Canadian experience with testing for alkali-aggregate reactivity in concrete

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Cement & Concrete Composites 15 (1993) 27-47

Canadian Experience with Testing for Alkali-Aggregate Reactivity in Concrete Marc-Andrd Bdrubd D6partement de G6ologie et de Gdnie Gdologie, Universit6 Lava1, Sainte-Foy, Qudbec, Canada, GIK 7P4

& Benoit Fournier Canada Centre for Mineral and Energy Technology, Energy, Mines and Resources Canada, Resource Utilization Lab., 405 Rochester, Ottawa, Ontario, Canada, K1A OG1

Abstract In the past few years, intensive work has been undertaken in Canada on test methods for determining the potential alkali-reactivity of concrete aggregates. The paper summarizes and discusses the principal methods investigated and the results obtained. A decision chart is proposed which retains only two rapid test methods: the petrographic examination (ASTM C 295) and the accelerated mortar bar method (ASTM C 9-ProposalP 214), in addition to the concrete prism method (CAN/CSA-A23.2-14A) which is much longer but considered the most realistic test for alkali-reactivity. Keywords: Concrete, mortar, cement, aggregates, alkalis, alkali-aggregate reactions, expansion tests, standard tests, accelerated tests, petrography, water/cement ratio.

INTRODUCTION A critical question when planning the construction of a concrete structure that will be exposed to a severe environment (high humidity, de-icing salts, etc.) is: ~ r e the proposed aggregates alkalireactive in concrete?' To answer this question, the most realistic information is provided by the field performance of these aggregates in existing structures. However, this information is accessible only for aggregates frequently used in the past, for many years. Indeed, problems related to

alkali-aggregate reaction (AAR) usually arise years after construction. In the particular case of hydraulic structures, the above conditions are often not satisfied, as there are rarely pre-existing aggregate sources in the construction area, and local materials must therefore be used, often the excavated bedrock. The field survey may also be inconclusive for other reasons: (1) a limited number of sufficiently aged and sufficiently exposed structures built with the aggregates under study (insufficient information about the aggregate sources in the construction fdes); (2) lack of information on the other conditions that affect A A R and the field performance of concrete in general (alkali content of the cement, cement content, curing methods, etc.); (3) variations in exposure conditions from one structure to another (humidity, freezing/thawing, wetting/drying, seawater, de-icing salts, etc.); and (4) variations in aggregates produced by the source between the construction period and the survey of structures built with materials from this source (changes in the exploitation levels or zones, modifications in the methods of exploitation and preparation, etc.) For instance, a structure that contains very reactive aggregates will not deteriorate if the concrete has been made with a low-alkali cement or effective supplementary cementing materials in sufficient amounts. Thus, the actual determination of the potential alkali-reactivity of aggregates is often only possible through laboratory tests, which ensure that all aggregates are evaluated under the same conditions. On many occasions, the aggregates must be evaluated very quickly before construction; this

27 Cement & Concrete Composites 0958-9465/93/$6.00 © 1993 Elsevier Science Publishers Ltd, England. Printed in Great Britain

28

Marc-Andr~ B~rub~, Benott Fournter

calls for test methods that are rapid, reliable, simple, and reproducible. In the past few years, intensive work has been undertaken in Canada on rapid test methods for determining the potential alkali-reactivity of concrete aggregates. ~ This paper reviews the principal methods (standardized or not) that are at present used or under development in Canada. The methods are listed in Table 1. First, it must be pointed out that all the methods described hereafter are accelerated tests (even the CSA concrete prism method, which requires 1 year), and that they cannot exactly reproduce field conditions. Indeed, they all try to simulate in less than 1 year what may happen in the field after many years. To achieve this goal, at least one of the following conditions must be increased: (1) alkali concentration (high-alkali mixes or immersion in alkaline solutions); (2) temperature (38"C, 80"C, autoclave); (3)pressure (autoclave); (4) humidity (100% RH or immersion in aqueous solutions); (5) specific area (reduction of aggregates to powder or sand size).

PETROGRAPHIC EXAMINATION ASTM C 2952 The petrographic examination of aggregates in thin sections under the optical microscope usually allows recognition of potentially reactive mineral phases such as opal, cristobalite, tridymite, volcanic glass, chert, chalcedony and microcrystalline quartz. 3,4 However, Grattan-Bellew5,6 suggested that quartz with undulatory extinction could not be deleterious, in contrast to microcrystalline quartz which is often also present in aggregates containing strained quartz. When necessary, the petrographic examination may be completed using other techniques such as X-ray diffraction, scanning electron microscopy or IR spectroscopy. 2 As pointed out by Grattan-Bellew: 6 'Petrographic examination alone cannot supply information on the expansiveness of a particular cement-aggregate combination; however, experienced petrographers can predict the likely behavior of aggregates with which they are familiar'. Indeed, when conducted by a petrographer with experience of AAR, the petrographic examination can sometimes be sufficient to accept or reject the aggregates under study, in accordance with the past field performance of similar aggregates, ff there is doubt, the petrographic examination will help to determine what tests to perform,

considering the nature of the aggregates under study. In fact, the petrographic examination must always be performed before any other test. 7,8 This remark holds particularly for rapid test methods. CHEMICAL METHOD ASTM C 2 8 9 9 The ASTM C 289 chemical method is certainly one of the most widely used tests for evaluating the potential reactivity of silica-bearing aggregates. In this test, the aggregate is reduced to 150-300-/~m particles and immersed in a 1N NaOH solution at 80°C for 24 h. The solution is filtered and analyzed for dissolved silica (Sc) and reduction in alkalinity (Rc). The results are plotted on a standard graph showing three areas corresponding to innocuous, deleterious and potentially deleterious aggregates (Fig. 1). The test does not apply to alkali-carbonate reactive aggregates which do not involve reactive silica. ~0Moreover, a significant number of known alkali-silica reactive aggregates from all over the world pass the test whereas other aggregates with good field performance fail. 10-16 There are many reasons for these poor results, in particular interference by mineral phases such as calcium, magnesium and iron carbonates, hydrated magnesium silicates, gypsum, zeolites, clay minerals, organic matter, or iron oxides.l 5.J7-~9 These interferences result in underestimated Sc values (precipitation of silica or interference during chemical analysis), or in overestimated Rc values (reactions with Na ÷ and OH- ions). 19 In particular, calcium carbonates lead to precipitation of some of the silica dissolved as CSH, then to the acceptance of several reactive aggregates. As the Rc values are affected more, many researchers consider only the Sc values (dissolved silica), and most of them suggest a limit of 100 mmol/litre. 15 In Canada, the chemical method appears inapplicable to rocks from Nova Scotia. ~j At Ontario Hydro, it is considered as lacking in reliability and has been rejected. 16 In Quebec, this method is incapable of detecting many deleterious aggregates (Fig. 1), e.g. the reactive siliceous limestones from the St Lawrence Lowlands (carbonate interference),l~' ~s.20 the Potsdam sandstones used in the Beauharnois dam 21-23 (removal of most of the reactive phase, e.g. the quartzitic cement around the quartz grains, during aggregate preparation, e.g. crushing and sieving),23 the rhyolitic tufts and associated shales used in the Sartigan dam (carbonate interference)2L23'24 and

29

Canadian experience with alkali-aggregate testing Table !. Test methods used in Canada for alkali-aggregate reactivity Petrographic examination (ASTM C 295)( z I day) Chemical method (ASTM C 289) (2-3 days) Modified chemical method (on insoluble residues) (CSA proposal) (2-3 days) Mortar bar method (ASTM C 227) (6 months) Accelerated mortar bar method (NBRI, ASTM C9 -- Prpoposal -- P 214) (2 weeks) Autoclave mortar bar methods (e.g. Laval University method) (3 days) Concrete prism method (CAN/CSA-A23.2-14A) (1 year) Accelerated concrete prism method (used in Quebec) (1 month) CNR concrete method ('Dugggan test') (1 month)

chloritic schists from the Eastern Townships. 2L'23"25 On the other hand, the test is severe for a number of innocuous aggregates, such as many Appalachians lithic gravels, although parent sands from the same sources perform better (crushing effect; Fig. 2). With natural gravels, crushing creates news fracture planes through aggregate particles and siliceous mineral phases. These freshly exposed surfaces present more broken siloxane bridges (Si-O-Si) and silanol groups (Si--OH) than surfaces that were exposed for a long time in the natural deposit. Therefore, the corresponding aggregates may be more susceptible to react and to release silica in the alkali solution, in particular the lithic gravels which contain significant amounts of microcrystalline quartz.

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MODIFIED CHEMICAL METHOD ON INSOLUBLE RESIDUES (CSA DRAFT DOCUMENT z6) Carbonate aggregates In Quebec, limestones and dolostones are largely used in concrete. To allow detection of the reactive varieties and to prevent precipitation of dissolved silica as a result of carbonate interference, Bdrard and Roux 's proposed that the chemical method ASTM C 289 should be performed on the insoluble residues. In this modified method, the test sample, also of size 150-300 /zm, is immersed in concentrated HCI until carbonates are completely dissolved. The residue is screened and washed on a 150-/zm sieve. The retained material is dried and submitted to the ASTM C 289 test. The Sc and Rc values are multiplied by two to account for the lower mass of material used (12-5 g rather than 25 g), because the insoluble residues are very porous (not enough room in the test containers). The results are plotted on the ASTM graph without any other correction, and interpreted in accordance with the standard ts (see

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Fig. 2. Results of the modified chemical method (ASTM C 289 on insoluble residues) for natural sands and gravels from Quebec. Lithic gravels appear more reactive than sands from the same source, whereas granitic gravels look better than parent sands. These differences are attributed to the crushing effect (beneficial for granitic particles, for which the interior seems less reactive than the weathered surface, and deleterious for fithic particles, for which the interior appears relatively more reactive as a result of microcrystalline quartz in significant amounts).

Marc-Andri B~rub~, Benoit Fournter

30

Fig. 3; in this figure, the Sc and Rc values were not mulitplied by two). A study by Fournier and Brrub615 on representative limestones and dolostones from the St Lawrence Lowlands, in Quebec, showed a better correlation between the modified chemical method and the CSA concrete prism method when: (1) the chemical test is performed on the overall insoluble residues (0-300 /~m in size) obtained by fdtration after carbonate acid digestion, rather than on the residual 150-300-#m fraction obtained after sieving, and (2) the Sc values are corrected to account for the actual amount of insoluble residues in the aggregate under study (Sc*=(Scx% insoluble residue)/ 100). Also, the reduction in alkalinity (Rc) appeared not to be useful, and it was recommended that concentrated hydrochloric acid be used for carbonate digestion rather than diluted acid. Following this preliminary stage, a CSA draft document has been proposed by the CSA Subcommittee A S , 26 which specifies measuring the amount of dissolved silica (Sc) only, and retaining a limit of acceptance of 10 mmol/litre for the corrected amount of dissolved silica (Sc*). The test was subjected to a multi-laboratory study involving six laboratories and six aggregates) 5 For the two selected aggregates containing dolomite in significant amounts (and for which the values of dissolved silica were relatively low, e.g. < 200 mmol/litre), high coefficients of variation were obtained (53 and 70% for Sc.) This was mainly 250 AGGR,-t.lm t , - ~ I

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100 1000 Se (mmok~/litre) Fig. 3. Resultsof the modified chemicalmethod (ASTM C 289 on insoluble residues) for carbonate aggregates from Quebec. When using the standard ASTM graph, 97% (37/ 38) of the expansive aggregates tested (> 0-06% in the CSA concrete prism method) are classed deleterious or potentially deleterious, whereas only 33% (11133) of the non-expansive aggregates are evaluated correctly

attributed to incomplete dolomite dissolution in some laboratories during cold acid leaching. Indeed, dolomite has already been recognized as causing unreliable results in the chemical method. 17 For the other four aggregates, all limestones, the coefficients of variations were much better (11-29% for Sc), with the highest value corresponding to the limestone with the lowest amount of dissolved silica? 5 However, it is likely that such significant variations could result in the acceptance of some marginally reactive aggregates. In the meantime, at Laval University, the test was applied to 71 different carbonate aggregates from the St Lawrence Lowlands, with measurement of both Sc and Rc values, t5 When the results are placed on the standard ASTM C 289 graph and interpreted in accordance with this standard, 97% (37/38) of the expansive samples in the CSA concrete prism method (using a limit at 1 year of 0.06%, instead of the 0.04% CSA value, as the cement content was 350 kg/m 3 rather than 310 kg/m3), are classed deleterious or potentially deleterious in the modified chemical method (Fig. 3). On the other hand, the modified test was very severe for many innocuous carbonate aggregates: only 33% (11/33) of the non-expansive samples in the CSA concrete test (e.g. with expansion < 0.06% at 1 year) were classed innocuous (Fig. 3), even if the Rc and Sc values were not multiplied by two to take account of the smaller samples tested (12-5 g rather than 2 5 g). However, the investigated samples meeting at least one of the following criteria: (1) Sc<100 mmol/litre (Fig. 4(A)); (2) Sc*< 10 mmol/litre (Fig. 4(B)); or (3) insoluble residues < 5% (Fig. 4(C)), with only one exception in the latter case, were classed non-expanswe in the CSA concrete test. Thus, aggregates satisfying at least one of these three criteria can be considered as nonexpansive. However, all samples exceeding these three criteria at the same time are not always reactive. Indeed, using these criteria, the proportion of the non-expansive carbonate aggregates (CSA concrete test) that were classified correctly, i.e. as innocuous, is only 58% (19/33). This value depends on the geological Group, being 100% (9/ 9), 57% (4/7), 44% (4/9), and 25% (2/8), for the samples belonging to the Trenton, Black River, Chazy, and Beekmantown Groups, respectively. The efficiency of each of the three above criteria taken alone is lower (see Fig. 4). Hence, it appears clear that the modified chemical method is less efficient for the last two geological Groups; there-

Canadian experience with alkali-aggregate testing

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Fig. 4. Results of the modified chemical method (ASTM C 289 on insoluble residues) for carbonate aggregates from Quebec. The mounts of dissolved silica (Sc; A), corrected dissolved silica (Sc*=Scx% insoluble residues/100; B), and insoluble residues (%RI; C) are compared with expansioas in the CSA concrete prism method. When using a Sc limit of 100 mmolflitre (A), all the (38) expansive aggregates ( > 0-06% in the CSA concrete prism test) axe classed as potentially reactive, whereas only 39% (13/33) of the non-expansive aggregates are classed as innocuous: 67% (6/9) for the Trenton Group, 29% (2/7) for Black River, 33% (3/9) for Chazy, and 25% (2/8) for Beekmantown. However, all expansive samples also show Sc* and %RI values in excess of 10 mmol/litre (B) and 5% (C), respectively, with only one exception in the latter case. Using these two other criteria, a higher proportion of the non-expansive aggregates, 58% (19/33), are classed as innocuous: 100% (9/9) for the Trenton Group, 57% (4/7) for Black River, 44% (4/9) for Chazy, and 25% (2/8) for Beekmantown.

Silicate aggregates Many silicate aggregates contain carbonates in

contain only a few per cent of calcium carbonate, are now classed as reactive (Fig. 1). On the other hand, many natural gravels which contain some carbonate particles now fail, although they are non-expansive in the CSA concrete prism method

significant m o u n t s . Thus, to p r e v e n t c a r b o n a t e interference and u n d e r e s t i m a t e d Sc values, the modified test (on insoluble residues) is also m o r e r e c o m m e n d e d than the standard m e t h o d A S T M C 289. For instance, the deleterious chloritic schists and rhyolitic tufts m e n t i o n e d above, which

( C A N / C S A - A 2 3 - 2 - 1 4 A ) 21.27 (Fig. 2). W h e n the modified chemical m e t h o d is applied to silicate aggregates, 25-g sub-samples o f insoluble residue can be tested, and it is r e c o m m e n d e d again to test the overall residue rather than only the 1 5 0 - 3 0 0 /zm size fraction, for a better representation.

fore the petrographic examination of the aggregates before the test is strongly recommended.

32

Marc-Andrd Bdrubd, Benott Fournter

MORTAR BAR METHOD ASTM C 2272s Mortar bars are made with the aggregate under study and a high alkali cement. The bars are stored over water at 38"C and 100% RH in sealed containers with wicks, and their length is measured periodically. The expansion limits are 0-1% at 6 months, or 0.05% at 3 months• According to Grattan-Bellew, 6 they should be reported at 12 and 6 months, respectively. These revised limits are already used by many agencies, including Ontario Hydro. -~9 The test does not apply to alkali-carbonate reactive aggregates, t°,~6,3° and also proved to be incapable of detecting many slowly reactive aggregates (which correspond to the majority of the Canadian reactive aggregates), in particular greywackes and argiilites, t6'3° According to Hobbs, ~ all the reactive aggregates from the UK pass the test• The test is largely affected by the storage conditions (the container), which differ from one laboratory to another, and particularly by the presence or the absence of wicks inside the container used) ~ Indeed, with containers with wicks, for instance the reference ASTM container, 28 most of the Canadian reactive aggregates satisfy the test requirements. 2L32 The presence of wicks promotes leaching of alkalis from the mortar bars and leads to lower expansions. 3t As a result, numerous tests performed in the past that indicated aggregates were innocuous are doubtful if the bars have been stored in containers with wicks inside. When evaluating an aggregate, it is recommended that a reference reactive aggregate which does not release significant alkalis to the pore solution be tested at the same time. 7'31 Also, the alkali content of the cement used, which is not specified in the current standard, '-s may explain experimental variations (Fig. 5). A current practice in many laboratories consists of adding N a O H to the mix water to increase the alkali content to 1.25% (Na20 equiv.) of the mass of cement. This practice is also recommended by CSA 7 for siliceous carbonate aggregates. Variations in the water/cement (w/c) ratio, which is not specified in the standard (water being added to reach the specified flow), may also affect the results• As observed in Fig. 6, with typical reactive aggregates from Quebec, a lower w/c ratio, at least between 0.60 and 0-45, results in higher expansion. A similar trend was observed by Brotschi and Mehta? 3 This is attributed mainly to a lesser amount of pore solution, which there-

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Canadian experience with alkali-aggregate testing

above for the ASTM C 227 mortar bar method (see Fig. 6). In this immersion test, the concentration of alkalis in the pore solution is greatly affected by the 1N NaOH test solution, with migration of alkali ions in the bars likely to be slower with a lower w/c ratio (lower permeability). For silicate aggregates from Quebec, the accelerated mortar bar test can detect all known reactive aggregates except some varieties of Postdam sandstones z3.39,4° (Figs 7 and 8). However, the test is too severe for many aggregates which perform well in the CSA concrete prism method or in the field, such as greywackes from the Quebec City area, lithic gravels from the Eastern Townships, some hornfelses, gabbros, or andesites (Figs 7 and 8). Also, most of the Appalachian lithic gravels from Quebec fail in the test, whatever their actual field performance. 27'4° The results obtained by Grattan-Bellew s (Fig. 9) and by Hooton and Rogers 29 (Fig. 10) on other silicate aggregates from Canada are in good agreement with the above results. In Fig. 9, the expansions shown for the concrete specimens are the maximum expansions obtained when the expansion curves flattened out. Moreover, because of variations in the test conditions, the absolute amounts of expansion shown in this figure should not be considered as a measure of the actual expansiveness of the aggregates tested, s For carbonate aggregates from Quebec, tests at Laval University on 71 limestones and dolostones

227 mortar bar test. At least, when the mortar test is performed, it is highly recommended to use a container without wicks, to increase the alkali content to 1.25% (Na20 equiv.) of the mass of cement by adding NaOH to the mix water, and to control the w/c ratio to 0.50 (0.44 for uncrushed natural sands), as in the accelerated mortar bar method (see below).

ACCELERATED MORTAR BAR METHOD ASTM C 9-ProposaI-P 2 14 35

In this test, mortar bars are made in accordance with ASTM C 227, immersed for 2 weeks in a 1N NaOH solution at 80"C, and measured each working day. The aggregates showing expansion lower than 0.1% at 14 days (12 days in the original NBRI proposal3~), are considered innocuous, those with expansions between 0-1% and 0.25% are classed as slowly expansive, and expansions in excess of 0.25% correspond to rapidly expansive aggregates. -'~'35,36 Since first proposed by Oberholster and Davies, 36 this method has been intensively investigated all over the world. In the corresponding ASTM document 35 the bars are made with a constant w/c ratio (0.44 for natural sands, 0"50 for crushed material), after numerous experiments showed that lower w/c ratios lead to lower expansions, 6'23'37-39 in contrast to the results described

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Fig 7. Results obtained at Lava] University for the accelerated mortar bar method, for silicate aggregates from Quebec. The results are compared with expansions m the CSA concrete pnsm method. When using the proposed lumt of 0 1 V• ¢xpansnon, one deleterious aggregate (bad field performanceand/or expansion > 0-04% in the CSA concrete prism test) is classed as umocuous (13, Postdam sandstone), whereas many innocuous or presumably innocuous aggregates (1, 5, 6, 8, ] 1, 12, 23, 24) appear slowly expansive (expansion between 0.1% and 0.25%) to rapidly expansive (expansion > 0-25%) in the accelerated test. In fact, only 56% (10/18) of the innocuous samples tested are evaluated correctly. For sources 22 and 23 the gravel was used for the concrete test and the sand was used for the accelerated mortar test. .

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Fig. 8. Results obtained at the Ecole PolytechniqueJ9 for the accelerated mortar bar method, on aggregates from Quebec. The results are compared with expansions in the CSA concrete prism method. When using the proposed limit of 0'1% expansion, one deleterious aggregate (bad field performance, expansion > 0-04% in the CSA concrete prism test) is classed as innocuous (4, Postdam sandstone), whereas two presumably innoeuons aggregates (17 and 14) appear slowly expansive (expansion between 0.1% and 0.25%) in the accelerated test.

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Fig. 9. Results obtained at NRC 8 for the accelerated mortar bar method, for Canadian aggregates (except no. 1). The results are compared with maximum expansions obtained in the CSA concrete prism method. Because of variations in the test conditions, these results should not be considered as representative of the actual expansiveness of the a g F e p t e s in concrete. For instance, aggregate no. 1, despite low expansion in the test concrete, is reactive in field structures in South Africa, whereas aggregate 20 is probably also reactive)

from the St Lawrence Lowlands were very satisfying 40-43 (Fig. 11): 97% (37/38) of aggregates expanding more than 0-06% at 1 year in the CSA concrete prism test exceeded the proposed limit of 0.1% at 14 days, and 85% of the non-expansive samples (28/33) satisfied this limit. The proportion of non-expansive aggregates (e.g. using a 1 year expansion limit criteron of < 0"06% in the CSA concrete test) that are evaluated correctly does not depend greatly on geology, being 100% (9/9), 86% (6/7), 7 8 0 (7/9), and 75% (6/8), for the samples belonging to the Trenton, Black

River, Chazy and Beekmantown Groups, respectively. The only expansive sample that was not detected in the accelerated mortar bar method is the only expansive one containing less than 5% insoluble residue (see Fig. 4(C)). The results obtained at the Ecole Polytechnique39 (Fig. 8), at NRC s (Fig. 9), and at the University of Toronto 29 (Fig. 10), confirm that a limit of 0-1% is required to detect the alkali-silica reactive carbonate aggregates, whereas it is too severe for a certain number of imaocuous ones (No. 17 in Fig. 8, Nos 5 and 7 in Fig. 10).

Canadian experience with alkali-aggregate testing 0.4 o12

o Silicate Agg. • Carbonate Agg.

oll

o10 :E

o9

~o.2

o8

o7 • 5

|go.t

o6

w4

1 4 5 6 7 8 9 10 11

Nelsondolostone Guelphcarbonate sand Panscarbonatesand Neyesstliceoussand Panscarbonate gravel Grantsiliceous gravel Sdeeous sand (Michigan) Sudbury siliceous gravel Lower Notch quarried metasediments 12 Spratt Ilrnestone

Hooto'--n& Rogers 1989 ]

el

0.0

35

Excellent

Reactive

Field Performance

Fig. 10. Results obtained at Toronto Universityz9 for the accelerated mortar bar method, for a number of aggregates from Ontario. The results are compared with field performance. When using the proposed limit of 0"1% expansion, all the deleterious aggregates (bad field performance) are classed as expansive, whereas two of the four innocuous aggregates tested (5 and 7) appear slowly expansive (expansion between 0.1% and 0-25%) in the accelerated test.

0,5

~~

CARBONATE I AGGREGATES

0,4 0,3 A

~

0,2"

ol3 A

•

A

"~jt. 0 & ~ A " ~ " ' 0 , 1 ~!~( < , A

0,0 0,00

A

A

•

,

6,

Trenton o BlackRiver -I- Chazy o Beekmantown A

*'

,

•

•

,

•

0.12 0,24 0.36 0,48 CSA Concrete Test (% exp. after 1 year) (350 kg/m3 of cement)

Fig. 11. Results obtained at Laval University for the accelerated mortar bar method, for carbonate aggregates from Quebec. The results are compared with expansions in the CSA concrete prism method. When using the proposed limit of 0.1% expansion, 97% (37/38) of expansive aggregates ( > 0"06*/. in the CSA concrete prism test) are classed as reactive, whereas 85*/0 (28•33) of the non-expansive aggregates appear innocuous: 100% (9•9) for the Trenton Group, 86% (6/7) for Black River, 78*/0 (7/9) for Chazy, and 75°/. (6/ 8) for Beekmantown.

According to Grattan-Bellew,a the accelerated mortar bar test is incapable of recognizing the alkali-carbonate reactive aggregates from the Kingston area (Ontario). For alkali-silica reactive aggregates, as also suggested by the results of DeMerchant and Soles, 32 Grattan-Bellewa suggested using expansion limits which vary with the type of aggregates under study (for instance, 0.1% for reactive siliceous limestones, 0-2% for grey-

wackes and argillites, and 0.15% for the other types of aggregates), and called for petrographic examination of the aggregates before testing. Bdrub6 et aL 4° suggest 0.2% for natural sands and gravels, and 0.1% for quarried silicate and carbonate aggregates. It appears clear that the accelerated mortar bar method should not be used for rejecting aggregates; any negative results should only mean that further testing is required, in particular for aggregates expanding between 0.1% and 0"25%. 29'40'43 As pointed out by Grattan-Bellew,6 'the larger expansions obtained with the NBRI method create a danger that aggregates with a satisfactory field performance might be classified as deleteriously expansive'. For example, all the Appalachian and Superior lithic gravels from Quebec tested by Mongeau, 27,4° expanded more than 0"15% in the accelerated mortar bar test, with a large proportion over 0.25%, even though only a few of them are suspected to be deleterious in concrete structures. Nevertheless, the accelerated mortar bar method appears very useful, as it is capable of recognizing most deleterious aggregates within 2 weeks only (except some Potsdam sandstones and the alkali-carbonate reactive aggregates), and allows the acceptance of a high proportion of the innocuous aggregates. The test is therefore a very powerful screening tool. Moreover, it was demonstrated that the reaction products are exactly the same as those found in reactive field concrete. .3"44 A multi-laboratory study has been undertaken in Canada, 4s involving nine laboratories, three

36

Marc-Andr~ BOrub~, Benoit Fournter

aggregates (two reactive and one non-reactive), and three cements with different alkali contents (two in common and one variable). For the two aggregates expanding more than 0.1% after 14 days, when the results from two inexperienced laboratories are excluded plus those from another laboratory that had not used the specified w/c ratios, the coefficients of variation were close to 10%, suggesting a very good reproducibility for this test, even better than that reported in a previous study conducted in South Africa. 37 This better result could be partly related to the fact that the w/c ratio was controlled in the multi-laboratory study conducted by Hooton. ~ This study also demonstrated that the cement used has no significant effect on the expansions in the absence of supplementary cementing materials, as observed by other researchers2 ,3~ It may be mentioned that the accelerated mortar bar method has been used with success to deterrmne the effectiveness of supplementary cementing materials such as silica fume, fly ash and blast furnace slag in the presence of alkali-silica reactive aggregates,46 for instance with siliceous limestones from Ottawa (Spratt Quarry), Trois-Rivi~res and Quebec City, and with rhyolitic tufts from Beauceville (Quebec). Indeed, the results obtained at Laval University by Duchesne and B~rubd 47 and B~rub~ and Duchesne'~8 correlate very well with concrete prism tests performed for CANMET by Lafarge Canada 49,5° with the same supplementary cementing materials. Hudec 5~ proposed some modifications to the accelerated mortar bar test: the use of samples that are small cores (19-25 mm diameter x 70 mm length) taken from mortar (or concrete) blocks, and the use of linear variable differential transformer gauges for the measurements. According to Hudec, the expansions obtained are not sufficiently reproducible, but they could be normalized in accordance with the expansions obtained for two reference aggregates tested in parallel, a reactive one and a non-reactive one.

AUTOCLAVE MORTAR BAR METHODS

Many test methods using an autoclave have been proposed in the literature, mostly by Chinese and Japanese authors. Most of them are reviewed in a few papers. 6' ~3,52The methods proposed by Nishibayashi et aL ~3 and Tang e t aL 54 have been applied to mortar bars made with 12 Canadian aggregates in accordance with ASTM C 227. 29

The results obtained were not satisfactory. However, when testing Canadian aggregates by the Chinese method,54 using the originally proposed specifications for mix proportions and specimen size, Grattan-Bellew (NRC, pers. comm., 1990) obtained good results, which suggest that mix proportions are critical in autoclave tests, as pointed out by Nishibayashi e t al. s3 In the method developed at Laval University by Fournier e t al. 5"- the test mortar bars are made in accordance with ASTM C 227, but with a constant w/c ratio of 0-50 and an alkali content of 3.5% (NazO equiv.) of the mass of cement (NaOH addition to the mix water). The bars are placed in an autoclave commonly used for testing cements, under 0-17 mPa or 25 psi (at about 130"C ) for 5 h. Preliminary tests with a few silicate55 and carbonate 52 aggregates had been undertaken first to determine the expernnental conditions which allowed the best differentiation between innocuous and deleterious samples, within a working day. Autoclave tests have been performed on 17 quarried silicate aggregates from Quebec. ~5,56The results appear in Fig. 12. According to a proposed limit of 0.10% expansion after 5 h under the above conditions,56 all four deleterious samples tested were detected whereas 77% (10/13) of the

0.6

~

117

SILICATE AGGREGATES

0,5

01

~0.3

ii 19

5

8 11

~ "40.1

==16

9~ °~1~-

_.13 (2,3,4,7,8,10,14,15,18)

o innocuous J • Delet~ious

J

L

0.0

I

0.00

0.04

'

!

"

I

~

!

'

008 0.12 0 16 0.20 0.24 028 CSA Concrete Prism Test (% exp. after 1 year) Fig. 12. Results obtained at Laval University for the autoclave mortar bar method, for silicate aggregates from Quebec. The results are compared with expansions in the CSA concrete prism method. When using the proposed fimh of 0.10% expansion, all 4 deleterious aggregates (bad field performance and expansion > 0-04% in the CSA concrete prism test) are classed as innocuous, whereas 77% (10/I3) of the innocuous or presumably innocuous aggregates arc evaluated correctly. This result is better than for the accelerated mortar bar test (in which 56% of the non-expansive samples tested were evaluated correctly; see Fig. 7). (Refer to Fig. 7 for aggregate identification )

Canadian experience with alkali-aggregate testing innocuous or presumably innocuous samples tested were evaluated correctly with the autoclave method. In another study, 5~,~7the method allowed detection of all nine aggregates (1 dolostone, 1 gravel and 7 quarried silicate aggregates) which proved to be reactive in a number of Canadian dams, while classifying properly the two innocuous quarry silicate aggregates used as controls, for a 100% efficiency. Thus for the quarried silicate aggregates tested, this test appears better than the accelerated mortar bar method (in which 56% of the innocuous aggregates tested were classed properly; see Fig. 7). The results by Mongeau 27,56 on 39 natural sands and gravels used in Quebec also confirm that the Laval autoclave method is less severe for this type of aggregate than the accelerated mortar bar method. 56 Autoclave tests have been also performed at Laval University on 40 representative limestones and dolostones from the St Lawrence Lowlands. 4t.42.52.56 The results obtained are also impressive (Fig. 13). Using a limit of 0' 15% after 5 h in the autoclave, 96% (22/23) of samples expanding more than 0.06% at 1 year in the CSA concrete prism test, which is the limit used, were

detected, whereas 88% (15/17) of the non-expansive samples (in concrete) were evaluated correctly. This percentage is quite similar for the four geological Groups: 100% (3/3), 100% (4/4), 83% (5/6) and 75% (3/4) for Trenton, Black River, Chazy, and Beekmantown, respectively. Therefore, for the carbonate rocks from Quebec, the proposed autoclave method appears as efficient as the accelerated mortar bar method (in which 85% of the innocuous aggregates tested were classed properly; see Fig. 11). The only expansive aggregate that is not detected in the autoclave method is the same that was not detected in the accelerated mortar bar method ASTM C 9 -- Proposal -- P 214 (Figs 11 and 13).

37

0.5 * A &

~u~ 0,3

CARBONATE [ AGGREGATES

. &

&

&

&

~

&

>= ~o,2 .ff~

A

A

A

A

¢ 0,0

& Trenton o BlackRwer -t- Chazy a Beekrnantown

0,1

,

0,00

&

&

o

...We <

&O &

&&

•

,

•

,

•

0,12 0,24 0,36 CSA Concrete Test (% exp. after 1 year) (350 kg/m3 of cement)

0.48

Fig. 13. Results obtained at Laval University for the autoclave mortar bar method, for carbonate aggregates from Quebec. The results are compared with expansions in the CSA concrete prism method. When using the proposed limit of 0.15% expansion, 96% (22/23) of expanswe aggegates (> 0.06% in the CSA concrete prism test) are recognized, whereas 88% (15/17) of the non-expansive samples are evaluated correctly. The test appears as efficient as the accelerated mortar bar method (in which 85% of the non-expansive aggregates were classed as innocuous; see Fig. 11 ).

0,24 Alkali content 0 66 "----D---1.03 1.08

~ 0.20 ~ 0.16 ~E 0.12 • a.

~,~ _J

1.17 .L

0,08

A ~ lirnit . ~

o~ 0,04 < 0.00

o

-0,04

0

4

8 12 Time (months)

16

20

Fig. 14. Effect of the alkali content (% Na20 equivalent of the mass of cement) in the CSA concrete prism method (rhyolitic tuff from Quebec, Canada).

CONCRETE PRISM METHOD CAN/CSAA23.2-14A ~ Concrete prisms with dimensions not less than 75 m m x 75 m m x 300 mm and not more than 120 m m x 1 2 0 m m x 4 5 0 mm are made with the aggregates under study, a non-reactive sand, and a normal cement containing between 0.8 and 1.2% alkalis (Na~O equiv.). Since 1986, ss the alkali content of the mix must be increased to 1.25% of the mass of cement (310 kg/m a) by adding NaOH to the mix water. The prisms are stored at 100%

RH at 23 or 38"C, in a wet room (tests at 23"C) or more frequently over water in sealed containers, and their length is measured periodically. The expansion at 1 year should not exceed 0.025% (at 23"C) or 0.04% (at 38"C). The test is recommended for all types of aggregates, t°'59 A temperature of 23"C is sufficient for recognition of alkali-carbonate reactive aggregates. However, 38"C is recommended for all other types of aggregates, 7 particularly the slow/

38

Marc-Andr~ B~rub~, Benoit Fournier

late expanding silica/silicate reactive aggregates, for which the limit of 0.04% seems still reasonable. 6° As a result of the modifications proposed in 1986 ~s (higher temperature and alkali content), many deleterious aggregates which were not detected in the past can now be recognized (see Fig. 14). Variations in the w/c ratio, which is not at present controlled (water being adjusted to obtain a slump between 70 and 90 mm), may affect the results. Figure 15 indicates that, with reactive limestone aggregates, in contrast to previous findings with opaline aggregates, 61 a lower ratio (at least down to 0.45) could lead to higher expansion, as observed previously for mortar bars tested using ASTM C 227 (see Fig. 6), and for the same reasons. Sprung and Adabian 62 observed the same trend with greywackes and argillites. Unfortunately, the w/c ratio may vary with the aggregate and with the crushing procedure. For instance, jaw crushing tends to produce flat particles with some aggregates, which in turn leads to higher w/c ratios (to reach the specified slump) and possibly to lower expansions. Therefore a marginally deleterious aggregate may have more chance to satisfy the test if the sample contains a large amount of flat and elongated particles! The w/c ratio should be controlled, as it is in other countries using a concrete test (for instance, the UK and Japan 13,63). In practice, this ratio is controlled in most Canadian laboratories which currently perform CSA concrete prism tests. The amount of expansion in the CSA test could be also a function of the cement fineness. The finer the cement, the higher is the expansion, according to Kreil. 6= This could be explained by the fact that the alkalis originally present in the cement go more rapidly in the solution, then being more rapidly available for the reactions. 6 The results are also affected by the storage conditions (temperature and humidity), 31,64 and some workers recommend testing a reactive reference aggregate is parallel to control laboratory variations. Indeed, with an alkali-carbonate reactive limestone, Rogers and Hooton 3t tested four sets of conditions: (1) normal humid room at 23"C; (2) sealed plastic bags containing 100 ml of water and stored in the same room at 23"C; (3) immersion in a 5% NaCI solution at 23"C; and (4) over water at 38°C in a sealed box with fdter paper wicks. Except for condition (3), significant amounts of alkalis were leached from the prisms after 2"5 years, e.g. 63%, 22% and 42%, for conditions (1), (2) and (4), respectively. The amount of

expansion was related to the amount of alkalis remaining in the prisms. In fact, the average expansion after 1 year was the lowest under condition (1) (humid room at 23"C, probably as a result of more alkali leaching), and the highest values were obtained under condition (4) (over water in sealed containers at 38"C, as a result of the higher temperature). Therefore, the storage conditions (4) used in most laboratories (e.g. prisms stored at 380C over water in sealed plastic containers with wicks) seem to allow leaching of a large proportion of the alkali initially present inside the specimens. In the long term, this would explain why the expansion curves tend to flatten out as a result of alkali depletion. In their study, Rogers and Hooton 3~ did not test the effect of wicks on alkali leaching. However, experiments conducted at N R C 6 and at Laval University4 suggest that expansions (over water at 38*C, in sealed containers) are similar or even lower when the wicks are removed from the containers. It therefore seems that high humidity is more critical for concrete prisms than alkali leaching, in contrast to the case for mortar bars. We may mention here that Ranc et al. ~5 observed slightly lower expansions for the Spratt limestone aggregates when using wicking, although with different storage equipment: the specimens were stored over water in a sealed metal container which was itself stored over water inside an isolated container, caged a 'reactor', in which the temperature was maintained at 38°C by heating the bottom water. When used, the wicking material covered the inner walls of the reactor. Ranc et al. 65 obtained significantly lower expansions when

0,40

i £ o,32

W/C ratio =

0 45

•

0.50

~

i 0,24

./J7

oJ 0,16

OSA hma

8 0,08

,'.

0

4

8

, .',

12

.

16

20

24

Time (months)

Fig. 15. Effect of the water/cement ratio in the CSA concrete prism method (siliceous limestone from Quebec City, Quebec, Canada).

Canadian experience with alkali-aggregate testing the concrete specimens were stored in plastic bags (at 38°C). However, preliminary data from a multi-laboratory study in progress suggests that prisms wrapped in paper, placed in sealed plastic bags containing 100 ml of water, and stored over water in buckets at 38°C do not expand more than prisms stored over water in air inside the buckets. Some experiments conducted at Laval University also suggested that the expansions are slightly lower, by about 15-20%, when the concrete specimens are immersed in water for 30 min before each measurement (as specified in the CSA standard), compared with no immersion? This was attributed to alkali leaching by water. The CSA concrete prism test can detect most reactive aggregates except several reactive aggregates from New Brunswick, 32 including argiUites and natural gravels, and other lithic gravel aggregates from Ontario (Sudbury area)s° and Quebec. 27 According to Rogers, s° to recognize the slowly reactive aggregates, such as greywackes, argillites, quartzwackes, quartzites, phyUites, arkoses, sandstones and granites with highly strained quartz, the test should be modified to prevent excessive alkali-leaching (for instance by storing the prism in sealed plastic bags) or to compensate for this phenomenon (by adding more alkalis or by using more cement in the mix). Grattan-Bellewa suggested using 410 kg/m 3 of cement (rather than 310 kg/m3), because he observed a better correlation between laboratory concrete expansion and field performance. Mongeau 27 suggests 365 kg/m 3 for natural aggregates from Quebec. On the other hand, referring to the much higher content (700 kg/m 3) recommended in the BS 812 test method of the British Standards Institution, t4 Grattan.BeUew 6 also pointed out that 'excessive increases in the cement content of concrete prisms can, however, lead to satisfactory aggregates being classed as deleteriously expansive'. Hooton ~s also considered that 'the use of high alkali conditions to accelerate alkali-silica tests may cause petrographically marginal but satisfactory aggregates to be rejected, and needs to be viewed with caution'. Concerning reproducibility, the results of a multi-laboratory study involving 20 laboratories and alkali-carbonate reactive aggregates from Ontario suggest that the coefficient of variation for the CSA concrete prism method is about 23% for the four sets of storage conditions described above. 64 Results by other workers suggest that the test reproducibility could be worse with alkali-silica reactive aggregates, as shown in Table

39

2; this calls for other multi-laboratory studies on such aggregates. One study is in progress which involves a siliceous limestone (Spratt Quarry) and a lithic gravel (Sudbury). In our opinion, the CSA concrete prism method needs additional adjustments or controls to be more reproducible and to simulate field performance better. It seems necessary to control the w/c ratio (rather than the slump), the cement fineness, the storage conditions, and proportions between coarse and fine aggregates. At present, the coarse aggregates may represent 50-65% of all aggregates. Despite experimental variations, in Canada the current CSA concrete prism method is considered the most realistic method for evaluating the alkali-reactivity potential of concrete aggregates.6 Indeed, the test is capable of recognizing most Canadian reactive aggregates. However, this test needs 1 year to complete, and is then not satisfactory on many occasions. Moreover, the test is not capable of detecting a number of slowly reactive aggregates, for which it seems that a higher cement content is required. Recently, a CSA Task Group 66 worked on the revision of the test and proposed a number of modifications to: (1) allow detection of slowly reactive aggregates; and (2) reduce experimental variations from one laboratory to another. In particular, (1) the cement content should be increased to about 420 kg/m 3, and the alkali content of the mix should be increased to 1.25% (Na20 equiv.) of the mass of cement by adding NaOH to the mix water (to obtain a total alkali supply from the cement of 5"25 kg/m 3 rather than 3.9 kg/m 3 as in the present standard); (2) the w/c ratio should be controlled between 0-42 and 0.45; (3) the prisms should be stored over water in specified sealed plastic buckets with wicking; (4) the proportions between coarse and fine aggregates should be fixed at 60/40; and (5) the cross-section of the concrete prisms should be fixed (75 mm x 75 mm), with their length varying between 275 and 405 ram. Moreover, the test should be always performed at 38"C (even when testing for alkali-carbonate reactivity), and it is recommended to use the test also for testing sands (in the presence of a non-reactive coarse aggregate) or coarse-t-me aggregate combinations. The expansion limit should remain at 0"04% after 1 year. However, it can be expected from the above results for carbonate aggregates (1 year limit moved from 0"04% to 0.06% with a cement content increased from 310 to 350 kg/m3), and from

Marc-Andr~ B~rub~, Benott Fournier

40

Table 2. Results for the CSA Concrete Prism Method by various laboratories, for the same aggregates = Lab. MTO a

Reference Rogers 67 Rogers ~°

NRCC / LafargeS

Grattan-BeUew s Ranc etaL 6s

Gemtec Laval Univ.

DeMerchant & Soles 32 Oueget 23

B~rub~ et al.+B MTNB/

Mongeau 27 King. pers. comm. 1991

NBP k

Thompson 69

Alkah b (kg/m9

Cement (kg/m s)

L,mestone (SpratO

39 4.9-5-1 9-2-9-4 3-9 3-9 5-1 3-9 36 3-9 3-9 3.9 5-4 3-9

310 415 310 310 310 410 310 310 310 310 310 430 310

0-082 0.134 0 193 ~ 0.130 t 0-148 h 0-140' 0-221

Gravel (Sudbury)

RhyoL tuff (Beauceville)

Greywacke (Springhilly

0-021 0-174

0,142 0,188 = 0'230 t

0,097 / 0.206 I ==0-250 t

0-063 0-108 0-014

0 071 0,244

0.274 0-036 0.020 0.370 ==0-032:

aAli tests at 38"C and 100% RI-I with containers with wicks (except for Lafarge), bNazO equivalent basis. 'Similar aggregates used in the Mactaquac dam 69 The samples may differ from one study to another. aMinistry of Transportation of Ontario. "Expansions at 273 days. /National Research Councd of Canada. The expansions quoted are the maximum expansions obtained when the expansion curves flattened out. gWithout wicking; specimens stored over water in a sealed container which is itself stored over water inside another ~solated container m which the temperature is maintained at 38"C. *Three replicate tests performed at different times on the same aggregates gave 0.131%, 0-167% and 0-145%. 'Three replicate tests performed at different times on the same aggregates gave 0.144%, 0.136% and 0.140%. JMinistry of Transportation of New Brunswick. ~New Brunswick Power. t ==Estimated from graphs found in corresponding references.

016

the results of another study on natural aggregates, 27 that the new procedure will be severe for many aggregates with no bad recorded field performance until now.

~.E ~

ACCELERATED CONCRETE PRISM METHOD CurSED IN QUEBEC)

o t~ . ~

In Quebec, concrete prisms are made in accordance with the CSA concrete prism method, usuaUy with a constant w/c ratio (0.50 or 0-55), but are cured in a 1~ NaOH solution at 80"C. Blanchette 39 suggested a limit of expansion of 0.04% after 24 days (Fig. 16), which agrees very well with the results obtained at Laval University by Oueget 23 for quarried silicate aggregates (Fig. 17), by Fournier and B~rub~ 4t,63 for quarried carbonate aggregates (Fig. 18) as well as for a series of 10 other quarried aggregates used in Canadian dams (9 silicate rocks and 1 dolostone). 57 Such a limit ensures that all the deleterious quarried aggregates tested (15 silicates and 22 carbonate rocks) are classed as expansive. However, many quarried carbonate aggregates (points located in the upper left field in Figs 16 and 18) expanded significantly in this immersion

• Carbonate Aggregates o Silicate Aggregates

,3

°

d'.~,¢ 0.12

10 b16 el

o.o8

.s

171¢ '7

e9

4 ~1 5

_g004 13o6 08

8 <

0.00

P2 0.00

I

(Blanchette 1989) '

I

'

I

'

I

0 04 0.08 0.12 0 16 CSA Corcrete Prism Test (% exp after 1 year)

"

0 20

Fig. 16. Results obtained at the Ecole Polytechnique39 for the accelerated concrete prism method (immersion in 1N NaOH at 80"C), for aggregates from Quebec. When using the proposed limit of 0-04% expansion after 24 days, all the deleterious aggregates tested (bad field performance, expansion > 0"04% in the CSA concrete prism test) are classed as expansive, whereas four of the eight presumably innocuous aggregates tested are classed as expansive. (Refer to Fig. 8 for aggregate identification).

test, although they performed well in the CSA concrete prism test and/or in existing structures. In fact, only 50% (8/16) of the non-expansive carbonate aggregates tested are classed correctly

Canadian experience with alkali-aggregate testing

in the accelerated concrete test• This is not as good as with the accelerated mortar bar method (in which 85% of the innocuous carbonate aggregates tested were classed properly; see Fig. 11). Concerning quarried silicate aggregates, one andesitic aggregate (No. 1 in Fig. 17) and one granitic gneiss s7 expanded significantly in the immersion test, although they performed well in the CSA concrete prism test. Other innocuous or presumably innocuous quarried silicate aggregates, unfortunately not tested until now in the accelerated concrete test, could behave similarly, in particular those that also expanded in the accelerated mortar test (see Fig. 7). The results are clearly bad for natural gravels from Quebec: 27 three of the six granitic gravels tested expanded more than 0.04% at 24 days in the accelerated concrete test, whereas only one expanded in the accelerated mortar bar method, showing a very marginal expansion (0.11%). The accelerated concrete prism method is very severe, and therefore can be used only as a screening test, with further testing necessary for all aggregates showing expansion. The accelerated mortar bar method is much less severe, and is more highly recommended. Nevertheless, testing field concrete (core) specimens in NaOH at 80"C still remains an interesting method for determining rapidly the reactivity of aggregates present in existing concrete structures.7°. 7

41

CN RESEARCH'S CONCRETE METHOD In the test method proposed by Scott and Duggan72 from CN Research, concrete test prisms are cast and submitted to accelerated curing. Then small cores (22-ram diameter) are drilled and cut

0,16 A o 4[]

&

0,) I--

.~ ~0,12 &

A A

~cM 0

0

/I, & 0

0 []

,% b-~. CARBONATE AGGREGATES

0

o < 0,00

,

0,00

•

O

el 7 1

• 16

•

t2

_ o.o2 o o

SILICATE AGGREGATES

014

000

•

000

0.04

I

•

I

•

i

"

I

008 0.12 0.16 0.20 CSA Cor~ete Prism Test (% exp. alter 1 year)

"

I

024

0,48

A=rcooling (1 hour)

I

°

°s

"

0

e19

==oo4

,

I Dry heat [ 82 . . . . ~ 4 _ ~

13

8=.

•

Fig, ]8. Resultsobtained at Lava] University for the accelerated concrete prism method (immersion m IN NaOH at 80=C), for carbonate aggregates from Quebec. When using the proposed limit of 0"04% expansion after 24 days, all fourteen (14) expansive aggregates tested (>0'06% in the CSA concrete prism test) are classed as reactive, whereas only 62% (8/13) of the non-expansive aggregates tested are evaluated correctly. Therefore the test is less efficient than the accelerated mortar bar method (in which 85% of the innocuous aggregates tested were classed properly; see Fig. ll).

• Deleterious o Innocuous

2o

,

0,12 0,24 0,36 CSA Concrete Test (% exp. after I year) (350 koJm3of cement)

0.08 (D I--

Trenton Black R i v e r Chazy Beekmantown

"

21

Dist=l~edwater

Zero

I I

Distilledw a t e r Expans=onpenod

i

0.28

Fig. 17. Results obtained at Laval University for the accelerated concrete prism method (immersion in 1N NaOH at 80°C), for silicate aggregates from Quebec. When using the proposed limit of 0.04% expansion after 24 days, all five deleterious aggregates tested (bad field performance, expansion > 0'04% in the CSA concrete prism test) are classed as expansive, whereas one of the five presumably innocuous aggregates tested (1: andesite) appears expansive. (Refer to Fig. 7 for aggregate indentification).

•

0

I

2

w

I

"

I

"

I

4 6 8 Cycling ~ penod

"

I

0 ~

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I

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I

"

I

"

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"

6 8 10 12 14 Expansion penod

Days

Fig. 19. In the CN Research's test, small cores of concrete (22 mm diameter x 50 mm length) are submitted to cycles of immersion in distilled water at 21°C, followed by heating in air at 82°C. Then the first reading is taken, and the cores are stored in distilled water, with their length measured periodically. The proposed expansion limit is 0.1% after 20 days of immersion.

Marc-Andr~ B~rubd, Benoit Fournier

42

to 50-mm length. The test procedure is shown in Fig. 19. The suggested limit of expansion at 20 days after the cycling period is 0-1%. However, a recent study established that the expansions obtained in this test depend mainly on the sulphate content of the cement used, and not on the aggregate. In fact, the long-term expansion correlates with the amount of ettringite in the sampies. 73

than ISO bars, and the Duncan method j4 (ASTM C 227 mortar bars stored at 100% RH and 64°C), have also been investigated. 29 These two tests failed in recognizing the reactive aggregates tested. Other rapid methods used outside Canada have been reviewed by Grattan-BeUew, 6 Hobbs, ~3 and Bdrub6 and Fournier. 63

DISCUSSION OTHER METHODS INVESTIGATED IN CANADA Hooton and Rogers 29 tested 12 Canadian aggregates with known petrographic characteristics and field performance, mostly from Ontario, with a number of rapid test methods. The results obtained in the accelerated mortar bar method, and in autoclave tests (modified from the original Chinese and Japanese proposals), have been discussed above. The Danish salt method TM (mortar bars immersed in saturated NaCl solution at 50"C), using ASTM C 227 mortar bars rather [ AmI1E

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Fig. 20. Proposed decision chart for determination of the potential alkali-reactivity of concrete aggregates. This chart is based mainly on Quebec experience.

On many occasions, aggregates must be evaluated very quickly before construction, which calls for test methods that are rapid, reliable, simple and reproducible. Among the rapid test methods, the petrographic examination is always the first step. When performed by a well-experienced petrographer, it can be used to accept or even reject an aggregate under study, or at least to select the most appropriate tests to run, then preventing wrong choices and reducing the amount of test work. Indeed, some test methods are not capable of detecting deleterious aggregates, while other methods are too severe for some inocuous ones. Among the other rapid test methods, the chemical method ASTM C 289 lacks reliability and is not recommended, mainly because of interference by carbonates, which would result in the acceptance of numerous deleterious aggregates. The modified chemical method (ASTM C 289 on insoluble residues) is also not recommended, because it is too complex, poorly reproducible and not more efficient than the accelerated mortar bar method, which takes just a little longer. However, in the St Lawrence Lowlands of Quebec, carbonate aggregates with less than 5% insoluble residues are non-expansive, a simple criterion that is also useful in this Province. In addition to the petrographic examination, the only recommended rapid test is the accelerated mortar bar method ASTM C 9 -- Proposal -- P 214. However, this test is severe for numerous innocuous aggregates (natural gravels, limestones, dolostones, sandstones, greywackes, etc.), therefore cannot be used for rejecting aggregates. It also fails in recognizing a few reactive aggregates such as some Potsdam sandstones, which cause a problem in the Beauharnois Hydro complex, and the alkali-carbonate reactive aggregates from the Kingston area. This accelerated test remains a very powerful tool, however, because only a few deleterious aggregates cannot be detected. Moreover, it is much less severe than the accelerated concrete prism method (immersion in 1N NaOH at 80"C), which

Canadian experience with alkafi-aggregate testing is currently used in Quebec. The autoclave mortar bar method developed at Laval University appears very promising. Before being used as a routine test, this method as well as any new test method must always be checked by many other workers. Unfortunately, many of the proposed methods found in the literature need more investigation, and the following remark by Grattan-Bellew~ clearly reflects thi.~ situation: ~dl the rapid test methods appear to give satisfactory results, at least with the limited range of aggregates which have been tested,' If any doubt remains after performing the petrographic examination and the accelerated mortar bar method (i.e. significant expansion), there is no other choice than to run the 1-year concrete prism method CAN/CSA A23.2-14A at 38"C. The mortar bar method ASTM C 227 is not recommended because the results are greatly affected by the storage conditions (type of container, wicking), the water/cement ratio and the alkali content, and because the length of the testing period (6 months) is almost as long as in the more realistic CSA concrete test. When time is not critical, it is recommended that the CSA concrete test be run immediately. Indeed, this test is more realistic and could be required anyway; for instance, each time expansion in excess of 0-1% is obtained in the accelerated mortar bar method. However, the concrete method has also its disadvantages; for instance, it is affected by the water/cement ratio, the cement fineness and the storage conditions, and possibly the relative proportions of fine and coarse aggregates. These parameters will probably be controlled in the next version of the CSA standard. Moreover, the specified alkali content of 3"9 kg/ m 3, corresponding to a cement content of 310 kg/ m 3 with the alkalis adjusted to 1"25% (Na20 equiv.) of the mass of cement (by adding NaOH to the mix water), appears insufficient for detection of a number of reactive aggregates, e.g. some greywackes, argillites and natural gravels from New Brunswick 32 and Nova Scotia, some natural lithic gravels from the Sudbury-New Liskeard area in Ontario, 6° and a number of Appalachian lithic gravels from Quebec. 27 All these aggregates cause significant expansion in the accelerated mortar bar method, but this is not sufficient to reject them, as this accelerated test is severe for many innocuous aggregates. In most cases, the uncertainty could be avoided by specifying a higher cement content (still increasing the alkalis to 1-25% of the mass of cement). This practice was recommended by Grattan-Bellew s for aggregates

43

that expand more than 0.1% in the accelerated mortar bar method. In the revised version of the CSA standard, a cement content of 420 kg/m 3 will probably be specified, 66 which could render the test too severe for many innocuous aggregates, unless the expansion limit criterion used for aggregate acceptance is less severe for some aggregate types, e.g. 0.04"/0 at 6 or 8 months rather than 1 year.

CONCLUSION As a result of the above discussion, only three test methods are finally recommended: (1) the petrographic examination, which is always necessary; (2) the accelerated mortar bar method (ASTM C 9 -- Proposal -- P 214), the only statistically dependable rapid test method; and (3) the CSA concrete prism method, which is required if there is any doubt from the petrographic examination and if the aggregates expand in the accelerated mortar bar method. If time is not critical, immediate use of the concrete test is recommended. However, it is clear that none of these recommended methods can be successfully applied to every type of aggregate; therefore~ as pointed out by Hooton, ~6 it is always preferable to perform many different tests. A decision chart based on the above three recommended test methods is proposed (Fig. 20) for determining the potential alkali-reactivity of concrete aggregates. This chart is based on Quebec experience and could not apply to all aggregates found in other Provinces or in other countries. Even for Quebec, a doubt still remains about the actual performance of most lithic gravels exploited in many areas (Abitibi, Eastern Townships and Gaspesia). As mentioned above, these aggregates show significant expansions in the accelerated mortar bar method, although they perform well in the CSA concrete prism method. However, a number of existing structures built with this type of aggregate have been recently recognized as affected to some extent by alkali-aggregate reactions. For the present, field performance provides the only useful information to evaluate these aggregates correctly. Increasing the cement content in the CSA concrete test procedure to about 365 kg/m 3 should help to overcome this particular problem. 27 Three conditions must prevail to maintain A A R in concrete: (1) the aggregates must be reacfive; (2) the alkalis must remain abundant in the concrete pore solution -- these are mostly sup-

44

Marc-Andrd Bdrubd, Benott Fournier

plied by the cement, but some may also be provided by chemical or mineral additives, by some mineral phases present within the aggregate particles (e.g. altered feldspar or zeolites), or by secondary sources (sea-water or de-icing salt); (3) the concrete must be exposed to high humidity, over 80-85% RH according to many w o r k e r s ; 4,57,75 n o problem should arise in concrete that is not submitted to humid conditions, even with highly reactive aggregates. To prevent or minimize A A R in a concrete component that will be built with reactive or potentially reactive aggregates and exposed to high humidity, it is recommended that (1) low-alkali cements (typically < 0.6% Na20 equiv.) or low cement contents be used to ensure that total alkalis provided by the cement are low (typically < 3 kg/m 3 of concrete66), provided the other concrete constituents do not supply significant alkalis to the pore solution and that the concrete will not be subjected to or is protected against external sources of alkalis such as sea-water and de-icing salts (e.g. by using surface sealers, water repellents or membranes); and/or (2) a sufficient amount of the cement be replaced by supplementary cementing materials (e.g. condensed silica fume, pulverized fly ash, ground granulated blast furnace slag or natural pozzolan), making sure that the selected materials have already proved to be effective with the reactive aggregates to be used at the proposed proportion of cement replacement.

2.

3. 4.

5.

6.

7.

8.

9.

10.

11.

12.

ACKNOWLEDGEMENTS The work reported in this paper has been supported by the National Science and Engineering Research Council (NSERC), the Fonds pour la Formation des Chercheurs et l'Aide h la Recherche of Qudbec (FCAR), the Ministry of Transportation of Qutbec and Hydro Qutbec. They are all gratefuly acknowledged. Thanks are also due to Jean Frenette for his greatly appreciated contribution.

13 14.

15.

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16.

Ministry of TransportaUon of Ontario, Downsvtew, Ont., Canada, Report EM-92, 1990. ASTM C 295-90. Standard guide for petrograpluc examination of aggregates for concrete. In Annual Book of ASTM Standards, 04.02 Concrete and Aggregates. Amencan Society for Testing and Materials, Philadelphia, PA, USA, 1992, pp. 179-86. Dolar-Mantuani, L., Handbook of Concrete Aggregates -- A Petrographic and Technological Evaluation. Noyes, Park Rtdge, NJ, USA, 1983. Fourmer, B & Bdrul0d, M. A., General notions on alkali-aggregate reactions. In. Petrography and Alkali-Aggregate Reactivity -- Course Manual. CANMET-EMR, Ottawa, Canada, 1991, pp. 6-69. Grattan-Bellew, P. E, A high undulatory extraction in quartz mdicauve of alkah-expansivity of granitic aggregates 9 In: Concrete Alkali-Aggregate Reactions. (Proc. 7th Int. Conf. on AAR, Ottawa, Canada, 1986) Noyes, Park Ridge, NJ, USA, 1987, pp. 434-9. Grattan-Bellew, P. E., Test methods and critena for evaluating the potential reactivity of aggregates. In: Alkah-Aggregate Reaction -- 8th International Conference. (Proc 8th Int. Conf. on AAR, Kyoto, Japan, 1989). Society of Materials Science of Japan, Kyoto, Japan, 1989, pp. 279-94 CAN/CSA A23.I-M90, Concrete materials and methods of concrete construction, and CAN/CSA A23.2-M90, Methods of test for Concrete. Canadian Standards Association, Rexdale, Ont., 1990. Grattan-Bellew, P. E., Canadian experience with mortar bar rapid tests for AAR. In: Canadian Developments m Testmg Concrete Aggregates for Alkali-Aggregate Reactivity. Ministry of Transportation of Ontario, Downsview, Ont., Canada, Report EM-92, 1990, pp. 17-34 ASTM C 289-87, Standard test method for potentml reactivity of aggregates (chemical method). Annual Book of ASTM Standards, 04 02 Concrete and Aggregates. American Society for Testing and Materials, Philadelphia, PA, USA, 1992, pp. 163-9. Grattan-Bellew, P. E., Canadian expenence of alkaliexpanslvity in concrete, m: Proc. 5th Intemauonal Conf Alkah-Aggregate Reaction m Concrete (Proc. 5th lnt Conf. on AAR, Cape Town, RSA, 1981) NBRI-CSIR, Pretoria, Republic of South Africa, 1981, Paper $252/6. Duncan, M. A. G., Swenson, E G., Gillott, J. E & Foran, M. R., Alkah-aggregate reaction in Nova Scotia: I. Summary of a five year study. Cement and Concrete Research, 3 (1)(1973)55-70. Sims, I, The importance of petrography in the ASR assessment of aggregates and existing concretes. In. Concrete Alkali-Aggregate Reacuon. (Proc. 7th Int. Conf. on AAR, Ottawa, Canada, 1986). Noyes, Park Ridge, NJ, USA, 1987, pp. 358-67. Hobbs, D. W., Alkah-Sdica Reaction In Concrete. Thomas Telford, London, 1988. Hobbs, D. W., AAR in the UK: diagnosis, concretes affected, preventive measrues and remedial actions. In: International Workshop on Alkali-Aggregate Reactions in Concrete: Occurrences, Testing and Control. CANMET-EMR, Ottawa, Canada, 1992 (Workshop held in Halifax, Canada, 1990). Fournier, B. & Bdrubt, M. A., Evaluation of a modified chemical method to determine the alkali-reactivity potential of siliceous carbonate aggregates. In: Canadian Developments in Testing Concrete Aggregates for Alkali-Aggregate Reactivity. Ministry of Transportation of Ontario, Downsview, Ont., Canada, Report EM-92, 1990, pp. 118-35. Hooton, R. D, Case studies of Ontano Hydro's experience with standard tests for alkali-aggregate reactivity.

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ence. (Proc. 8th int. Conf. on AAR, Kyoto, Japan, 1989). Society of Materials Science of Japan, Kyoto, Japan, 1989. Also in: Canadian Developments in Testing Concrete Aggregates for Alkali-Aggregate Reactivity, Ministry of Transportation of Ontario, Downsview, Ont., Canada, Report EM-92, 1990, pp. 1-9. Rogers, C. A. & Hooton, R. D., Leaching of alkalis in alkali-aggregate reaction testing. In: Alkali-Aggregate Reaction -- 8th International Conference. (proc. 8th Int. Conf.on AAR, Kyoto, Japan, 1989). Society of Materials Science of Japan, Kyoto, Japan, 1989, pp. 327-32. DeMerchant, D. P. & Soles, J. A., CANMET research on alkali-aggregate reactivity in New Brunswick. In: International Workshop on Alkali-A~egate Reactions in Concrete: Occurrences, Testing and Control. (Workshop held in Halifax, Canada, 1990). CANMET-EMR, Ottawa, Canada, 1992, 35 p. Brotschi, J. & Mehta, K. P., Test methods for determining potential alkali-silica reactivity in cements. Cement and Concrete Research, 8 (2)(1978) 191-9. Kishitani, K., Nishibayashi, S. & Morinaga, S., Response of JCI to alkali-aggregate reaction problem -- guideline for determining potential alkali reactivity. In: Concrete Alkali-Aggregate Reaction. (Proc 7th Int. Conf. on AAR, Ottawa, Canada, 1986). Noyes, Park Ridge, NJ, USA, 1987, pp. 264-8. ASTM C 9 -- Proposal -- P 214, Proposed test method for accelerated detection of potentially deleterious expansion of mortar bars due to alkali-silica reaction. Annual Book of ASTM Standards, 04.02 Concrete and Mineral Aggregates. American Society for Testing and Materials, Philadelphia, PA, USA, 1991, pp. 755-8. Oberholster, R. E. & Davies, G., An accelerated method for testing the potential alkali reactivity of siliceous aggregates. Cemem and Concrete Research, 16 (1986) 181-9. Davies, G. & Oberholster, R. E., An interlaboratory test programme on the NBRI accelerated test to determine the alkah-reactivity of aggregates. National Building Research Institute, CSIR Special Report BOU 92, Pretoria, RSA, 1987. Fournier, B. & B~rub~, M. A., Application of the NBRI accelerated mortar bar test to siliceous carbonate aggregates produced in the St Lawrence Lowlands (Quebec, Canada) -- Part I: Influence of various parameters on the test results. Cement and Concrete Research, 21 (1991) 853-62. Blanchette, A., Evaluation du potentiel de r~activit~ alcaline des granulats ~ I'alde d'essals acc~l~r~s. Presented at: Progress in Concrete 1989, ACI Meeting, Montreal, Canada, 1989. B~rub~, M. A., Fournier, B., Mongeau, P~ Dupont, N., Ouellet, C. & Frenette, J., Effectiveness of the accelerated mortar bar method, ASTM C 9 -- Proposal -- P 214 or NBRI, for assessing potential AAR in Quebec (Canada). In: The 9th International Conference on Alkali-Aggregate Reaction in Concrete. (Conference held in London, 1992). The Concrete Society, Wexham, Slough, UK, 1992, pp. 92-101. Fournier, B. & Berub~, M. A., Alkali-reactivity potential of carbonate rocks from the St Lawrence Lowlands (Quebec, Canada). In: Alkali-Aggregate Reaction -- 8th International Conference. (proc. 8th Int. Conf. on AAR, Kyoto, Japan, 1989). Society of Materials Science of Japan, Kyoto, Japan, 1989, pp. 363-8. Foumier, B. & Berub~, M. A., F'valuation du potentiei de r~activit~ alcaline des granulats ~ b&on produits dans les Basses-Terres du Salnt-Laurent du Quebec. Canadian Journal of Civil Engineering, 18 (2) (1991) 282-96.

46

Marc-Andrd Bdrubd, Benoit Fournter

43. Fournier, B. & B6rubd, M. A., Application of the NBRI accelerated mortar bar test to siliceous carbonate aggregates produced in the St Lawrence Lowlands (Quebec, Canada) -- Part II: Proposed limits, rates of expansion, and mierostructure of the reaction products. Cement and Concrete Research, 21 (1991) 1069-82. 44. Shayan, A. & Quick, G., Microstructure and compos~aon of AAR products in conventional standard and new accelerated testing. In: Alkali-Aggregate Reaction -- 8th International Conference. (Proc. 8th Int. Conf. on AAR, Kyoto, Japan, 1989). Society of Matenals Science of Japan, Kyoto, Japan, 1989, pp. 475-82. 45. Hooton, R. D., lnterlaboratory study of the NBRI rap~d test method and CSA standardization status. In: Canadian Developments in Testing Concrete Aggregates for Alkali-Aggregate Reactivity. Ministry of Transportation of Ontario, Downsview, Ont., Canada, Report EM-92, 1990, pp. 225-40. 46. Davies, G. & Oberholster, 1L E., Use of the NBRI accelerated test to evaluate the effectiveness of mineral admixtures in preventing the alkah-silica reaction. Cement and Concrete Research, 17 (1987) 97-107. 47. Duchesne, J. & Btrubd, M. A., An autoclave mortar bar test for assessing the effectiveness of mineral admixtures in suppressing expansion due to AAR. In: The 9th International Conf. on Alkali-Aggregate Reaction in Concrete. (Conference held in London, 1992). The Concrete Society, Wexham, Slough, UK, 1992, pp. 279-86. 48. B~rubd, M. A. & Duchesne, J., Evaluation of testing methods used for assessing the effectiveness of mineral admixtures in suppressing expansion due to alkali-aggregate reaction. Proc. 4th CANMET/AC1 Int. Conf. on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, Istanbul, Turkey. ACI SP-132, 1992, pp. 549-75. 49. Chen, H. & Suderman, R. W., The Effectiveness of Canadian Supplementary Cementing Materiab in Reducing Alkali-Aggregate Reactivity. Final Report submitted to CANMET-EMR, DSS File Number 23SQ.23440-29200, Ottawa, Canada, 1990. 50. Chen, H., Soles, J. A. & Malhotra, V. M., Investigations of supplementary cementing materials for reducing alkali-aggregate reactions. In: International Workshop on Alkah-Aggregate Reactions in Concrete: Occurrences, Testing and Control. (Workshop held in Halifax, 1990). CANMET-EMR, Ottawa, Canada, 1992. 51. Hudec, P. P., Rapid test for predicting alkali reactivity: promises and problems. In: Canadian Developments in Testing Concrete Aggregates for Alkali-Aggregate Reacuvtty. Ministry of Transportation of Ontario, Downsvlew, Ont., Canada, Report EM-92, 1990, pp. 111-17. 52. Fournier, B., Btrubt, M. A. & Bergeron, G., A new autoclave mortar bar test to determine the alkali-reactivity potential of the carbonate aggregates produced in the St Lawrence Lowlands (Quebec, Canada). Cement, Concrete and Aggregates, 13 (1) (1991 ) 58-71. 53. Nishibayashi, S., Yamura, K. & Matsushita, H., A raptd method of determining the alkali-aggregate reaction m concrete by autoclave. In. Concrete Alkali-Aggregate Reaction. (Proc. 7th Int. Conf. on AAR, Ottawa, Canada, 1986). Noyes, Park Radge, NJ, USA, 1987, pp. 299-303. 54. Tang, M. S., Han, S. F. & Zhen, S. H., A rap~d method for identifica,on of alkali-reactivity of aggregate. Cement and Concrete Research, 13 (1983) 417-22. 55. Dupont, N., Essal h rautoclave: Ddtermination des conditions de ressai et application h divers granulats sdicatts de la Province de Qudbec. Dtpartement de Gtologle et de Gdme Gdologlque, Universitd Laval, Sainte-Foy, Qudbec, Canada, 1990. 56. Bdrubt, M. A, Fournier, B., Dupont, N, Mongeau, P. &

Frenette, J., A simple autoclave mortar bar method for assessing potential alkali-aggregate reactivtty in concrete. In:- The 9th lnternattonal Conference on Aikah-Aggregate Reaction in Concrete. (Conference held m London, 1992). The Concrete Society, Wexham, Slough, UK, 1992, pp. 81-91. 57. B~rubd, M. A., Pigeon, M., Dupont, N., Frenette, J. & Langlois, M., Expansion test methods for mass concrete exposed to alkali-aggregate reaction -- Project CEA No. 715 G 687, Canadian Electrical Association, Montreal, Canada, 1992. 58. Supplement No. 2-1986 to CSA Standards CAN3A23.2-M77 (Concrete Materials and Methods of Concrete Construction), and CAN3-A23.2-M77 (Methods of Test for Concrete). Canadian Standards Association, Rexdale, Ont., 1986. 59. Grattan-BeUew, P. E., Re-evaluation of standard mortar bar and concrete prism tests for alkali-aggregate rea,:tivity. Mat~riaux et Constructions, 16 (94) (1983) 243-50. 60 Rogers, C. A., Concrete prism expansion testing to evaluate slow/late expanding alkali-silicate/silica reactive aggregates. In: Canadian Developments tn Testing Concrete Aggregates for Alkali-Aggregate Reactivity. Ministry of Transportation of Ontario, Downsxaew, Ont., Canada, Report EM-92, 1990, pp. 96-110. 61. Krell, J., Influence of mix design on alkali-silica reaction m concrete. In: Concrete Alkali-Aggregate Reaction. (Proc 7th Int. Conf. on AAR, Ottawa, Canada, 1986). Noyes, Park Ridge, NJ, USA, 1987, pp. 441-5 62. Sprung, S. & Adabmn, M., The effect of admixtures on alkali-aggregate reaction in concrete. Proc 3rd Int. Conf on AAR, London, UK, 1976, pp. 125-38. 63. Btrubt, M. A. & Fournier, B., Accelerated test methods for alkali-aggregate reactivity. In: Advances in Concrete Technology. (Pro(:. Int. Symp. on Advances m Concrete Technology, Athens, Greece, 1992). CANMET/EMR, Ottawa, Canada, 1992, pp 583-627. 64 Rogers, C. A., lnterlaboratory study of the concrete prism expansion test for the alkali-carbonate reaction. In: Canadian Developments tn Testing Concrete Aggregates for Alkah-Aggregate Reacttvity. Ministry of Transportation of Ontario, Downsview, Ont., Canada, Report EM-92, 1990, pp. 136-49. 65. Ranc, R., Cariou, B. & Sorrentino, D., Storage conditions and reliability of the ASTM C 227 mortar bar and CSA A23 2-14A concrete prism tests: another look. In: Canadian Developments m Testing Concrete Aggregates for Alkali-Aggregate Reactivity. Ministry of Transportation of Ontario, Downsview, Ont., Canada, Report EM92, 1990, pp. 190-200. 66. Cement-Aggregate Reactwity Sub-Committee CSA-A5 Task Group. Proposed changes to CSA A23.1 and A23.2 as regards alkali-aggregate reactivity and assocrated test methods. Draft Document, 1992. 67 Rogers, C. A., General Informaaon on Standard AlkahReactive Aggregates from Ontario, Canada. Engineering Materials Office, Mimstry of Transportation of Ontario, Downsvlew, Ont., Canada, 1988. 68. Bdrub6, M. A., Fournier, B. & Frenette, J., l~valuation de la performance de divers ciments face aux r~actions aicalis-granulats darts le b~ton. Report GGL-88-20, Dtpartement de Gtologie et de Gtme G~ologtque, Universit6 Laval, Samte-Foy, Qutbec, Canada, 1988. 69. Thompson, G. A., Alkali-aggregate reactivity remedial measures: Maetaquac intake structure. In: International Workshop on Alkah-Aggregate Reactions in Concrete Occurrences, Testing and Control. (Workshop held in Halifax, Canada, 1990) CANMET-EMR, Ottawa, Canada, 1992. 70 Btrub6, M. A & Fourmer, B., Testing field concrete for

Canadian experience with alkali-aggregate testing future expansion by alkali-aggregate reactions. In: Canadian Developments in Testing Concrete Aggregates for Alkali-A~regate Reactivity. Ministry of Transportation of Ontario, Downsview, Ont., Canada, Report EM92, 1990, pp. 162-80. 71. l~rub~, M. A. & Foumier, B., Testing field concrete for further expansion due to alkali-aggregate reactivity. In: Petrography and Alkali-Aggregate Reactivity -- Course Manual. CANMET-EMR, Ottawa, Canada, 1991, pp. 283-349. 72. Scott, J. E & Duggan, C. R., Potential new test for alkali-aggregate reactivity. In: Concrete Alkali-Aggregate Reaction. (Proc. 7th Int. Conf. on AAR, Ottawa, Canada, 1986). Noyes, Park Ridge, NJ, USA, 1987, pp. 319-23.

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