High quality and durable concrete is required to reduce the rapid deterioration of concrete in severe conditions. This paper reports the results of a study conducted to evaluate the performance of different types of Pakistani cements exposed to various aggressive sulfate and chloride environments. Mortar and concrete (plain and embedded with reinforcing steel) specimens were cast using three types of cements, namely Type I (OPC), Type V (SRC) and Type I plus granulated blast furnace slag (BFSC). Mortar specimens were exposed to three sodium and magnesium sulfate solutions to study the deterioration due to sulfate attack. Plain concrete specimens were exposed to 4% NaCl, MgSO 4 and Na2SO4 solutions. Concrete specimens embedded with reinforcing steel were exposed to wetting and drying cycles in 4% MgSO4 solution to determine the corrosion resistance by comparing the weight loss measurements. Maximum deterioration was noted in BFSC cement followed by OPC and SRC cements. The performance of OPC and BFSC was not significantly different from each other.
SBEIDCO – 1st International Conference on Sustainable Built Environment Infrastructures in Developing Countries
ENSET Oran (Alegria) – October 12-14, 2009
T.4. Durability Of Materials And Structures, Performance Of Different Types Of Pakistani Cements Exposed To Aggressive
Environments, A.R.Khan & N.S.Zafar
17
PERFORMANCE OF DIFFERENT TYPES OF PAKISTANI
CEMENTS EXPOSED TO AGGRESSIVE ENVIRONMENTS
A.R. Khan1, N. S. Zafar2
T.4. Durability of Materials and Structures
ABSTRACT
High quality and durable concrete is required to reduce the rapid deterioration of concrete in severe
conditions. This paper reports the results of a study conducted to evaluate the performance of different
types of Pakistani cements exposed to various aggressive sulfate and chloride environments. Mortar
and concrete (plain and embedded with reinforcing steel) specimens were cast using three types of
cements, namely Type I (OPC), Type V (SRC) and Type I plus granulated blast furnace slag (BFSC).
Mortar specimens were exposed to three sodium and magnesium sulfate solutions to study the
deterioration due to sulfate attack. Plain concrete specimens were exposed to 4% NaCl, MgSO4and
Na2SO4 solutions. Concrete specimens embedded with reinforcing steel were exposed to wetting and
drying cycles in 4% MgSO4 solution to determine the corrosion resistance by comparing the weight
loss measurements. Maximum deterioration was noted in BFSC cement followed by OPC and SRC
cements. The performance of OPC and BFSC was not significantly different from each other.
KEYWORDS: Performance, Concrete, Pakistani cements, Aggressive environments
_______________________
1Department of Civil Engineering, NEDUET, Karachi, Pakistan, [email protected]
2Department of Civil Engineering, NEDUET, Karachi, Pakistan, [email protected].
SBEIDCO – 1st International Conference on Sustainable Built Environment Infrastructures in Developing Countries
ENSET Oran (Alegria) – October 12-14, 2009
T.4. Durability Of Materials And Structures, Performance Of Different Types Of Pakistani Cements Exposed To Aggressive
Environments, A.R.Khan & N.S.Zafar
18
1. INTRODUCTION
Performance of concrete is generally judged by strength and durability properties. Deterioration due to
reinforcement corrosion and degradation of concrete exposed to sulfate-bearing environments are
probably the most important durability issues with reinforced concrete. The durability of reinforced
concrete depends on the surrounding environmental and exposure conditions. Corrosion, one of the
main causes of deterioration in concrete structures, initiates due to its exposure to harmful chemicals
that may be found in nature such as in some ground waters, industrial effluents and sea waters. The
most aggressive chemicals that affect the long term durability of concrete structures are the chlorides
and sulfates. The chloride dissolved in waters increase the rate of leaching of portlandite and thus
increases the porosity of concrete, and leads to loss of stiffness and strength [Wee et al., 2000].
Calcium, sodium, magnesium, and ammonium sulfates are-in increasing order of hazard-harmful to
concrete as they react with hydrated cement paste leading to expansion, cracking, spalling and loss of
strength [Wee et al., 2000].
Sulfates attack concrete by reacting with free Ca(OH)2to produce calcium sulfate and with aluminate
hydrate to produce calcium sulfoaluminate and thus severe cracking and disintegration of the cement
strength. C3A is a Portland cement compound that reacts with sulfates and chlorides in ground water
and/or soil forming an insoluble compound, thus slowing down their destructive effect on reinforcing
steel. The C3A in cement contributes little or nothing to the strength of cement, and when hardened
cement paste is attacked by sulfates, expansion due to the formation of calcium sulfoaluminate from
C3A lead to disruption of the hardened paste [Sakr, 2005].
Recent modifications in the cement manufacturing technology and the extensive use of mineral
admixtures have introduced changes in the chemical and mineralogical composition of the present-day
cements. These changes may significantly affect the durability of concrete, particularly the sulfate
attack. Due to these modifications, the need for understanding the mechanisms of sulfate attack
through laboratory and field exposure studies becomes all the more important [Al-Amoudi 2002]. The
development and use of blended cements is growing rapidly in the construction industry mainly due to
considerations of cost saving, energy saving, environmental protection and conservation of resources
[Ha et al., 2005]. Previous studies [Irassar et al. 2000, Hossain and Lachemi 2004] have shown that
use of cement replacement materials such as blast-furnace slag, fly ash, silica fume, etc. may reduce
greatly the probability of steel corrosion as well as the permeability of concrete.
Problems of concrete durability are a cause of major concern all over the country especially in the
coastal areas where the structures have undergone deterioration well before their expected life and
need proper attention and care. Realizing the aggressive nature of the environmental conditions and the
local construction materials of the country, research was initiated at the Department of Civil
Engineering, NED University of Engineering and Technology, to assess performance of concrete made
with locally available cements under aggressive environmental conditions. This paper reports the
results of a study conducted to evaluate the performance of different types of Pakistani cements
namely Type I (OPC), Type V (SRC) and Type I plus granulated blast furnace slag (BFSC), exposed
to various aggressive sulfate and chloride environments. The performance was evaluated by evaluating
the reduction in compressive strength and assessing the resistance to salt attack by visual inspection
and weight loss measurements.
2. EXPERIMENTAL PROGRAM
Mortar and concrete (plain and embedded with reinforcing steel) specimens were cast using three
types of cement available in market namely OPC, SRC, BFSC. Mortar specimens were exposed to
three sodium and magnesium sulfate solutions with sulfate concentrations of 1%, 2%, and 4% to study
the deterioration due to sulfate attack. Plain concrete specimens were exposed to 4% NaCl, 4% MgSO4
and 4% Na2SO4solutions. Concrete specimens embedded with reinforcing steel were exposed to
wetting and drying cycles in 4% MgSO4to determine the corrosion resistance of embedded rebars.
SBEIDCO – 1st International Conference on Sustainable Built Environment Infrastructures in Developing Countries
ENSET Oran (Alegria) – October 12-14, 2009
T.4. Durability Of Materials And Structures, Performance Of Different Types Of Pakistani Cements Exposed To Aggressive
Environments, A.R.Khan & N.S.Zafar
19
2.1. Mortar Specimens
Cement mortar specimens measuring 50 × 50 × 50 mm [Al-Dulaijan 2007] were prepared by mixing
the selected cements with sand. The sand to cement ratio in the mortar mixes was 2.5 and the water to
cement ratio was 0.5. After casting and finishing, the molds were covered with plastic sheets and kept
under laboratory conditions for 24 hours and then demolded. After demolding, the specimens were
cured under water maintained for further 27 days.
After 28 days of curing, the mortar specimens were divided into two groups. One group of specimens
was continuously cured under water while the second group was placed in three tanks with 1%, 2%,
and 4% sodium and magnesium sulfate solutions. These conditions represent very severe sulfate
exposure conditions according to ACI 318-99. However, these concentrations represent the sulfate
concentrations noted in saline soils [Rasheeduzzafar et al. 1990, Al-Amoudi 1992]. The exposure
solutions were prepared by mixing reagent grade magnesium and sodium sulfate with distilled water.
Specimens representing similar composition were placed in each solution for up to 180 days. Three
mortar specimens representing similar composition were retrieved from the test solutions after 90 and
180 days of exposure. The effect of sulfate concentration on the performance of selected cements was
evaluated by visual examination and measuring the reduction in compressive strength. The mortar
specimens were inspected after the designated exposure period and the deterioration was classified on
a six point scale ranging from 0 to 5 [Al-Amoudi 1992]. A rating of 0 would indicate no deterioration
while a rating of 5 indicates complete failure. The degree of deterioration was also evaluated by
measuring the reduction in compressive strength. The reduction in compressive strength was
calculated as follows:
Reduction in compressive strength (%) = 100
A
BA (1)
where A is the average compressive strength of three specimens cured under water, MPa; and B is the
average compressive strength of three specimens exposed to the test solution.
2.2 Plain and Reinforced Concrete Specimens
Two types of concrete specimens (plain and embedded with reinforcing steel [Guneyisi et al. 2005]
were used in this study. The concrete had a water to cement ratio of 0.65 and a cement content of 300
kg/m3. Grading of the aggregate mixture was kept constant for all concretes. All concretes were mixed
as per ASTM C192 in a pan mixer by first mixing the dry ingredients for one minute, and then adding
the water and mixing for an additional three minutes.
Cylinders having dimensions of 100 × 200 mm were cast for the compressive strength. After casting,
the molded specimens were covered with a plastic sheet and left in the casting room for 24 hours.
After demolding, the specimens were cured under water maintained for further 27 days. After 28 days
of curing, specimens were divided into two groups. One group of specimens was continuously cured
under water while the second group was placed in three tanks with 4% NaCl, 4% MgSO4and 4%
Na2SO4solutions. Specimens representing similar composition were placed in each solution for up to
180 days. Three mortar specimens representing similar composition were retrieved from the test
solutions after 90 and 180 days of exposure. The effect of chloride and sulfate concentrations on the
performance of selected cements was evaluated by measuring the reduction in compressive strength.
The reduction in compressive strength was calculated as discussed earlier.
The reinforced concrete specimens for the corrosion resistance of embedded bars were 100 × 200 mm
concrete cylinders in which a 16mm diameter steel bar was centrally embedded. The steel bar was
SBEIDCO – 1st International Conference on Sustainable Built Environment Infrastructures in Developing Countries
ENSET Oran (Alegria) – October 12-14, 2009
T.4. Durability Of Materials And Structures, Performance Of Different Types Of Pakistani Cements Exposed To Aggressive
Environments, A.R.Khan & N.S.Zafar
20
embedded into the concrete cylinder such that its end was at least 30mm from the bottom of the
cylinder. The initial weight of the rebar sample was taken before casting for gravimetric weight loss
measurements. The specimens were cast in three layers and compacted using a vibrating table. After
casting, the molded specimens were covered with a plastic sheet and left in the casting room for 24
hours. After demolding, the specimens were cured under water for further 27 days. After 28 days of
curing, all the specimens were completely immersed in 4% MgSO4 solution. The specimens was
maintained in the same condition for 15 days and then subjected to drying in open air at room
temperature for another 15 days. Each wetting and drying cycle thus consisted of 30 days. All the
specimens were subjected to 6 complete cycles (180 days) of test period.
3. RESULTS AND DISCUSSION
3.1. Visual Inspection
No wear and tear was observed in the OPC and SRC cement specimens in all sulfate concentrations
while marginal deterioration was noted in the BFSC specimens exposed to 2% and 4% Na2SO4
solutions. Table 1 shows the deterioration rating for cement specimens exposed to 1%, 2% and 4%
Na2SO4sulfate solution. The deterioration increased with the period of exposure in BFSC specimens
only. No deterioration was noted in all specimens after 90 days exposure. However, after 180 days of
exposure, expansive cracking, typical of the sodium sulfate attack in moderate to high C3A cements
[Rasheeduzzafar et al. 1990, Al-Amoudi 1998], was visible in BFSC mortar specimens exposed to 2%
and 4% sulfate solution. A deterioration rating of 1 was assigned to the BFSC specimens. Formation of
expansive cracks contributed towards the reduction in compressive strength as discussed in later
sections.
Table 1. Deterioration rating of specimens exposed to Na2SO4 Solution
Figs. 1 – 3 show cement mortar specimens exposed to 1%, 2%, and 4% MgSO4solutions for 180 days.
Disintegration of the edges and breakup was noted in the OPC and SRC cement specimens, while
cracking of the surface skin, localized at the edges, was noted in BFSC specimens exposed to 1%
MgSO4 solution (Fig. 1). In the specimens exposed to 2% MgSO4solution, the deterioration was more
severe in BFSC specimens as compared to other specimens. Deterioration represented by
disintegration and cracking of edges, was noted in all other specimens, as shown in Fig. 2. A similar
behavior was noted in all specimens exposed to 4% sulfate solution, as shown in Fig. 3. The severity
of deterioration in all specimens exposed to 4% sulfate solution was, however, more than that in
similar specimens exposed to solutions with lower sulfate concentration. This type of deterioration is
typical of the magnesium sulfate attack in moderate to high C3A cements [Cohen & Bentur 1988,
Lawrence 1990]. Magnesium sulfate significantly reduces the integrity of the cement thereby leading
to a reduction in the compressive strength. This type of deterioration is related to eating away of the
hydrated cement paste and progressive reduction into non-cohesive granular mass. Table 2 shows the
deterioration rating for the plain and blended cement mortar specimens exposed to 1%, 2% and 4%
Cement Deterioration rating (days)
90 180
1% 2% 4% 1% 2% 4%
OPC 0 0 0 0 0 0
SRC 0 0 0 0 0 0
BFSC 0 0 0 0 1 1
SBEIDCO – 1st International Conference on Sustainable Built Environment Infrastructures in Developing Countries
ENSET Oran (Alegria) – October 12-14, 2009
T.4. Durability Of Materials And Structures, Performance Of Different Types Of Pakistani Cements Exposed To Aggressive
Environments, A.R.Khan & N.S.Zafar
21
MgSO4solution. There was no deterioration in all specimens exposed to 1% MgSO4solution for 90
days. For specimens exposed to 2% MgSO4 solution deterioration rating after 90 days of exposure for
BFSC and other specimens was 1 and 0 respectively. After 90 days of exposure to 4% MgSO4
solution, the deterioration rating for BFSC specimens was 2 while for OPC and SRC it was 1. After
180 days, deterioration was noted in all cement mortar specimens. The deterioration rating after
exposure to 1% MgSO4solution was 2 for BFSC specimens while a deterioration rating of 1 was
assigned to OPC and SRC cement specimens. For specimens exposed to 2% MgSO4 solution severe
deterioration (a rating of 4) was noted in the BFSC mortar specimens while it was moderate (rating of
2 and 1) in OPC and SRC specimens respectively. The deterioration rating was the highest (5) for the
BFSC cement mortar specimens in 4% MgSO4solutions followed by OPC and SRC specimens (rating
of 4 and 2).
Figure 1. Mortar Specimens of OPC, SRC and BFSC after 180 days of exposure in 1% MgSO4
Figure 2. Mortar Specimens of OPC, SRC and BFSC after 180 days of exposure in 2% MgSO4
Figure 3. Mortar Specimens of OPC, SRC and BFSC after 180 days of exposure in 4% MgSO4
Table 2. Deterioration rating of specimens exposed to MgSO4 Solution
Cement Deterioration rating (days)
90 180
1% 2% 4% 1% 2% 4%
OPC 0 0 1 1 2 4
SRC 0 0 1 1 1 2
BFSC 0 1 2 2 4 5
Comparison of deterioration ratings, presented in Table 2 indicates that the rate of deterioration
generally increased with increasing sulfate concentration in all cements.
SRC
SRC
BFSC
SBEIDCO – 1st International Conference on Sustainable Built Environment Infrastructures in Developing Countries
ENSET Oran (Alegria) – October 12-14, 2009
T.4. Durability Of Materials And Structures, Performance Of Different Types Of Pakistani Cements Exposed To Aggressive
Environments, A.R.Khan & N.S.Zafar
22
3.2. Reduction in Compressive Strength
The reduction in compressive strength of cement mortar specimens exposed to 1%, 2% and 4%
Na2SO4solution is depicted in Fig. 4. The compressive strength of the BFSC specimens decreased
from 6% to 27% for 180 days of exposure to 1%, 2% and 4% Na2SO4solutions. No strength reduction
was observed in OPC and SRC cement specimens within 180 days of exposure. The reduction in
compressive strength of cement mortar specimens exposed to 1%, 2% and 4% MgSO4solution is
plotted in Fig. 5. A higher strength reduction, ranging from 18% to 71%, was noted in BFSC
specimens. Further, strength reduction in OPC cement specimens, ranging from 17% to 26%, was
more than that in SRC cement specimens (2% to 3%). After 180 days of exposure to the sulfate
solutions the reduction in strength, due to sulfate attack, was the highest in BFSC specimens followed
by OPC and SRC specimens.
The reduction in compressive strength of plain concrete specimens exposed to 4% NaCl, 4% Na2SO4
and 4% MgSO4solutions is depicted in Fig. 6. No strength reduction was observed in all concrete
specimens within 180 days of exposure to 4% NaCl solution. For plain concrete specimens exposed to
4% Na2SO4 solutions, strength reduction in SRC concrete specimens was 5% while for OPC and BFSC
specimens it was 8%. Highest strength reduction (12%, 13% and 17%) was observed in SRC, GBFS
and OPC specimens exposed to 4% MgSO4 solutions respectively.
0
5
10
15
20
25
30
1% 2% 4%
Concentration of Sodium Sulfate Solution
Reduction in Compressive Strength (%)
OPC SRC BFSC
Figure 4. Comparison of reduction in compressive strength in the mortar specimens exposed to 1%,
2% and 4% Na2SO4solutions for 180 days.
0
10
20
30
40
50
60
70
80
1% 2% 4%
Concentration of Magnessium Sulfate Solution
Reduction in Compressive Strength (%)
OPC SRC BFS
Figure 5. Comparison of reduction in compressive strength in the mortar specimens exposed to 1%,
2% and 4% MgSO4 solutions for 180 days.
SBEIDCO – 1st International Conference on Sustainable Built Environment Infrastructures in Developing Countries
ENSET Oran (Alegria) – October 12-14, 2009
T.4. Durability Of Materials And Structures, Performance Of Different Types Of Pakistani Cements Exposed To Aggressive
Environments, A.R.Khan & N.S.Zafar
23
0
2
4
6
8
10
12
14
16
18
4% NaCl 4% Na2SO4 4% MgSO4
Concentration of Solutions
Reduction in Compressive Strength (%)
OPC SRC BFS
Figure 6. Comparison of reduction in compressive strength in plain concrete specimens exposed to
4% NaCl, 4% Na2SO4 and 4% MgSO4 solution for 180 days.
3.3 Weight Loss Measurements
The corrosion resistance of OPC, SRC and BFSC reinforced concrete specimens was related to weight
loss in embedded rebars and is shown as a bar chart in Fig. 7. From the figure it can be observed that
the weight loss was minimum (2.5% per 180 days) in SRC specimens followed by BFSC and OPC
specimens (6.1% and 10.8% per 180 days respectively).
0.0
2.0
4.0
6.0
8.0
10.0
12.0
4% MgSO4
4% MgSO
4
Solution
Weight Loss (%)
OPC SRC BFS
Figure 7. Comparison of weight loss in reinforced concrete specimens exposed to wetting and drying
cycles in 4% MgSO4 for 180 days.
4. CONCLUSIONS
1. For the cement mortar specimens exposed to 1%, 2% and 4% Na2SO4solutions, maximum
strength reduction, due to sulfate attack, was noted in BFSC mortar specimens, while no reduction
in strength was observed in OPC and SRC cement mortar specimens. The strength reduction in
BFSC specimens increased with the increase in sulfate concentration in the exposure solution.
2. For the cement mortar specimens exposed to 1%, 2% and 4% MgSO4solutions, maximum
strength reduction, due to sulfate attack, was noted in BFSC mortar specimens followed by OPC
and SRC mortar specimens. The strength reduction in all specimens increased with the increase in
sulfate concentration in the exposure solution.
3. For the plain concrete specimens exposed to 4% NaCl, 4% Na2SO4 and 4% MgSO4solutions
maximum strength reduction, was noted in OPC and BFSC specimens followed by SRC cement
specimens. The strength reduction in all specimens was maximum in MgSO4solution followed by
Na2SO4solution. No reduction in strength was observed in NaCl Solution.
4. The weight loss method for determining the corrosion resistance indicated that the SRC reinforced
concrete specimens exposed to severe MgSO4 environment had superior performance as compared
to the specimens with OPC and BFSC specimens.
SBEIDCO – 1st International Conference on Sustainable Built Environment Infrastructures in Developing Countries
ENSET Oran (Alegria) – October 12-14, 2009
T.4. Durability Of Materials And Structures, Performance Of Different Types Of Pakistani Cements Exposed To Aggressive
Environments, A.R.Khan & N.S.Zafar
24
5. Poor performance of BFSC mortar and plain and reinforced concrete specimens can be attributed
towards the fact that the amount of BFS blended with OPC was not available from the
manufacturer and quantity of replacement material may play a vital role in the sulfate resistance of
concrete.
6. The results in this study are in close agreement with the view regarding the influence of cement
type in sulfate environments, in that the performance of SRC was better than that of OPC and
BFSC. Therefore, realizing the role of C3A on sulfate attack, cements with low C3A are
recommended in situations where the sub-structural components are exposed to severe and very
severe sulfate as recommended by ACI 318 also.
ACKNOWLEDGEMENTS
The authors are indebted to the Department of Civil Engineering at NED University of Engineering &
Technology, Karachi, Pakistan and the University itself, in the pursuit of this work.
REFERENCES
Al-Amoudi, O.S.B. 1992. Studies on soil foundation interaction in the sabkah environment in eastern
province of Saudi Arabia, PhD dissertation, Department of Civil Engineering, King Fahd University of
Petroleum and Minerals, Dhahran, Saudi Arabia.
Al-Amoudi, O.S.B. 1998. Sulfate attack and reinforcement corrosion in plain and blended cements
exposed to sulfate environments. Building Environments 33(1): 53-61.
Al-Amoudi, O.S.B. 2002. Attack on plain and blended cements exposed to aggressive sulfate
environments. Cement & Concrete Composites 24(3-4): 305-316.
Al-Dulaijan, S. U. 2007. Sulfate resistance of plain and blended cements exposed to magnesium
sulfate solutions. Construction and Building Materials 21: 1792-1802.
Cohen, M.D. & Bentur, A. 1988. Durability of Portland cement-silica fume pastes in magnesium
sulfate and sodium sulfate solutions. ACI Materials Journal 85(3): 148 – 157.
Guneyisi, E., Ozturan, T. & Gesoglu, M. 2005. A study on reinforcement corrosion and related
properties of plain and blended cement concretes under different curing conditions. Cement &
Concrete Composites 27: 449-461.
Ha, T., Muralidharan, S., Bae, J., Ha, Y., Lee, H., Park, K. & Kim, D. 2007. Accelerated short-term
techniques to evaluate the corrosion performance of steel in fly ash blended concrete. Building and
Environment 42: 78-85.
Hossain, K.M.A. & Lachemi, M. 2004. Corrosion resistance and chloride diffusivity of volcanic ash
blended cement mortar. Cement and Concrete Research 34(4): 695-702.
Irassar, E.F., Gonzalez, M. & Rahhal, V. 2000. Sulphate resistance of SRC cements with limestone
filler and natural pozzolana. Cement and Concrete Composites 22: 361- 368.
Lawernce, D. 1990. Sulphate attack on concrete. Magazine of Concrete Research 42(153): 249-264.
Rasheeduzzafar, Dakhil, F.H., Al-Gahtani, A.S., Al-Saadoun, S.S. & Bader, M.A. 1990. Influence of
cement composition on the corrosion of reinforcement and sulfate resistance of concrete. ACI
Materials Journal 87(2): 114-122.
Rasheeduzzafar, Al-Amoudi, O.S.B., Abduljawad, S.N. & Maslehuddin, M. 1994. Magnesium–
sodium sulfate attack in plain and blended cements. Journal of Materials in Civil Engineering 6(2):
201-222.
Sakr, K. 2005. Effect of cement type on the corrosion of reinforcing steel bars exposed to acidic media
using electrochemical techniques. Cement and Concrete Research 35: 1820-1826.
Wee, T.H., Suryavanshi, A.K., Wong, S.F. & Rahman A.K. 2000. Sulfate resistance of concrete
Content retrieved from: https://www.researchgate.net/publication/281685757_PERFORMANCE_OF_DIFFERENT_TYPES_OF_PAKISTANI_CEMENTS_EXPOSED_TO_AGGRESSIVE_ENVIRONMENTS.
