GUIDELINES FOR CONCRETE DURABILITY TESTING IN THE U.A.E. Adil K. Al-Tamimi, Mufid Al-Samarai, Ali Elian, Nigel Harries, and David Pocock Synopsis: The construction industry in UAE in particular and the GCC in general, is witnessing a boom in constructing remarkable infrastructure and buildings. The massive amounts of material be- ing used have been produced either locally or imported from inter- national resources. However, the extensive use of materials has not been accompanied by parallel research and development to vali- date proper techniques, quality control standards and codes of practice. There exist numerous test methods related to concrete durability, developed internationally and proved to varying extents in practice. However, confusion exists on how these methods should be applied, how to interpret the results on projects and what are the criteria to be used in UAE by the industry, particularly when using local materials in the harsh environment of the region. Four international durability testing procedures have been eva- luated in this study. It has been shown that durability performance of existing structure is different than the performance of concrete prepared in test samples whether these samples are prepared at site or at the lab due to the differences between the preparation proce- dure of samples and the actual concrete pouring, compacting and curing methods in structures. Keywords:Concrete durability, diffusion, macro-environment, micro-environment, permeability, diffusion, absorption.
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8/12/2019 GUIDELINES FOR CONCRETE DURABILITY TESTING.PDF
Adil K. Al-Tamimi, Mufid Al-Samarai, Ali Elian, Nigel Harries,
and David Pocock
Synopsis: The construction industry in UAE in particular and theGCC in general, is witnessing a boom in constructing remarkable
infrastructure and buildings. The massive amounts of material be-
ing used have been produced either locally or imported from inter-national resources. However, the extensive use of materials has not
been accompanied by parallel research and development to vali-
date proper techniques, quality control standards and codes of practice. There exist numerous test methods related to concrete
durability, developed internationally and proved to varying extents
in practice. However, confusion exists on how these methods
should be applied, how to interpret the results on projects and whatare the criteria to be used in UAE by the industry, particularly
when using local materials in the harsh environment of the region.
Four international durability testing procedures have been eva-
luated in this study. It has been shown that durability performanceof existing structure is different than the performance of concrete prepared in test samples whether these samples are prepared at site
or at the lab due to the differences between the preparation proce-dure of samples and the actual concrete pouring, compacting and
Adil K. Al-Tamimi: Associate Professor of Civil Engineering at
the American University of Sharjah, UAE.
Mufid Al-Samarai, Professor of Civil Engineering at SharjahUniversity, UAE.
Ali Elian: Head of Engineering Materials Lab Section, Dubai Mu-nicipality, UAE.
Nigel Harries: General Manager, Icon Precast LLC, UAE.
D C Pocock : Market Sector Director , Halcrow.
DURABILITY PRINCIPLES
The durability of concrete structures is closely related to the nature
and severity of the environment in which they are located, as wellas the nature of the concrete construction. This section considers
the environments and associated mechanisms by which the envi-
ronment can penetrate into concrete. The influence of the concrete
itself in permitting or resisting environmental penetration is consi-dered in later sections.
The general environment is termed the “macro-environment”,e.g. coastal, inland.
The specific environments, more than one of which often oc-curs around a single structure, are termed “micro-
environments”, e.g. tidal zone, splash zone.
Both macro- and micro- environments may be natural, i.e. re-lated to geography and geometry, or may be man-made, whereoperational processes lead to exposure, e.g. in industrial plants
or watering for plant irrigation.
The macro- and micro- environments, in which a structure is lo-
cated, determine the transport mechanisms by which the environ-ment, i.e. water, chlorides, gases, can penetrate into concrete.
Therefore a definition of the various environmental conditions is
useful as a basis for discussing the transport mechanisms, and thetest methods themselves. This basic explanation of the environ-
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mental zones and the transport mechanisms should enable the re-
levance of each test to be considered when concrete durability testsare selected for specific projects.
These definitions are set out below, with reference to the followingdeterioration mechanisms:
Chloride-induced reinforcement corrosion: Parts of structureswhich are in contact with seawater, splash, spray, salty-dust, orother chloride sources (e.g. industrial process water, or irriga-
tion water), are at risk from chloride penetration leading to
reinforcement corrosion.
Carbonation-induced reinforcement corrosion: Parts of struc-tures which are not regularly wet, are subject to carbonation,
the rate of penetration of which is subject to humidity and con-crete mix. Good quality concretes which are durable against
chloride-induced corrosion are also unlikely to be vulnerable tocarbonation, subject to concrete mix details.
Sulphate attack: Severity of sulphate exposure should bechecked on a structure-by-structure basis, following systematic
methodology such as that provided by BRE Special Digest 1:2005 Concrete in Aggressive Ground.
Salt-scaling: Spalling of thin layers form concrete surfaces dueto splitting pressures arising from crystallization of salts in
concrete pores within the surfaces.
It is assumed that both alkali-silica reaction and the use of chlo-ride-containing concreting materials, are avoided by proper speci-
fications, and therefore are not relevant to a discussion on envi-
ronmental exposure and transport mechanisms.
Environmental conditions and zones
The following main macro-environments apply to concrete struc-tures in the UAE and most of the Gulf region and in each case
there are applicable micro-environments, as summarized in Table
1. This definition may not be comprehensive, and other situations
may occur outside the defined categories. Reference codes are
provided, to assist in illustrating the definition.
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Marine/coastal (M): Concrete structures which are close to orin contact with seawater, such as ports, harbors, jetty structures
or some bridge piers.
Micro-environments
Underwater (M-U): Parts of structures are exposed to constantimmersion in seawater.
Tidal zone (M-T): Parts of structures in the tidal range are sub- ject to alternating cycles of seawater immersion and drying.
Splash zone (M-S1): Parts of structures above high tide aresubject to splashing by sea-water wave action and drying by
wind and sun, all according to orientation and geometry.Spray zone (M-S2): Parts of structures above high tide andsplashing by waves are subject to wind-blown seawater spray,and drying according to wind and sun, all according to orienta-
tion and geometry, and are also exposed to carbonation.
Above the spray zone (M-S1), any other parts of marine/coastalstructures should be regarded as near-coastal (N-A).
Macro-environment NEAR-COASTAL
Near-coastal (N): Buildings or structures are typically locatedwithin 25- 250 m of the sea.
Micro-environments:o Above-ground (N-A): Parts of structures are exposed to
wind-blown spray/sand/dust, and are also exposed to car- bonation.
o Near-ground (N-N): Parts of structures are exposed to salts
rising from the ground water by capillary action and evapo-ration
o Below ground (N-B): Parts of structures are exposed to sa-
line ground-water, and probably sulphates.
Macro-environment INLAND
Inland (I): Typically buildings or structures beyond 25 – 250 mfrom the sea. Typically dry except for occasional rain, season-
al dewfall, and operational water sources.
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Above-ground (I-A): Parts of structures are exposed towind-blown sand/dust, which may be salty, and are also
exposed to carbonation.
o Near-ground (I-N): Parts of structures may be exposed to
salts rising from the ground water by capillary action and
evaporation.
o Below ground (I-B): Parts of structures may be exposed to
saline ground-water, and possibly sulphates, depending
upon the height and salinity of the water-table.
Operational-micro-environments
In any of the above macro-environments (M, N, I), micro-environments may occur which result from operational
processes (-O-), as opposed to natural situations.
Underwater, tidal (i.e. wetting/drying), splash or spray condi-tions may also be created by process operations such as pump-
ing chambers or cooling water intakes/outfalls in industrial
plants, or irrigation watering at e.g. hotels or road interchanges.For example, a splash zone at a coastal outfall (M-O-S1), or
salt-water irrigation spray on inland concrete (I-O-A).
Internal Environment
The interior of buildings or structures is normally dry, and con-crete durability should be controlled by the combination of
good quality concrete so that carbonation is not excessive, and
proper building envelope detailing so that moisture is notavailable to support reinforcement corrosion in the event that
carbonation does penetrate to reinforcement; (N-I, I-I).
Measures other than concrete durability testing are required tocontrol non-typical situations such as leaking basements,excess moisture in kitchens, bathrooms, laundries, etc, or spe-
cial indoor structures such as swimming pools; (N-O-I, I-O-I).
TRANSPORT MECHANISMS
The section describes the principle mechanisms by which water,
ions; gases may be transported through concrete, to provide a basis
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by reinforcement, compaction or curing may lead to an accuracy as
low as +-30%.
Ingress of moisture testsThe most important parameter that leads to premature deterioration
of reinforced concrete is the ingress of moisture, by absorption or
permeation, which can therefore. be used as an indicator of its
durability. Transport processes, which describe the movement ofaggressive substances through concrete, can be absorption, per-
meability or diffusion.
Absorption tests
In Absorption concrete takes in liquid by capillary suction to fillthe pore space available. Absorption tests should measure the
property mentioned and the sorptivity. However, due to the diffi-culty in achieving a unidirectional penetration of water and prob-
lems of determining the water penetration depth without actually
splitting open the concrete sample, the absorption characteristics ofconcrete are usually measured indirectly. The most common of
these tests are:
Standpipe tests
Initial Surface Absorption Test (ISAT) (Fig. 1)
Autoclam sorptivity test
Water-absorption test
Permeability tests
Permeability is where a fluid passes into concrete under the action
of pressure gradient. Experimental evidence of permeabili-
ty/durability correlation was well established from experimentscarried by Basheer. Permeability tests measure the transfer of a
liquid or gas into the concrete under the action of a pressure gra-
dient. They can be either steady state or non-steady state depend-ing on the condition of flow established within the pore system ofthe concrete. The most common of these tests are:
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Single Operator Precision--the single operator co-efficient of varia-
tion of a single test result has been found to be 12.3%. Thereforethe results of two properly conducted tests by the same operator on
concrete samples from the same batch and of the same diametershould not differ by more than 35%.
Multi – laboratory Precision--the multi-laboratory co-efficient ofvariation of a single test result has been found to be 18%. There-
fore results of two properly conducted tests in different laborato-
ries on the same material should not differ by more than 51%. The
average of three test results in two different laboratories should notdiffer by more than 29%.
DIN Water Penetration TestThe DIN standard does not address the issue of precision of the
test, Geiker et al reported data suggesting the maximum of three
results could deviate more than 100% from the mean with this test.The DIN test is based on the engineering principles relating to flow
of liquid subject to pressure. Research has proven that the test
method is highly susceptible to variations in specimen preparation,
curing and surface preparation. Furthermore measurement of theingress is a visual process prone to operator bias.
Water Absorption Test
The water absorption test gives a modification of total void spacein concrete. The variability of the test method is fairly low howev-er when applied to samples extracted from cubes during production
it gives little useful information. Whilst the absorption value is partially dependent on mix quality, it is also greatly affected by the
degree of compaction and effectiveness of initial curing. It is
therefore extremely difficult to determine whether „high results‟are caused by material or cube making / curing problems.
CONCLUSIONS
Over recent years an increasing amount of premature steel corro-
sion in concrete structures has created a big problem. In order to
ensure adequate durability and long-term performance of rein-
8/12/2019 GUIDELINES FOR CONCRETE DURABILITY TESTING.PDF