cur recommendation 102_inspection and assessment of concrete structures in which the presence of asr...

8/12/2019 CUR Recommendation 102_Inspection and Assessment of Concrete Structures in Which the Presence of ASR is Su

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CUR - Recommendation 102

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Recommendation 102

Inspection and assessment ofconcrete structures in which thepresence of ASR is suspectedor has been establishedAn alkali-silica reaction (ASR) is a reaction between the alkalis present in the pore

water of concrete and certain components of the aggregate that contain reactive silica.

The reaction leads to the formation of a gel, which expands when it absorbs water. As a

result of this expansion cracks are formed and the mechanical properties of the concrete

may change. This may have an adverse effect on the behaviour and the load-bearing

capacity of the structure. ASR is characterised by a crazed pattern of cracks. Depending

on the design of the structure and stresses in the material, however, more or less straightcracks may also occur.

It is important to recognise the presence of ASR in view of its potential consequences

for the load-bearing capacity and the structural safety of the structure. This

Recommendation provides a procedure on the basis of which it can be established

whether cracks that are present are actually caused by an alkali-silica reaction in the

concrete. To be able to estimate the effect on structural safety a procedure is described

in this Recommendation for gathering all the material characteristics required of the

structures in question, including strength properties. In this CUR Recommendation

guidelines are provided for the structural assessment of a number of specific structures

on the basis of these material properties. Finally, this Recommendation also discusses

the maintenance measures that are to be taken when ASR is present.

At the time this Recommendation was published CUR Research Committee C 106,

Structural aspects of alkali-silica reaction in concrete structures, had the following

members:

ir. J.D. Bakker (chair), ir. C.A. van der Steen (secretary and reporter), ir. G. Chr.

Bouquet, dr. M.A.T.M. Broekmans (corresponding member), ing. J. Dudar, ir. J.

Hartogsveld*, ing. N. Kaptijn*, ir. E.J.C. Rademaker, ir. R. van Selst, ir. A.J.M.

Siemes*, dr. ir. C. van der Veen*, drs.E. Vega (coordinator) en W. Buist (mentor).

The structural section, chapter 8, of this Recommendation was prepared by a designers

working group, consisting of the committee members above indicated by an *, together

with ir.G.G.A. Dieteren, ir.U. Frster, ir.F.B.J. Gijsbers, dr. ir.E. Schlangen and ir.

J.A. den Uijl. Furthermore, an important contribution to establishing the calculation

methods in this Recommendation was made by ir.A.J. Wubs.

CUR Recommendation 102 was approved by the General Regulations Committee

Concrete and is supported by NEN/CUR Committee 353 039 / RC 12 Concrete and

NEN/CUR Committee 353 001 09 / RC 20 TGB concrete structures.

This Recommendation was found to be consistent with NEN 6702, NEN 6720, NEN

6723, NEN-EN 206-1 and NEN 8005.


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content

1 Subject 4

2 Area of application 4

3 Terms and definitions 4

4 Classification 54.1 Inspection and study classes 54.2 Reporting 84.3 Specification of study and reporting, data 8

5 Nature and scale of the study 95.1 General information 95.2 Exploratory inspection 95.2.1 Contents of inspection 95.2.2 Performance method 10

5.3 Technical study 105.3.1 Contents of study 105.3.2 Performance method 105.4 Targeted study 115.4.1 Contents of study 115.4.2 Performance method 115.4.3 Establishing the reinforcement configuration 125.5 Structural study 125.5.1 General information 125.5.2 Contents of study 13

6 Sample-taking 136.1 General information 136.2 Marking and drilling 146.3 Treatment of drilled cores 146.4 Repairing drilled holes 14

7 Measuring and assessment methods 14

7.1 Crack pattern, crazing 147.2 Cumulative crack width 147.3 Assessment of data and structure 167.3.1 Assessment of data 167.3.2 Assessment of structure 17

7.4 Polarisation and fluorescence microscopy (PFM) 177.4.1 Procedure 177.4.2 Aspects to be established 177.4.3 Microscope requirements 187.5 Uniaxial tensile strength 187.5.1 Determination of the uniaxial tensile strength 187.5.2 Verification of uniaxial tensile strength measured 187.6 Compression strength 19


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8 Structural analysis 19

8.1 Analysis principles 198.2 Deflection verification 198.3 Verification of shear forces 198.3.1 Principles 198.3.2 Design value of shear stress according to NEN 6720, based on average tensile strength 208.3.3 Design value of shear stress based on experimental research 20

8.3.4 Upper limit of the design value of shear stress 218.3.5 Special load combinations 228.4 Punch and torsion 22

9 Reporting 22

9.1 Class A 229.2 Class B 229.3 Class C 229.4 Control strategy and control measures 239.4.1 Data required for control measures 239.4.2 Specification of control measures 23

Titles of standards and CUR Recommendations stated 25

Appendix A Preparation of fluorescent epoxy 26Appendix B Preparation Of Thin Sections 28


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1 Subject

This CUR Recommendation provides procedures and guidelines for:

establishing whether an alkali-silica reaction (ASR) is present in concrete;

establishing the relevant material properties;

assessing a concrete structure for ASR, whereby methods are given for the structural

assessment of a number of specific structures.

In addition to this, possible control measures are discussed. These depend on the extent

of the damage by ASR.

2 Area of application

This CUR Recommendation applies to concrete structures in the Netherlands. The

structural assessment methods in chapter 8 of this Recommendation are only valid for

certain structures with structurally deleterious ASR. More specifically, the calculation

methods determined from experimental research (8.3.3) may only be used if:

it concerns plate-shaped structures (plates, walls) with a thickness of at least 400

mm;

a bidirectional reinforcement (in one plane) is used in these plates;

the damage by ASR has resulted in delamination parallel to the plane of the plate;

this has resulted in anisotropy of the uniaxial tensile strength.

3 Terms and definitions

3.1 Alkali-silica reaction (ASR):the reaction of certain components of aggregate containing

reactive silica with the alkalis that are present in the pore water of concrete, which leads

to the formation of gel-like reaction products.

3.2 Structurally deleterious ASR: the situation whereby the occurrence of ASR results in

deterioration of the mechanical properties of the concrete to such an extent that this

affects structural safety and usability.

3.3 Exploratory inspection: a mainly visual assessment of the structure with the aim to

establish whether any (deleterious) ASR may be present.

3.4 Technical study: a study performed on the structure and in a laboratory to establish

whether ASR is actually present, including exploratory tests to determine whether

material properties, such as compression and tensile strength, have been adversely

affected.

Explanation

These reaction products may absorb pore water, which makes them swell up and

exert pressure within the concrete. As a result of this, some of the mechanical

properties will initially deteriorate, including the tensile strength, and the concrete

may eventually start to crack. The deterioration of mechanical properties can be

deleterious to the structure.

Explanation

For newly to be built concrete structures, please refer to CUR Recommendation 89

Measures to prevent damage to concrete by alkali-silica reaction (ASR).

The limitation to concrete structures in the Netherlands is necessary, as the

calculation methods were derived from Dutch calculation regulations or as these

calculation regulations are used for the assessment. The limited applicability of

calculation methods determined by experimental research stems from the fact that

only the structure described was studied.


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3.5 Targeted study: a study with the aim to determine the strength properties of the concrete

affected by ASR more extensively.

3.6 Structural study:a study into the structural consequences for the concrete affected by

ASR.

3.7 PFM (polarisation and fluorescence microscopy):a microscopic research technique that

is applied on very thin, impregnated preparations of concrete in order to obtain an imageof the microstructure of the cement paste, the water-cement ratio, the type of cement,

the lithological composition of the aggregate and any converted substances in it, the

presence of cracks as well as the spatial distribution and the homogeneity of these

properties.

3.8 Reactive silica:the amorphous or low-crystalline silica present in some aggregates that

reacts faster with alkalis on the basis of its less well-ordered crystal structure and/or its

greater specific surface area compared to coarse crystalline quartz.

3.9 Relative cumulative crack width ASR: an indicative measure for the extent to which

cracks have formed that is determined by adding all the widths of the cracks that

intersect with a measuring line placed along a cracked area of the structure and then

dividing it by the length of the measuring line.

3.10 Structural risk: a measure for the seriousness of the consequences relating to the possible

presence of ASR.

3.11 Control strategy: the strategic choice of the period in which and level at which a

structure will be maintained by performing control measures.

3.12 Control measure: the package of measures that are to be taken immediately and in the

future to keep a structure in a prearranged condition or to achieve a predetermined

situation.

4 Classification

4.1 Inspection and study classes

The class of inspection and/or nature and scale of the study to be performed must be

agreed upon in advance by reporting a class as stated below. It is possible to agree onseveral different classes at the same time (see table 1).

Explanation

Examples of control measures are reinforcing the structure or measures to delay or

prevent the progress of the damage mechanism, such as limitation of the moisture

load.

Explanation

The structural risk is determined by analysing the reinforcement configuration and

the consequences of the damage observed for aspects such as safety and functioning.

Explanation

Well-known reactive components are opal, chalcedony, moganite, cristobalite,tridymite, cryptocrystalline quartz, (porous) flintstone (silex / chert / flint), impure

sandstone (grey wacke, siltstone), siliceous limestone and certain types of volcanic

rock due to the glass that is present in it.


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Class I Exploratory inspection

The purpose of this inspection is to find out whether ASR is present in the structure or

whether the cracks that were observed are more likely to have a different cause.

Class II Technical study

The purpose of this study is to confirm that ASR is indeed present, as well as to obtain

an initial indication of the seriousness of the damage. Among other things, this is done

by establishing whether a relatively low uniaxial tensile strength is present.

Class III Targeted study

The purpose of this study is to gather more information in a targeted manner, to be able

to determine reliable material properties on the basis of this, among other things, for the

structural assessment calculation and the specification of control measures.

Class IV Structural study

The purpose of this study is to obtain an insight into the structural safety of the

structure. The structural study is divided into:

Class IVA Manual inspection of transverse forces in representative cross-sections,

either with or without basic calculation software.

Class IVB Numerical inspection of transverse forces in representative cross-sections.

Class IVC Structural assessment of the entire structure.

A representative cross-section is the cross-section in which the modified mechanical

properties of the concrete have the greatest effect on the load-bearing capacity and the

structural safety of the entire structure.

Figure 1 shows the relationship between the various components. The various studies

are specified in more detail in 5.2 to 5.5.

The diagram in Figure 1 will only have to be followed if the structural risk is medium

or high, see 7.3.1.

Explanation

To assess the structural safety calculation models are used that are only valid for

certain structures, see 8. The determination of representative cross-sections requires

a good structural understanding and can therefore best be left to an experienced

structural engineer.

Explanation

The tests described in this Recommendation serve as a supplement to the inspection

and test methods in CUR Recommendation 72, Inspection and testing of concrete

structures, and describe tests that are related to ASR in more detail. In certain cases

it is recommended to ascertain whether it is desirable to perform an inspection or

study according to CUR Recommendation 72 at the same time, supplementary to a

study according to this Recommendation.


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Figure 1 Flow chart for inspection and studies

Explanation of flow chart

In the flow chart used the various study classes are described in a mutual context.

Generally speaking, an increasing amount of information is obtained from top to

bottom in the flow chart, whereby the study effort also increases. Please note that a

step-by-step approach was chosen, whereby different levels of study are performed

in succession. In some situations the additional costs and nuisance (traffic measures)

may be such, that it will be better to decide to take all the samples in advance, in

anticipation of a possible targeted study in the laboratory. With regard to this, it is

important to have a clear image of the desired results of the study in advance. The

studies mentioned will only be useful in practice if the structural risk is medium or

high.

Y

Y

Y

Y

Y

N N

N

N

N

N

Class I

exploratory inspection

Class II

technical study

Class III

targeted study

Class IV

structural study

ASR

possible

ASR

Indication of low

tensile strength

Safety now

guaranteed

Report

Report

Report

Report with

safety

measures

Possibly further

study into cause of

cracks

Low tensile

strength

Report


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4.2 Reporting

Based on their contents, reports are divided into:

Class A Reporting of data.

Class B Reporting of data and measures to be taken.

Class C Reporting of data and control measures to be taken.

For the contents of the reports, please refer to chapter 9.

4.3 Specification of study and reporting, data

In order to determine which study is required and which type of report is to be prepared,

at least the following must be agreed:

a. the type of inspection or study, based on the classification in 4.1;

for an exploratory inspection it must also be agreed whether the pattern of cracks

is to be recorded in accordance with 7.1;

for a technical study it must also be agreed whether impregnated cores are to be

assessed;

for a targeted study it must also be agreed whether the reinforcement

configuration is to be determined;

b. the method and contents of the required report, based on the classification in 4.2.

Prior to an inspection or study of a concrete structure at least the following data must be

available:

the definition of the problem relating to the inspection or the study;

the location of the structure to be studied;

the nature and type of the structure;

the shape and size of the structure;

the age of the structure and, where available, the design life;

the component or components of the structure to be studied;

whether any previous studies have been performed on these components or thestructure;

the accessibility of the structure as a whole and of the most important structural

components at which the study is aimed;

the possibilities of closing-off the building site as well as the need to take traffic

measures.

If a structural study is prescribed the following must also be agreed:

whether the (original) design calculations, verification calculations and reinforce-

ment drawings are available;

the number of representative cross-sections that must be tested (see 5.5).

If any control measures are to be specified, the client should provide information about

the control strategy that applies to the concrete structure in question.

Explanation

Please note that a link exists between the type of study and the possible reports. For

example, an inspection according to class 1 will provide insufficient data to prepare

a report according to class C.

This Recommendation is aimed at identifying ASR and the consequences of it. If

ASR cannot be identified as a cause or the only cause of the cracks observed, it is

advisable to have these cracks and the consequences of them assessed further by an

expert. It may also be useful for maintenance purposes to obtain information about

other defects and shortcomings in the structure. For the recording of a study different

to one concerning ASR, please refer to the various inspection classes that are statedin CUR Recommendation 72.


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5 Nature and scale of the study

5.1 General information

In this chapter the inspection and studies stated in 4.1, which may either be performed

separately or together, are described in more detail.

When prescribing a particular study or a combination of studies the intended objective

must be clear, for example, merely determining whether ASR is present or, for example,

answering the question of whether the structural safety is still guaranteed. Table 1indicates which study is required to obtain a particular result.

Table 1 Overview of relevant questions and studies required

Scale of study at least

Exploratory

inspection

Technical study Targeted study Structural studyQuestion

See 5.2 See 5.3 See 5.4 See 5.5

Could ASR have occurred? To be performed

Could the mechanical properties

have been affected in a negative

manner?

To be performed To be performed

Has ASR currently led to a

structurally unsafe situation?

To be performed To be performed To be performed

5.2 Exploratory inspection

5.2.1 Contents of inspection

For each component to be studied, an exploratory inspection must at least consist of the

following:

Establishing whether a crazed pattern of cracks is present, which is the case if the

cracks are more or less perpendicular to each other. The crazing may exhibit apreferred direction, for example, due to the forces in the structure.

Establishing whether the crazing is uniform over the entire surface or whether there

are areas with limited crazing and areas with a large amount of crazing.

Identifying other cracks and crack patterns, whereby at least the following is recorded:

the shape of the cracks, the crack distance, the crack width and an estimate of the

cumulative crack width.

If this has been agreed, the crack pattern should also be recorded in accordance with 7.1.

The following must also be recorded for the structure that contains the component to be

assessed:

Any visually identifiable expansion and deformation of the structure, for example,the structure being out of centre at joint interfaces, lopsidedness of bearings as well

as unusual curvature, lopsidedness or shifting of faces.

Explanation

The reliability of statements relating to the damage, the consequences and the

measures to be taken is determined for a large part by the study. For example, an

exploratory inspection provides an insufficient basis for specifying control measures.

Table 1 shows which studies are considered to be required at the least to be able to

make a particular statement.

If any previous studies were performed on the structure, either with regard to ASR or

other types of damage, it will be useful to provide this information as well.

Depending on the nature and scale of the previous study it may be decided to limit

the study described in this Recommendation.


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Any environmental factors relating to the moisture load, for example, for car decks

the possibility of loads exerted as a result of de-icing salts and excessive forms of

moisture load as a result of the design and/or inadequate drainage of the structure.

Any secretion of alkali-silica gel present or the spalling of pieces of concrete for

reasons other than reinforcement corrosion.

The presence of a coating or signs of concrete repairs performed previously. In

particular, the possibility must be taken into account here that a coating may hide

previous damage by ASR that was repaired.

5.2.2 Performance method

Where agreed, the pattern of cracks must be recorded in accordance with 7.1 in at least

three locations where the most severe form of crazing is visible.

5.3 Technical study

5.3.1 Contents of study

The technical study must at least consist of:

Removing drilling cores for polarisation and fluorescence microscopy (PFM test)

and to determine the mechanical properties.

Recording the relative cumulative crack width according to 7.2 in at least 3 locationswith a crazed pattern of cracks.

An analysis of the structure on the basis of information provided, see 7.3.1,

including any exploratory inspections performed.

A verification of the tensile strength of the cores measured against the designed

tensile strength and the low tensile strength criterion according to 7.5.2.


For the technical study a sufficient number of cores with the correct length must be

drilled out of the structure or structural components in order to perform the test of the

mechanical properties and for the presence of ASR. The diameter of the drilling cores

must be around 75 mm. The length of the drilling cores is derived from the property that

is to be determined.

Explanation

Depending on the size of the object, it may be decided to have the pattern of cracks

recorded in a greater or smaller number of locations. For possible testing of the

uniaxial tensile strength perpendicular to the span, in other words, in the plane of the

element, it is recommended that at least three cores be drilled. To establish thenecessity of a test of the uniaxial tensile strength in the plane of the element, please

refer to 8.3.1.

Explanation

It may be useful to draw and record the pattern of cracks in order to monitor possible

developments.

Explanation

To recognise damage patterns that may be related to ASR, please refer to the ASR

picture-book, a publication of the Public Works Service of the Directorate-General

for Public Works and Water Management, which can be accessed via

www.bouwdienst.nl.


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The number of cores required and the length of the cores is:

at least 6 to determine the uniaxial tensile strength according to 7.5, their length

must be equal to twice the diameter of the core;

at least 3 to determine the compression strength according to 7.6, their length must

at least be equal to the diameter of the core.

The drilling locations of the cores must be spread out over the bad areas, but not on a

crack and preferably in representative cross-sections in terms of transverse force.

In addition to the cores stated, it may be necessary to collect additional sample material

for a PFM test. These cores must have a length of at least 100 mm and should

preferably be drilled on a crack. The core must also include the outside surface.

All drilled cores must be assessed visually for signs of ASR. At least one core

containing material suitable for the PFM test according to 7.4 must be selected from the

available sample material.

5.4 Targeted study


The targeted mechanical study must at least consist of drilling cores for mechanical

testing. Where agreed, the reinforcement configuration must also be determined.


Drilling cores

The locations where drilling cores are to be removed for the structural test must bedetermined by an experienced concrete maintenance expert with a structural

understanding, or else in consultation with the structural engineer who is responsible for

the more detailed structural study. The cores should basically be removed from areas in

which transverse forces are present.

Explanation

Please note that the areas in which the transverse force is normative are particularly

interesting; more so than areas in which it is at its maximum.

Explanation

Additional cores are required for PFM testing, as a sufficient number of cores must

be available to test the mechanical properties. It cannot be excluded that additionalmaterial is obtained when drilling cores for mechanical testing before the number of

cores with the correct length stated is collected. This material could be used for PFM

testing. A drilling core can be used for more than one purpose, provided that its

length is sufficient.

Please note that a core with a greater diameter, for example, 100 mm, and a length of

more than 300 mm may provide more information when this core is fully

impregnated compared to the minimum dimensions prescribed. This is simply

because more material will then be available.

By impregnating cores with a fluorescent resin a greater insight is obtained into the

cause and the severity of the cracks that are present. The presence of ASR is often

shown with PFM, but it is difficult to ascertain whether ASR really is the primary

cause of the cracks that are present due to the limited dimensions of the test piece. Abetter insight is obtained by impregnating entire cores.


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A sufficient number of cores must be drilled from each area designated for the test. The

diameter of the drilling cores must be around 75 mm. The number of cores must be:

at least 3 to determine the uniaxial tensile strength according to 7.5, their length

must at least be equal to twice the diameter of the core;

at least 3 to determine the compression strength according to 7.6, their length must

at least be equal to the diameter.

The cores for the uniaxial tensile strength and compression strength test should

preferably be taken from one and the same location to prevent weakening as much as

possible, for example, by drilling a core with a length of at least 250 mm and then

cutting it into sections.

If cores were already drilled before in the cross-section in question as part of a technical

study in accordance with 5.3, the compression strength and uniaxial tensile strength of

these were determined and if these results are available, the number of cores may be

reduced in accordance with the number of tests performed before.

5.4.3 Establishing the reinforcement configuration

It must be ascertained whether the configuration of the (outside) reinforcement matches

the reinforcement pattern stated on the drawing. In at least two locations per structural

component the diameter of the reinforcement present and the type of reinforcement

must be determined by means of destructive testing. If the reinforcement configuration

differs this must be discussed with a structural engineer.

If drawings are unavailable the scale of the study into the reinforcement configuration

must be such that an image is created of the main reinforcement present in the structural

component to be assessed that is sufficiently reliable to allow a verification calculation

to be performed on the basis of it.

5.5 Structural study

5.5.1 General information

Regardless of the type of structural study (IVA, IVB or IVC) at least the followingaspects must be considered:

cracks as a result of ASR;

deformation of the structure by ASR;

the compressive and tensile strength present with special attention for uniaxial

tensile strength;

the variation in the uniaxial tensile strength and possibly other mechanical properties

for each cross-section observed and between the various individual cross-sections

observed.

Explanation

To be able to determine the diameter the surrounding reinforcement will have to be

cleared away sufficiently. The type of reinforcement can be derived from the profileof the rebar. In consultation, the number of locations where destructive testing is to

be performed may be limited. The purpose of establishing the reinforcement

configuration is to obtain an impression of whether the structure was built in

accordance with the drawings. If this is not the case, a structurally unsafe situation

may also be present even without ASR. It is therefore advisable to assess the

consequences of a differing reinforcement configuration first.


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A structural class IVA study at least includes:

A verification calculation of the transverse force on the agreed cross-sections,

performed either manually or with basic computer software. Here the design

calculation with regard to the distribution of forces in the structure may be used if it

is available and usable.

A structural class IVB study at least includes:

A numerical calculation of the shear stress present in the agreed cross-sections. In

this case the modelling of the structure must be performed using shell elements.

A structural class IVC study at least includes:

An assessment of the transverse force stated under IVA and IVB.

A test of the entire structure, taking into account the material properties that were

derived from the test results in accordance with chapter 8.

A study according to classes IVA, IVB or IVC does not require a test of the bending

moment capacity.

For the assessment method, please refer to chapter 8.

6 Sample-taking

6.1 General information

When removing drilling cores the drilling through structural reinforcement present must

be prevented as much as possible. To achieve this at least the outside reinforcement

must be located in advance using a concrete cover meter.

Prestressed reinforcement must not be drilled through.

The load-bearing capacity of the structure must not be affected substantially by the

sample-taking. If this is a possibility, the number of drilling cores to be removed mustbe agreed in advance.

For each core the following must be recorded:

The location of the core by indicating the position of the centre of the drilling core on a

drawing or relative to recognisable parts of the structure with an accuracy of 0.1 m.

Visually recognisable aspects of the removed core that may be a sign of ASR and

that provide information about the condition of the concrete, for example, the

presence of reaction edges around coarse aggregate, stained drying, the presence of

gel, cracks, a layered structure, honeycombing, construction joints, etc.

Visually recognisable aspects of the concrete surrounding the core, for example,

extensive cracking, weathering, moist patches, etc.

Whether anything unusual has occurred while drilling, for example, breakage whiledrilling.

Explanation

Practical tests on severely damaged structural parts and theoretical studies have

shown that the failure moment does not differ from that of a structural part not

affected by ASR. The tension in the reinforcement must be allowed to build up

gradually. The ends of the bars must be located in the zero points of the moments or

the reinforcement must include hooks or bends that can transfer the force in the

reinforcement to the concrete. The practical tests were performed on beams cut from

sheets with severe horizontal cracks, whereby the uniaxial tensile strength in a

direction perpendicular to the sheet plane had dropped to 1/7 of the expected value

for the tensile strength based on a splitting test.


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6.2 Marking and drilling

The location and orientation of the core in the structural component to be tested must be

indicated clearly on both the core and in a drawing or sketch of the structure in question.

The following must be indicated on the core with a permanent marker:

An orientation cross on the top face, whereby the axes match the span direction of

the component and the transverse direction of the component, respectively. Both

directions must be recognisable by different colours or a pattern of lines.

Which side of the core was in the original structural surface.

An unambiguous number of the core.

The drilling core must be drilled and removed with care. The occurrence of undesirable

effects such as cracks, which may adversely affect both the observations during the

PFM test and the values measured during the mechanical study, must be prevented.

6.3 Treatment of drilled cores

After removing and assessing the core it must be handled and stored as follows:

Clean the core immediately after removing it using a minimum amount of water to

remove any attached material.

A unique sample number must be applied additionally or again.

Wrap the core in an uncoloured, hand-wrung cloth and wrap it in self-adhesive film

to prevent drying-out and damage during transport.

Place each of the cores in one piece with a diameter-length ratio of 1:2 or more

slender and cores that already consist of various fragments in a tightly fitting,

durable plastic tube for transport.

Short, compact whole cores may be transported after wrapping them in cloth and

film.

The number of the drilling core must be printed on the wrapping. The cores must be placed in the means of transport or in additional packaging in

such a way that they cannot be damaged during the journey to the laboratory.

6.4 Repairing drilled holes

Unless agreed differently, drilled holes must be sealed using a cement-based low-

shrinkage mortar in accordance with CUR Recommendation 54, application class RC2,

environmental class 3.

Holes in asphalt must be sealed with liquid asphalt.

Ancillary materials, such as formwork, must be stripped from the mortar after

hardening. Drilled holes, etc. must be sealed.

7 Measuring and assessment methods

7.1 Crack pattern, crazing

Crazing must be recorded by marking the cracks on a measuring square, preferably with

edges of 1 metre in length. The orientation of the measuring square should preferably

match the orientation of the pattern of cracks.

7.2 Cumulative crack width

The relative cumulative crack width ASRmust be determined as follows:

draw two orthogonal lines within the measuring square;

measure the crack width wiof all the cracks n that cross the line in question. The

crack width must be measured perpendicularly to the crack;

measure the angle ibetween crack iand the edge in question;

Explanation

It is recommended to attach the drilling installation to the structure in a fixed

position and prevent wobbling of the core drill.


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adjust the crack width wito the direction of the measuring edge according to wi/cos

I (Figure 2);

for each measuring line add the corrected crack widths and divide them by length l

of the relevant measuring line, as a result of which the relative cumulative crack

width ASRis obtained:

l

wn

i i

i

ASR

=

=1cos

in which:

ASR is the relative cumulative crack width in mm/m;

l is the length of the measuring line when determining ASR, in m;wi is the crack width of crack iin mm;

i is the angle between measuring line and crack iwhen determining ASR.

Figure 2 Principle of measuring Figure 3 Detail of measuring the crack

the relative cumulative width and angular correction

crack width ASR

Instead of the previous procedure, it will also be sufficient to estimate the value of ASR

for the exploratory inspection. This can be done simply by counting the number of

cracks n that cross a measuring line with length l. Following this the average crack

width waveragecan be estimated or roughly measured. Then the relative cumulative crack

width ASRcan be calculated as follows:

l

wn averageASR

=

in which:

ASR is the relative cumulative crack width in mm/m

l is the length of the measuring line when determining ASR, in mn is the number of cracks

waverageis the average crack width in mm

The cumulative crack width that is determined must be classified in a class on the basisof table 2.


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Table 2 Classification based on relative cumulative crack width

Relative cumulative crack width Class

0 mm/m

< 0.6 mm/m

0.6 mm/m to 1.0 mm/m



2.5 mm/m

none

very little

little

limited

significant

very significant

7.3 Assessment of data and structure

7.3.1 Assessment of data

The assessment of the available data must at least consist of the following, see table 3:

Determining the high-risk components with regard to ASR based on the

reinforcement configuration.

Determining high-risk components with regard to safety and the functioning of the

concrete structure.

A classification of the risk of ASR for a structure (structural risk).

Aspects that must at least be weighed when determining high-risk components with

regard to safety and functioning are:

The feeling or perception of safety.

The risk of significant consequential damage and/or loss of function as a result of

continued expansion, for example, the jamming of moving parts.

The (economic) damage, both direct and indirect, as well as the amount of human,

emotional and/or social suffering if the structure fails entirely or partially.

Table 3 Structural risk derived from reinforcement configuration and the conse-

quences for safety and functioning

Consequences for safety andfunctioning

Reinforcementconfiguration

Notes on reinforcement configuration

Major Minor

High-quality 3D

reinforcement, see Figure

4, for example

The concrete is enclosed on all sides. ASR expansion is

slightly tensioning the reinforcement. This limits the

consequences.

Watch out for detachment of the prestress and

delamination in the plane of the prestress.

Structural risk

= medium

Structural risk

= low

3D reinforcement with

moderate anchoring

Watch out for detachment of lap joints due to the ASR

expansion.

Structural risk

= medium

Structural risk

= low

2D reinforcement with goodor moderate anchoring or

no reinforcement, Figure 5.

ASR expansion concentrated in 1 direction. In thisdirection the tensile strength drops. Layers may form in

the concrete. The ASR may cause transverse force or

shearing problems.

Structural risk

= high

Structural risk

= medium

Figure 4 Cross-section of beam, column Figure 5 Cross-section of plate, wall


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7.3.2 Assessment of structure

When assessing the structure watch out for signs that may indicate ASR. Special

attention must be paid here to aspects such as:

(Restrained) deformation of components.

Indications of possible failure.

When indications of possible failure are found for critical components of the structure,

measures must be taken immediately.

7.4 Polarisation and fluorescence microscopy (PFM)

7.4.1 Procedure

For each PFM study the drilling core with a length of at least 100 mm must be

impregnated as a whole in vacuum with a UV-fluorescent epoxy resin prepared in

accordance with Appendix A.After the epoxy resin has fully hardened the impregnated core must be cut lengthwise in

two pieces and both halves must be petrographically tested for cracks and other relevant

signs (of damage) as stated in 7.4.2.

An impregnated thin section must be prepared from at least one of the two halves

according to the method described in Appendix B. The thickness of the thin section

must be (20 1) m and the surface area must be at least 30 mm x 45 mm.

7.4.2 Aspects to be established

The combined data of the assessment of the impregnated core and the thin section must

at least establish the following:

whether any cracks are present or not, assessed for various scale sizes, as well as the

excessive presence of these; whether any potentially reactive components with regard to ASR are present and

whether these components actually show signs of a reaction;

the bonding of the cement matrix to the aggregate;

the number of aggregate grains affected in the overall concrete (level of ASR);

a qualitative impression of the amount of gel that is present;

the lithological composition of the entire aggregate, regardless of any ASR-sensitive

behaviour assumed or observed;

the possible type of cement, an indication of the water-cement ratio and the level of

hydration;

whether, on the basis of observation, ASR could be the primary cause of any cracks

observed and whether the ASR observed is more than would be expected for a

material without a reactive aggregate.

Explanation

Due to the reinforcement configuration or an irregular moisture load ASR expansion

may occur irregularly in the concrete. As a result of this deformations may occur,

resulting in tensions that were not taken into account during the design, for example,

as a result of eccentricity in columns.

Deformation by ASR can be prevented by the surroundings of the components

affected by ASR. As a result of this tensions may occur in the affected component

and the neighbouring component. These tensions were often not taken into account

during the design and in some cases they may result in damage to one component or

both components.

Indications of possible failure are large cracks and deformation. Other indicationsare: detachment of lap joints, buckling of components or, if cracks are present,

mutual shifting of the crack planes.

For the observations mentioned above no generally decisive criterion can be

defined. Which measures are to be taken depends on the specific structure.


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7.4.3 Microscope requirements

The assessment of the thin sections must be performed using a stereo microscope with a

magnification factor of around 50 to 80. To assess a thin section the petrographic

polarisation microscope must have a blue-light fluorescence system.

7.5 Uniaxial tensile strength

7.5.1 Determination of the uniaxial tensile strength

The uniaxial tensile strength must be determined for cylinders with a diameter of 75

mm and a length of 150 mm. Both ends of the cylinder must be flattened in a plane-parallel fashion, perpendicularly to the axis of the core. The required smoothness is 0.1

mm per 100 mm.

Steel tie plates with a diameter equal to the diameter of the core must be attached to the

ends by glueing them on.

The test pieces must be conditioned at 20C and 98% R.H. for at least 2 periods of 24

hours.

After sufficient hardening the test pieces must be pulled from the glue in a tensile

testing machine tester. Their capacity must not be more than 5x the expected tensile

strength. It must be possible to read the load with an accuracy of 1%. The load must be

increased gradually at a rate of (0.05 0.01) N/mm2per second.

The tensile strength must be calculated with an accuracy of 0.1 N/mm2using:

AF

ctf =

in which:

fct is the tensile strength in N/mm2

F is the force at failure in N

A is the surface area of the core in mm2

If failure occurs directly underneath the pulling head the measurement will be invalid.

7.5.2 Verification of uniaxial tensile strength measured

It must be determined whether the uniaxial tensile strength measured is much lower

than the strength assumed during design. This will be the case if the following applies:

bm,ref< 0,7 (1,00 + 0,05 c,design)

in which:

fbm,ref is the average uniaxial tensile strength based on test pieces in accordance

with 7.5.1, in N/mm2;

cc,design is the average cube compressive strength used during design, in N/mm2;

0.7 is the conversion factor to convert the splitting tensile strength into uniaxial

tensile strength.

Explanation

For the best possible results the following characteristics are recommended for the

fluorescence filters:

A so-called band-pass excitation filter for blue light with a wavelength range

of 450 to 490 nm.

An emission filter for green light for a wavelength of 515 nm or more.

A frequency splitter (beam splitter) that is centred around a wavelength of 510

nm.


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7.6 Compression strength

The compression strength of cylinders (diameter equal to height) must be determined in

accordance with CUR Recommendation 74. The lowest value measured, using at least 6

cylinders, is the value for the characteristic compression strength present.

8 Structural analysis

8.1 Analysis principles

a. Regardless of the type of structural study (IVA, IVB or IVC) it must be established

whether one of the following may be the case due to the deformation of the

structure:

changes to the distribution of internal forces;

changes to the eccentricity of normal forces;

additional external loads to the structure due to kinematical restraint of swelling

deformation, for example, a bridge deck that rubs against abutment.

If the deflections in the structure are smaller than the allowable deflection according

to NEN 6702 or if the eccentricities are smaller than 30% of the eccentricity to be

taken into account according to 7.3.4 of NEN 6720 the changes mentioned above

will not require further structural consideration.

b. The structural analysis must be based on NEN 6702, NEN 6720 or NEN-EN 206-1

with the accompanying NEN 8005 and, for bridges and similar structures, NEN

6723.

c. Contrary to the standards and regulations mentioned above, the material strengths

derived from the test results using the method described in this chapter must be

used.

8.2 Deflection verification

For a structural analysis of the structure in accordance with this Recommendation no

verification of bending is required, see the explanation of 5.5.2.

8.3 Verification of shear forces

8.3.1 Principles

a. The verification of shear forces and the calculation of the calculation value of the

resulting shear stress must be performed in accordance with 8.2.1 and 8.2.2 of NEN

6720:1995, respectively.

b. To calculate the design value of shear stress the calculation methods in 8.3.2 must be

used. If c has been met the calculation methods in 8.3.3 may also be used, whereby

the more favourable result may be used.

c. The calculation methods in 8.3.3 may only be used if the conditions stated in it are

met.

d. For the design value of shear stress 1no value greater than the upper limit accor-

ding to 8.3.4 may be taken into account, regardless of the value calculated in 8.3.2 or

8.3.3.

Explanation:

For the calculations in this Recommendation it was assumed that ASR causes a

significant reduction in the uniaxial tensile strength perpendicular to the plane of the

element, which was also established in the experiments on which the calculation

methods are based (see explanation 5.5.2).

It may happen that the uniaxial tensile strength is relatively low, both in the plane of

the element and perpendicular to it, even without ASR. In that case the calculation

methods included in 8.3.3 may not be used.

If a low uniaxial tensile strength is measured compared to the original compressive

strength, it is strongly recommended to complete the flow chart in figure 1 to

determine the structural safety or to determine which control measures to take.


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If these conditions are met the calculation value for the design value of shear stress 1

may also be calculated from:

mmld /6,0 ,11 =

in which:

0.6 is a coefficient used for determining the characteristic lower limit of thedesign value of shear stress from the average ultimate design value of shear

stress 1,m;ld is a factor for calculating the long-term tensile strength of the concrete (=

0.9);

1,m is the average ultimate design value of shear stress, in N/mm2;

m is the material factor (= 1.5).

The effect of any transverse force reinforcement that may be present must not be taken

into account. If the calculated value is more favourable than the value calculated

according to 8.3.2, the calculated value may be used, taking into account the maximum

value stated in 8.3.4.

The average ultimate value of shear stress 1,mmust be calculated with the formula:

)'.( 90,,0,,1 bmdctrefctdSI

m ff +=

in which:

I is the second moment of area of the cross-section that is assumed to be

uncracked, in mm4

d is the effective depth, in mm

S is the largest value for the first moment of area of the cross-section, in mm3

bmd is the average concrete compressive stress in the cross-section due to thenormal force generated by the prestress load and the other loads on the

structure (+bmdfor pressure; -bmdfor tension), in N/mm2;

ct,0,ref = bm,ref: the average uniaxial tensile strength of n test pieces. The tensile

strength must be determined in a direction perpendicular to the axis of the

structural component, in N/mm2;

)'05,01( ,,0,90, measuredccrefctct fff += , in N/mm2

in which:

cc, measuredis the measured average cube compressive strength, in N/mm2.

8.3.4 Upper limit of the design value of shear stress

The maximum value to be used for 1is

1 030 4= , f k kb h (1not smaller than 0.4 fb)

Explanation

The material factor m of 1.5 is a rather safe value due to model uncertainties (as the

formulas are based on a limited number of experiments). In the formula forfct,spl it is

tacitly assumed that the value of 1 is a fixed value. This is not actually the case. The

value is subject to scatter and the formula too is an approximation of reality, based

on the best line that can be fit through a large number of test results.


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For an explanation of k, khand 0and the values to be used for these, please refer to

8.2.3.1 of NEN 6720. The value for fb must be calculated from the characteristic

concrete compression strength as stated in 6.1.2 of NEN 6720. However, a value of 0.9

can be used for the long-term strength.

8.3.5 Special load combinations

For special load combinations the factor for the long-term effect (ld= 1.0) is no longer

used and mcan be reduced to

- m= 1.1 for a calculation according to 8.3.2;

- m= 1.25 for a calculation according to 8.3.3;

- m= 1.0 for the calculation of the upper limit according to 8.3.4.

8.4 Punch and torsion

The values calculated for the design value of shear stress may not be used for the

verification of punch and torsion.

9 Reporting

9.1 Class A

A written report according to class A should at least include:

the definition of the problem;

a description of the structure in question;

a description of the study performed and the measurements, including the test

method;

an indication of the measuring locations;

the results of the visual inspection; a description of the cracks found and the classification of the cumulative crack width

(crazed pattern, etc.);

the results of any measurements performed and laboratory testing;

the results of the calculations performed.

9.2 Class B

A written report according to class B should include the points stated in 9.1, with the

addition of:

a discussion of the results;

the consequences of the findings and results for the component assessed or the

structure;

any measures or actions to be taken immediately.

And more specifically for the various studies:

Technical study: a statement whether ASR is present;

the classification of the relative cumulative crack width ASR;

a statement whether a relatively low uniaxial tensile strength

determined in accordance with 7.5.2 is present.

Targeted study: a statement whether the results show that a further structural

study is required.

Structural study: a statement whether the structure can still be considered safe.

9.3 Class C

A report according to class C should at least include the points stated in 9.2, with the

addition of possible control measures, see 9.4.

Explanation

The effects of structurally deleterious ASR on punch and torsion are still not

sufficiently known.


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9.4 Control strategy and control measures

9.4.1 Data required for control measures

The client must indicate what the control strategy is for the structure in question. At

least the following must be recorded here:

the planned period in which the client wishes to continue using the structure;

the minimally required state of repair of the structure, for example, whether damage

to preservations on concrete is allowed or not, or the presence of concrete damage; the loads and/or traffic class the structure must be able to absorb.

For the specification of a control plan at least the following data must be available and

must have been verified:

the control strategy;

the exposure conditions of the various structural components;

the current damage.

9.4.2 Specification of control measures

Which control measures are to be taken depends on many factors and they may

therefore differ for each structure. As an indication, Table 4 provides an overview of

possible control measures depending on the risk classification according to Table 3, the

presence of a relatively low uniaxial tensile strength and the level at which cracks are

present.

Explanation of table 4

V Sealing against moisture; targeted drying of the concrete

More damage is usually observed in locations where moisture transport is high

compared to locations where a structure is fully submerged. Where possible,

one measure may therefore be aimed at limiting moisture transport through

(ASR) cracks. Puddles must be prevented from remaining directly on the

concrete.

Targeted drying of the concrete can be achieved by draining moisture correctly,keeping moisture out of wet faces and allowing drying on dry faces. It is

pointless to wrap up a structure completely, as any moisture present will not

be able to get out. Here a role is played by the fact that structures with their

base in the water easily absorb moisture through the cracked concrete. In this

case wrapping-up the concrete will increase the wetness of the structure.

M Monitoring

Cracks can be monitored in a number of ways:

The easiest way is to monitor the development of cracks in the structure. In

some cases it will be sufficient to visit the structure periodically.

Periodically marking the cracks in the same location (see also 7.1) and

copying these cracks to a sheet of Perspex, whereby crack widths are

measured and stated. It is advisable to use the same person for this each

time, as the width of a crack changes starting at the surface and the edges of

cracks are not always clear-cut. This means that different people may

interpret things differently.

Monitoring the cumulative crack width as described in 7.2.

Several measuring techniques (wire recorders) are available for monitoring

expansion in concrete. In this case it must be taken into account that expansion

is always related to temperature and, to a limited degree, moisture.

Moisture can be measured in various ways. Moisture can be measured

indirectly based on the relative humidity of the concrete. The electric

alternating-current resistance and the electric impedance of the concrete arealso moisture indicators.


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Table 4 Selection table for control measures. The table only provides an initial

indication for possible measures; these require further consideration for

each situation

Necessary measure(s) Optional measuresRisk classification

of the structure

Relatively low

tensile strength

indication *)

Level of crack

formation

(indicative) V M VF C V M VF C

Low Yes < 1 mm/m 1 2 4

Yes > 1 mm/m 2 4 5 4 1 1 1

No < 1 mm/m 2 3

No > 1 mm/m 1 4 3 4 1 1

Medium Yes < 1 mm/m 2 6 2 4 1 2

Yes > 1 mm/m 6 6 2 4 2 1

No < 1 mm/m 2 4 1 2 2 1 2

No > 1 mm/m 5 4 2 4 1 2 1

High Yes < 1 mm/m 5 4 4 2

Yes > 1 mm/m 6 4 5 4 2

No < 1 mm/m 6 5 2 2 2

No > 1 mm/m 6 6 3 4 1 2*) obtained from 7.5.2, as the number of options may be limited based on the results if a structural

study has already been performed.

Table 4 indicates the importance of the measures using the numbers 1 to 6. The number 6 indicates

that the measures are highly recommended, the number 1 indicates that the measures are

considered to be the least urgent. If a cell is empty this means that the measure will not be useful.

The ratio of the numbers for necessary and optional measures provides an indication as to whether

it is better to choose the necessary or optional measure.

These moisture measurements are often related to temperature. It is therefore

recommended to determine both parameters at the same time. By measuring the

moisture content periodically it can be established whether the structure is

drying up.

VF Measures for guaranteeing safety and functioning

When considering measures for guaranteeing safety and functioning, they must

always be tuned to the specific situation. The Recommendation provides a

number of guides for this in Table 4. However, these are not exhaustive.

Examples of measures to guarantee safety / functioning are limiting the load or

applying a local reinforcement or support. If structural damage is about to

occur due to jamming of a structure, room for expansion may be created.

C Limiting the risk of reinforcement corrosion

If a structure damaged by ASR is cracked, reinforcement corrosion may occur

by penetration of chlorides and carbonation in these cracks. Depending on the

local situation, measures may be taken to seal the concrete from chlorides. One

option is to inject cracks. This will be required especially if a changeable wet-

dry situation is present with enough moisture.


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Titles of standards and CUR Recommendations stated

NEN 6702:2001 Technical principles for engineering structures. TGB

1990. Loads and deformations.

NEN 6720:1995 Concrete regulations. Structural requirements and cal-

culation methods (VBC 1995), incl. amendment A3:2004.

NEN 6723:1995 Concrete regulations. Bridges. Structural requirements

and calculation methods (VBB 1995), incl. amendment

A1:2003

NEN 8005:2004 Dutch specification of NEN-EN 206-1. Concrete, part 1.

Specification, performance, production and conformity.

NEN-EN 206-1:2001 Concrete; part 1. Specification, performance, production

and conformity.

CUR Recommendation 54 Concrete repair using manually applied or poured cement-based mortar.

CUR Recommendation 72 Inspection and testing of concrete structures.

CUR Recommendation 74 Studying of concrete structures Studying of compres-

sion strength.

CUR Recommendation 89 Measures to prevent damage to concrete by alkali-silica

reaction ASR.

Dutch standards are publications by Stichting Nederlands Normalisatie-instituut,

Vlinderweg 6, Postbus 5059, 2600 GB Delft. Orders can be placed at NEN, sales and

information hotline, tel. +31 (0)15 2690391.


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Appendix A Preparation of fluorescent epoxy

A1 Introduction

This appendix describes the preparation of fluorescent epoxy for the impregnation of

sample material.

A2 Composition

For the preparation of fluorescent epoxy the following substances and materials arerequired:

a fluorescent dye, namely finely ground powder of Hudson Yellow, for example,

EpoDye produced by Struers or equivalent;

epoxy resin, for example, BY 158 by Ciba Geigy, or equivalent;

epoxy hardener, for example, HY 2996 by Ciba Geigy, or equivalent;

materials required: fume cupboard, plastic beaker, wooden spatula, bucket/tray of

cold water, magnetic stirrer, balances with a variety of weighing ranges.

A3 Safety

If the instructions and safety regulations of the manufacturer are not strictly observed

the handling of epoxy resin may be harmful to a persons health. Epoxy resin must

therefore only be handled in a fume cupboard.

A4 Procedures

A4.1 Adding dye to the resin

Carefully add one weight percent of dye to a weighed quantity of epoxy resin in asealable container; also add a stirring magnet. Be careful with the dye, as it may even

contaminate the laboratory if a slight draught is present.

Seal the container and firmly mix the contents by hand. Place the glass on a magnetic

stirrer and leave it to stir for at least two days. Firmly shake the glass again by hand at

least once every 24 hours. Remove the stirring magnet with a steel pin after stirring and

clean it thoroughly.

The hardener and the coloured resin must be stored in the dark in a ventilated location

or in a fume cupboard.

A4.2 Mixing the two componentsThe coloured resin must be mixed with the hardener according to the instructions of the

manufacturer. Table A1 provides the current mixing ratio for products by Ciba Geigy.

Place a plastic beaker on a balance and add the required amount of coloured resin to it

first, then add the correct amount of hardener.

Explanation

Hudson Yellow is also known as Brilliant Yellow and by the trade name Epodye; it

is a fluorescent dye that lights up as light yellowish green under filtered blue lightwith a wavelength of around 476 nm when viewed through an LWP 515 emission

filter.

Explanation

The final amount of coloured resin in the glass may contain a few lumps of undis-

solved fluorescent dye. To prevent false-positive fluorescence this contaminated

amount of resin must not be used for the impregnation of slices.


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Table A1 Mixing ratio by weight (g) for Ciba Geigy products

Coloured resin

BY 158

Hardener

HY 2996

Coloured resin + hardener

40

80

120

200

12

24

36

60

52

104

156

260

Start stirring the mixture immediately with a wooden spatula; stir in a circular motion

and in figures of eight in both a horizontal and vertical direction. Regularly scrape the

sides and bottom of the beaker. Stir vigorously for two whole minutes.

In addition to other problems, incomplete mixing may result in insufficient hardening.

The mixed epoxy must be used for impregnation within 30 minutes of mixing.

The hardening of the epoxy generates heat. Keep any epoxy that has not (yet) been used

in plastic beakers that are placed in cold water to prevent the epoxy from boiling. Make

sure that no water is added to the epoxy. After hardening (the next day) the excess

epoxy can be removed as regular waste.


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Appendix B Preparation of thin sections

B1 Introduction

These instructions describe the procedure for the preparation of thin sections for the

PFM test.

B2 Materials required

The following materials are required for the preparation of thin sections: diamond cutter with water cooling and a fully straight cutting blade that does not

vibrate;

suitable diamond cutting (and lapping) equipment with water cooling;

support slide matted on one side to be used as a reference for plane-parallel

treatment when impregnating and also as external glued-on reinforcement for

fragile samples;

sample slide with one matted side;

covering slide;

UV-hardening glue;

UV lamp;

polarisation microscope; micrometer (optional);

soft brush, or better yet, a clean ultrasonic cleaning bath to clear the sample of

cutting and grinding sludge;

soft brush, or better yet, an electrostatic brush to clean the slide and the samples

before glueing;

acetone and/or alcohol;

soft paper, for example, cleaning paper for optical lenses;

siphon or spray bottle of alcohol (60% V/V).

B3 Procedures

B3.1 General informationThe slices are prepared as follows:

select a location for a slice in the drilling core that was cut in half;

cut a piece of at least 30 x 40 x 10 mm3from the selected section of the impregnated

sample;

never reduce the amount of surface cut off; this will affect the representative

character of the sample;

glue the section that was cut off to the support slide using a thin and even layer of

Loctite 330 or a similar alternative;

cut off the sample parallel to the support slide so that a thickness of 2 to 5 mm is

obtained;

grind the surface parallel to the support slide with a fine-grained diamond so that a

smooth and even surface is formed;

glue a sample slide to the final surface;

cut off any excess material;

grind the surface further with increasingly fine diamond to a thickness of (20 1)

m;

print the sample number on the finished slice.

A number of procedures are described in more detail below.

B3.2 Sample number

It is of essential importance that the unique sample number remains linked to the

samples at all times. This is why samples must be placed and processed in a logical


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order. Any residue that is cut off must be kept with the sample during all practical

procedures. Reattach the sample code to the treated sample as quickly as possible.

B3.3 Cutting with a diamond wheel

The following applies to cutting with a diamond wheel:

1. Use the thinnest possible diamond wheel.

2. Cut with the diamond wheel using an even pressure that is as low as possible and

always use water cooling (for some special applications, for example, for water-soluble substances, cooling with alcohol is recommended). A sharp diamond cutter

will cut through the material almost without pressure.

3. If the cutting is too slow the diamond wheel may be worn-out or it may require

sharpening or needs to be replaced.. It may be that the wrong type of diamond wheel

is mounted to the cutter.

4. Diamond wheels require inspection and maintenance, and they must be replaced

where required:

Where required, sharpen the wheel by cutting a soft material, for example, a

brick.

Use a magnifying glass to check whether the outer layer is still covered in

diamond grains.

Replace the diamond wheel if it is worn-out or if any wobbling, vibration or

shocking occurs, as this may damage the sample.

B3.4 Grinding

The grinding procedure largely depends on the equipment used. For good results the

following general points must be taken into account:

Grinding is to be performed with a gradually decreasing grain size.

Grinding with a particular grain size will not be finished until all the scratches from

the previous, coarser treatment (grinding or cutting) are removed.

Prevent grains or particles from breaking free from the surface, especially along the

edges of the sample, by making sure that the sample is fully impregnated.

After each grinding round, check the surface under an angled beam of light(floodlight) for completely even grinding results, in other words, a flat surface

without ridges.

Clear the surface of grinding waste after every treatment and then moisturise the

surface with alcohol by spraying, then dry it off with soft paper in a single swipe.

The preparation may never dry up during the entire treatment. Water may leave

circles of microscopically small crystals, may contribute to artificial carbonation of

the cement paste and has a negative effect on the UV-hardening glue.

The final surface quality must be sufficient for an unambiguous identification of

components and microstructural characteristics.

B3.5 Glueing-on the sample slide and the covering slide

It has been shown that the procedure below results in good and even glueing: Apply a diagonal cross of glue to the impregnated and finished sample surface (to

prevent air bubbles from becoming trapped).

Place the slide at the centre of the sample.

Only for the sample slide:

leave the layer of glue to even out by itself for 5 minutes and recentre the slide;

hold the sample and the slide together for 10 minutes using a force that is evenly

distributed over the surface;

expose the sample to UV light for 20 minutes.


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Only for the covering slide:

leave the glue to even out by itself for 5 minutes;

remove any excess glue from the edges of the covering slide with a pipe cleaner,

recentre the slide;

place the sample under UV light for around 1 minute;

carefully remove any excess glue with a Stanley knife and acetone or alcohol;

place the sample under UV light for around 10 minutes;

clean all surfaces with acetone or alcohol.

B3.6 Checking the thickness

The thickness of the thin section is checked with the polarisation microscope. The

correct thickness of around 20 m is determined based on the white or light-grey

birefringent colour of quartz For some automatic grinding equipment the thickness can

also be measured with a micrometer, whereby the thickness of the UV-hardening glue

must be taken into account.

B4 Storing impregnated fluorescent thin sections

The fluorescent power of the thin sections is reduced noticeably if they are exposed to

strong light for a prolonged period of time. This is why thin sections must be stored in

the dark.


31/31


It should be pointed out that this CUR Recommendation reflects the state of the art at

the moment of publication. Any suggestions for experiences with the use of this

Recommendation will be gratefully received by CURNET. CUR Recommendations are

evaluated three years after publication and are updated if necessary. This will be

reported in the press.

Copyright

All rights reserved. No part of this publication may be reproduced, stored in a retrievalsystem, or transmitted, in any form or by any means, electronic, mechanical, photocopy-

ing, recording and/or otherwise, without the prior written permission of CURNET.

It is allowed, in accordance with article 15a Netherlands Copyright Act 1912, to quote

data from this publication in order to use this in articles, essays and books, provided that

the source of the quotation, and, insofar as this has been published, the name of the

author, are clearly mentioned. CUR-Recommendation 102 Inspection and

assessment of concrete structures in which the presence of ASR is suspected or has been

established, April 2008, Gouda, The Netherlands.

Liability

CURNET and all contributors to this publication have taken every possible care in the

preparation of this publication. However, it cannot be guaranteed that this publication is

complete and/or free of errors. The use of this publication and data from this publication

is entirely at the users own risk and CURNET hereby excludes any and all liability for

any and all damage which may result from the use of this publication or data from this

publication, except insofar as this damage is a result of intentional error or gross

negligence of CURNET and/or the contributors.

Gouda, April 2008The Board of CURNET

Stichting CURNET, Groningenweg 10, P.O. Box 420, 2800 AG GOUDA,

The Netherlands

tel. +31 (0)182540600

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