RILEM Recommended Test Method: AAR-0—Outline Guide to the Use of RILEM Methods in the Assessment of the Alkali-Reactivity Potential of Aggregates

Abstract

AAR-0 provides guidance on the integrated use of the assessment procedures described in AAR-1.1 & 1.2, AAR-2, AAR-3, AAR-4.1 and AAR-5 including preliminary advice on the interpretation of their findings. The principles are illustrated by the flow chart given in Fig. 1. Guidance on the specialised assessment of carbonate rock aggregates for alkali-reactivity potential is given in Annex A

Appendices

Annex A: Assessment of Carbonate Rock Aggregates for Reactivity Potential

1.1 A1 Scope

This Annex describes procedures for the assessment of potentially reactive carbonate rocks in concrete. The procedures include those in AAR-1.1 & 1.2, which does not include specific guidance on the assessment of carbonate rocks for reactivity in concrete. As a result of undergoing the procedures described in this Annex, carbonate rocks should be classified according to one of the following classes:

• Very unlikely to be alkali-reactive—Class I

• Alkali-reactivity uncertain—Class II

• Very likely to be alkali-reactive—Class III

It is very important that the petrographic analysis is carried out by a qualified geologist with experience of materials used for concrete and good local knowledge of alkali-reactive aggregates, minerals and in this case especially carbonate rocks.

1.2 A2 Definitions

1.2.1 A2.1 Alkali Carbonate Reaction (ACR)

Chemical-physical expansive reaction in concrete between certain impure coarse grain-sized dolomitic carbonate rocks and the cement paste. The reaction appears to be associated with dedolomitization and an associated swelling reaction, but is not yet fully understood and documented.

Note 1: The reaction might occur concurrent with Alkali-Silica Reaction (ASR) caused by the same aggregate particle. Some researchers suggest that ASR is the only expansive reaction in reacted carbonate aggregates.

1.2.2 A2.2 Carbonate Rock

A rock composed of more than 50 % by mass of carbonate minerals such as calcite or dolomite. They are sedimentary or metamorphic, and very rarely igneous (carbonatites) in origin.

1.2.3 A2.3 Carbonate Sedimentary Rocks

Calcareous rock is a rock containing an appreciable amount of calcium carbonate. It can be sedimentary limestone (e.g. chalk, tufa or calcarenite). Dolomitic limestone contains 10–50 % dolomite and 50–90 % calcite. Dolomite rock (dolomite) contains more than 50 % of the mineral dolomite. Dolomite occurs in crystalline and microcrystalline forms. The term “dolostone” is synonymous with dolomite rock, but has not gained universal acceptance.

Carbonate rock deposits can often contain intermixed layers of clay, shale, sandstone or siltstone. Silicification of carbonate rock deposits with dispersed crypto- and micro-crystalline quartz or opal is not uncommon.

1.2.4 A2.4 Metamorphic Carbonate Rocks

Metamorphic carbonate rock is termed marble. Dolomitic marble is composed mostly of the mineral dolomite.

1.2.5 A2.5 Dedolomitization

A process resulting from chemical weathering, diagenesis or metamorphism, wherein part or all of the magnesium component in a dolomite or dolomitic limestone is consumed in the formation of magnesium hydroxides and silicates (e.g. brucite, forsterite), resulting in an enrichment in the calcite content.

1.2.6 A2.6 Chemical Reaction of Dolomite in Concrete

Dolomite can be unstable in concrete under certain conditions. The instability and decomposition of dolomite in concretes produce more stable phases, such as calcite and brucite. It could be the result of the following reaction:

$$ \begin{aligned} &{\text{CaMg}}\left( {{\text{CO}}_{ 3} } \right)_{ 2}{\,}+ {\text{ 2M}}\left( {\text{OH}} \right) \, = {\text{ CaCO}}_{ 3} + {\text{ Mg}}\left( {\text{OH}} \right)_{ 2}{\,}+ {\text{ M}}_{ 2} {\text{CO}}_{ 3} \hfill \\ &\quad dolomite \qquad \qquad \qquad \qquad \quad calcite\quad \quad brucite \hfill \\ \end{aligned} $$

where M is an alkali metal.

It remains uncertain whether or not this dedolomitization process alone can sometimes cause damage to concrete.

1.3 A3 Principles

The AAR-1.1 & 1.2 petrographic examination method describes the visual recognition and quantification techniques for rocks and mineral constituents of aggregates sources with special emphasis on their potential for alkali reactivity. This Annex gives supplementary information and methods for assessing carbonate rocks for potential reactivity in concrete.

Thin-sections (optionally polished thin-sections) stained for carbonate rocks should be prepared and used to determine the types of carbonate rocks. The procedures for carbonate rocks are summarised in Fig.  A.1. The procedure is generally used for aggregates originating from quarries dominated by carbonate rocks.

Fig. A.1

Flow chart for AAR assessment of carbonate rocks. * There is limited experience in using AAR 4.1 for carbonate rocks/aggregates

Note 2: Crystalline carbonate rock without dolomite and impurities should be assessed unlikely to be reactive and further testing is not necessary. Carbonate aggregates intended to be used only as fines (sand) in concrete are unlikely to exhibit ACR but would still need to be assessed for ASR potential.

The procedure allows for the additional use of 3 optional methods when carbonate rocks have been identified in thin section:

• (1) X-ray fluorescence analysis (XRF),

• (2) X-ray diffraction analysis (XRD),

• (3) Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray analysis (EDX).

Note 3: Detection of dolomite and the potential degree of dedolomitization (and reaction products) can be made using the following techniques:

• 1. XRD, using an internal standard of very well known d-spacing to determine the d-spacing of dolomite.

• 2. Petrography, using alizarin-red dye, to determine zoning, crystal shape, partial dedolomitization or iron oxides stains as well as EMPA, SEM/EDX.

Rather than proceeding with XRF analysis, XRD analysis and/or SEM/EDX (or WDX, see A6) analysis, this procedure also includes direct application of screening tests according to AAR-5 or even the longer-term AAR-3 or AAR-4.1 concrete expansion tests.

1.4 A4 Assessment Using XRF Analysis (Optional Method)

When carbonate minerals are identified by thin-section, an X-ray fluorescence (XRF) analysis on the bulk sample might be carried out. Minimum elements to be analysed are calcium and magnesium to indicate the carbonate minerals (calcite and dolomite), and aluminium to indicate the possible presence of clay minerals (see also Note 5 below).

For the assessment of reactivity, the calcium/magnesium oxide ratio should be calculated and the ratio plotted in Fig. A.2 against the aluminium oxide content. Two possibilities will result, based upon empirical observations in Canada, namely to be “considered potentially expansive” or “considered non-expansive”. Because of limited experience with the method outside Canada, a further assessment of possible expansion should be carried out according to AAR-5.

Fig. A.2

Suggested interpretation of XRF analysis findings. Figure modified from C.A. Rogers [8]

1.5 A5 Assessment Using XRD Analysis (Optional Method)

When carbonate minerals are identified by thin-section (see AAR-1.1 & 1.2), an X-ray diffraction (XRD) analysis on a bulk sample might be carried out. Generally the major (>5 %) and minor minerals (<5 %) are analysed and reported. Normally XRD analysis is used for qualitative identification of crystalline minerals (Note 4), but can also be used for semi-quantitative measurements.

The carbonate minerals magnesite, dolomite, ferroan dolomite and calcitic dolomite are considered indicative of potentially ACR reactive material. At present, the identification of any detectable quantity of these phases should classify the aggregate sample as “potentially expansive” and further testing according to AAR-5 should then be performed (see Fig. A.1).

If ACR indicative minerals have not been identified by the XRD analysis, ACR is unlikely to occur, but ASR is still possible. In that case testing according to AAR-2 and/or AAR-3 and/or AAR-4.1 could be performed (see Fig.  A.1).

Note 4: XRD analysis, which identifies only crystalline materials, will not be able to characterize amorphous constituents (e.g. opal-A, glass, or other non crystalline constituents).

Note 5: In some carbonate rocks, clay minerals can occur that might also cause problems and non-AAR expansion in concrete. When necessary, clay minerals can be characterised using specialised XRD. In sedimentary carbonate rocks, the total alumina content is also a useful indicator of the amount of clay minerals, since alumina is normally only derived from clay minerals in the absence of feldpars (authigenic or detrital); clay mineral content is approximately 3 x the content of alumina (Al ₂ O ₃ ).

1.6 A6 Assessment Using SEM/EPMA Analysis (Optional Method)

When carbonate minerals are identified by thin-section analysis (see AAR-1.1 & 1.2), examination by use of Scanning Electron Microscopy (SEM) and/or Electron Probe Micro Analyser (EPMA) can be carried out. This examination should be carried out by qualified personnel with knowledge of these techniques. It is recommended to use polished thin-sections or polished samples. Elements can be detected and quantified by use of Energy Dispersive X-ray (EDX) analyses and minerals by use of Wavelength Diffraction X-ray (WDX) analysis.

Interpretation of results obtained by EDX is the same as given in Fig. A.2. Interpretation of results obtained by WDX analysis is the same as given above for XRD.

1.7 A7 Assessment of Reactivity According to AAR-5

An accelerated screening test procedure for aggregates comprising or containing carbonate material has been developed as AAR-5 and has been assessed by an international trial.

In this procedure, the aggregate material is subjected to testing using both the RILEM AAR-2 mortar-bar test and a new derivative test using ‘concrete-bar’ specimens, in which a 4/8 mm aggregate grading is used instead of the 0/4 mm grading used in AAR-2. In this application, both the AAR-2 and AAR-5 procedures employ ‘short fat’ prism specimens (40 × 40 × 160 mm).

The interpretation of the AAR-5 findings is based upon comparing the results of these two test methods. In typical ASR, the mortar-bar (AAR-2) method may be expected to produce greater expansion than the ‘concrete-bar’ method. However, investigations and trials have shown that expansion is greater in the ‘concrete-bar’ test in the case of carbonate aggregates that have been associated with expansion in concrete structures, and also that these materials are not necessarily identified using the AAR-2 method alone. Therefore, in the AAR-5 procedure, if the concrete-bars expand more than the mortar-bars, the reactivity of the aggregate is probably not that of the normal ASR type and further investigation using the longer-term AAR-4.1 and/or AAR-3 concrete prism tests will be required.

Interpretation of the comparison between the AAR-2 and AAR-5 results (both using the ‘short-fat’ specimen option) may be summarised as follows (where appropriate, the 0.08 % expansion criterion shown may be replaced by a locally determined value):

• RILEM AAR-2 ≥ 0.08 % and:

  • AAR-5 < AAR-2 = potential ASR

  • AAR-5 ≥ AAR-2 = possible combination of ASR and ACR

• RILEM AAR-2 < 0.08 % and:

  • AAR-5 ≥ AAR-2 = possible ACR

  • AAR-5 < AAR-2 = unlikely to be reactive (no further testing necessary)

1.8 A8 Assessment of Reactivity Using AAR-3 and/or AAR-4.1

If potential ASR and/or potential ACR are detected, the longer-term (at least 12 months) 38 °C concrete prism test (AAR-3) may be carried out. Concrete test prisms are prepared from the aggregate combination and are stored in warm, humid conditions for 12 months to promote any alkali-silica reaction or alkali-carbonate reaction. The findings of the concrete prism tests should always take precedence over the results of AAR-2 or AAR-5.

Alternatively, aggregates may be assessed for ASR or ACR using the 60 °C concrete prism test AAR-4.1, which can be interpreted after 15 weeks. It is envisaged that the AAR-4.1 method might be used as an accelerated version of the AAR-3 test. However, at present there is only limited experience of using the 60 °C concrete prism method for ACR detection.

1.9 A9 Limitations and Need for Research

The suggested test procedures are based on the present knowledge of ACR. The optional XRF method (see Fig.  A.2) is based primarily on Canadian experience and some rarer cases internationally. Therefore, experience and testing of carbonate rocks other than Canadian materials are needed to validate or revise the Canadian procedures and criteria.

The mechanism of ACR is not fully understood and more research is needed on this issue. Carbonate rocks are internationally important and widely used aggregate types for concrete. The guidance given in this Annex will hopefully be a step forward in producing durable concrete with carbonate rocks, but will need to be reviewed periodically and updated as appropriate.

Annex B: Guide to Reference Materials

1.1 B1 Preamble

This guide is intended to provide assistance to any laboratories undertaking the RILEM expansion tests, using either mortar-bar or concrete-bar specimens (AAR-2 & AAR-5) or concrete prism specimens (AAR-3 & AAR-4.1). It includes information on the use of reference cement or aggregate materials and various accessories required for conducting the tests.

1.2 B2 Introduction

The use of reference cement and aggregate materials is not mandatory in the AAR-2, AAR-3, AAR-4.1 and AAR-5 test methods. However, in any testing, the use of reference materials, with known and constant properties or behaviour, may be useful, or stipulated, in certain circumstances, including the following:

• to establish the reliability and accuracy of a new test procedure;

• to assess the competence of a laboratory or the testing personnel;

• to provide reassurance in the case of tests yielding variable results;

• to provide controls for direct comparison with material under evaluation.

In particular relation to the three TC 219-ACS expansion tests for alkali-aggregate reaction, reference materials may be specifically used as follows:

• Reference High-Alkali Cement: to minimise any variations arising from using cements of different sources, compositions and properties;

• Reference Reactive Aggregate: to provide reassurance to laboratories undertaking tests for the first time, to enable routine checking of testing facilities or their personnel and for use in inter-laboratory precision experiments;

• Reference Non-Reactive Aggregate: to enable a baseline movement to be established for testing facilities and for use in programmes for identifying any pessimum behaviour.

1.3 B3 Selected Reference Materials

1.3.1 B3.1 High-Alkali Cement

A source of suitable high-alkali Portland cement has been selected, as follows:

• Norcem, Norway:

  Cite reference: RILEM reference cement

  Contact: Dr Knut Kjellsen,

  Norcem AS, R&D Department,

  3950 Brevik, Norway

  Telephone: +47 35 57 20 00

  Fax: +47 35 57 04 00

  E-mail: knut.kjellsen@norcem.no

  Minimum quantity: 25 kg (& supplied in multiples of 25 kg)

Property data for this cement are given in Table B.1.

Table B.1 Property data—reference high-Alkali Cement*

1.3.2 B3.2 Reactive Aggregates—ASR

Many ‘reactive’ aggregates have been used in experimental research into ASR, variously using natural and synthetic materials. RILEM recommends that a natural aggregate should be selected and that the preferred material should have exhibited a sensibly uniform behaviour in various test methods. After reviewing the options, a crushed siliceous limestone from Spratt’s Quarry, near Ottawa in Canada, has been selected.

A stockpile of material from the appropriate strata at Spratt’s Quarry has been established by the Ontario Ministry of Transportation, who are prepared to supply modest amounts, as follows:

• Ontario Ministry of Transportation:

  Cite: 20–5 mm crushed Spratt’s aggregate

  Contact: Mrs Carole Anne MacDonald, Petrographer, Soils and Aggregates Section

  Building C, Room 220, 1201 Wilson Avenue, Downsview, Ontario, M3 M 1J8, Canada

  Telephone: +1 416 235 3738

  Fax: +1 416 235 4101

  E-mail: caroleanne.macdonald@ontario.ca

  Minimum quantity: 25 kg

Geological information, together with some analytical and test data, is given in Figs. B.1, B.2 and Tables B.2, B.3.

Fig. B.1

Geological map showing location of Spratt’s and Pittsburg Quarries. Reproduced by courtesy of the Ontario Ministry of transportation

Fig. B.2

Stratigraphic column showing layers exposed in Spratt’s Quarry. Reproduced by courtesy of the Ontario Ministry of transportation

Table B.2 Information and data—reference reactive Spratt’s aggregate*

Table B.3 ASR test data—reference reactive Spratt’s aggregate

A precision trial using an accelerated mortar-bar test [9] was carried out in North America in 1995 (Rogers et al. 1996). This indicated an average 14-day expansion of about 0.42 %, with all compliant laboratories yielding results greater than 0.30 %. A further study with new samples in 2007 produced a similar average 14-day expansion of 0.39 % [10].

In a concrete prism test (CSA method), using cement with an alkali content of 1.25 % (as Na₂O eq.) and 38 °C storage, expansion values with Spratt’s coarse aggregate (and non-reactive sand) at 1 year have been reported in the range 0.08–0.16 %. An inter-laboratory concrete prism test study (CSA method), using mixtures of Spratt’s coarse aggregate and non-reactive sand, produced average expansion values in the range 0.16–0.18 %, depending upon mix details and storage conditions [11].

1.3.3 B3.3 Reactive Aggregates—Carbonate

A stockpile of reactive carbonate aggregate material from the Pittsburg Quarry at Kingston, Ontario, Canada, has been established by the Ontario Ministry of Transportation, who are prepared to supply modest amounts, as follows:

• Ontario Ministry of Transportation:

  Cite: 20–5 mm crushed Pittsburg Quarry aggregate

  Contact: Mrs Carole Anne MacDonald, Petrographer, Soils and Aggregates Section

  Building C, Room 220, 1201 Wilson Avenue, Downsview, Ontario, M3 M 1J8, Canada

  Telephone: +1 416 235 3738

  Fax: +1 416 235 4101

  E-mail: caroleanne.macdonald@ontario.ca

  Minimum quantity: 25 kg

The geological location of Pittsburg Quarry is shown in Fig.  B.1 and some preliminary analytical and test data are given in Table B.4.

Table B.4 Analytical and test data—reference reactive Pittsburg carbonate aggregate

1.3.4 B3.4 Non-reactive Aggregate

A suitable non-reactive aggregate is defined using an unusually demanding criterion of less than 0.05 % expansion in the AAR-2 accelerated mortar-bar test.

In the RILEM trials of the AAR-4.1 60 °C concrete prism test, a crushed limestone from Boulonnais in France has been identified for use as the non-reactive reference coarse and fine aggregates. Arrangements have been made for ex-Boulonnais coarse and/or fine aggregates to be stocked and supplied by the following organisation:

• Carrières du Boulonnais (http://www.lesgranulatsdugroupecb.com):

  Cite: Coarse and/or Fine Boulonnais Aggregate

  Contact: Ms Sophie Citerne (Export/Industry Sales Manager)

  530 BD du Parc d’affaires Eurotunnel

  62231 Coquelles

  France

  Mobile/Cell: +33 (0)6.08.33.57.76

  E-mail: sciterne@groupecb.com

1.4 B4 Test Accessories

1.4.1 B4.1 Storage Containers for Concrete Prisms

The AAR-3 concrete prism test involves the storage of specimens in a suitable container, as defined in the method. One source of suitable containers is as follows:

• LINPAC Ropak

  Cite: 5 gallon or 19 litre round container 10540 Talbert Avenue, Suite 200 Fountain Valley, CA 92708, USA

  Tel: +1 (714) 845 2845

  Web: www.linpac.com

  E-mail: info@linpacpackaging.com

1.4.2 B4.2 Reactor Storage for Concrete Prisms

The recommended storage for concrete prisms in the AAR-4.1 test utilises the reactor system, which can also be used for the AAR-3 test. Information on this apparatus may be obtained from the following:

• Chaudronnerie Mecanique Generale:

  27 rue de la Constellation

  Parc St Christophe, BP 8262

  95801 Cergy Ontoise Cedex, France

• Espo-Sud:

  Quartier les Ramières, BP37

  07350 Cruas

  France

• Schleibinger Geräte Teubert u Greim GmbH:

  Gewerbestr. 4

  D-84428 Buchbach

  Germany

  Tel: +49 8086 94010

  E-mail: schlei@schleibinger.com

• Ratio TEC Prüfsysteme GmbH:

  In der Au 17

  88515 Langenenslingen

  Germany

  Tel: +49 7376 9622-0

  E-mail: ratio.tec@t-online.de