DESIGNING DURABLE CONCRETE STRUCTURES IN
THE ARABIAN GULF: A DRAFT CODE
H. Al-Khaiat*, Kuwait University, Kuwait
B. Jones, Kuwait University,Kuwait
M. N. Haque, Kuwait University, Kuwait
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DESIGNING DURABLE CONCRETE STRUCTURES IN
THE ARABIAN GULF: A DRAFT CODE
H. Al-Khaiat*, Kuwait University, Kuwait
B. Jones, Kuwait University,Kuwait
M. N. Haque, Kuwait University, Kuwait
Abstract
The severity of the Arabian Gulf environment demands certain provisions for a
design code that would cater to local challenges in concreting. With this view in
mind, an apparent climatic divide was identified for the Arabian Peninsula viz. ‘HotDry’ and ‘Hot-Humid’ zones which were further classified into an order of exposures,
detailing the potential dangers to concrete durability. Moreover, suggestions are
included based on both research and experience in the Gulf, to practice essential
quantitative and qualitative checks on concrete mix design parameters. It is
intended that this contribution would help formulate a design code for concrete
durability in this part of the world.
Keywords: carbonation, chloride, code, durability, sulfate.
1. Introduction
The Arabian Gulf environment has adverse impact on concrete structures. The combination of high
ambient temperature, low relative humidity, salt-contaminated dust, sea water and underground salts
makes up for the destructive elements that exacerbate concrete deterioration in the region. Typically,
one of the reasons speculated for such poor performance of concrete has been the use of
1
2
3
international building codes of concrete practice such as ACI-318 , AS 3600 , EuroCode and
likewise. These codes catered more to their own countries of origin. But when they are followed for
the Gulf; their provisions fail to account for the harsh environmental conditions. Hence the
development of a regional code of practice would help deal with the challenges of hot weather and
various exposures.
With ‘durability’ taking the foreground these days, such a code must duly incorporate all factors
that ensure the same viz. type and amount of cement, aggregates, methods of curing and its duration,
cover, water-cement ratio, chloride and sulfate limits and minimum compressive strength required for
different kinds of exposure. These provisions are vital in maintaining the structural integrity of
concrete.
Upholding this concept, the authors have highlighted significant exposure conditions for the
Arabian Gulf in order to suggest appropriate measures of concrete practice for long-term durability.
These recommendations are designed to help draft a concrete code to benefit construction practice in
the region.
2. Exposure conditions in the Arabian Gulf
An analysis of the climate, geology and location of the Arabian Peninsula reveals that this region does
not have a uniform environment throughout. Broadly speaking, this region can be differentiated by
two climatic zones where one zone encloses parts of the Peninsula in and around inland deserts and
the other encloses those parts near the water bodies viz. the Arabian Gulf, Arabian Sea and the Red
Sea. Hence these zones are named as ‘Hot-Dry’ (inland) and ‘Hot-Humid’ (coastal) zones as
illustrated in figure 1. It is thought that such a classification would enable better concreting practices
respecting the nature and location of each zone.
Figure [1]: ‘Hot-Dry and ‘Hot-Humid’ Zones of the Arabian Peninsula
Furthermore, these zones, by itself, are a confluence of exposures; otherwise known as
4
microclimates (immediate surroundings of a structure). Microclimates of a structure determine the
potential for deterioration from various elements in the environment. In the following sections, the
authors focus on the Arabian (Persian) Gulf strip of the Peninsula and classify the exposures based
on both their severity and location from the sea to explain the actual extent of ‘hot-dry’ and ‘hot-humid’
conditions in the Gulf.
2.1. Classification based on degree of threat to concrete
This classification is described in Table 1 and is similar to that found in design codes such as BS:
5
6
8110: Part I: 1985 and IS: 456 – 1994 .
Exposure
Mild
Moderate
Severe
Table [1]: Classification based on degree of threat
Description
Structures in dry and chloride-free service environments
Structures submerged in water, structures sheltered from rains, salt spray and
heavy winds, structures exposed to dry winds, underground structures.
Structures exposed to spray or abrasive action of sea water, alternate wetting
and drying, structures exposed to corrosive fumes in industrial areas,
underground structures.
2.2. Classification based on proximity to the sea
A survey conducted in Kuwait pointed out how the location of a structure from the sea could affect the
7, 8
rate of chloride and sulfate ingress and also the depth of carbonation in concrete . Figures 2 – 6
validate the idea behind this exposure classification where structures located within 0 – 2 km from the
sea are recognized as coastal, those within 3 – 10 km are near-coastal and those above 10 km are
inland. It is found that coastal structures (Figure 2) have a yearly surface chloride increment of 0.16
3
3
kg/m of concrete while it is nearly less than half of that (0.07 kg/m ) for inland structures (Figure 3).
These values, though highly conservative, are used for comparison since only a combination of
factors (cover, concrete quality, chloride source etc.) can decide the exact rate of chloride build-up on
the surface.
0.35
Chloride (% wt. of cement)
Chloride (% wt. of cement)
0.7
0.6
0.5
Actual Data
0.4
Linear (Actual
Data)
0.3
0.2
0.1
0.3
0.25
Actual Data
0.2
Linear (Actual
Data)
0.15
0.1
0.05
0
0
2
4
6
8
10
2
4
time in years
6
8
10
time in years
Figure [2]: Surface chloride build-up
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near the coast
Figure [3]: Surface chloride build-up
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further inland
Likewise, the chloride content, sulfate content and carbonation depths in structures of the same
age vary with distance from the sea. The chloride profile (Figure 4) has a declining slope indicating
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the decreasing severity of sea exposure with distance . The sulfate profile (Figure 5) records high
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values both near the coast and further inland since soils and groundwater here are rich in sulfates .
The carbonation profile (Figure 6) has high values (12 – 14 mm) near the coast due to high heat and
relative humidity; decreases with decreasing humidity as it approaches inland and rises further inland.
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Haque and Al-Khaiat have speculated this rise in areas inland, possibly due to the vast drop in
temperature during the night. All this implies that structures located near the coast have a greater risk
of concrete deterioration such as reinforcement corrosion while structures inland face other
challenges arising from climate and soil conditions. Hence Table 2 presents a possible classification
of the Arabian Gulf into GM (Gulf Marine), GC (Gulf Coastal), GI (Gulf Inland) and GL (Gulf Low-Risk)
exposures along with their effects on concrete structures.
Surface - Sulfate profile with distance from the
sea
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Sulfates (% wt. of
cement)
Chloride (% wt. of
cement)
Surface-Chloride profile with distance from the
sea
Actual
Linear (Actual)
0
10
20
30
40
8
7
6
5
4
3
2
1
0
Actual
Linear (Actual)
0
50
10
20
7
Figure [4]: Chloride-distance profile
Depth of carbonation (mm)
40
Figure [5]: Sulfate-distance
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Carbonation Depth with distance from the sea
16
14
12
Actual
Poly. (Actual)
10
8
6
4
2
0
0
30
Distance from sea (km)
Distance from sea (km)
5
10
15
20
Distance from sea (km)
8
Figure [6]: Carbonation depth-distance profile
50
Exposure
Gulf Marine
Zone
Gulf
Coastal
Zone
Gulf Inland
Zone
Gulf LowRisk Zone
Table [2]: Classification based on distance from the sea
Distance
Subdivision
Description of attach
from sea
 Active corrosion due to aerosols
GM1
Spray
and salts.
 Acute chloride-induced corrosion
0-100 m
GM2
Splash/tidal
due to sea waves and current
GM within the
abrasion.
shore
 Minimum corrosion risk.
GM3
Submerged  Chloride and sulfate decomposition.
 Biological attack.
 Dampness on structures attracting
salts and fungal growth.
100 m
 Chloride build-up from salt spray,
soils and ground water.
from the
GC
-shore up
 Carbonation due to high relative
to 5 km
humidity (55-75%).
 Sulfate-rich coastal soils induce
sulfate attack.
Within
 Attack due to sulfates and chlorides
capillarypresent in soil and groundwater
rise zone
GIA
from either natural or industrial
(i.e., 3 m or
sources.
GI
5-50 km
less above
water table)
Above
due
to
salt Deterioration
GIB
capillary-rise
weathering/carbonation and/or dry
zone
winds carrying aggressive salts.
50 km
 Occurrence of contamination or
GL
and
-attack is low.
above
The ‘hot-dry’ and ‘hot-humid’ climates are better understood in the order of predominance of
specific Gulf exposures as shown in Table 3. Also, these exposures can be attributed a degree of
severity thereby creating a link between the two classes of exposure (Figure 7). It is to be noted that
GIB exposure has been grouped under 3 different categories such that when it involves ‘salt
weathering’, the danger can be highly moderate to severe. Where ‘carbonation’ is more likely, it would
be of moderate threat whereas with ‘dry winds laden with salts’, it would only have a mild to moderate
degree of threat.
Table [3]: Exposures in the descending
order of predominance for each zone
Hot-Dry Zone
Hot-Humid Zone
GI
GM
GL
GC
Severity of Exposures
GM1,GM2
GIB,GIA,GC
GIB
GIB,GM3
GL
re
v e ve re te
e
S s e e ra ate d
r il
e- d e
at Mo od M
M
er
d
o
i ld
M
M
Figure [7]: Relationship model between
the two classes of exposure
3. Concrete code - specifications
3.1. Cement
Along with other factors, the amount of Portland cement used in concrete is hugely responsible for the
ill-effects of cracking due to plastic shrinkage and thermal gradients resulting from cement hydration in
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the region . Furthermore, lime, a product of cement hydration is susceptible to chemical attack.
Hence, an injudicious use of cement content would only do more harm than good. Also the quality of
cement used greatly controls the permeability of the hydrated paste. The authors suggest that an
3
amount of Portland cement maintained at 350 to 410 kg/m of concrete with water-cement ratios not
greater than 0.45 or 0.5, should be sufficient to obtain concrete of adequate strength, density and
durability for the Gulf.
3.2. Cover
The cover to reinforcement is the breastplate of concrete in aggressive exposure. Apparently, the
rate of progress of carbonation and chlorides in concrete could be predicted as a function of the
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square root of time as shown in equation (1) where‘t’ is the time of measurement in years.
Depth = k√t
(1)
1/2
On study, it is observed that ‘k’ has a value of 4.5 mm/yr and above for chloride penetration in
1/2
hot-humid exposures whereas it is below 4 mm/yr in hot-dry exposures for concrete of compressive
strength 20 - 30 MPa. At the same time, carbonation penetrates at a rate ‘k’ equivalent to 10 times
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‘B’, where ‘B’ is a constant depending on the strength of concrete and storage conditions . Haque
and Al-Khaiat have investigated the values of ‘B’ in a survey conducted on various structures in
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Kuwait. Its value was approximated as 0.3 for concrete of compressive strength 30 to 50 MPa .
These values of penetration rates are thought to be instrumental in determining proper covers for
concrete structures exposed to different environments. A minimum cover thickness of 40 mm is an
agreeable specification for the region. Table 4 specifies concrete covers for various exposures.
Table [4]: Recommended mix design parameters for reinforced ordinary Portland cement concrete*
Minimum 28-day
Minimum Cover
Maximum watercompressive strength
Type of Exposure
(mm)
cement ratio
(MPa)
**
GM (Gulf Marine)
60-80
0.35-0.4
35-45
**
GC (Gulf Coastal)
60-70
0.4
35-40
GI (Gulf Inland)
GL (Gulf Low-risk)
50-60
25-40
0.45
0.5
30-45
30
* Quantities in the table are provided in ranges since above exposures vary in their degree of threat
from ‘mild’ to ‘severe’.
** 70-80 mm cover should only be adopted in the event that other measures of reinforcement
protection are not feasible or ineffective.
3.3. Curing
This might be considered a low-key and tedious operation but its negligence, especially in the Gulf,
could highly impair the concrete, calling upon huge costs in terms of repair of cracks and
reconstruction. Curing can be done both by external wetting and membranes. But for Gulf conditions,
membrane curing should not be counted as a sole alternative to wet curing. Rather both should go
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hand in hand such that the membranes (hessian) are kept wet permanently. Haque further brought
out that a mandatory initial curing period of 7 days is satisfactory for achieving good quality concrete.
A more general rule of thumb is to continue curing until concrete has attained nearly 70% of its design
strength. Moreover, sea water should never be used for curing.
3.4. Minimum compressive strength
It was a long-held myth that compressive strength and durability of concrete are synonymous when in
reality; strength is only one of the indicators of durability. Today, high strength is achieved by
implementing high quality materials, lower water-cement ratios, state-of-the-art superplasticisers and
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so on. Haque and Khaiat recommend that structural reinforced concrete in the Gulf should have a
minimum 28-day compressive strength of 30 MPa. This is essential to ward off the effects of harsh
exposure. Refer Table 4 for desired compressive strength.
3.5. Protection from chloride attack
Reinforcement holds out much longer in a corrosion-free, passive environment offered by concrete
but this fails, when concrete renders itself inadequate with time in a hot and aggressive environment.
Without mentioning the importance of cement, cover and curing all over again, plain concrete with low
water-cement ratio (0.35 - 0.5) is found to have slower chloride penetration and lesser sensitivity to
14
carbonation and external chemical attack . The impermeability of concrete does not arise with the
use of low water-cement ratios solely but also comes with proper mixing, consolidation, placing and
curing techniques.
It is crucial that concrete mixes adhere to the limits set for chlorides due to huge risks of corrosion
from external salt contamination encountered in the Gulf. The critical levels of chloride that would
trigger corrosion in reinforcement vary from code to code. For durability performance in the Gulf, total
(acid-soluble) chloride content of around 0.15 - 0.2 % by weight of cement and 0.3 % by weight of
cement would serve as reasonable limits for highly aggressive and moderate exposures respectively.
Table 5 presents these limits for reinforced concrete using ordinary Portland cement in different
exposures. However, all pre-stressed concrete should have chloride limits never exceeding 0.08 0.1%.
Table [5]: Maximum limits for chlorides in concrete at the time of placing
Max. total chlorides
Type of exposure
(% weight of cement)
Mild
0.4
Moderate
0.3
Severe
0.15 - 0.2
3.6. Protection from sulfate attack
Sulfate contamination from both inherent mix ingredients and external sources (soil and groundwater)
has a disintegrating effect on concrete causing the formation of large cracks. Sulfate attack can be
controlled by the use of highly impermeable concrete and more recently, surface coatings provide an
added safeguard for footings and foundations located in areas susceptible to a rise in ground water
15
table. Guides like the CIRIA recommend that the amount of water soluble sulfates in the concrete
7
mix be limited to 4 % by weight of cement. Haque and Al-Khaiat have stated that sulfate
contamination in the concrete mix should not be allowed to exceed 2 % by weight of cement.
4. Conclusions
(1) The Arabian Gulf is not influenced by a single climatic pattern but is a combination of extreme
humid conditions near the coast and lesser humid conditions, inland. Also, the various exposures
are grouped according to their severity and proximity to the sea.
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(2) Cement content of 350 - 410 kg/m of concrete is satisfactory for high strength and durability.
(3) Maximum water-cement ratios in the range of 0.35 to 0.5 are recommended for ordinary
Portland cement concrete.
(4) Concrete structures perform better in severe conditions with minimum compressive strength
specified in the range of 30 to 45 MPa.
(5) Curing should take place uninterruptedly during the first one week of placing.
(6) Concrete covers for each exposure must be strictly followed to prevent external attack.
(7) Abidance of limits set for both chlorides and sulfates in concrete enable high performance of
structures.
5. References
[1]
ACI 318M-95 & 02, Building Code Requirements for Structural Concrete and Commentary,
American Concrete Institute, Farmington Hills, MI, USA.
[2]
Standards Australia, Concrete Structures, AS 3600, Sydney, Australia, 1994.
[3]
European Standard, Concrete Specification, Performance, Production and Conformity, BS EN
206-1, 2001.
[4]
P. Fookes, “Concrete in Hot, Dry and Salty Environments,” Concrete, Jan/Feb 1995, pp. 34-39.
[5]
British Standard Institution, The Structural Use of Concrete, BS 8110: Part 1:1985.
[6]
Indian Standard, Code of Practice for Plain and Reinforced Concrete, IS: 456 – 1994, Bureau of
Indian Standards, pp. 28-29.
[7]
M.N. Haque and H. Al-Khaiat, “Durable Concrete Structures in a Chloride-Sulfate Rich
Environment,” Concrete International, 21(9), September 1999, pp. 49-52.
[8]
M.N. Haque and H. Al-Khaiat, “Carbonation of Concrete Structures in Hot Dry Coastal
Regions,” Cement and Concrete Composites, 19, 1997, pp. 123-129.
[9]
A. Neville, “Good Reinforced Concrete in the Arabian Gulf,” Materials and Structures, 33(234),
December 2000, pp. 655-664.
[10] Walker, M., Guide to evaluation and repair of concrete structures in the Arabian Peninsula,
Concrete Society Special Publication CS 137, 2002, pp. 31-35.
[11] I. Sims, “The Assessment of Concrete for Carbonation,” Concrete, 28(6), 1994, pp. 33-38.
[12] M.N. Haque, “Give it a Week: Seven days initial curing,” Concrete International, 20(9), 1998, pp.
45-48.
[13] H. Al-Khaiat, and M.N. Haque, “Carbonation of some Coastal Concrete Structures in Kuwait,”
ACI Materials Journal, 94, 1997, pp. 602-607.
[14] Aitcin, P.C., “Durable Concrete – Current Practice and Future Trends,” Concrete Technology –
Past, Present and Future, Conference Proceedings of V. Mohan Malhotra Symposium, SP-144,
1994, pp. 85-104.
[15] Walker, M. and Ted, Guide to Construction of reinforced concrete in the Arabian Peninsula,
CIRIA Publication C 577, Concrete Society Special Publication CS 136, 2002.