CEMENT and CONCRET RESEARCH, Vol. 21, pp. 1069-1082, 1991. Printed in the USA.
0008-8846/91. $3.00+00. Copyright (c) 1991 Pergamon Press plc.
APPLICATION OF THE NBRI ACCELERATED MORTAR BAR TEST TO SILICEOUS
CARBONATE AGGREGATES PRODUCED IN THE ST. LAWRENCE LOWLANDS
(QUEBEC, C A N A D A )
PART 2: PROPOSED LIMITS, RATES OF EXPANSION, AND
MICROSTRUCTURE OF REACTION PRODUCTS
B. Fournier* and M.A. B~rub~**
* CANMET, 405 Rochester Street, Ottawa (Canada), K1A 0G1
** Department of Geology, Laval University, Quebec City (Canada), G1K 7P4
(Communicated by M. Moranville-Regourd)
(Received March 26, 1991)
ABSTRACT
The NBRI Accelerated Mortar Bar Test has been applied to 71 carbonate aggregates representing
the vadous petrographic facies exploited along the St. Lawrence Lowlands. Limit cdteda are
proposed based on the behavior of these aggregates under standard testing conditions and on
field performance. The microstructure of reaction products formed in the mortar bar during the
accelerated test has been studied under the stereomicroscope and the SEM.
Introduction
Intensive work is presently in progress to determine the efficiency of the NBRI Accelerated Mortar
Bar Test for evaluating the potential alkali-reactivity of concrete aggregates produced in this country. A
CSA draft version of the procedure has been recently proposed and evaluated through a multilaboratory
study (1-3). Grattan-Bellew (4) recently reviewed the behavior of numerous Canadian rocks tested by the
NBRI test, and concluded that a 0.15% expansion limit (at 14 days) could probably be used to distinguish
non-reactive and reactive aggregates. This probably constitutes an acceptance limit since many nonreactive rocks (at least in Quebec and Ontario) exhibit expansion values considerably in excess of this limit
while inducing only negligible expansion in the CSA Concrete Prism Test, and give good field
performance. This certainly emphasizes the importance of running a careful petrographic examination of
the investigated aggregates before doing any accelerated test, in order to avoid misleading and
erroneous interpretation.
In the St. Lawrence Lowlands (Quebec, Canada), sedimentary rocks of Ordovician age are the
main source of concrete aggregates. Some siliceous limestones exploited in the Ottawa, Montreal, TroisRivi~res and Quebec City areas have already been recognized as alkali-silica reactive in concrete (5-10).
However, the degree of deterioration affecting concrete structures shows large variations within a
particular area and from one area to another. This is mainly attributed to variations in the alkali-reactivity
potential of aggregates, but also to the exposure conditions of the affected structures (application of
deicing salts, etc.). This paper evaluates the efficiency of the NBRI accelerated mortar bar test to
determine the potential alkali-reactivity of such aggregates.
Materials and Methods
The St. Lawrence Lowlands consist mainly of relatively unfolded and flat-lying beds of limestones,
dolostones, sandstones and shales, extending along the St. Lawrence River. These are bordered to the
northwest by the Precambdan Shield, along a series of normal faults, and to the southeast by the folded
rocks of the Appalachian belt (11). 71 samples were collected (bed-by-bed sampling) from twenty-one
quarries, representing the lateral and vertical vadations within this large structural domain. Stratigraphic
1069
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Vol. 21, No. 6
NBRITEST, SILICEOUSCARBONATEAGGREGATES,EXPANSION
1071
correlations were based mainly on petrographic considerations but also on stratigraphic markers,
consisting of beds of altered volcanic ash, called "K-Bentonites" (12). Figure 1 and Table 1 give the
location of the quarries, the regional geology and the petrographic characteristics of the samples.
TABLE 1'. Petrography of the Geological Formations or Members Investigated
FormatiQn
(Member)
Petro~,raohv
v
.
.
Tetreauvill¢
Neuvil[¢
Fine grained, micritic and dark argillaceous limestone,
thin bedded (5 - 15 cm), with numerous shale interbeds
(Grondines)
(sometimes forming more than 25% of the overall sequence).
Fine to medium grained and medium grey siliceous
Neuvill¢
limestone, medium bedded (15 - 30 cm); occasional
(St. Casirair)
nodules of dark grey chert.
Montreal
Fine to medium grained, dark grey, siliceous and
( R o s e m o n t ) argillaceous limestone, thin bedded; also dark grey and
(St. Michel)
medium grained skeletal limestone, medium bedded.
Fine grained, medium bedded and medium grey
siliceous limestone (I); Coarse grained, pale grey to
Deschambault beige, high-calcium and thick bedded (> 30 cm) skeletal
limestone (II); occasional nodules of black chert.
Mile End Fine to medium grained, medium grey, micritic and
shelly limestone, medium to thick bedded.
OuarCag
Fine grained, medium grey, sometimes brownish,
L~riiy
Bobcav~eon medium bedded and micrific limestone; nodules of chert.
Fine grained massive bluish-grey limestone, medium
Lowville
bedded; '~oird eye" texture; high-calcium content.
Fine to medium grained and massive dolostone, greenishPamelia
grey, medium to thick bedded, locally calcareous and sandy;
characteristic "orange-weathering" surface color.
Coarse grained and pale-grey skeletal limestone, more or
Laval
less dolomitic, sandy or oolithic, thick-bedded; also, dark
grey, fine grained sandstone, massive bedding; some
(St. M a r t i n )
zones contain large amounts of shale.
Massive dolostone, sometimes laminated, fine to medium
Bea~hamoiG grained, various colors, medium to thick bedded; vugs
filled with white calcite and gypsum, pink dolomite.
Massive, fine grained, thick bedded, high-calcium and
Beldejas
pale grey limestone; also, dark grey and fine grained
dolostone, thick bedded, "orange weathering" surface color.
Fine to medium grained, medium grey dolostone, thick
Theresa
bedded; interbedded fine grained and dark grey sandstone,
in thin layers of a few centimeters.
.
v
Table 2 gives the detailed characteristics of the vadous tests performed. All the mortar bars were
made according to ASTM C227, using the same high alkali cement (C1 - Table 3) and a fixed 0.50 w/c
ratio. The 71 samples collected were tested under the NBRI test conditions, 23 of them being also
submitted to the standard ASTM C227 test. In the latter case, the alkali content of the mixes was raised to
1.25% (Na20 equivalent), and plastic pails without wicks were used in order to minimize the risk of alkali
leaching (17,18). For a reference, concrete prisms were made and cured according to the CSA
Standards (19). The mixes had an aggregate:sand:cement:water ratio of 3.18 : 2.19 : 1 : 0.50, with a
cement content of 350 kg/m3, and a total alkali content raised to 1.25% (Na20 equivalent). Length
change measurements were followed up to 1 year. An expansion limit of 0.04% at 6 months was chosen
1072
B. Foumier and M.A. B6rub6
Vol. 21, No. 6
to distinguish reactive or potentially reactive aggregates from non-reactive ones. It was observed that a
0.04% expansion value generally corresponds to the detection of visible cracks at the surface of the
concrete prisms.
TABLE 2: Caracteristics of the Various Tests Performed in this Project.
Tests
Materials
Mix D e s i e n
Curine
A) ~
3 bars
13) Alkali content:
not raised.
CO W/C: 0.50
D) ~4m~.:cernent =
2.25 : 1
2 days precuring ( 1 day in
in the molds & 1 day in
moist cabinet at 23°CO.
Immersion in the 1N NaOH
solution (23°C).
Zero reading after 24 hours
in NaOH solution at 80°C.
Measurements up to 21 days.
A) Idem NBRI
13) Idem NBRI
CO Idem NBRI
A) Idem NBRI
B) Alkali content:.
raised to 1.25%
(Na20 equiv.)
C) ldem N B R I
D) Idem NBRI
38°C, 100% R.H.
Container: 22 litre plastic
pail, no wicks.
(12 bars / pail)
Measurements up to 1 year.
A) G~arse A~,reeatcs;
- 20 + 14 mm
-14÷10mm
-10+5ram
(equal mass)
B) Sand: Granitic
COCement:. Type I0
(1% Na20 equiv.)
D) Water. Tap water
A) G¢ment content
350 kg/m3
B) Alkali content
Raisedto 1.25%
(Na20 equiv.)
with NaOH)
C) w/¢. 0 . 5 0
D) % c. agT. :% sand
59 : 41
38.._°C,100% R.H.
Container: 22 ].itre
plastic pail + wicks;
3prisms/pail.
Measurements up to
1 year.
Petrographic exam.
of the prisms at each
measurement.
A) ~f,grggl~: Washed,
grading according to
AS'I'MC227.
Mortar Bar Test B) ~emen~. High alkali
(Sth African Test)
type 10 (1% Na20
(NBRI Method)
equivalent).
CO Water. distilled
Mortar Bar Test
(ASTM C227)
F.aufazte_Em~
Test
(Reference test)
TABLE 3: Characteristics of the Cement (C1) Used in this Study.
(~hcmical A n a l y s i s (Major 9xides %):
SiO2
CaO
20.73
63.09
A120 3 F e 2 0 3
5.58
Boeue Comvounds:
2.67
MgO
SO3
TiO2
SrO
P205
LOI
Na20
K20
2.18
2.85
0.28
0.22
0.26
0.89
0.32
1.06
C3S
C2S
C3A
C4AF
49.8
22.0
10.3
8.1
Blaine: 3460 c m 2 / g
The microstructure of the reaction products developed within the mortar bars submitted to the
NBRI Test, and made with non-reactive to highly expansive aggregates, was studied under the
stereomicroscope and the SEM (JEOL 25S3) equipped with an EDXA Tracor Northern 5500. After 18
days of storage at 80°C, the containers were removed from the oven. When the temperature of the
solution had cooled to approximately 23°C, the bars were removed from the solution and broken in two
pieces. For each sample, the first piece was cut lengthway and polished with alumina powder (1000 grit)
for petrographic examination, while the other was placed in a plastic bag and stored at room temperature
for approximately 3 months. Two days before SEM examination, the bars were broken into cubic pieces
and vacuum dried for 48 hours. The cubes were then broken, and the newly formed surface coated with
a thin carbon film.
Vol. 21, No. 6
NBRITEST,SILICEOUSCARBONATEAGGREGATES,EXPANSION
1073
Results and Discussion
Limit Crlterl~
Figure 2 shows the 14 day expansion values obtained from the NBRI Accelerated Mortar Bar Test
plotted against the 6 month expansion values measured from the Concrete Prism Test, for the 71
investigated carbonate aggregates. The results are shown according to the stratigraphic association of
the corresponding rocks, with empty and filled symbols corresponding to samples with less and more
than 6% insoluble residue, respectively. A 0.1% mortar bar expansion limit (after 14 days) can be drawn
since lower expansion values always correspond to concrete expansions less than the 0.04% criterion. It
was observed that no aggregate with less than 6% insoluble residue produces concrete expansions
higher than the 0.04% proposed limit, while only two aggregates containing less than 6 0 insoluble
residue (Black River limestones H1 & H3) induce excessive expansion from the NBRI Test. All the
investigated siliceous or massive dolostones, dolomitic/sandy limestones and quartzitic sandstones
associated with the Beekmantown, Chazy and Black River (Pamelia Formation) Groups give expansion
values < 0.04% in the Concrete Prism Test (after 6 months). 28% (5/18) of these rocks produce 14 day
mortar bar expansion • 0.1% (L3, M3, K1, K3 & R2). Such behavior was also observed for two Black River
limestones of the Chicoutimi area (H1 & H3), and one argillaceous Trenton limestone of the Clermont
Area (A3), for a total of 8 aggregates falling in the upper left field of figure 2. These high mortar bar
expansion values could be indicative of long term expansive behavior in concrete. In fact, 75% (6/8) of
these aggregates effectively show concrete expansion values > 0.04% after 1 year (for mixes with a
cement content of 350 kg/m3). This includes the Trenton limestone A3 which produces a high mortar bar
expansion (0.322%). On the other hand, 11% (3/28) of the aggregates considered as non-reactive
(lower left field in Figure 2) show concrete expansion > 0.04% after 1 year, but give accelerated mortar
bar expansion < 0.1%, even after 21 days. The potentially reactive aggregates (i.e those falling in the
upper right field in Figure 2) consist of siliceous Trenton and Black River limestones containing more than
6% insoluble residue. This residue is composed of micro- to crypto-crystalline quartz (the reactive
phase), and small amounts of argillaceous minerals (illite, interlayered illite-smectite, chlorite, kaolinite),
plagioclase and potassium feldspars, and pyrite. They form an alveolar network around the calcite grains
(micrite & microsparite) (Figures 3A & B).
0.12
!!ii iii
0
0.10
o.o4
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0.00
0.00
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o.o62
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0•
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Concrete Prism test - Expansion 6 months %)
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FIG 2: Expansion values at 14 days (NBRI test) as a function of the 6 month expansion values
measured in the Concrete Prism Test. Results are grouped according to the geological
association of the samples. Filled and empty symbols represent samples with more and less
than 6% insoluble residue, respectively.
Figure 4 shows the relation between the expansion values obtained after 1 year in the ASTM
C227 Mortar Bar Test, and after 14 days in the NBRI test. When a 0.1% limit after I year is used for the
ASTM test, all the mortar bars tested under the NBRI conditions, which show expansion values > 0.18%
after 14 days, also produce excessive expansion (> 0.04%) for the Concrete Prism Test (filled symbols).
However, a grey zone appears for mortar bar expansion values between 0.075-0.1% (ASTM) and 0.150.18% (NBRI), where reactive and non-reactive aggregates fall together.
1074
B. Foumier and M.A. B6rub6
Vol. 21, No. 6
FIG 3: A. SEM micrograph showing the typical alveolar microtexture of the insoluble residues in
reactive siliceous limestones after slight attack with diluted HCI. B. Enlarged portion of the
network showing molds of preexisting carbonate grains. The insoluble material is mainly
composed of cryptocrystalline quartz (Si) and clay minerals, mostly illite and chlorite.
0.40
>.
[3 B e e k m a n t o w n
0.35 1 :O Chazy
0.30 t O Black River
o
0.25
ua
#
e,I
e~
Trenton
!ii!
0.20
0.15
~J
0.10
b~t3
<
0.05
•
•
I
Standard l i m i t i : ::
ilia' ~
04
j|
.....
•
I
0
FIG 4: Expansion values after 1 year for
the ASTM C227 Test plotted
against those after 14 days for
the NBRI Test. Results are
classed according to the
geological association of the
samples.
Filled
symbols
represent aggregates which
produce concrete expansion >
0.04% after 6 months.
0.00
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40
•
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•
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NBRI Test - Expansion 14 days (%)
The results of testing and research programs conducted in different countries cn various types
of aggregates are summarized in Table 4. There is a general agreement to use an expansion limit around
0.1% for non-reactive aggregates. However, the limits associated with reactive aggregates vary. South
African researchers (22) suggested a 12 day expansion between 0.1 and 0.25% for slowly expansive
siliceous rocks, and expansion values > 0.25% for rapidly expansive siliceous rocks. However, Shayan et
al. (23) observed that a phyllite from Victoria (Australia) that had reacted in a dam needed up to 22 days to
produce excessive expansion in the accelerated mortar bar test. Consequently, the authors suggested
that 1) aggregates producing expansion > 0.1% after 10 days are considered rapidly reactive, and 2) the
test has to be continued up to 22 days for petrographically suspicious aggregates producing expansion
< 0.1% after 10 days. Hooton & Rogers (25) reported the results of tests conducted on various Canadian
rocks, mostly from Ontario. They observed that some aggregates with good field perlormance but
petrographically marginal, and others which appeared slowly reactive in concrete structures, produced
expansion between 0.1 and 0.25% in the NBRI test. They thus suggested further testing for such
aggregates. Grattan-Bellew (4) presented a very interesting overview of the Canadian experience with
the NBRI test. He observed that it may be necessary to consider various criteria according to the type of
aggregate tested. He finally concluded that a 0.15% limit (after 14 days) could satisfy most of the
investigated cases, with the exception of siliceous limestones exploited in the St. Lawrence Lowlands
for which a 0.1% limit appeared more appropriate. In addition, alkali-carbonate reactive rocks are not
correctly evaluated through the NBRI Test, since they produce expansion lower than the proposed limit.
Vol. 21, No. 6
NBRI TEST, SILICEOUSCARBONATEAGGREGATES,EXPANSION
1075
TABLE 4: Summary of accelerated mortar bar test results and criteria (NBRI Method).
Author(s)
Innooao~ PotentiaIly reactive Period
(Exp. %)
(Exp. %)
(days)
Aggregates Tested
Remarks
Oberholster
(1983)(20)
< 0.08 0.08 - 0.20: slowly exp.
> 0.20 rapidly exp.
10
Hornfels/greywackes,
Results compared to
Quartzite, Granite,
ASTM C227 and to the
opal + non reactive sand Concrete Prism tests.
Oberholster
& Davies
(1986)(21)
< 0.11
> 0.11
12
Davies &
Oberholster
(1987)(22)
<0.1
0.1 - 0.25: slowly exp.
> 0.25: rapidly exp.
12
Quartz-bearing agg.,
Interlaboratory test
Malmsbury metased.,
Program; Precision
Norite, Quartz, Quartzite
determination
Shayan et al. < 0.1
(1988)(23)
Shayan
(1989)(24)
> 0.1: slowly exp. - > 0.1: rapidly exp. - -
22
10
River Gravel, Sandstone,
M e t a d o l e r i t e , Phyllite,
Basalt, Metagreywacke,
Andesite (Japan)
3 days precuring in
Fog room (23°C)
Exp. < 0.1% (10 d.)
continued up to 22 d.
M a l m s b u r y metased.,
Quartzite, Granite
Limits based on a
poor correlation (0.67)
with ASTM C227.
Hooton &
Rogers
(1989)
(25)
< 0.1
0.1 - 0.25: not clear
> 0.25: reactive
14
Carbo. & siliceous Sands
& Gravels, Doiostone,
Siliceous limestones,
Metasediments
Further testing
needed for agg. with
expansion between
0.1 and 0.25%
GrattanBeilew
(1990)(4)
< 0.1
> 0.1: siliceous limest.
> 0.20: greywackes
>0.15: safe limit
14
Greywacke, Argillite,
Siliceous limestone,
Gravel with chert,
Granite, Gabbro,
Silicified Tuff.
A proposed 0.15%
limit applies
to aggregates used
with high alkali
cements.
The results of our research program, illustrated in Figure 2 and summarized in Table 5, agree with
the criteria proposed in the literature. Indeed, 100% of the investigated carbonate aggregates which
show accelerated mortar bar expansion values < 0.10% (after 14 days) are non-reactive in the CSA
Concrete Prism Test, while no case of reactivity in concrete structures involving these aggregates has
been officially reported to date. Further testing could be necessary for the Beekmantown dolostones
exploited in the Montreal area, since one case of alkali-silica reactivity has been recently reported (26).
When using a 0.1% expansion limit (after 14 days) to distinguish non-reactive from potentially
reactive aggregates, the NBRI Test gives percentages of efficiency of 98% (42/43) for the Trenton
Limestones, 73% (8/11) for the Black River limestones and dolostones, 78% (7/9) for the Chazy
sandstones and dolomitic limestones, and 75% (6/8) for the Beekmantown dolostones (89% overall 63/71). When considering the 6% of insoluble residue mentioned earlier as an additional criterion, the %
of efficiency of the NBRI Test increases to 92% (65/71), since two non-reactive Black River limestones
which produce excessive mortar bar expansion contain less than 6% of insoluble residue. On the other
hand, most of the aggregates producing expansion > 0.25% also induced excessive expansion during
the Concrete Prism Test (i.e > 0.04%), and proved to be reactive in concrete structures (6-10,27,28).
Hooton & Rogers (25) also obtained a "grey zone" for accelerated mortar bar expansion values between
0.1 and 0.25%, where non reactive to highly expansive aggregates coexist (Figure 2).
Figures 2, 5 & 6 indicate that there is no clear relation between the expansion values obtained
from the NBRI test and those obtained from the Concrete Prism Test. Indeed, the highly reactive
siliceous limestones of the Ottawa and Trois-Rivi~res areas, which promote rapid concrete structure
1076
B. Foumierand M.A. B4rub~
Vol. 21, No. 6
deterioration in the field and very high concrete prism expansion (Figure 5), produce similar or even lower
mortar bar expansion than other less reactive aggregates exploited in adjacent parts of the St. Lawrence
Lowlands (Figures 2 & 6). For example, the highest accelerated mortar bar expansion value (0.412%)
was obtained from an argillaceous-siliceous limestone aggregate from La Malbaie area which produced a
concrete prism expansion of 0.046% after 6 months. Since only minor signs of alkali-silica reaction have
been recognized in La Malbaie Area, and are mostly observed in concrete components exposed to
severe conditions and deicing salts, these aggregates are thus considered potentially reactive but only
in severe conditions. It is believed that the presence of swelling clay minerals (interlayered illite-smectite)
in the insoluble residue of limestones from the Grondines Formation of the Quebec City and Clermont
areas is partly responsible for the excessive expansion measured in the autoclave test. Besides, a similar
behavior has been observed when the same aggregates are subjected to an accelerated autoclave
expansion test [29]. The higher surface area created by crushing the coarse aggregate particles to
produce the sand fractions used in the mortar bar tests may make the swelling clay minerals more
accessible to attack by the alkaline pore solution. This is discussed elsewhere (30-32).
TABLE 5: Percentages of samples tested from the various geological groups investigated, and
classed according to their behavior in the Concrete Prism and the NBRI Mortar Bar Tests.
Group
Trenton
Black River
Chazy
Beekman.
Total
N (samples)
43
11
9
8
71
Concrete
Reac. N.R.
Reac. N.R.
N.Ro
N.R.
Reac. N.R.
32
11
(74%) (26%)
3
8
(27%) (73%)
9
(100%)
8
(100%)
35
36
(49%) (51%)
Prism
Test
Exp. 0.04%1
NBRI Test
0
10
0
Exp. < 0.1%2 (0%) (91%)
NBRI Test
32
1
Exp. > 0.1%3 (100%) (9%)
7
6
(0%) (63%)
5
(78%)
(75%)
0
28
(0%) (78%)
3
3
(100%)(37%)
2
(22%)
2
(25%)
35
8
(100%) (22%)
1 Samples classed according to the 6 month expansion values obtained from
the Concrete PrismTest (Non Reactive: Exp. < 0.04%, Reactive: Exp. > 0.04%).
2 Samples showing 14 day expansion < 0.1% from the NBRI Mortar Bar Test.
3 Samples showing 14 day expansion > 0.1% from the NBRI Mortar Bar Test,
~
E E
•~ ~
,=
.~
~
0
u ~.
X
0.400.36-'
0-32i
0.280.24-'
0.200.16"
0.12-
[]
~),
O
A
O
Beekrnantown
Chazv
BlackRiver
Trenton
O A A
A
~
Proposed
Limit
0.08:
0.04"
0.00
1
2
3
4
5678
AREAS
1: Ottawa
2: Aylmer
3: Montreal
St-Dominique
4: Joliette
5: Trois-Rivi~res
6: St-Marc
7: Quebec City
8: La Malbaie
9: Chicoutimi
9
Various Areas - South-West to North-East
FIG 5: Six month expansion values for the Concrete Prism Test, as a function of the geological
association of the aggregates from various areas of the St. Lawrence Lowlands.
Vol. 21, No. 6
NBRI TEST, SILICEOUS CARBONATE AGGREGATES, EXPANSION
[]
~"
oe
AA
K 0.5
,~ 0.4
Beekmantown
Chazy
Black River
Trenton
AREAS
•
•
0
•~ 0.3
A
× 0.2.
|
o
e-~
~ 0A
b,
j
0.0
Z
1077
A A
A
A
o
1: Ottawa
2: Aylmer
3: Montr6al
St-Dominique
4: Joliette
5: Trois-Rivi~res
6: St-Marc
7: Quebec City
8: La Malbaie
9: Chicoutimi
1 2
3
4 56
789
Various Areas - South-West to North-East
FIG 6 : 1 4 day expansion values for the NBRI Accelerated Mortar Bar Test as a function of the geological
association of the aggregate samples from various areas of the St. Lawrence Lowlands. Filled
symbols represent aggregates producing concrete expansion values • 0.04% at 6 months.
Rate of ExDansl0n
Figure 7 shows the relation between the 7 day and the 14 day expansion values measured in the
NBRI test, for the 71 investigated carbonate aggregates. The values are presented according to the
geological association of the aggregates, with filled symbols representing those producing concrete
prism expansions > 0.04% (after 6 months). It is clear from these results that all the aggregates tested
follow a steady and similar normalized rate of expansion, at least from 7 to 14 days. Figures 8A and B give
the average rate of expansion for non-reactive and expansive aggregates, respectively, as expressed by
the percent of the 14 day expansion reached as a function of time. Even if the statistical data given in
these figures indicate that the vadations are much more important for the non-reactive aggregates, a
good indication of the ultimate expansion (after 14 days) may be obtained after only 7 days in the NaOH
solution using the relation presented in Figure 7. 97% (35/36) of the Black River and Trenton limestones
containing more than 6% insoluble residue and producing 7 day expansion values > 0.05%, also induce
concrete expansion higher than the 0.04% proposed criterion. In addition, aggregates which produced
7 day expansion > 0.15% can be considered highly potentially reactive since 92% of them reached
expansion • 0.25% after 14 days. On the other hand, none of the aggregates tested producing
accelerated mortar bar expansion < 0.05% after 7 days induced either mortar expansion values • 0.1%
after 14 days, or concrete prism expansion values • 0.04% after 6 months.
0.5
y = 1.4262e-3 + 1 . 7 4 9 ~
0.4
O I Black River
0.3
~[ T r e n t o n
0.2
i
Z
[] B e e k m a n t o w n
Chazy
FIG 7: Relation between the expansion
values after 7 days and 14 days
for the NBRI Accelerated Mortar
0.1
I Cement= C11
Bar Test. Results are presented
according to the geological
0.0
association of the samples. Filled
symbols represent aggregates
0.00 0.05 0.10
0.15 0.20
0.25 0.30
with concrete prism expansion
NBRI Test - Expansion 7 d a y s (%)
values > 0.04% after 6 months.
1078
B. Fournier and M.A.B6rub~
[A]
150
•~ 100
Vol. 21, No. 6
[B]
120
Samples with 14 day expansions > 0.1%) ]
Samples with 14 day expansions < 0.1%) ] ]
;>
100
r~
t~ Min - Max
• Avg.
[] Min- Max I
• A
v
g
.
~
e~
r~
~ 50
ICement=Cll
W/C - 0 50
•
Min. (%)
Max. (%)
Avg. (%)
STD (%)
C.V. (%)
n
2
4
4.1
53.3
20.4
13.3
65.0
23
3.7
75.0
35.3
17.4
49.4
24
'B
6
8
10
Time (days)
35.3
87.5
52.9
17.5
33.0
17
44.4
125
66.5
16.1
24.3
24
64.7
100
85.5
10.2
11.9
15
12
66.7
125
91.3
14.2
15.5
19
Min (%) 0.00 0,001 0.007 0.010 0.015 0.01
Max (%) 0.015 0.023 0.040 0.049 0.062 0.069
FIG 8:
ICement =
~ 20
,.
0
0
2
Min.(%)
Max.(%)
Avg.(%)
STD (%)
C.V. (%)
1.4
12.4
7.4
2.6
34.6
40
14
C1
4
j
6
8
10
Time (days)
36.0
57.3
47.1
5.6
11.9
34
12
50.0
73.5
62.2
5.7
9.2
39
77.0 85.2
86.9 96.8
82.5 91.3
3.4 25
4.1
2.8
17
26
Min. (%) 0.00 0.021 0.036 0.052
Max. (%) 0.04 0.116 0.189 0.232
0.075 0.09
0.342 0.376
n
16.4
37.3
26.7
5.3
19.8
37
I
14
Average normalized rate of expansion for the NBRI Test (for aggregates producing 14 day
expansion values < 0.1% [A] and > 0.1% [B]), expressed by the % of the 14 day expansion
values reached as a function of time. Statistical data are presented for the normalized average
rate of expansion. In addition, the maximum and minimum expansion values obtained at each
time are given. (Avg: Average; STD: Standard Deviation; C.V.: Variation coefficient).
Mlcrostructure of the reaction oroducts
The petrographic examination of mortar bars which produced expansion values from 0.1 to
0.35%, after 14 days, revealed signs of ASR similar to those found in deteriorated concrete structures
built with reactive siliceous limestone aggregates from the St. Lawrence Lowlands (5-9). Similar
observations have been reported for reactive quartz-bearing aggregates by Shayan & Quick (33), and
Davies & Oberholster (34). Thus, these authors concluded that the mechanisms involved are similar or at
least not altered by the NBRI Test conditions, except for the rates of reaction. The examination of
polished mortar bar sections under the stereomicroscope revealed the presence of thin dark rims at the
periphery of many aggregate particles, and numerous microcracks filled with secondary reaction products
(Figure 9A). Under the SEM, calcium rich massive gels were observed lining small pores (Figure 9B), and
microcracks in the cement paste (Figures 9C & 9D). The massive gels filling pores of the cement paste
sometimes presented a reticular or sponge-like surface microtexture, with corresponding high silica and
sodium contents (Figure 9E). White and powdery reaction products were seen tilling many large pores of
the cement paste as well as most of the microcracks within the reactive aggregate particles (Figure 9A).
This material generally corresponds to a partially crystallised silica rich phase showing a microreniform
surface texture (Figure 9F), or relatively well-formed platy crystals (Figure 10A). The secondary white
veinlets within the aggregate particles (Figure 10A) could be easily detected after a slight attack with
diluted HCI (Figure 10B). Observations at high magnification of a mortar sample which was stored for 80
days in the 1N NaOH solution (80°C) revealed that these white veinlets often consist of partially filled
microcracks, with two separate layers of partially crystallized gels lining the opposite walls of the
rnicrocracks (Figure 10C). Each of these layers is composed of a more or less thick zone of massive gel
which changes, without any evident discontinuity, to a rosette-like phase toward the center of the
microcracks (Figures 10D & 10E). Qualitative analysis with EDXA revealed only slight difference in
composition between these two zones or products, the massive gel in contact with the aggregate having
a slightly higher Ca/Si ratio relative to the adjacent microcrystalline product.
Vol. 21, No. 6
NBRI TEST, SILICEOUS CARBONATE AGGREGATES, EXPANSION
1079
The well-shaped rosette-like phase frequently reported in the literature as a typical alkali silica
reaction product was not observed in the first series of mortar bars stored for only 18 days in the NaOH
solution (but left for three months in sealed plastic bags, in air at 23°C, before SEM examination), even if
some of these bars suffered expansion up to 0.35%. In fact, this phase was only observed in pores of
FIG 9: StereomicroscoD~ and SEM microaraDhs from mortar bars which soent 18 days in the 1N NaOH
~g.JLLt~gJ~_~: A. Thin dark rim at the periphery of a reactive limestone particle, with white and
powdery reaction products filling a microcrack within the particle and a pore in the cement paste
(Polished section, magnification: 17x; Agg: G1). Calcium rich massive gel lining voids (B), and
microcracks (C,D) in the cement paste (Agg: G1). E. Reticular or sponge-like surface
microtexture of a silico-calco-alkaline massive gel lining a void in the cement paste (Agg: H3). F.
Partially crystallised silica rich gel with a microreniform surface texture, lining a microcrack in a
reactive limestone particle (Agg.: G1).
1080
B. Fournier and M.A. B~rub~
Vol. 21, No. 6
FIG 10: SEM microaraDhs from mortar bars which soent 18 days (A & C - AOg: GI~ or 80 days (B. D-F Aga: Wl~ in the NaOH solution:
A. Relatively well-formed platy crystals filling a pore of the cement paste. B. Secondary white
veinlets within the aggregate particles after a slight attack with diluted HCI (1/100). C. Partially
filled microcrack within a reactive limestone particle, and adjacent to a large crinoid fragment. D
& E. Enlargements of micrograph C showing parts of the separate layers of partially crystallized
gels lining the walls of the microcrack. Massive gel is often found in contact with the aggregate,
and changes toward the centre of the microcrack, without any evident discontinuity, to a wellshaped rosette-like phase. F. Well-shaped rosette-like phase filling a pore in the cement
paste.
Vol. 21, No. 6
NBRI TEST, SILICEOUS CARBONATE AGGREGATES, EXPANSION
1081
mortar bars (Figure 10F) containing a very reactive siliceous limestone (Wl), stored for 80 days in the 1N
NaOH solution (expansion 1%), and air dried in the laboratory for approximately 1 year before SEM
examination. Shayan & Quick (33) concluded from their SEM observations of mortar bars, which spent
60 days in the NaOH solution (at 80°C), that "the gel material is the precursor to the crystalline platy or
rosette shaped materials". Davies & Oberholster (34) reported the presence of a typical rosette-like
phase in mortar bars which spent only 14 days in the NaOH solution, but were air dried for 1 year before
SEM examination. All these observations suggest that this rosette-like phase corresponds to a stabilized
end-product, and that its formation is consequently time-dependent and probably not responsible for
the expansive pressures developed at least at short terms or in the proposed time limit of the NBRI test
(i.e 12-14 days). In addition, this crystalline product generally forms in pores of the cement paste and in
microcracks within the aggregate particles, that is, where space is available for its crystallisation, Figures
9F, 10E and 10F indicate that partially crystalline to welt-shaped phases preferentially form inside open
microcracks within the aggregate particles. They suggest a drusic-type mode of recrystallisation from the
gel phase, or crystallisation directly from the pore solution which migrates through these open spaces.
This subject is discussed in more detail elsewhere (30).
Conclusions
a) The NBRI Accelerated Mortar Bar Test can be used as a preliminary method (concurrently with
petrographic examination) to determine the potential alkali-reactivity of carbonate aggregates
produced in the St. Lawrence Lowlands. In general, carbonate aggregates with less than 6%
insoluble residue or producing less than 0.1% expansion after 14 days (in the NBRI Test) can be
considered as non reactive aggregates.
b) Black River and Trenton limestones with more than 6% insoluble residue and producing 14 day
mortar bar expansion > 0.1% can be considered as potentially reactive in concrete. In addition, those
producing 14 day expansion values • 0.25% can be considered as highly potentially reactive since
signs of alkali-silica reactivity have been recognized in concrete structures built with them.
c) Some non-reactive siliceous or massive dolostones, dolomitic/sandy limestones and quartzitic
sandstones associated with the Beekmantown, Chazy and Black River (Pamelia Formation) Groups
produce excessive expansion (between 0.1 and 0.25% after 14 days) in the NBRI Test. Further
testing may thus be necessary for such aggregates, mainly through the CSA Concrete Prism Test.
d) A good indication of the 14 day expansion values measured in the NBRI test, and consequently of
the potential alkali-reactivity of the investigated carbonate aggregates, can be obtained after only 7
days of immersion in the NaOH solution. Most of the potentially deleterious samples investigated
induced mortar bar expansion in excess of 0.05% after 7 days, with those producing 7 day
expansion values • 0.15% also reaching expansions • 0.25% after 14 days.
e) The petrographic examination of mortar bars containing reactive siliceous carbonates and subjected
to the NBRI Test revealed the presence of reaction products similar to those found in deteriorated
concrete structures built with similar coarse aggregates produced from the St. Lawrence Lowlands.
f) Calcium rich massive gels were found lining microcracks and small pores of the cement paste. Larger
pores and microcracks within the aggregate particles often contained a white and powdery reaction
product. Under the SEM, this product corresponds to silica rich partially crystallised gels to relatively
well-shaped platy crystals.
g) The well-formed classical rosette-like phase was not observed in mortar bars subjected to the
accelerated test for 18 days, but was observed in bars made with a very reactive siliceous limestone,
immersed for 80 days in the NaOH solution, and air dried at room temperature for approximately 1
year before SEM examination. Our observations suggest that the crystallisation process of this
phase is time-dependent and possibly not involved in the short term expansion developed by the
alkali-silica reaction processes.
Acknowledaments
The authors wish to thank Mr. Jean Frenette, Mr. Jean B~rub~ and Mr. Guy Bergeron for their
interest in our work. This study has been supported by the Quebec Ministry of Transportation and the
Quebec Ministry of Energy and Resources. The financial support of FCAR and NSERC is also
acknowledged. Special thaks are also given to Mr. P.E. Grattan-Bellew, Mr. C.A. Rogers and Mr. D.
Williams for their help in the edition of this manuscript.
1082
B. Foumier and M.A. B6rub6
Vol. 21, No. 6
References
1.
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(1990).
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Aggregates Produced in the St. Lawrence Lowlands (Quebec, Canada). - Part 1: Influence of
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the St. Lawrence Lowlands (Quebec, Canada): Study of the Reaction Mechanisms. In preparation.
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