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ICCEA-2019-030
INVESTIGATION ON EFFECT OF PARTIALLY REPLACING CEMENT BY GGBFS
(GROUND GRANULATED BLAST FURNACE SLAG) IN CONCRETE
T.Kajaharan1*, T. Tharsigan 2, K. Baskaran3
1,2 University of Mortuwa, Sri Lanka.
3Senior Lecturer, University of Moratuwa, Sri Lanka.
*Correspondence E-mail: kajaharan28@gmail.com, TP: +94777634204
Abstract: Strength and durability are two key aspects of the construction industry all over the
world. Even though durability still holds an important position and it will have a huge impact in
the maintenance period of a structure, at present the importance of strength has overtaken
durability considerations due to fast pace of construction. This paper focuses on improving the
durability aspects of concrete without reducing the strength of concrete to ensure the fast pace
construction in an efficient and eco-friendly way. It would be achieved through the partial
replacement of GGBFS (Ground Granulated Blast Furnace Slag) to cement. Cement has been
partially replaced by GGBFS up to 30% in the research and several tests were done to find strength
and durability properties of concrete. For strength, compressive strength test was done in 7 days
(early strength) and 28 days and for durability, water absorption test and sorptivity tests were
done. By comparing the results with each other replacements (10%, 20%, and 30%) and control
mix by considering both strength and durability properties conclusions and recommendations
were made. Conclusions of this research show that the 20% GGBS is a good replacement to
cement by considering the strength, durability and future expectations of the industry.
Keywords:
Durability; Early strength; concrete; GGBFS; Partial replacement
1.0 Introduction
Selection of construction materials heavily
depends on their availability, strength and
durability properties and cost. Concrete is
the main construction material, which is
heavily being used, all over the world for
construction due to its advantages. Strength
and durability are the two main aspects of
concrete, which have to be given adequate
attention in the construction process.
However, due to the fast pace of
construction, the attention of the Sri Lankan
Construction industry has more focused on
concrete strength to ensure the design
requirements and durability aspects are
only considered in the quality control
process. Since, fast pace constructions are
the main expectation of the society from
construction industry, strength has to be the
main aspect of the concrete. But at the same
time, durability can’t be omitted totally.
OPC (Ordinary Portland Cement) and rapid
hardening cement are often used in the
construction industry to gain high early
strength for fast pace construction process.
On the other hand, PPC (Portland
Pozzolana Cement) and PSC (Portland Slag
Cement) are used when durability holds the
upper hand than strength such as marine
environment constructions. Jain (2007)
stated that OPC and rapid hardening
cement are less durable compared to the
PPC and PSC, and PPC and PSC will not
give early strength as OPC.
GGBFS or GGBS (Ground Granulated Blast
Furnace Slag) is a by-product of steel
industry. It has cementitious properties to
perform hydration reactions and also has
the durability aspects. Adding GGBS to
OPC cement mix concrete may increase the
durability characteristics. Also, the early
strength characteristics of the concrete mix
must be considered. So, cement must be
replaced by GGBS to a certain amount to
maintain the early strength and achieve
significant improvement in durability of
concrete. In a recent study Patil et al (2013)
concluded that, normally cement can be
replaced by GGBS up to 70% of cement
content without considering the early
strength parameters. But when taking
consideration of early strength, replacement
percentage should be lower.
GGBS to cement
as a replacement is the most ecological solution
for the greenhouse gas emission and global
warming issues. Also, durability enhancement
ICCEA-2019-030
by adding GGBFS is the most important
objective of this research. If this objective is
accomplished with maintaining the early
strength, this will be a big relief to the
ecologists. Also, GGBS itself a waste by-product
in the industry, so, it is always conservative
idea to improve the environment state.
Practical applications of this research will be a
big step-forward in the construction industry in
Sri Lanka. It is a big move to a sustainable
construction process with fast pace
construction process. Since OPC is the most
common cement in the industry. This research
implication will be a boost to construction
industry to try various other GGBS kind of
materials to achieve durable and strong
constructions in the future.
2.0 Methodology
2.1 Literature review
GGBS inclusion into concrete mix has had
many researches in the past in all over world.
Several combinations were tried in those
researches to achieve several objectives.
Considerable related literatures were analyzed
during the research process to achieve the
objective of this research.
OPC concrete cube and OPC, GGBS and Silica
fume concrete cube were checked for water
absorption test and compressive strength test
(Vireen, 2016). Adding GGBS and Silica fume
(SF) to OPC concrete results in less water
absorption than OPC concrete cube. This
indicates GGBS and Silica fume are enhancing
the concrete durability. Results are stated in
table 1 and it contains water absorption rate
against the mix ratio.
Table 1: Water absorption rate of OPC, GGBS
and SF concrete cubes
(Vireen, 2016)
Proportion ratio
Water absorption
rate
OPC 60%
GGBS 30%
SF 10%
Sample 1 3.47%
Sample 2 3.83%
Sample 3 3.22%
OPC 60%
GGBS 25%
SF 15%
Sample 1 3.22%
Sample 2 3.21%
Sample 3 3.86%
Control
OPC 100%
Sample 1 3.50%
Sample 2 3.52%
Sample 3 3.80%
Vireen (2016) concluded that the compressive
strength of OPC 60%/ GGBS 25%/ SF 15% is
greater than OPC concrete in 28 days.
Jain (2007) concluded several points in his
research paper which are stated below.
❖ Using GGBS would give many
technological, environmental and
economic advantages without any
performance issues. Sometimes GGBS
added to concrete as a high volume
mineral admixture.
❖ GGBS is also can act as cement because
of its cementing property with
activation of GGBS by any medium.
CSH gel is the product of hydration
process of cement. GGBS can also
produce CSH gel in the hydration
process with low Calcium/Silicon ratio
and denser.
❖ Mineralogical and chemical properties
of OPC and GGBS will decide the
reactivity of OPC and GGBS
composition. Reactivity could be
predicted by the Slag Activity Index
method. Reactivity depends on higher
glass content and fineness of GGBS.
❖ OPC with GGBS concrete mixture has
higher workability than OPC concrete
mixture. By adding GGBS consistency
of concrete will increase due to its
fineness. Also, water demand,
segregation and bleeding chances will
be reduced. Hydration process of GGBS
concrete will be slower. So, the time for
achieving the peak temperature rise will
be higher.
❖ GGBS blended concrete is having good
resistance again the freeze-thaw
weathering condition when compared
to normal OPC concrete.
In this paper, evidence for enhancement of
durability properties by adding GGBS was
given. But early strength in 7 days wasn’t
considered with durability. So, it must be
considered in future researches to improve both
durability and early strength development with
GGBS content to assure both aspects.
ICCEA-2019-030
OPC, GGBS and waste glass particles (GP)
concrete cube and OPC control concrete cube
were checked for compressive strength test,
water absorption test and split tensile strength.
OPC 50%, GGBS 35% and GP 15% concrete cube
has high compressive strength and tensile
strength than OPC concrete and lower water
absorption rate.
Ramakrishnan (2017) reported that three days
strength is greater when using GGBS and GP
(Glass Particles) than OPC. So, early strength is
achieved by using GGBS and GP as a
replacement to OPC.Table 2 clearly indicates
that adding GGBS and glass particles will
increase the strength of OPC concrete.
Table 2: Compressive strength results using
GGBS and GP (Ramakrishnan, 2017)
Azadeh Attari (Azadeh Attari, 2016), concluded
that, in 56 days compressive and tensile
strengths of various proportions of GGBS (50%,
70%, 90%) were closed to each other. Early
strength developments weren’t provided in the
research paper.
2.2 Experiments
In this research, compressive strength tests and
durability tests (water absorption test,
sorptivity test) were done for various mixes
(Control mix (0% GGBS mix), 10% GGBS mix,
20% GGBS mix, 30% GGBS mix). Pretests like
sieve analysis test, moisture content test for
river sand were done. Slag activity index of
GGBS given as 0.4 by the cement plant. Grade
40 concrete mixes were selected and according
to the results of pretests, mix design was done.
Trial mixes were done with the admixture
Chryso SL 183 and strengths were checked.
According to the trial mixes, mix proportions
and amount of admixture were decided.
Cubes and cylinders were casted for the types
of mixes mentioned above and curing was done
after casting. 7 days, 28 days compressive
strength test of cubes was done. Water
absorption test and sorptivity test were done
for the cylinders according to the ASTM
standards.
2.2.1 Water absorption test
Specimens were dried in the oven before the
tests. After taken from the oven, mass of the dry
specimens were measured (M dry). Then the
specimens were put in the water for 24 hours.
After removing the surface water of the
specimens, the wet specimens were measured
(M wet). Two specimens for each mix were used
for this test.
(1)
Water absorption was calculated by using
above equation 1. The test was done by using
the guidelines of ASTM C- 642- 97. The average
water absorption was calculated and
compared. The water absorption test procedure
is shown in figure 1.
Figure 1: Water absorption test
2.2.2 Sorptivity test
Cylinder specimens having a height of 50mm
and diameter of 100mm were selected. After
Mix types
Compressive strength (kPa)
3 days
7 days
28 days
OPC 50%
GGBS 35%
GP 15%
13.38
17.12
31.46
Control
OPC 100%
9.78
12.77
20.45
ICCEA-2019-030
casting and curing process, they were dried in
oven for 24 hours and selected for the test. Side
surfaces and top surface were sealed to avoid
water penetration through it. Mass of the
specimen before the test was measured (W1).
With the time, mass of the specimen was
measured (W2).
(2)
▪ I - Absorption
▪ W1 - Mass before test with the sealing
▪ W2 - Mass after testing
▪ A - Exposed surface area
▪ d - Density of water – 0.001g/mm3
(3)
▪ I – Absorption
▪ s – Time in seconds
Exposed surface area was calculated by
measuring average diameter of the specimen.
Water absorption was calculated by using
equation 2 and sorptivity was calculated by
using equation 3. The test was done by using
guidelines of ASTM C 1585- 04. Sorptivity test
procedure is shown in figure 2 below.
Figure 2: Sorptivity test
3.0 Results and analyses
Compressive strength test
Strengths are given in N/mm2
▪ 7 days
Table 3: Compressive strength after 7 days
Above table 3 indicates the early strength
development of the mixes. The control mix has
the highest compressive strength among the
mixes. But 10%, 20% and 30% GGBS mixes has
got the 70% of target mean strength. This
indicates all the samples with partial
replacements have achieved early strength
eventhough control mix has maximum.
▪ 28 days
Table 4: Compressive strength after 28 days
Table 4 indicates the 28 days strength
development of the mixes. Even here, control
mix has the maximum strength and others were
lacking. Only 10% GGBS has achieved the
target mean strength in the 28 days. But GGBS
mixed concrete is known for continuous
strength development. So other mixes would
get their strengths in time. Since the early
strength is the main focus of the research, all the
mixes were good enough. But two of them
failed in the rapid strength gaining after early
Cube
No
Control
mix
10%
GGBS
20%
GGBS
30%
GGBS
1
40.1
44.5
38.8
39.1
2
46.6
40.3
38.6
36.3
3
43.2
40.1
40.2
37.4
Average
43.3
41.63
39.2
37.6
Cube
No
Control
mix
10%
GGBS
20%
GGBS
30%
GGBS
1
61.5
55.5
53.2
46.7
2
59.3
54.1
49.8
48.2
3
58.9
55.3
51.6
48.1
Average
59.9
54.9
51.5
47.6
ICCEA-2019-030
strength development. They were slowly
gained strength since the GGBS percentage was
high. So only early strength development
considered for this research to propose a
conclusion and 56 days compressive strength
test will be a recommendation for the further
research in this area.
Water absorption test
Table 5: Water absorption test results
Mix
type
dry
weight
(g)
After one
day
immersion
in water (g)
Water
absorption
(g)
Water
absorption
percentage
(%)
Control
mix
935
975
40
4.27
Control
mix
765
798
33
4.31
10%
GGBS
965
997.5
32.5
3.36
10%
GGBS
995
1033
38
3.81
20%
GGBS
930
958
28
3.01
20%
GGBS
790
815
25
3.16
30%
GGBS
765
787
22
2.87
30%
GGBS
940
966
26
2.76
Water absorption results are shown in table 5. It
indicates some variations on the same mix. But
variations weren’t that significant. The control
mix has the higher amount of water absorption
since there were no GGBS presented. When
GGBS percentage increased in the other mixes
water absorption rate were reduced. Since there
were two specimens for one mix, the average
water absorption was calculated and stated in
table 6.
Table 6: Water absorption comparison
Mix type
Water
absorption (%)
Average water
absorption (%)
Control
mix
4.27
4.29
4.31
10% GGBS
3.36
3.585
3.81
20% GGBS
3.01
3.085
3.16
30% GGBS
2.87
2.815
2.76
Average water absorption indicates that 30%
GGBS mix has the high durability
characteristics and the control mix is showing
worst durability characteristics. Since water
absorption is the main reason of many
durability issues, GGBS is showing
characteristics of water resisting ability when
comparing to cement.
Sorptivity test
▪ Control mix
Table 7: Sorptivity test results for control mix
Time
Dry
mas
s (g)
Wet
mas
s (g)
Absorptio
n (mm)
Sorptivit
y
(mm/s0.5)
4
hrs.
784.
5
785.
1
0.076
6.333
1
day
784.
5
785.
8
0.165
5.613
2
days
784.
5
786.
3
0.229
5.509
Sorptivity test results of control mix are shown
in table 7, which indicates high water suction
from the exposed surface area. Even though
mass difference was decreasing with the time,
the absorption was high. This shows the
inability of control mix against the water
ICCEA-2019-030
penetration. Introduction of GGBS might
reduce the water penetration compared to
control mix.
▪ 10% GGBS mix
Table 8: sorptivity test results for 10% GGBS mix
Time
Dry
mass
(g)
Wet
mass
(g)
Absorption
(mm)
Sorptivity
(mm/s0.5)
4
hrs.
815
815.6
0.076
6.333
1
day
815
816.2
0.153
5.205
2
days
815
816.6
0.204
4.907
Sorptivity test results of 10% GGBS mix are
given in table 8. When comparing with control
mix results, initial water suction wasn’t
changed. But with time water prevention was
high. This indicates the involvement of GGBS in
reduction of water penetration. Since the
percentage of GGBS is low, the influence of
GGBS is lower in durability aspects.
▪ 20% GGBS mix
Table 9: Sorptivity test results for 20% GGBS mix
Time
Dry
mas
s (g)
Wet
mas
s (g)
Absorptio
n (mm)
Sorptivit
y
(mm/s0.5
)
4 hrs.
769.
2
769.
7
0.064
5.333
1 day
769.
2
770.
4
0.153
5.205
2day
s
769.
2
770.
7
0.191
4.594
Sorptivity test results of 20% GGBS mix are
shown in table 9 and it indicates the more
influential results of GGBS, which was
increased to 20%. Initial rate has decreased and
with time also rate was decreasing further. In 2
days the absorption was low comparing to
previous mixes. It proves the role of GGBS in
the durability aspects of concrete.
▪ 30% GGBS mix
Table 10: Sorptivity test results for 30% GGBS mix
Tim
e
Dry
mass
(g)
Wet
mass
(g)
Absorptio
n (mm)
Sorptivit
y
(mm/s0.5
)
4
hrs.
817.9
818.3
0.051
4.25
1
day
817.9
818.8
0.115
3.912
2
days
817.9
819
0.14
3.369
Table 10 indicates the sorptivity test results of
30% GGBS mix. The absorption rates were very
low. So the durability characteristics of the mix
were improved with the GGBS percentage. The
initial absorption rate was very low and with
time absorption was decreasing. So the 30%
GGBS mix is the most durable mix.
Figure 3: Graphical comparison of sorptivity
results
Figure 3 shows the graphical view of sorptivity
test results. It clearly shows a decline of
absorption rate when the GGBS percentage is
increasing.
ICCEA-2019-030
Figure 4: Early strength (N/mm2) comparison
Figure 4 indicates graphical comparison of
early strength after 7 days. It shows that almost
all the mixes are showing similar early strength
development. But the compressive strengths of
control mix are little higher. This indicates that
GGBS is reducing the early strength
development, even though early strengths
when considering the target mean strength is
achieved in all mixes which is indicated in the
figure 4 by a red line. Since the early strength is
achieved in all the mixes, the research can be
extended to high replacements in future to get
the optimum replacement content considering
both strength and durability aspects.
4.0 Conclusions and Recommendations
4.1 Conclusions
❖ Compressive strength is reducing when
increasing the GGBS percentage from
0% to 30% as a replacement for cement.
Average compressive strength
after 28 days for control mix is
59.9 N/mm2 and for 30% GGBS
mix is 47.6 N/mm2
❖ Compressive strength after 7 days
(Early strength) is achieved in all the
mixes when considering the 70% of
target mean strength.
❖ Compressive strength after 28 days is
achieved in control mix and 10% GGBS
mix only. 20% GGBS mix is lacking the
target by a small margin.
❖ Water absorption is reducing when
increasing the GGBS percentage from
0% to 30% as a replacement for cement.
Water absorption for control mix
is 4.29% and for 30% GGBS mix
is 2.82%
❖ Sorptivity is reducing when increasing
the GGBS percentage from 0% to 30% as
a replacement for cement.
Water absorption after two days
for control mix is 0.23 mm and
30% GGBS mix is 0.14 mm.
Even though early strength is considered in the
research, achieving target mean strength is also
most important aspect of a mix design. So, the
recommendations are made considering early
strength, 28 days strength and durability
results.
4.2 Recommendations
Cement can be replaced by GGBS
about 20%
Above recommendation proposed
based on following conclusions and
assertions.
➢ Early strength is achieved when looking
to the target mean strength
➢ Compressive strength after 28 days is
not that much reduced below the target
mean strength
➢ Durability tests (water absorption test,
sorptivity test) shown better results
comparing to control mix
➢ Hydration reactions will continue due
to GGBS addition to cement which can
enhance the strength continually
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