International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 6- March 2016
Effect of Calcium Sulphate on Durability
parameters of Fly ash Blended Cement
G.Narasimhulu#1, C.Sashidhar*2, G.Reddy Babu#3and B.Madhusudhana Reddy*4
1
Civil Engineering Dept., JNTUA, Anantapuaramu, Andhra Pradesh, India(Presently working at Kasturba
Institute of Technology, Civil(PHEE)Dept., Govt. of Delhi,Pitampura,Delhi-88)
2
Professor, Civil Engineering Dept., JNTUA, Anantapuramu, Andhra Pradesh, India
3
Prof& HOD (Civil Engg. Dept.) Narasaraopeta Engineering college, Narasaraopeta, A.P, India.
4
Senior Environmental Engineers, Delhi Pollution Control Committee, Govt. of Delhi, Delhi, India
ABSTRACT:
The effect of Calcium Sulphate(CaSO4) chemical
added in deionised water on Fly ash based Blended
Cement(FBC) on various properties such as setting
time, compressive strength, chloride ion permeability
were studied apart from XRD analysis. The FBC
cubes of size 70.6x70.6x70.6mm are prepared with
different dosages of 1000, 1500, 2000, 2500, 3000,
3500 and 4000mg/l of calcium sulphate in mixing
water for compressive strength analysis. Control
specimens were prepared with deionised water for
comparison purpose. The setting times were found out
and compressive strength of FBC were evaluated for
7days, 28days, 90days and 180days apart from
studying rapid chloride ion permeability on 28 days
aged specimens. The results showed that, as Calcium
sulphate concentration increases, there is increase in
initial and final setting of FBC. The percentage
increase of initial setting time (IST) of FBC with
calcium sulphate chemical is 21.08% to 58.82% and
final setting time (FST) is 7.69% to 24.43%.
Compressive strength of FBC cubes, when tested on
compressive strength testing machine has shown that
loss or gain is marginal compared to control
specimens. It was also observed that chloride ion
permeability trend followed more or less same when
compared with control samples. In addition, XRD
analysis was carried out for finding out new
compounds at Calcium Sulphate concentration of
2.5g/l of 28 days aged specimens along with control
sample.
sulphate attack
have not been thoroughly
investigated. Sulphate ions present in mixing water,
soils, and ground water in more than permissible limit
cause deterioration of mortar. In hardened cement C3A
reacts with sulphate ions in the presence of calcium
hydroxide to form ettringite and gypsum, leading to
degradation of concrete into a non cohesive granular
mass and disruptive expansion given by
Rasheeduzzafar et al,1994, Al-Amoudi OSB et
al,1995 [1,2]. Sulphate attack on concrete is a complex
process as reported by MD Cohen et al,1991[3]. Many
factors, such as cement type, sulphate cat ion type,
sulphate concentration exposure period and water are
essential ingredients which may affect the sulphate
resistance. The permissible limits of sulphate in
mixing water for ordinary Portland cement were given
by various codes, such as IS:456-2000 has given
400mg/l[8], AS 1379 has given 1000 mg/l[9], BS EN
1008-2002 has given 2000mg/l[10] and ASTM C94–
1992 has given 3000mg/l [7]. Generally, the sulphate
encountered in mixing water, soils, and ground water
are combined with different cat ions such as, calcium,
magnesium, sodium etc. In nature, sulphates may
present in surface water, soils and ground water more
than or equal to two compounds. Despite the above
codes had given broad limits on sulphates in mixing
water for ordinary Portland cement, but they did not
give permissible limit of a particular sulphate in a
particular combination in mixing water for blended
cement mortar. For this reason, a guideline based on
careful scrutiny on tolerable limit of a particular
sulphate in a particular combination in mixing water
for blended cement is needed.
Key Words: CaSO4, FBC, IST&FST, Compressive
Strength, Rapid Chloride Ion Permeability, XRD.
2. Research significance:
1. INTRODUCTION:
Mortar deterioration due to sulphate attack is the
second major durability problem, after reinforcement
corrosion in concrete structures. This type of
deterioration is noted in the structures exposed to
sulphate bearing soils, ground water and waste waters.
Though, deterioration due to sulphate attack is
reported from many countries, the mechanisms of
This research examines the maximum permissible
limit of a calcium sulphate in a particular combination
in mixing water, when the sulphate attack is from
exterior surface of blended cement mortar. External
sulphate attack is caused by sulphates from ground
water, soils, solid industrial waste and fertilizers,
atmospheric SO2 or liquid industrial wastes. Torres et
al,2003 [4], Senhadji et al,2005 [5] reported that ready
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 6- March 2016
availability of these sulphates causes damage to
concrete, depending on its concentration. Many
studies had shown that the ingress of sulphates into a
concrete structure by ground water containing soluble
sulphates or soils laden with sulphates led to several
expansive reactions and the alteration of the
microstructure[6] (Crammond and Halliwell,1995).
Ettringite is a common mineral formed during this
process and may lead to the volume expansion and
microcracking of mortar. Besides Ettringite, Gypsum
is also formed in the system, which is depending upon
the type of cement. As per literature and practical
observations, sulphate degrades quality of strength of
ordinary portland cement mortar, but strength
degradation severity is less in blended cement mortar
compared to that of ordinary Portland cement mortar.
Formation of gypsum softens the cement paste and
therefore leads to the deterioration of the cement
microstructure. Even though, considerable work was
done on the external attack of sulphates on blended
cement mortar, but a little or negligible work was
carried out on maximum permissible limit of a
particular sulphate and sulphates in a particular
combination in mixing water for blended cement
mortar when a sulphate and no sulphate present in
mixing water. Hence, this investigation will be carried
out to precise permissible limit of a Calcium sulphate
in the above conditions.
3. MATERIALS AND METHODOLOGY:
3.1 Fly ash Blended Cement(FBC)
Portland Fly ash based blended Pozzolana Cement
containing fly ash was used in this investigation. The
compositions of major compounds present in the
cements are presented in Table 1.
3.2 Fine Aggregate
The fine aggregate (sand) used throughout the
experimental work was obtained from the river
Pandameru near Anantapuramu (Andhra Pradesh).
According to IS 650-1996, the sand used in cement
mortar should confirm to the following specifications.
Sand shall be of quartz, light grey or whitish variety
and free from silt. The grains shall be angular. The
shape of grains shall approximate to spherical form,
enlarged and flattened grains shall be present only in
negligible quantities.
3.3 Grading of Aggregate
Passing through 2mm I.S. Sieve
Retained on 90 I.S. Sieve
Particle size greater than 1mm
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100%
100%
33.33%
Particle size smaller than 1mm
and greater than 500
Particle size smaller than 500
33.33%
33.33%
Sand shall be free from organic impurities. Loss of
weight on interaction with hot hydrochloric acid
(specific gravity 1.15) shall not exceed 0.25%. The
specific particle size composition of the sand was
prepared as per the I.S.Code 650-1966 and I.S. Code
383-1970. Sand was thoroughly washed with tap
water to remove impurities like decayed vegetable
matter, humus, organic matter and deleterious
materials like clay, fine silt, and fine dust was oven
dried for 42 hours and cooled to room temperature.
3.4 Water
Deionised water spiked with Calcium sulphates
(CaSO4) at different concentrations i.e. 1000, 1500,
2000, 2500, 3000, 3500 and 4000 mg/l. Control
sample is prepared without adding any sulphate
chemical for comparison purpose.
4. Experimental programme
The influence of Calcium sulphate mentioned above
at different concentrations was studied when the
calcium sulphate are spiked with deionised water and
test samples are compared with the control samples.
This comparison may not be possible in case of
control samples made with locally available potable
water since it varies in chemical composition from
place to place. This is the reason for mixing of
calcium sulphate with the deionised water as per the
dosage mentioned above. This water is used for
preparation of samples for setting times of FBC. For
determining the initial and final setting times of
blended cement, Vicat’s apparatus is used and to
assess the compressive strength, 96 Blended cement
mortar cubes of size 70.6x70.6x70.6mm were cast and
tested on compressive strength testing Machine. To
determine the chloride ion permeability, RCPT
apparatus was used, for which 24 specimens were cast
and tested.
Table 1: Chemical composition of blended cement
(Fly ash based)
Sl
.
N
o
1.
2.
3.
4.
5.
6.
7.
8.
9.
Composition
Lime (CaO)
Silica (SiO2)
Alumina (Al2O3)
Iron oxide (Fe2O3)
Magnesium oxide (MgO)
Soda (Na2O)
Potash (K2O)
Sulphur trioxide (SO3)
Loss on Ignition (% by mass)
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Result (%)
17.25
36.83
30.14
4.15
3.64
0.95
1.09
2.40
3.55
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 6- March 2016
5. RESULTS AND DISCUSSION
Table 2. Setting times of Fly ash Blended Cement
(FBC) corresponding to CaSO4 concentrations.
5.1 EFFECT OF CALCIUM SULPPHATE
The effect of presence of chemical calcium sulphate
(CaSO4) on various properties such as setting time,
compressive strength and chloride ion permeability
were discussed in the following sub sections in
addition to XRD analysis.
Setting time in minutes, Percentage change in setting
times & Difference of setting time in minutes
Sl.No
Water sample
Initial
%
change
Diffe
rence
Final
%
cha
nge
Diffe
rence
1
Deionised
water(control)
85
0
0
260
0
0
The effect of presence of Calcium sulphate (CaSO4,)
in mixing water on setting times, compressive
strengths of fly ash Blended Cement (FBC) for 7days,
28days, 90days & 180days and chloride ion
permeability of 28 days aged specimens were
presented in the following sub sections.
2
1.0 g/l
103
21.18
18
280
7.6
9
20
3
1.5g/l
110
29.41
25
285
9.6
2
25
4
2.0g/l
114
34.12
29
288
10.
77
28
5.1.1.1 Effect of Calcium sulphate on setting times
of Fly ash Blended Cement(FBC)
5
2.5 g/l*
122
43.53
37
300
15.
38
40
6
3.0 g/l
130
52.94
45
313
20.
38
53
7
3.5 g/l
133
56.47
48
318
22.
31
58
8
4.0g/l
135
58.82
50
323
24.
23
63
The effect of Calcium sulphate on initial and final
setting times of Fly ash Blended Cement (FBC) is
presented in Table 2, Fig.1 and Fig 2. From the table
and figure, it is observed that both the initial and final
setting times have increased with the increase in
concentration of Calcium sulphate in deionised water.
The range of increase in percentage change of Initial
setting times was 21.18% to 58.82% and final setting
time was 7.69% to 24.43% for different concentrations
of Calcium sulphate in the range of 1 to 4g/l with an
increment of 0.5g/l.The Initial setting times and final
setting times at and above 2.5 g/l of Calcium sulphate
concentration in mixing water used for casting the test
specimens, differed significantly when compared with
the experimental results obtained with deionised
water. When the concentration of the Calcium
sulphate is 2.5g/l, the difference in the initial and final
setting times is 37 minutes and 40 minutes (which is
more than 30 minutes & considered to be significant
as per IS 456 code) respectively when compared with
control sample. It was also observed that, When the
concentration of the Calcium sulphate is 2.5 g/l , the
percentage increase in the initial setting time and final
setting is 43.53% and 15.38% respectively when
compared with control mix. So, from the present
experimentation study it is concluded that the setting
times will get increased as Calcium sulphate
concentrations increases. Laure et al,2011[12] also
reported that due to calcium sulphate, setting times are
increased.
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*- Significant
320
300
280
Setting Time (Minutes)
5.1.1 Effect of Calcium sulphate (CaSO4,)
260
240
INITIAL
FINAL
220
200
180
160
140
120
100
80
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
CaSO4 Concentration (g/l)
Fig.1Setting times (Initial and Final) of Fly ash
Blended Cement (FBC) vs CaSO4, concentrations
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 6- March 2016
Table 3. Compressive strength of FBCM
corresponding to CaSO4 concentrations.
65
60
PIIST
DIST
PIFST
DFST
55
Setting time(%and Diff,)
50
45
Fly ash Blended Cement Mortar (FBCM)
Compressive
Strength(MPa)
40
35
Water
Sample
Sl.No
30
25
20
7
days
28
da
ys
90
da
ys
180d
ays
7
da
ys
28
days
90
da
ys
180d
ays
15
i
Deionise
d water
(Control)
25.
60
40.
42
46.
84
50.
31
0
0
0
0
ii
1.0 g/l
25.
72
40.
71
46.
98
50.
85
0.
47
0.72
0.
30
1.07
iii
1.5 g/l
25.
90
40.
53
46.
88
51.
12
1.
17
0.27
0.0
9
1.61
iv
2.0 g/l
25.
80
41.
14
47.
50
51.
53
0.
78
1.78
1.
41
2.42
v
2.5 g/l*
26.
10
41.
40
47.
80
51.
70
1.
95
2.42
2.
05
2.76
vi
3.0 g/l
26.
08
41.
84
47.
83
51.
71
1.
87
3.51
2.
11
2.78
vii
3.5 g/l
26.
00
41.
83
47.
55
51.
70
1.
56
3.49
1.
52
2.76
viii
4.0 g/l
25.
99
41.
82
47.
35
51.
69
1.
52
3.46
1.
09
2.74
3.5
4.0
10
5
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
CaSO4 Concentration (g/l)
PIIST: Percentage Increase in Initial Setting Time
DIST: Difference in Increase in Initial Setting Time
PIFST: Percentage Increase in Final Setting Time
DFST: Difference in Increase in Final Setting Time
Fig.2 Percentage variation and difference in Setting
times of Fly ash Blended cement (FBC) vs CaSO4,
concentrations
5.1.1.2 Effect of Calcium Sulphate on Compressive
Strength of Fly ash Blended Cement (FBC)
The effect of Calcium sulphate concentrations on the
compressive strength of fly ash blended cement
(FBC) is presented in Table.3 and Fig.3. The degree of
percentage variation in compressive strength is also
presented in Fig.4. The results indicate that there is a
slight fluctuation in loss or gain of compressive
strength of the FBC irrespective of CaSO4
concentration for 7days, 28days, 90days and 180days.
Compressive strength for FBC with CaSO4
concentration from 0 to 2.5 g/l, has increased from
25.72 to 26.10MPa for 7days, 40.71 to 41.40MPa for
28days, 46.98 to 47.80MPa for 90days and 50.85 to
51.70MPa for 180days aged specimens respectively.
When CaSO4 concentration is 2.5 g/l the percentage
increase in compressive strength is 1.95% for 7days,
2.42% for 28days, 2.05% for 90days and 2.76% for
180days aged specimens when compared with that of
cubes prepared with the deionised water(control test
sample). Ettringite and Gypsum formation causes
volume increase or expansion, thereby causing
damage and cracking of concrete leading to strength
loss as given by Roziere E et al,(2009)[14].The said
enhancement in compressive strength may be due to
residue of anhydrous fly ash in the mix and its
reaction with CaSO4 which is affecting the hydration
process in turn giving increased compressive
strengths.
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*- Significant
55
50
Compressive strength (MPa)
0.0
% variation
45
40
7 days
28 days
90 days
180 days
35
30
25
0.0
0.5
1.0
1.5
2.0
2.5
3.0
CaSO4 Concentration (g/l)
Fig.3 Compressive strength of Fly ash Blended
Cement Mortar (FBCM) vs CaSO4concentrations
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 6- March 2016
Table4.Chloride ion Permeability of
sulphate concentration (28 days)
4.0
calcium
% variation in Comp. Strength
3.5
7 days
28 days
90 days
180 days
3.0
2.5
Flyash Blended Cement Mortar (FBCM)
Sl.No
Water Sample
Coulombs passed for
28 days
% variation
Calcium Sulphate
Calcium Sulphate
2.0
1.5
1.0
i
Deionised
water(Control)
2295
0
0.5
ii
1.0 g/l
2294
-0.04
iii
1.5 g/l
2292
-0.13
iv
2.0 g/l
2293
-0.09
v
2.5 g/l
2290
-0.22
vi
3.0 g/l
2293
-0.09
vii
3.5 g/l
2291
-0.17
viii
4.0 g/l
2292
-0.13
0.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
CaSO4 Concentration (g/l)
Fig.4 Percentage variation in compressive strength of
Fly ash Blended Cement Mortar (FBCM) vs CaSO4
concentrations
5.1.1.3 Effect of Calcium sulphate (CaSO4,)
concentration on Chloride ion Permeability test.
2296
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2295
caso4
Coulumbs passed
The rapid chloride permeability levels in terms of
coulombs passed through Fly ash Blended cement
mortars are observed for 28 days aged specimens were
tabulated and listed in the Table.4. By comparing the
coulombs passed, which gives a measure of chloride
ion permeability, it was observed that the chloride ion
permeability has shown marginally more or less same
with reference samples as the concentration of calcium
sulphate increases. Quantum of coulombs passed and
percentage of variation in the charge passed were
depicted in Fig.5 and Fig.6 below. The pozzolanic
reactions formed with different sulphate solutions
consume CH and generate additional C-S-H, which
promotes densification and lowers the permeability of
paste as suggested by K K Veiga et al, 2012 [11]
2294
2293
2292
2291
2290
2289
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Calcium sulphate concentration of 28 days(g/l)
Fig.5 Couloumbs passed vs Calcium sulphate
concentration
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 6- March 2016
-0.25
% variation in couloumbs passed
CaSO4
-0.20
-0.15
-0.10
-0.05
0.00
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Calcium sulphate concentration of 28 days(g/l)
CH: Calcium Hydroxide,
C3A:TricalciumAluminate,
C3S:TricalciumSilicate,
C2S:DicalciumSilicate,
C-S-H:Calcium Silicate
Hydrate,
E:Ettringite G:gypsum
Fig.6 Percentage variation in Couloumbs passed vs
calcium sulphate concentration
5.1.1.4 Powdered X-ray Diffraction (XRD) Analysis
with calcium Sulphate
The Powder X-ray diffraction analysis was carried out
to know the behaviour and probable chemical
reaction(s) showing the new compounds formed at
different angles. Fig.7 depicts the Powder X-ray
Diffraction patterns for FBC prepared with deionised
water(control sample) and mixing water containing
CaSO4 concentration of 2.5g/l are presented after a
curing period of 28 days.
Calcium sulphate(CaSO4.2H2O) reacts with calcium
hydroxide (Ca(OH)2) forming Gypsum(G) as shown
in eq.(i), which in turn reacts with Tri calcium
Aluminate(3CaOAl2O3)
forming
Tricalciumsulphoaluminate, known as Ettringite(E)
(3CaO.Al2O3.3CaSO4.32H2O) as given in eq.(ii).
Formation of this Ettringite shall cause sulphate attack
causing strength loss, volume expansion, cracking on
surface of mortars. After sulphate ions enters in to the
mortar pores, they react with hydrated cement
compounds and ions in the cement pore solution on
cement pore surfaces. The reaction led to formation of
Tricalciumsulphoaluminate Hydrate causing volume
increase and responsible for expansive forces and
microcracking as given by
Bonakdar A et
al.(2010)[13].The typical chemical reactions are
shown below .
Fig.7 Comparison of XRD pattern of Fly ash Blended
Cement Mortar (FBCM) spiked with CaSO4
Concentration (2.5g/l) and control sample prepared in
Deionised water (28 days)
The bottom portion of the said graph at Fig.7
indicates the XRD pattern of the control sample
prepared with deionised water. Perusal of the said
graph establishes that the compounds such as,
Calcium Hydroxide(CH) at 18.240 and 27.040, C3A at
29.580, C2S at 32.900, C3S at 34.440, and C-S-H at
50.280 are found respectively. On Comparing with
test
sample,
the
new
compounds
3CaO.Al2O3.3CaSO4.32H2O (Ettringite) was formed
at 33.660, 44.780 & 51.640 along with Gypsum
forming at 40.700 & 48.720.
Compressive strength has shown slight fluctuations in
strength loss or gain due to formation of Ettringite(E)
and Gypsum(G) at different locations as shown in the
XRD pattern. The XRD pattern indicate that the high
peaks of CH, C3A, C2S, C3S and C-S-H are
consumed and new sulphate attacking compounds
such as E and G are developed due to chemical
reactions.
6.CONCLUSIONS
CaSO4.2H2O+Ca(OH)2→CaSO4.2H2O+2Ca(OH)2
(i)
CaSO4.2H2O+CaOAl2O3+26H2O→3CaO.Al2O3.3CaSO4.32H2O (ii)
Based on the results obtained in the present
investigation the following conclusions can be drawn.
The permissible limit of Calcium sulphate
(CaSO4) concentration in water increase the
initial and final setting times of FBC.
The percentage increase of Initial setting time of
FBC with calcium sulphate chemical is 21.18%
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 6- March 2016
to 58.82% and final setting time is 7.69% to
24.43%.
The compressive strength variation has shown
a little increase in strength at a concentration
of 2.5 g/l.
Compressive strength of FBC cubes, has
shown slight fluctuations in strength loss/gain.
[12] Laure Pelletier-Chaignat, Frank Winnefeld, Barbara
Lothenbach, Gwenn Le Saout
Christian Jörg Müller,
Charlotte Famy, Influence of the calcium sulphate source on
the hydration mechanism of Portland cement–calcium
sulphoaluminate clinker–calcium sulphate binders, Cement &
Concrete Composites 33 (2011) 551–561
[13] A.Bonakdar, B.Mobasher, Multi-parameter study of external
sulfate attack in blended cement materials, Construction and
Building Materials 24 (2010) 61– 70
[14] E. Rozière, A.Loukili, R.El Hachem, F.Grondin, Durability of
concrete exposed to leaching and external sulphate attacks,
Cement and Concrete Research 39 (2009) 1188–1198
The percentage strength loss in Compressive
strength of FBC for calcium sulphate is in the
range of 0.47 to1.95%, for 7days and 0.72 to
3.51% for 28days, 0.3 to 2.11% for 90days and
1.07 to 2.78% for 180 days on comparison
with the control specimens
Chloride ion permeability has shown
marginally more or less same with reference
specimen.
The formation of new compounds such as
Ettringite(E), Gypsum(G) and Portlandite(P)
were found on XRD analysis.
References:
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Rasheeduzzafar, Al-Amoudi OSB, S N Abduljawad, M,
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[3] MD Cohen, B Mather, sulphate attack on concrete research
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magnesium sulphate attack,” Cement Concrete Composites,
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[5] Y. Senhadji, M.Mouli, H.Khelafi, and A.S Benosman,
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