mm]
cube specimens)’’. As soon as mortar was mixed, it was
poured into 50 mm 9 50 mm cube mold and stored in the
25 C laboratory for a day. Specimens were demolded after a
day, and placed in 25 C lime saturated solution for addition
27 days, to ensure total of 28 day curing period. The
compressive strength was measured at 28 days.
3.1 Basic Properties of Dredged Sea Soil
3.1.1 Chemical Compositions
Table 3 shows the XRF data and loss on ignition of
metakaolin and the dredged sea soil from South Harbor in
Busan and Jangsaengpo harbor in Ulsan. Metakaolin
contains 56.96% of SiO2 and 35.54% of Al2O3. SH contains
53.5% of SiO2, 12.6% of Al2O3, 12.8% of CaO, 3.5% of
SO3, and 5.2% of Fe2O3. Whereas JH contains 65% of
SiO2, 13.3% of Al2O3, 2.1% of CaO, 5.5% of SO3, and
4.7% of Fe2O3. JH has higher SiO2 and Al2O3 content than
SH, and thus if those are in amorphous state, JH may
develop higher pozzolanic activity after heat treatment
(Akindahunsi and Alade 2010)
. SH has higher calcium
content, and it is associated with the disposal of shells due
to the geographical location of South Harbor that is nearby
Jagalchi fish market in Busan, Republic of Korea. The loss
on ignition of metakaolin and dredged sea soil was
measured by burning the materials at 550 C for 2 h. Loss on
ignition of metakaolin, SH, and JH were 3.3, 8, and 6.2%,
3.1.2 Particle Size
Figure 1 shows the particle size distribution of the dredged
sea soil and metakaolin. The particle size of SH (dotted line)
is mainly distributed in between 70 and 140 lm. The mean
size of SH was 109.682 lm, and the median size was
104.911 lm. The particle size of SH was found to be in the
range of very fine sand
(Blott and Pye 2001)
. However, the
particle size of the JH (solid line) had a much wider
distribution that that of SH, showing its size distribution in
between 6 and 120 lm. The particle size of JH was mainly
distributed in two sections, silt size (7–36 lm region) and
very fine sand (57–120 lm region)
(Blott and Pye 2001)
The mean size of JH was found to be 42.479 lm, and its
median size was 22.173 lm. The particle size of metakaolin
(alternate long and short dash line) was mainly distributed in
Fig. 2 XRD patterns of metakaolin.
between 20 and 130 lm. The mean size of metakaolin was
found to be 52.495 lm, and its median size was 37.294 lm.
3.1.3 Mineral Composition
Figure 2 shows the XRD patterns of metakaolin. Crystalline
phases found in metakaolin were quartz and albite. Figure 3
shows the XRD patterns of SH and JH. Both dredged sea soil
samples contained minerals such as quartz, orthoclase, and
muscovite. However, these are known to be stable minerals, it
is difficult to expect pozzolanic activity from them. In
addition, due to the presence of highly crystalline quartz mineral,
it was difficult to identify poorly crystalline clay minerals with
relatively low intensity. According to Fig. 3, a weak kaolinite
hump was found in 12 –13 2h area. If this hump is based on
kaolin mineral, this hump will disappear after heat treatment
by conversion into metakaolin, showing higher chance to
present pozzolanic activity
(Souri et al. 2015; Ilic´ et al. 2010;
Vizcayno et al. 2010)
3.1.4 Heat Treatment
TG/DTA analysis was used to select the temperature for
heat treatment of the dredged sea soil. When the inflection
point occurs in the DTA graph, it means that there is a
dehydration event, decomposition, or change in the crystal
structure (phase conversion) of the mineral at that point. It
was reported by many scientists that kaolinite has
endothermic reaction around 500 C, which is related to the
conversion from kaolin to metakaolin
(Ilic´ et al. 2010;
Vizcayno et al. 2010; Kakali et al. 2001; Rabehi et al. 2014)
According to Fig. 4(a), it was found that SH has thermal
events at around 500 and 700 C. The weak thermal event at
lower temperature (lower than 500 C) seems to be
associated with the decomposition of organic matters and adhesion
water. The thermal event at about 500 C seems to be
associated with conversion of metakaolin. The thermal event
at 700 C was associated with the decomposition of calcite.
It was found from Fig. 4(b) that JH has thermal events, one
at about 400 C and the other at about 500 C. Theses
temperatures were selected for heat treatment of JH.
Figure 5 shows the XRD patterns of heat-treated SH and
JH. After the heat treatment above 500 C, it was clearly
observed that the kaolinite hump was disappeared. This
indicates that dehydroxylation of kaolinite and
transformation into metakaolin take place after heat treatment.
3.2 Pozzolanic Activity
Figure 6 shows the XRD patterns of 28 day old cement
pastes incorporating heat treated dredged sea soil. The
cement paste contains portlandite, ettringite, hemi- and
mono-carbonate, periclase, calcite, and unreacted b-C2S
(larnite). The quartz (inert mineral) peak in cement paste was
originated from dredged sea soil. It was found that
Fig. 6 XRD patterns of 28 day old cement paste (plain) and
10 wt% replacement of heat treated dredged sea soil
(w/b = 0.5).
incorporation of heat treated dredged sea soil did not
significantly affect phase compositions of hydrated cement
paste at 28 days.
3.2.2 Electrical Conductivity
The pozzolanic activity was evaluated using electric
conductivity method. Figure 7 shows the changes in electrical
conductivity of heat treated dredged sea soil and metakaolin.
Table 4 shows the difference between the initial value and
the electric conductivity after 2 min. The reduction in
electrical conductivity of metakaolin at 2 min was 4.61. At the
same time, the electrical conductivity of JH at 500 C
sample was 1.26. Large difference was observed between
metakaolin and JH at 500 C sample although both materials
fall in the category of good pozzolanic activity. The
electrical conductivity of JH at 420 C sample was 0.62,
showing variable pozzolanic activity.
According to Fig. 7, the electrical conductivities of both
SH samples (at 500 and 730 C) increased. This behavior
seems to be associated with the presence of soluble salts that
resides in the dredged sea soil. In addition, the conversion
from calcite to lime (also note the thermal data in Fig. 4(a))
with SH at 730 C sample has contributed to the increase in
ionic concentration due to the hydration of lime (CaO ?
H2O ? Ca(OH)2). For this reason, the pozzolanic activity
of SH samples cannot be identified using electrical
Figure 8 shows TG/DTA curve of 28 day old cement paste
sample. For evaluation of pozzolanic activity of dredged sea
soil, comparing decomposition amount of calcium hydroxide
in cement paste samples that occurred at about 450 C
(Alawad et al. 2015)
. The weight loss before and after this
thermal event was obtained using first derivative curve
(maximum and minimum point) at this region. The difference
of these values is the amount of water that is decomposed
during this thermal event (Ca(OH)2 ? CaO ? H2O). The
weight loss of plain cement paste before calcium hydroxide
decomposition was 77.425%, after decomposition of calcium
hydroxide, it was 74.124%. The weight loss associated with
the decomposition of calcium hydroxide was 3.301%. Using
this approach, the amounts of calcium hydroxide in cement
paste samples incorporating heat treated dredged sea soil were
obtained and summarized in Fig. 9 and Table 5.
According to Fig. 9 and Table 5, weight loss of cement
paste incorporating SH at 500 C, SH at 730 C, JH at
Fig. 8 TG/DTA analysis of 28 day old cement paste: plain (w/
b = 0.5).
420 C, JH at 500 C, and metakaolin were 3.144, 3.067,
2.960, 2.727, and 2.605%, respectively. It should be noted
that the dashed line in Fig. 9 represents 90% of the amount
of calcium hydroxide in the plain specimen (since dredged
soil and metakaolin were replaced by 10 wt% of cement),
and thus specimens showing lower than these value should
have consumed certain amount of calcium hydroxide by
pozzolanic reaction. It was found that the weight loss of
cement paste incorporating SH at 500 C and SH at 730 C
were higher than the value of dashed line (2.97%) in Fig. 9,
indicating that SH samples might be non pozzolanic by TG/
DTA analyses. The weight loss of cement paste
incorporating JH at 420 C (2.96%) was similar to the value of dashed
line (2.97%). The cement paste with JH at 500 C showed
2.747% of weight loss, definitely indicating that JH at
500 C is a pozzolanic material although reactivity is weaker
than metakaolin which showed 2.605% weight loss.
3.3 Compressive Strength
Figure 10 shows compressive strength data of 28 day old
mortar specimens incorporating heat treated dredged soil.
The compressive strength of the plain mortar was
33.84 MPa. The compressive strength of mortar
incorporating SH at 500 C and SH at 730 C were 33.24 and
32.61 MPa, respectively. The results were similar to that of
plain mortar. The compressive strength of mortar
incorporating JH at 420 C was 31.62 MPa, which is lower than that
of plain cement mortar. However, compressive strength of
mortar incorporating JH at 500 C was 37.62 MPa.
ComFig. 9 The amount of weight loss in w/b 0.5 cement paste at about 450 C (the dashed line indicates 90% of the weight loss in the
plain cement paste, which considered the 10% replacement of dredged sea soil and metakaolin with the cement).
pared to the plain cement mortar, approximately 10%
increase in compressive strength was observed although it is
still lower than that of metakaolin, whose compressive
strength was 39.52 MPa.
In this work, pozzolanic activities of heat treated dredged
sea soils from two different sources, SH (dredged sea soil
samples from South Harbor in Busan) and JH (Jangsaengpo
Harbor in Ulsan), were investigated. It was found that SH,
mostly consisting of very fine sand, did not present
pozzolanic activity by TG/DTA analysis. However, the 28 day
compressive strength did not show significant decrease with
replacement of SH, indicating that SH can still meet other
criteria for pozzolanic material, such as strength activity
index, etc. Thus, it should be noted SH can be weakly
pozzolanic although it was found to be non-pozzolanic by
JH, which contains some amount of silt particle, was
found to show pozzolanic activity by TG/DTA analysis.
Analyses of pozzolanic activity using decomposition of
calcium hydroxide and compressive strength showed that JH
heat treated at 500 C had clear pozzolanic activity. The
weight loss before and after decomposition of calcium
hydroxide at about 450 C and the improvement in
compressive strength by pozzolanic reaction was found to
present a significant correlation. The same tendency was also
observed from metakaolin, as expected and proved by other
(Poon et al. 2001; Sabir et al. 2001)
It was found that the pozzolanic activity of JH with
500 C heat treatment was lower than that of metakaolin. It
should be noted that both metakaolin and JH contains some
amount of crystalline phases. It is known that the presence of
crystalline phase in material is not beneficial in terms of
pozzolanic reaction because they are more stable in highly
alkaline environment than amorphous phases. The average
particle size of the metakaolin was even higher than that of
JH. Therefore, the lower pozzolanic activity of JH (with
500 C heat treatment) than metakaolin can be only
explained by the amount of amorphous clay mineral in the
material which, in case, can be used for pozzolanic reaction.
This means JH, although heat treated, has less amount of
metakaolin component than reference metakaolin material
used for this work. It should be noted that the 100 lm peak
in the particle size distribution curve (Fig. 1) with JH and
metakaolin might have been attributed to presence of
The incomplete pulverization of JH material might have
also contributed to the larger particle size (100 lm peak in
Fig. 1) of the JH. It was found that as received JH, which
was in a partially wet condition, behaved much like a mud,
and was found to solidify when JH was dried. For this
reason, the additional process was required in order to make
uniform distribution of the particles. A separate grinding was
carried out at 1,500 rpm for 3 s using a Retsch RS200
(Germany) disc mill, but it is still not certain that such a
short processing time is suitable to crush agglomerated clay
According to the results presented in this work, the
pozzolanic activity of dredged sea soil seems to be strongly
related to the size of the particle, and it should have finer
particle size similar to or smaller than that of silt. Heat
treatment is definitely necessary for pozzolanic activity of
dredged sea soil, but the amount of amorphous phases that
can be a crucial part for pozzolanic reaction can vary
depending on different sources of location. There should be
an optimum method for dredged sea soil to be used as highly
effective pozzolanic materials by controlling the particle size
of the dredged sea soil and adjusting the temperature and
time for heat treatment. It should be also noted that the
amount of chloride must be monitored during purification
process in order for heat treated dredged sea soil to be used
as a pozzolanic material for reinforced concrete structure. At
least, it is believed that heat treated dredged sea soil can be
used as a solidifying agent in combination with lime because
hydration of lime can provide necessary amount of calcium
hydroxide for pozzolanic reaction of heat treated dredged sea
This work was conducted for evaluating the pozzolanic
activity of dredged sea soil with fine particle size. According
to the results, following conclusions can be drawn:
(1) Heat treated dredged sea soil from South Harbor in
Busan (SH) did not show pozzolanic activity by TG/
DTA analysis. Although there was no significant
reduction in compressive strength with 10%
replacement of SH, it was found that SH cannot be used as a
(2) Heat treated dredged sea soil at 500 C from
Jangsaengpo Harbor in Ulsan (JH) did clearly present
pozzolanic activity by TG/DTA analysis. The 28 day
compressive strength also increased with 10%
replacement of JH.
(3) To present pozzolanic activity of dredged sea soil,
smaller particle size is necessary. At least, the material
should contain some portion of silt sized particles.
This research was supported by a Grant
(13RDRPB066470) from Regional Development Research Program
funded by Ministry of Land, Infrastructure and Transport of
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