GUIDELINES FOR CONCRETE DURABILITY TESTING.PDF

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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 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

curing methods in structures.

Keywords: Concrete durability, diffusion, macro-environment,

micro-environment, permeability, diffusion, absorption.



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-



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.



Macro-environment Marine

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 subject 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 carbonation.

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.



Micro-environments:o

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



for the following sections which describe durability test methods

and specifications.Transport is driven by pressure difference, for example water permeation through soil or concrete driven by hydrostatic pres-sure.

This typically applies to underwater zones of marine structures,or underground zones of structures built in the water-table such

as foundations, bridge piers, basements or tunnels.

The combination of ground-water permeation into concrete basements or tunnels, plus water evaporation on the inside of

these “hollow” structures, can result in more rapid transport of

water and salts into such concrete than by permeation alone.

Permeability measurement techniques and durability modelingare based on the Darcy equation for permeability based on

measurement of flow rate, and the Valetta equation for per-

meability based on measurement of penetration depth and time.

Transport is driven by concentration difference, for examplechloride ion diffusion through water, or carbon dioxide or wa-

ter vapor diffusion through air.

Diffusion is also used for representing the overall effect of wet-

ting and drying by salt-water which leads to chloride ingress,and is termed “effective diffusion”.

Measurement techniques and durability are based on Ficks

Laws of diffusion.Absorption

Transport is driven by capillary suction, for example waterabsorption into concrete or masonry.

This typically occurs in concrete structures around and justabove the ground-water table. Absorption is also the mechan-

ism by which a splashing wave penetrates into concrete, thecumulative effect of which is often termed effective diffusion,

as above.

The combination of absorption due to capillary suction, plusevaporation of the rising moisture, is often responsible for ver-

tical transport of salts from ground water leading to salt-scalingand/or reinforcement corrosion above the water-table.

Voltage-induced flow



Some forms of durability test involve measuring voltage-

induced chloride ion flow through water, in which the voltageis provided in order to shorten the test duration.

Such conditions are artificial and do not normally exist in prac-tice, and do not provide a direct measure of permeability, diffu-sion or absorption.

TEST IN CURRENT PRACTICES

The problem of concrete durability in hot weather is very complex.

It can be seen that concrete structures in the hot, arid environments

tend to deteriorate more rapidly than those in temperate regions ofthe world, unless particular precautions are taken. Increases in

temperature also increase the risks of cracking, including plasticshrinkage cracking and drying shrinkage cracking, and facilitate

the ingress of salt-laden water and moisture, causing disintegration

of concrete due to reinforcement corrosion.

Core Testing

The examination and compression testing of cores cut from har-

dened concrete is a well-established approach, enabling visual in-spection of the interior regions of a member to be coupled with

strength estimation, and other physical properties which can be

measured include density, chloride diffusion, water absorption, or

water permeability. There are many factors that influence results,among which are the concrete characteristics and the testing va-

riables.

Compressive strength testing variables include factors as,Length/diameter ratio of core, Diameter of core, Direction of drill-

ing, Method of capping and reinforcement. The likely coefficient

of variation due to testing is about 6% for carefully cut and testedcore, which can be compared with a corresponding value of 3% for

cubes. The difference is largely caused by the effects of cutting.

It is claimed that the likely 95% confidence limits on actualstrength prediction for a single core are +-12% when the Concrete

Society calculation procedures are adopted. Uncertainties caused



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:



Autoclam water and air permeability tests

Figg air permeability test

Schönlin air permeability test

Surface airflow test

Diffusion testsDiffusion is where a liquid, gas or ion migrates through concrete;

due to a concentration gradient. There is interest in ionic diffusion

tests because the rate at which chloride ions diffuse through con-

crete is closely related to the corrosion of reinforcement. There aretests which require cores to be extracted, while others can be car-

ried out in-situ. The most common of these tests are:

The rapid chloride permeability test

Steady state migration tests

In-situ chloride migration test

EVALUATION OF RESULTS AND REPORTING

Most tests have well-defined procedures and the methods used for

the calculation and assessment of different parameters from direct-ly measured values will depend to a large extent on the test method

used. Variation in properties of hardened concrete due to differ-

ences in materials, mixing, transportation, placing, finishing andcuring tend to be random and requires that the results be analyzed

using various statistical tools such as graphical and numerical me-

thods. The number of test types, test location and number of test

points used has a significant bearing on the ease with which thevariability of concrete within members and between members can

be assessed. For confidence, the variability of any tests employed

should be studied. Correlation differences between the laboratory

conditions under which results are obtained and site conditions canvary, and that this can affect the accuracy of our calibration. The

variability of the particular test method, the operator skill and the

variability of the concrete under test control the accuracy with



which test results can be calibrated against a particular desired

concrete property.Reports should present all these variations and correlation and also

the limitations of the testing methods. Recommendations should beclear. Engineering judgment based on his experience and the avail-

able data should not be ambiguous or vague.

Durability tests – actual resultsConcrete, like any material, varies in its properties. The variations

arise from the raw materials, production methods and sampling

techniques. Table 2 shows the contributing factors on strength

variability at typical batch plants.

Statistical law and routine tests are used to measure the variation between concrete batches. Cube strengths plotted on a frequency

histogram will exhibit a normal distribution (Fig. 2).When designing mixes to meet a particular strength, a minimum is

stated below which a certain proportion of results, termed failures,

are found. This minimum is the specified strength and the mix isdesigned for a target mean strength, which incorporates an appro-

priate safety margin. A typical failure level allowed by specifica-

tions is 2.5%, in this instance, statistical tables indicate that therequired safety margin shall be 1.96 x standard deviation.

For example:Specified Strength = 40 MPa

Standard Deviation = 4 MPa

Target Mean Strength = 40 + (4.0 x 1.96) = 48 MPa

VARIABILITY OF THE TESTS

RCP Test

ASTM C1202 states the test method is suitable for evaluation of

materials and material proportions for design purpose and research

development. The numerical results (total charge passed in coloumbs) from this

test method must be used with caution, especially in applications

such as quality control and acceptance testing.



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-



forced concrete structures exposed to aggressive environments,

relevant quality parameters are needed, which can provide a better basis both for job specification and control of in situ quality.

The requirements set for these four tests differed among partiesand projects, the range is as follows:

Test UnitTest

duration

Maximum

Limits

specified

From to

Water absorption BS1881 Part 122

% 30 min <1 3

Initial Surface AbsorptionTest BS 1881 Part 208

ml/(m2.s) 10 min 0.02 0.3

Water penetration BS EN

12390 Part 8mm 28 d 8 20

Chloride Permeability

ASTM C-1202Coulomb -- 800 3800

Further investigations are required to study in depth the relation

between the four above-mentioned tests. This is required to arriveat a sound conclusion that will enable choosing the most suitable

test or combination of tests and to specify the performance levellimits for given project circumstances and Clients‟ expectations for

the service lives of their structures

REFERENCES

1. AASHTO Designation T 277-83, Standard method of test forrapid determination of the chloride permeability of concrete,

AASHT Washington D.C, 1983. 2. Andrade, C., Sanjuan, M.A., Alonson, M.C., 1993, Measure-

ment of chloride diffusion coefficient from migration tests,

NACE Corrosion ‟93.



3. Andrews, R.J., Design and development of an in-situ chloride

migration test, PhD Thesis, Queen‟s University, Belfast, 1999,

4. ASTM: Standards test method for electrical indication of con-

crete‟s ability to resist chloride ion penetration, ASTM C 1202-94, American Society for Testing and Materials, 1994 Book of

ASTM Standards, Vol. 04.02, Concrete and Aggregates, Phila-

delphia, 1994. 5. Basheer, P.A.M., near – surface Testing for Strength and Dura-

bility of Concrete. Fifth CANMET/ACI International Confe-

rence on Durability of Concrete. Barcelona, Spain, 4-9 June

2000. 6. British Standards Institution, Testing Concrete – Recommenda-

tions for the assessment of concrete strength by near-to-surface

tests, BSI London, BS 1881, Part 207: 1992. 7. BSI (1981). BS 6089:Guide To the Assessment of Concrete

Strength in Existing Structures, BSI, London. 8. BSI (1986). BS 1881:Testing Concrete. Part 201:Guide To the

Use of Non- Destructive Tests for Hardened Concrete, BSI,

London. 9. Bungey, J.II. And Soutsos, M., Reliability of Partially-

Destructive Tests to Assess the Strength of Concrete on Site,Proceedings of the Fifth CANMET/ACI Conference on Dura-

bility of Concrete, Barcelona,2000 10. Whiting, D., Rapid measurement of the chloride permeability

of concrete, Public Roads, Vol.45, No. 3, pp. 101-112, 1981. 11. Nilsson, L.O., HETEK, Chloride penetration into concrete,

State-of-the-art, Transport processes, corrosion initiation, test

methods and prediction models, Report 53,Road Directorate,Copenhagen, 1996

12. RILEM – Committee “Nondestructive Testing Of Concrete

Materials and Structures “Vol. 2, No.10, July – Aug. (1969). 13. Specification for Roads and Bridge Works by Roads Depart-

ment, Dubai Municipality , 1992

ACKNOWLEDGMENT

This document has been prepared by a sub-committee of five se-

lected members of the steering committee. The members are the



American University of Sharjah, RMCTOPMIX, University of

Sharjah, Halcrow, Dubai Central Laboratory. It has been also dis-cussed by the steering committee during general meeting which

comprised professionals in the concrete construction from manyUniversities, UAE Society of Engineers, Consultants, Dubai Cen-

tral Laboratory, Sharjah Municipality and Ministry of Public

Works & Housing.



Table 1 - Macro- and Micro- Environment Summary

M a r i n e /

c o a s t a l

M a r i n e &

O p e r a t i o n a l

N e a r - C o a s t a l

N e a r - c o a s t a l &


I n l a n d

I n l a n d &


M M-O N N-O I I-O

Underwater (U) M-U M-O-U - - - -

Tidal (T) M-T M-O-T - - - -

Splash (S1) M-S1 M-O-S1 - - - -

Spray (S2) M-S2 M-O-S2 - - - -

Above-ground (A) - - N-A N-O-A I-A I-O-A

Near-ground (N) - - N-N N-O-N I-N I-O-N

Below-ground (B) - - N-B N-O-B I-B I-O-B

Internal (I) - - N-I N-O-I I-I I-O-I

Table 2 – Influence of various factors on standard deviation of

concrete strengths

Factors Plant A Plant B

Aggregates 1.2 1.5

Cement 2.0 2.5

Testing 1.0 1.5

Personnel and Plant 2.0 3.5

Total Standard Deviation 3.2 4.8

Note: The overall standard deviation is not calculated by simple

addition of individual figures, but on the square root of the sum of

the squared individual values.



Fig. 1- Initial Surface Absorption Test

2

8

14

20

22

26

30

26

22

20

14

8

0

5

10

15

20

25

30

35

40 41 42 43 44 45 46 47 48 49 50 51

Compressive Strength (Mpa)

N u m b e r o f r e s u l t s

Fig. 2

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