Report on Determining the Reactivity of Concrete Aggregates and
Selecting Appropriate Measures for Preventing Deleterious
Expansion in New Concrete Construction
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Table of Contents
1.0 Introduction................................................................................. 1
2.0 General Approach....................................................................... 1
3.0 Testing To Determine Aggregate Reactivity.............................. 3
3.1. Use of Field Performance History........................................ 3
3.2. Petrographic Assessment...................................................... 5
3.3. Determination of Potential Alkali-Carbonate Reactive
Rocks by Chemical Composition, CSA A23.2-26A............ 5
3.4. Accelerated Mortar Bar Test, ASTM C 1260....................... 6
3.5. Concrete Prism Test, ASTM C 1293 ................................... 7
3.6. Interpretation of Results from Laboratory Tests................... 7
3.7. Risk Evaluation..................................................................... 8
3.8. Other Test Methods............................................................... 8
4.0 Preventing Damaging Expansion In Concrete Containing
Alkali-Silica Reactive Aggregates............................................... 8
4.1. Performance Testing Using the Concrete Prism Test (CPT).. 9
4.2. Performance Testing Using the Accelerated Mortar Bar Test
(AMBT).................................................................................. 10
4.3. Prescriptive Approach for Selecting Preventive Measures..... 12
4.3.1. Degree of Aggregate Reactivity............................ 12
4.3.2. Level of ASR Risk................................................ 12
4.3.3. Determination of the Level of Prevention............. 13
4.3.4. Identication of Preventive Measures................... 14
5.0 Summary......................................................................................... 18
6.0 References....................................................................................... 19
1
Report A: Determining The Reactivity Of Concrete Aggregates
And Selecting Appropriate Measures For Preventing Deleterious
Expansion In New Concrete Construction
1.0 Introduction
Alkali-aggregate reactions (AAR) occur between the alkali hydroxides in the pore solution of concrete
and certain minerals found in some aggregates. Two types of AAR reaction are currently recognized
depending on the nature of the reactive mineral; alkali-silica reaction (ASR) involves various types of
reactive silica (SiO
2
) minerals and alkali-carbonate reaction (ACR) involves certain types of dolomitic
rocks (CaMg(CO3)
2
). Both types of reaction can result in expansion and cracking of concrete
elements, leading to a reduction in the service life of concrete structures.
This report describes approaches for identifying deleteriously reactive aggregates¹ and selecting appro-
priate preventive measures to minimize the risk of expansion when such aggregates are used in con-
crete. Preventive measures include avoiding the reactive aggregate, limiting the alkali content of the
concrete, using supplementary cementing materials, using lithium-based admixtures, or a
combination of these strategies.
2.0 General Approach
The ow chart in Figure 1 shows the general sequence of testing and decisions that have to be made
when evaluating a source of aggregate for potential AAR. Prior satisfactory eld performance of the
aggregate in concrete is considered in some cases to be sufcient for its acceptance in new concrete.
However, the use of eld performance in the absence of testing may not be sufcient to completely
safeguard against damage due to AAR in new construction because of the difculties in assuring that
the materials used in existing structures built ten to twenty years ago (time frame needed to ensure that
AAR has not occurred) are similar to those being proposed for use today. In most cases, it will be
necessary to conduct laboratory tests to determine whether or not the aggregate is deleteriously
reactive. There are many test methods available for evaluating aggregate reactivity, but only two ex
pansion tests, together with petrographic examination are recommended in this report. If the
aggregate is deemed to be non-deleteriously-reactive, it can be accepted for use in concrete with no
further consideration of mitigation (assuming that the physical properties of the aggregate render it
suitable for use). If the aggregate is found to be deleteriously reactive, it must then be determined
whether the reaction is of the alkali-carbonate or alkali-silica type. There are no proven measures for
effectively preventing damaging expansion with alkali-carbonate reactive rocks and such materials
must be avoided by selective quarrying or beneciation. If the aggregate is alkali-silica reactive, the
aggregate may be either rejected for use or accepted with an appropriate preventive measure.
¹The term deleteriously reactive is used to dene aggregates that undergo chemical reactions in
concrete which subsequently result in damage to the concrete. Some aggregates with minor amounts of reactive constituents may exhibit some small
amount of reaction without producing any damage to the concrete; these are non-deleteriously reactive aggregates.
2
There are a number of options for minimizing the risk of expansion with alkali-silica reactive rocks.
This report allows for preventive measures to be evaluated on the basis of performance testing or to be
selected prescriptively from a list of options based on previous experience.
In the approach outlined by this report, the level of testing and the test limits vary depending on the lev-
el of risk that is acceptable to the owner. For example, in regions where occurrences of AAR are rare
or where the aggregate sources in use have a long history of good eld performance; it may be
reasonable to continue to rely on the previous eld history without subjecting the aggregates to
laboratory tests. However, in regions where AAR problems are not infrequent and where the
reactivity of aggregates are known to vary from source to source, it may be necessary to implement a
rigorous testing regime to establish aggregate reactivity and evaluate preventive measures. In the
report described here the level of prevention required is a function of the reactivity of the aggregate, the
nature of the exposure conditions, and the availability of alkali in the system.
Select aggregate source
Figure 1. Summary of the Various Stages in the Process of Evaluation
Field Evidence
Is it satisfactory?
Laboratory Tests
Is the aggregate
deleteriously reactive?
Type of Reaction
Is the expansion due to
ACR or ASR?
Alkali
-
Silica
Reactive
Take preventive
measures or do
not use
Alkali
-
Carbonate
Reactive
Avoid reactive
components or
do not use
Non
-
Reactive
Accept for use
No precautionary
measures
necessary
Select aggregate source
Yes
Yes
AC
Field Evidence
Is it satisfactory?
No
R
ASR
No
Laboratory Tests
Is the aggregate
deleteriously reactive?
Type of Reaction
Is the expansion due to
ACR or ASR?
Alkali
-
Silica
Reactive
Take preventive
measures or do
not use
Alkali
-
Carbonate
Reactive
Avoid reactive
components or
do not use
Yes
Yes
AC
No
No
ASR
R
Non
-
Reactive
Accept for use
No precautionary
3
3.0 Testing To Determine Aggregate Reactivity
Figure 2 shows a ow chart of the sequence of testing for this report when evaluating the reactivity of
an aggregate source. Selecting an appropriate preventive measure will be dealt with in the next
section. Interpreting the results from these aggregate tests is discussed at the end of this section (see
Section 3.6 below).
3.1. Use of Field Performance History
The long-term eld performance history of an aggregate can be established by conducting a survey of
existing structures that were constructed using the same aggregate source. As many structures as
practical should be included in the survey and these structures should, where possible, represent
different types of construction (pavements, sidewalks, curb and gutter, elements of bridges, barrier
walls and even non-transportation structures). The following information should be collected for each
structure:
• Age – structures should be at least 10 years old and preferably more than 15 years old as dam
age due to AAR can take more than ten years to develop.
• Cement content and alkali content of the cement used during construction.
• Use of pozzolans or slag during construction.
• Exposure condition – availability of moisture, use of deicing chemicals.
• Presence of symptoms of distress due to AAR or other causes.
.
Cores should be taken from a representative number of these structures and a petrographic examination
be conducted in accordance with ASTM C 856 to establish the following:
• The aggregate used in the structures surveyed is close in mineralogical composition to that of
the aggregate currently being produced.
• There is no evidence of damage due to AAR.
• The presence and quantity of y ash or slag.
If the results of the eld survey indicate that the aggregate is non-deleteriously reactive, the aggregate
may be used in new construction provided that the new concrete is not produced with a higher cement
alkali loading, lower amount of pozzolan or slag, or more aggressive exposure condition than the struc-
tures included in the survey.
There is a certain level of risk associated with accepting aggregates solely on the basis of eld perfor-
mance due to difculties in establishing unequivocally that the materials and proportions used more
than 10 to 15 years ago are similar to those to be used in new construction.
4
Petrographic Examination
Is the rock a quarried carbonate?
Accelerated Mortar Bar
Test, ASTM C 1260
Is 14-day expansion
> 0.10%?
Type of Reaction
†
Is the expansion due to
ACR or ASR?
Alkali-Carbonate
Reactive
Avoid reactive
components or
do not use
Alkali-Silica
Reactive
Take preventive
measures or do
not use
Non-Reactive
Accept for use
No precautionary
measures
necessary
No
ASR
ACR
No
Concrete Prism Test,
ASTM C 1293
Is 1-year expansion
> 0.040%?
No
Chemical Composition,
CSA A23.2-26A
Does the composition fall in
the region of potentially
alkali-carbonate reactive?
Yes
No
Yes
Yes
Yes
Petrographic Examination
Is the rock potentially reactive?
Yes
No
Field History
Is there a history of satisfactory
field performance?
No
Yes
Petrographic Examination
Is the rock a quarried carbonate?
Accelerated Mortar Bar
Test, ASTM C 1260
Is 14-day expansion
> 0.10%?
Type of Reaction
†
Is the expansion due to
ACR or ASR?
Alkali-Carbonate
Reactive
Avoid reactive
components or
do not use
Alkali-Silica
Reactive
Take preventive
measures or do
not use
Non-Reactive
Accept for use
No precautionary
measures
necessary
No
ASR
ACR
No
Concrete Prism Test,
ASTM C 1293
Is 1-year expansion
> 0.040%?
No
Chemical Composition,
CSA A23.2-26A
Does the composition fall in
the region of potentially
alkali-carbonate reactive?
Yes
No
Yes
Yes
Yes
Petrographic Examination
Is the rock potentially reactive?
Yes
No
Field History
Is there a history of satisfactory
field performance?
No
Yes
Figure 2. Sequence of Laboratory Tests for Evaluating Aggregate Reactivity
†
The type of reaction only needs to be determined after the concrete prism test if the aggregate being tested is a
quarried carbonate that has been identified as being potentially alkali-carbonate reactive by chemical
composition in accordance with test method CSA A23.2-26A
†
Note: The heavier dotted lines represent the preferred approach whereas the faint dotted lines represent a
higher risk approach.
5
If eld performance indicates that an aggregate source is deleteriously reactive, laboratory expansion
testing is required to determine the level of aggregate reactivity and to evaluate prevention measures.
3.2. Petrographic Assessment
Petrographic examination of aggregates should be conducted in accordance with ASTM C 295.
Petrography can reveal useful information about the composition of an aggregate, including the
identication and approximate quantication of reactive minerals. Petrography may be used to classify
an aggregate as potentially reactive, but expansion testing is required to determine the extent of the
reactivity and appropriate levels of prevention. Aggregates may be accepted as non-reactive solely on
the basis of petrography but there is certain level of risk associated with such a decision as some
reactive phases may not be detected by optical microscopy (e.g. nely dispersed opaline silica found in
some siliceous limestones). Where a trained petrographer is examining aggregates from well-known
and tested sources, it is acceptable to use petrography to classify the aggregate reactivity on a routine
basis. For example, in deposits where chert is known to be the only reactive component and where
testing has shown that the chert content needs to exceed 5% to cause deleterious reaction, it may be
justied to permit acceptance of an aggregate with less than say 3% chert on the basis of petrography.
In addition to looking for alkali-silica reactive minerals such as opal, chalcedony, cristobalite,
tridymite, strained and micro-crystalline quartz, and volcanic glass, petrographers should also be
vigilant as to the presence of mineralogical and textural features characteristic of alkali-carbonate
rocks. Deleterious alkali-carbonate reactive rocks are often characterized by a microscopic texture
consisting of dolomitic rhombs oating in a ne-grained matrix of calcite, quartz and clay. However,
there have been reports of deleterious ACR with rocks that do not exhibit this “classic” texture (Ozol,
2006).
3.3. Determination of Potential Alkali-Carbonate Reactive Rocks by Chemical Composition,
CSA A23.2-26A
If the aggregate being assessed is a quarried carbonate rock, the potential for alkali-carbonate reaction
may be assessed on the basis of its chemical composition (Rogers, 1986). This is the basis for the test
method CSA A23.2-26A .² This test involves the determination of the lime (CaO), magnesia (MgO)
and alumina (Al
2
O
3
) content of the rock, and determining where the composition of the rock falls on a
plot of CaO/MgO ratio versus the Al
2
O
3
content, as shown in Figure 3. If the composition falls in the
range of “aggregates considered to be potentially expansive,” the aggregate is potentially
alkali-carbonate reactive. Such aggregates must be tested using the ASTM C 1293 (concrete prism
test) as ASTM C 1260 (accelerated mortar bar test) is not suitable for detecting alkali-carbonate
reaction.
²CSA is the Canadian Standards Association. CSA Standards such as A23.2 Method of Test and Standard Practices for Concrete can be
found at www.csa.ca
6
Figure 3. Using Chemical Composition as a Basis for Determining Potential Alkali-Carbonate Reactivity of
Quarried Carbonates (from CSA A23.2-26A)
3.4. Accelerated Mortar Bar Test, ASTM C 1260
If the aggregate is not a quarried carbonate or it is a quarried carbonate with a composition that falls
outside of the region of “aggregates considered to be potentially reactive” in Figure 3 when tested in
accordance with CSA A23.2-26A, the next step is to test the aggregate in accordance with ASTM C
1260.
Coarse aggregates for this test have to the crushed to sand size (< 5 mm) and then washed and graded
to meet the grading requirements of the test. Sands have to be washed and graded to meet the same
grading requirements. The test is intended to evaluate coarse and ne aggregates separately, and should
not be used to evaluate job combinations of coarse and ne aggregates.
In this test, mortar bars are produced with the aggregate being evaluated and at the age of two days the
bars are immersed into a solution of 1 M NaOH maintained at a temperature of 176oF (80oC) and the
length change of the bars is monitored. If the mortars do not expand by more than 0.10% after 14 days
immersion in this solution, the aggregate is considered non-deleteriously reactive. If the mortar bar
expands by more that 0.10% at 14 days, the aggregate is considered to be potentially reactivity and its
reactive should be conrmed in ASTM C 1293 (concrete prism test).
7
3.5. Concrete Prism Test, ASTM C 1293
The concrete prism test is suitable for evaluating all aggregate types and is considered to be the most
reliable laboratory test for predicting eld performance of aggregates. If the aggregate being tested is
a coarse aggregate it is blended with a non-reactive ne aggregate and vice-versa, and the coarse-ne
aggregate combination is used to produce concrete prisms with a specied high alkali loading. The test
is not intended for use with specic job combinations of coarse and ne aggregate, however, it is
generally considered acceptable to do this, but the results are not applicable if either the coarse or ne
aggregate is changed during the job.
The prisms are stored over water in sealed containers at 100oF (38oC) and the length change is moni-
tored periodically. If the prisms do not expand by more than 0.04% after 1 year, the aggregate is con-
sidered non-deleteriously reactive and may be used in concrete with no further testing (for AAR). If
the prism expands by more that 0.04% at 1 year, the aggregate is considered to be potentially reactive
and preventive measures are required if the aggregate is to be used in concrete construction.
If the aggregate tested was a quarried carbonate rock with a chemical composition that fell within the
region of “aggregates considered to be potentially reactive,” the concrete prisms must be examined to
determine whether alkali-carbonate reaction contributed to the expansion.³ If damaging ACR is
detected, either in isolation or in combination with ASR, the rock should not be used in concrete
without selective quarrying or aggregate beneciation to remove the reactive components.
3.6. Interpretation of Results from Laboratory Tests
Figure 2 shows dotted lines from the boxes marked “Field History”, “Petrographic Examination”, and
“Accelerated Mortar Bar Test” to the box marked “Non-Reactive” as there is an element of risk
associated with accepting aggregates solely on the basis of these tests. With eld history it is usually
difcult to rmly establish that the materials and conditions to be used in a new project are the same as
those used in a structure that is more than 10 to 15 years old. With some aggregates it may not be
possible to identify reactive constituents by petrographic examination.
The accelerated mortar bar test (AMBT) is generally recognized as a relatively severe test and it is well
established that it identies as deleteriously reactive many aggregate sources that have a history of
satisfactory eld performance and that perform well in the concrete prism test (CPT);
4
that is the CPT
identies the same aggregate as non-deleteriously reactive. For this reason, results from the accelerated
mortar bar test should not be used to reject an aggregate. If an aggregate fails the AMBT (expansion
> 0.10% at 14 days) its reactivity should be conrmed by testing using the CPT. If the results of the
AMBT and CPT are in disagreement, the results of the CPT shall prevail.
³The determination of the extent to which the alkali-carbonate reaction contributed to the expansion of the concrete should be con-
ducted by an expert with experience of ACR. Methods used might include a petrographic examination of the concrete (ASTM C 856),
accelerated microbar testing of the aggregate (Lu et al., 2004), and/or rock cylinder expansion tests (ASTM C 586) conducted on
samples of rock from the quarry. The ASTM C 1105 version of the concrete prism test for alkali-carbonate rock reaction may also be
used but the alkali content of the concrete should be kept sufciently low to ensure that expansion due to alkali-silica reaction is elimi-
nated during the test. Keeping the alkali content below 1.8 kg/m
3
(3.0 lb/yd
3
) Na
2
Oe should be sufcient for this purpose.
4
The term “false positive” is used to describe the case where a test method incorrectly identies an aggregate as deleteriously reactive.
Similarly, “false negative” describes the case where a test wrongly identies an aggregate as being non-deleteriously reactive.
8
Until recently it was assumed that aggregates that passed the AMBT (expansion ≤ 0.10% at 14 days)
were most likely to pass the CPT (expansion ≤ 0.04% at 1 year), and such aggregates could be accepted
for use in concrete without the need for conrmatory testing using the CPT. However, there appears
to be an increasing number of coarse aggregates that pass the AMBT and fail the CPT (Folliard et al.
2006) and this is somewhat disconcerting for specications that permit the use of aggregates passing
the AMBT with no further testing (that is no requirements for CPT).
5
Consequently, there is a risk as-
sociated with accepting an aggregate solely on the basis of the results from the AMBT.
In Figure 2, the AMBT is shown with a broken line as there is the possibility of incorrectly identify-
ing a deleteriously-reactive aggregate as being non-deleteriously-reactive using this test method. The
most reliable approach for determining aggregate reactivity is to use the CPT as the expansion test for
all cases (that is to exclude the AMBT from the evaluation process). However, it is recognized that the
long duration of the CPT makes it impractical for use in many circumstances and there is a need for
a more rapid test. Despite its limitations, the AMBT is probably the most viable accelerated test cur-
rently in use.
3.7. Risk Evaluation
The risk of AAR-damage occurring due to a failure to detect deleteriously reactive aggregate can be
reduced by implementing routine testing using petrography and/or laboratory expansion tests. Increas-
ing the complexity and frequency of testing will result in lower risks but higher costs. For example,
frequent petrographic and concrete prism testing of all aggregate sources may reduce the risk of failing
to identify deleteriously reactive aggregates to a negligible level, but the costs associated with this level
of testing may not be justied in a region where there are few cases of AAR and where most aggregate
sources have a good eld performance history. It is incumbent on the owner to dene what level of risk
is acceptable and thus determine the type and frequency of testing.
3.8. Other Test Methods
There are many other test methods for evaluating the reactivity of aggregates and a full discussion of
these tests is beyond the scope of this report. One of the more promising tests is an accelerated version
of the CPT, which is conducted at 140oF (60oC) to accelerate the reaction. A detailed discussion of
these tests can be found elsewhere (Thomas et al. 2006).
4.0 Preventing Damaging Expansion in Concrete Containing Alkali-Silica Reactive
Aggregates
This report provides two approaches for selecting preventive measures. In the rst approach, the
performance of the preventive measure is tested in combination with the reactive aggregate using either
5
It has been proposed to extend the duration of this test and to use an expansion limit of 0.10%, or even, 0.08% after 28 days immersion in 1 M
NaOH at 176 °F (80 °C). This more onerous requirement should be adopted only when it can be demonstrated that extension of the test period is
required to capture aggregates that have been identied as being deleteriously reactive either by concrete prism testing or eld performance. The ex-
tended test duration should not be applied across the board to all aggregates as this will result in an unacceptable number of cases where the acceler-
ated mortar bar test results in false positives (that is the test wrongly identies aggregates as deleteriously reactive). It should be noted that extending
the test duration does not capture all of the aggregates that have been found to pass the AMBT but fail the CPT.
9
the CPT or the AMBT. This approach is suitable for selecting the appropriate level of SCM’s or lithi-
um nitrate admixtures. The second is a prescriptive approach where the preventive measure is selected
on the basis of the reactivity of the aggregate, the nature of structure and its exposure, the required
service life, and the availability of alkalis in the system. This approach is suitable for selecting the ap-
propriate level of SCM and/or the maximum alkali content of the concrete.
The preventive measures determined by either performance testing or prescription using this report
will generally reduce the risk of expansion due to ASR to an acceptable level for most highway ap-
plications. However, it should be noted that the level of prevention arrived at by following this report
may not be sufcient for certain critical structures such as hydraulic dams or power plants where ASR
expansion of any level cannot be tolerated.
4.1. Performance Testing Using the Concrete Prism Test (CPT)
The ability of SCM’s such as y ash, slag, silica fume and natural pozzolans, or of chemical admix-
tures, such as lithium compounds, to control deleterious expansion with a reactive aggregate can be
evaluated using a modied version of the concrete prism test, ASTM C 1293. When testing SCM’s, the
total cementitious content is maintained at 708 lb/yd
3
(420 kg/m
3
), but the portland cement is partially
replaced with the desired amount of the SCM (or combination of SCM’s) under investigation. The al-
kali content of the portland cement component of the mix only is raised to 1.25% Na2Oe.
6
It is prudent
to conduct a number of tests using varying levels of SCM(s) to optimize the proportions in terms of
meeting the expansion criteria. The test duration for evaluating preventive measures is two years and
the expansion criterion used to demonstrate that the combination of SCM and reactive aggregate is suit-
able for use in concrete construction is expansion ≤ 0.04% at 2 years.
The only lithium compound included in this report is an aqueous solution of lithium nitrate.
7
When
testing lithium nitrate solution the procedure in ASTM C 1293 is followed with the following excep-
tions:
The alkali content of the portland cement is raised to 1.25% Na
2
Oe.
The desired quantity of lithium nitrate solution is added to the mix water prior to mixing. It is prudent
to conduct a number of tests using varying amounts of lithium to determine the minimum “safe” level
required to sufciently suppress expansion.
8
The amount of water contained in the lithium nitrate solution should be included in the calculation of W/
CM. In other words, this amount of water should be subtracted from the mix water content required for
the same mix without lithium.
6
The expansion of concrete prisms produced with cement alkalis raised to 1.25% Na
2
Oe provides a reliable prediction of the eld expansion of concrete
produced with cement with alkalis up to 1.0% Na
2
Oe. If the cement to be used in the eld has an alkali content above 1.00% Na
2
Oe, this same cement
should be used for the concrete prism test and the alkalis should be raised by 0.25% Na
2
Oe by the addition of NaOH to the mix water.
7
At the time of writing, the only commercially available products were all solutions containing 30% LiNO
3
.
8
The published literature indicates that the level of lithium required increases as the concentration of the other alkalis (Na+K) in the system increases.
For many aggregates, deleterious expansion appears to be prevented when the lithium-to-sodium-plus-potassium-molar ratio, [Li]/ [Na+K] ≥ 0.74. For
a 30%-solution of LiNO
3
, the molar ratio of 0.74 is achieved when the dose of lithium is equal to 0.55 gal LiNO3 solution per lb Na2Oe (4.6 L LiNO
3
solution per kg Na2Oe). The alkalis added to the mix water as NaOH should be included in the calculation of the lithium-to-sodium-plus-potassium-
molar ratio.
10
The test is extended to two years and the expansion criterion used to demonstrate that the combination
of lithium and reactive aggregate is suitable for use in concrete construction is expansion ≤ 0.04%
at 2 years.
4.2. Performance Testing Using the Accelerated Mortar Bar Test (AMBT)
Before the accelerated mortar bar test (AMBT) can be used to determine the performance of a specic
SCM-aggregate or lithium-aggregate combination, it must rst be demonstrated that the aggregate
being evaluated responds well to the accelerated test. This requires a comparison of the results from the
AMBT and the CPT test for the aggregate being used (without preventive measures). After subjecting
the aggregate to both tests, the results are plotted on Figure 4. Provided the data fall within the region
indicated in Figure 4, the AMBT can be used to determine the efcacy of both SCM’s and lithium nitrate.
The AMBT and CPT should be compared every two years unless the results of petrography or other tests
indicate a signicant change in the composition of the material in the quarry, in which case new tests
should be commenced immediately.
When testing the SCM in the AMBT, the modied version of the test, ASTM C 1567, should be used; this
test was developed specically for “determining the potential alkali-silica reactivity of combinations of
cementitious materials and aggregates.” Combinations of cementitious materials and aggregates will be
deemed acceptable for use if the expansion ≤ 0.10% after 14 days immersion in 1 M NaOH.
9
Note: this
test method is not suitable for evaluating SCM’s with high levels of alkalis (y ash with > 4.5% Na
2
Oe,
and slag and silica fume with > 1.0% Na
2
Oe) and such materials should be evaluated using the concrete
prism test.
9
If it has been determined that an extended test duration of 28 days in 1M NaOH and a lower expansion limit of 0.08% is required to correctly identify
the aggregate as deleteriously reactive then the same requirements should be used to evaluate the preventive measures.
11
0.0
0.2
0.4
0.6
0.8
1.0
0 0.1 0.2 0.3 0.4 0.5 0.6
Expansion in AMBT at 14 Days (%)
If AMBT vs CPT data fall
within this range - the AMBT
may be used to evaluate
preventive measures
Expansion in CPT at 1 Year (%)
Figure 4. Comparison of AMBT and CPT Data for the Purpose of Determining Whether the AMBT is
Suitable for Evaluating Preventive Measures with a Specic Aggregate
When using the AMBT to determine the lithium dose required with a specic aggregate the approach
proposed by Tremblay et al. (2008) will be used; the procedure is as follows:
1. Test the aggregate using the standard AMBT (ASTM C 1260). Extend the duration of the test
such that the mortar bars are exposed to 1M NaOH at 80oC (178oF) for a period of 28 days. Let E1 =
expansion of bars without lithium at 28 days.
2. Test the aggregate in a modied version of the AMBT. In this test add sufcient lithium
nitrate to the mortar bar mixture and the soak solution to achieve lithium-to-alkali molar ratios of [Li]/
[Na+K] = 0.74 in the mortar and [Li]/ [Na+K] = 0.148 in the soak solution. Conduct the rest of the test
in accordance with ASTM C 1260 extending the period in 1 M NaOH to 28 days. Let E2 = expansion
of bars with lithium at 28 days.
3. If (E
2
– E
1
)/E
1
< 0.1 then use the following lithium-to-alkali molar ratio:
(Eq.1)
LA=[LI]/[Na + K] = 1.0 + 0.7X [(E
2
- E
1
)/E
1
]
Where LA is the lithium-to-sodium-plus-potassium molar ratio. The amount of 30%-LiNO
3
solution
required in the concrete mix is then 0.55 x LA/0.74 gal of lithium solution per lb of Na
2
Oe in the con-
crete mixture (or 4.6 x LA/0.74 liters of lithium solution per kg of Na
2
Oe.
4. If (E
2
– E
1
)/E
1
≥ 0.1 then use the concrete prism test to determine the lithium content required
(see Section 5.2).
12
4.3. Prescriptive Approach for Selecting Preventive Measures
The level of prevention is determined by considering the class, size and exposure condition of the
structure, the degree of aggregate reactivity, and the level of alkalis from the portland cement (when
SCM’s are used as preventive measures). This approach is similar to that developed in Canada (CSA
A23.2-27A) and in Europe (RILEM TC191-ARP: AAR-7).
4.3.1. Degree of Aggregate Reactivity
The degree of alkali-silica reactivity of an aggregate is determined by testing the aggregate in the CPT
and using the expansion value at one-year. Aggregate-reactivity classes are given in Table 1.
Table 1. Classification of Aggregate Reactivity
Aggregate-
Reactivity Class
R0
R1
R2
R3
Description of Aggregate
Reactivity
Non-reactive
Moderately reactive
Highly reactive
Very highly reactive
One-Year Expansion
in CPT (%)
< 0.040
0.040 - 0.120
0.120 - 0.240
> 0.240
If data from the CPT are not available, the aggregate may be considered as very highly reactive (R3).
Where the coarse and ne aggregates are of different reactivity, the level of prevention should be se-
lected for the most reactive aggregate.
4.3.2. Level of ASR Risk
The risk of ASR occurring in a structure is determined by considering the aggregate reactivity and the
exposure conditions using Table 2.
13
Table 2. Determining the Level of ASR Risk
Size and exposure conditions
Aggregate-Reactivity Class
R0 R1 R2 R3
Non-massive
†
environment
2
concrete in a dry
Level 1 Level 1 Level 2 Level 3
Massive
†
elements in a dry
††
environment
Level 1 Level 2 Level 3 Level 4
All concrete exposed to humid
air, buried or immersed
Level 1 Level 3 Level 4 Level 5
All concrete exposed to alkalis in
service
†††
Level 1 Level 4 Level 5 Level 6
†
A massive element has a least dimension > 3 ft (0.9 m)
††
A dry environment corresponds to an average ambient relative humidity lower than 60%, normally
only found in buildings
†††
Examples of structures exposed to alkalis in service include marine structures exposed to seawater
and highway structures exposed to deicing salts (e.g. NaCl) or anti-icing salts (e.g. potassium acetate,
sodium formate, etc.)
4.3.3. Determination of the Level of Prevention
The level of prevention required is determined from Table 3 by considering the risk of ASR
from Table 2 together with the class of structure from Table 4.
Table 3. Determining the Level of Prevention
Level of ASR
Classification of Structure (Table 4)
Risk (Table 4)
S1 S2 S3 S4
Risk Level 1 V V V V
Risk Level 2 V V W X
Risk Level 3 V W X Y
Risk Level 4 W X Y Z
Risk Level 5 X Y Z ZZ
Risk Level 6 Y Z ZZ
††
††
It is not permitted to construct a Class S4 structure (see Table 4) when the risk of ASR
is Level 6. Measures must be taken to reduce the level of risk in these circumstances.
14
Table 4. Structures Classified on the Basis of the Severity of the Consequences Should ASR
†
Occur (Modified
for Highway Structures from RILEM TC 191-ARP)
Class
Consequences of
ASR
Acceptability of
ASR
Examples
††
S1
Safety, economic or
environmental
consequences small
or negligible
Some
deterioration
from ASR may
be tolerated
Non-load-bearing elements inside buildings
Temporary structures (e.g. < 5 years)
S2
Some safety,
economic or
environmental
consequences if
major deterioration
Moderate risk
of ASR is
acceptable
Sidewalks, curbs and gutters
Service-life < 40 years
Pavements
S3
Significant safety,
economic or
environmental
consequences if
minor damage
Minor risk of
ASR acceptable
Culverts
Highway barriers
Rural, low-volume bridges
Large numbers of precast elements where
economic costs of replacement are severe
Service life normally 40 to 75 years
S4
Serious safety,
economic or
environmental
consequences if
minor damage
ASR cannot be
tolerated
Major bridges
Tunnels
Critical elements that are very difficult to
inspect or repair
Service life normally > 75 years
†
Note: this table does not consider the consequences of damage due to ACR. This protocol does not permit the use
of alkali-carbonate aggregates
††
The types of structures listed under each Class are meant to serve as examples. Some owners may decide to use
their own classification system. For example, sidewalks and culverts may be placed in the S3 Class is some
jurisdictions.
4.3.4. Identication of Preventive Measures
Option 1 – Limiting the Alkali Content of the Concrete
Damaging alkali-silica reaction can be prevented by limiting the alkali content of the concrete. Maxi-
mum permissible alkali contents are given in Table 5. The alkali content of concrete is calculated on
the basis of the alkali contributed by the portland cement alone.
15
Table 5. Maximum Alkali Contents to Provide Various Levels of Prevention
Prevention
Level
Maximum alkali content of concrete (Na
2
Oe)
lb/yd
3
kg/m
3
V No limit
W 5.0 3.0
X 4.0 2.4
Y 3.0 1.8
Z
†
Table 7
ZZ
†
†
SCM’s must be used in Prevention levels Z and ZZ.
Option 2 – Using Supplementary Cementing Materials (SCM)
Damaging alkali-silica reaction can be prevented by using a sufcient quantity of a suitable supplemen-
tary cementing material (SCM) such as y ash, slag, silica fume or natural pozzolan. Table 6 provides
minimum replacement levels for Class F y ash with less than 18% CaO and meeting the requirements
of ASTM C 618, silica fume with more than 85% SiO
2
and meeting the requirements of ASTM C 1240,
and slag meeting the requirements of ASTM C 989. Class C y ashes or Class F y ashes with more
than 18% CaO are not covered by these prescriptive measures; the ability of these materials to control
ASR with a particular reactive aggregate should be determined by performance testing (see sections 4.1
and 4.2).
Many natural pozzolans such as metakaolin, calcined clays and shales, and volcanic ash have been
shown to be effective in controlling expansion due to ASR. However, no prescriptive measures are
provided for natural pozzolans in Table 6 as this class of materials covers a wide variety of pozzolan
types with a broad range of properties. When natural pozzolans are to be used to control ASR, the ef-
cacy of a particular aggregate-pozzolan combination should be determined by performance testing
(see sections 4.1 and 4.2). Information on natural pozzolans can be found in ACI 232.1R Use of Raw
or Processed Natural Pozzolans in Concrete.
16
Table 6. Minimum Levels of SCM to Provide Various Levels of Prevention
Type of SCM
Alkali level
of SCM
(% Na
2
Oe)
Minimum Replacement Level
†† (% by mass)
Level W Level X Level Y Level Z Level ZZ
Fly ash
(CaO ≤ 18%)
< 3.0 15 20 25 35
Table 7
3.0 – 4.5 20 25 30 40
Slag < 1.0 25 35 50 65
Silica Fume†
(SiO
2
> 85%)
< 1.0
1.2 x LBA
or
2.0 x KGA
1.5 x LBA
or
2.5 x KGA
1.8 x LBA
or
3.0 x KGA
2.4 x LBA
or
4.0 x KGA
†The minimum level of silica fume (as a percentage of cementing material) is calculated on the basis of the alkali
(Na
2
Oe) content of the concrete contributed by the portland cement and expressed in either units of lb/yd
3
(LBA in
Table 6) or kg/m
3
(KGA in Table 6). LBA is calculated by multiplying the cement content of the concrete in lb/yd
3
by the alkali content of the cement divided by 100. For example, for a concrete containing 500 lb/yd
3
of cement with
an alkali content of 0.81% Na
2
Oe the value of LBA = 500 x 0.81/100 = 4.05 lb/yd
3
. For this concrete, the minimum
replacement level of silica fume for Level Y is 1.8 x 4.05 = 8.1%. KGA is calculated by multiplying the cement
content of the concrete in kg/m
3
by the alkali content of the cement divided by 100. For example, for a concrete
containing 300 kg/m
3
of cement with an alkali content of 0.91% Na
2
Oe the value of KGA = 300 x 0.91/100 = 2.73
kg/m
3
. For this concrete, the minimum replacement level of silica fume for Level X is 2.5 x 2.73 = 6.8%.
Regardless of the calculated value, the minimum level of silica fume shall not be less than 7% when it is the only
method of prevention.
†† Note: the use of high levels of SCM in concrete may increase the risk of problems due to deicer salt scaling if the
concrete is not properly proportioned, finished and cured.
When two or more SCM’s are used together to control ASR, the minimum replacement levels given
in Table 6 for the individual SCM’s may be reduced provided that the sum of the parts of each SCM is
greater than or equal to one. For example, when silica fume and slag are used together, the silica fume
level may be reduced to one-third of the minimum silica fume level given in the table provided that the
slag level is at least two-thirds of the minimum slag level.
The minimum replacement levels in Table 6 are appropriate for use with portland cements of moder-
ate to high alkali contents (0.7 to 1.0 % Na
2
Oe). Table 7 provided recommendations for adjusting
the level of SCM when the alkali content of the portland cement is above or below this range. Where
SCM’s are combined with lower alkali cements (< 0.7% Na
2
Oe) it is probably safe to adopt the value
of the minimum replacement level for the next prevention level down. For example, if slag is to be
used in prevention level Y with a low-alkali cement, the level of slag can be reduced to the level speci-
ed for prevention level X (35%). The replacement levels should not be below those given in Table
6 for prevention level W, regardless of the alkali content of the portland cement. Similarly, if higher
alkali cements (> 1.0% Na
2
Oe) are used together with SCMs, the replacement level of SCM should be
increased to that required for the next prevention level up. For example, if slag is to be used in preven-
tion level Y with a high-alkali cement, the level of slag should be increased to the level specied for
prevention level Z (65%). This report does not provide guidance for using preventive measures with
reactive aggregates when the alkali content of the portland cement exceeds 1.25% Na
2
Oe.
17
Table 7. Adjusting the Minimum Level of SCM Based on the Alkali Content
of the Portland Cement
Cement Alkalis Level of SCM
(% Na
2
Oe)
< 0.70
Reduce the minimum amount of SCM given in
Table 6 by one prevention level†
0.70 to 1.00 Use the minimum levels of SCM given in Table 6
> 1.00
Increase the minimum amount of SCM given in
Table 6 by one prevention level
> 1.25 No guidance is given
†The replacement levels should not be below those given in Table 6 for prevention level W, regardless of the alkali
content of the portland cement.
Option 3 – Controlling the Alkali Level of Concrete and using SCMs when Exceptional Levels of Prevention
are Required (Levels Z and ZZ)
Where extreme levels of prevention are required, a combination of Options 1 and 2 may be required. This ap-
proach requires that a minimum level of SCM is used and that a maximum limit is placed on the alkali content
of the concrete contributed by the portland cement. Options for Prevention Levels Z and ZZ are given in Table
8.
Table 8. Using SCM and Limiting the Alkali Content of the Concrete to Provide Exceptional Levels of
Prevention
Prevention
Level
SCM as sole prevention Limiting concrete alkali content plus SCM
Minimum SCM level
Maximum alkali content,
lb/yd
3
(kg/m
3
)
Minimum SCM level
Z
SCM level shown for
Level Z in Table 7
3.0 (1.8)
SCM level shown for
Level Y in Table 6
ZZ Not permitted 3.0 (1.8)
SCM level shown for
Level Z in Table 6
18
5.0 SUMMARY
This document describes a report for determining the reactivity of concrete aggregates and selecting
appropriate measures for preventing deleterious expansion in new concrete construction. It is recom-
mended that the following sequence of testing is followed to determine aggregate reactivity: consid-
eration of eld performance history, petrographic examination, accelerated mortar bar testing and
concrete prism testing. Some agencies may adopt one or more of these test procedures depending on
prior experience with ASR and the acceptable level of risk of ASR in new construction. Appropriate
preventive measures can be selected either by performance testing using the accelerated mortar bar test
or concrete prism test, or by using prescribed measures which have been developed based on previous
experience and published research data. The level of prevention prescribed is a function of the class of
the structure, the reactivity of the aggregate, the alkali content of the portland cement, the composition
of the material used for prevention, and the exposure conditions. This report is not aimed at completely
eliminating the possibility of ASR expansion occurring in new construction but it does provide various
approaches for minimizing the risk of ASR to a level acceptable to the owner.
19
6.0 REFERENCES
American Concrete Institute (ACI), “Use of Raw of Processed Natural Pozzolans in Concrete,” ACI
221.1R, 2000.
American Standards for Testing and Materials (ASTM), “Standard Guide for Petrographic Examination
of Aggregates for Concrete,” ASTM International, ASTM C295.
American Standards for Testing and Materials (ASTM), “Standard Test Method for Potential Alkali
Reactivity of Carbonate Rocks as Concrete Aggregates (Rock-Cylinder Method),” ASTM International,
ASTM C586.
American Standards for Testing and Materials (ASTM), “Standard Specication for Coal Fly Ash and
Raw or Calcined Natural Pozzolan for Use in Concrete,” ASTM International, ASTM C618.
American Standards for Testing and Materials (ASTM), “Standard Practice for Petrographic Exami-
nation of Hardened Concrete,” ASTM International, ASTM C856, Annual book of ASTM Standards,
Section Four, Vol. 04.02 Concrete and Aggregates, pp. 434-450, 2003.
American Standards for Testing and Materials (ASTM), “Standard Specication for Ground Granulated
Blast-Furnace Slag for Use in Concrete and Mortars,” ASTM International, ASTM C989.
American Standards for Testing and Materials (ASTM), “Standard Test Method for Length Change of
Concrete Due to Alkali-Carbonate Rock Reaction,” ASTM International, ASTM C1105.
American Standards for Testing and Materials (ASTM), “Standard Specication for Silica Fume Used
in Cementitious Mixtures,” ASTM International, ASTM C1240.
American Standards for Testing and Materials (ASTM), “Standard Test Method for Potential Alkali
Reactivity of Aggregates (Mortar-Bar Method),” ASTM International, ASTM C1260.
American Standards for Testing and Materials (ASTM), “Standard Test Method for Determination of
Length Change of Concrete Due to Alkali-Silica Reaction,” ASTM International, ASTM C1293.
American Standards for Testing and Materials (ASTM), “Standard Test Method for Determining the
Potential Alkali-silica Reactivity of Combinations of Cementitious Materials and Aggregates,” ASTM
International, ASTM C1567.
Canadian Standards Association (CSA), “Determination of Potential Alkali-Carbonate Reactivity of
Quarried Carbonate Rocks by Chemical Composition,” CSA A23.2-26A, Canadian Standards Associa-
tion, Mississauga, Ontario, Canada.
Canadian Standards Association (CSA), “Standard Practice to Identify Degree of Alkali-Aggregate Re-
activity of Aggregates and to Identify Measures to Avoid Deleterious Expansion in Concrete (2000a),”
CSA A23.2-27A, Canadian Standards Association, Mississauga, Ontario, Canada, 2000.
20
Folliard, K.J., Barborak, R., Drimalas, T., Du, L., Garber, S., Ideker, J., Ley, T., Williams, S., Juenger,
M., Thomas, M.D.A., and Fournier, B., “Preventing ASR/DEF in New Concrete: Final Report,” The
University of Texas at Austin, Center for Transportation Research (CTR), CTR 4085-5, 2006.
Lu, D.Y., Fournier, B. and Grattan-Bellew, P.E., “Evaluation of the Chinese Accelerated Test for Alkali-
Carbonate Reaction,” Proceedings of the 12th International Conference on Alkali-Aggregate Reaction
in Concrete, Beijing (China), International Academic Publishes, World Publishing Corporation, ISBN
7-5062-7033-1, Tang, M.S. and Deng, M. Editors, Vol. 1, pp. 386-392, Oct 15-19 2004.
Nixon, P.J., and Sims, I., “Alkali-reactivity and Prevention – Assessment, Specication, and Diagnosis
of Alkali-reactivity,” International Union of Laboratories and Experts in Construction Materials, Sys-
tems and Structures (RILEM), International Specication to Minimise Damage from Alkali Reactions
in Concrete: Part 1 Alkali-Silica Reaction, RILEM TC 191-ARP AAR-7.1, 2006.
Ozol, M.A., “Alkali-carbonate Rock Reaction,” Signicance of Tests and Properties of Concrete, STP
169D, Chapter 23, American Society of Testing and Materials, West Conshohocken, PA, pp. 410-424,
2006.
Rogers, C.A., “Evaluation for the Potential for Expansion and Cracking of Concrete Caused by the
Alkali-carbonate Reaction,” Cement, Concrete and Aggregates, Vol. 8, No. 1, pp. 13-23, 1986.
Thomas, M.D.A., Fournier, B., Folliard, K., Ideker, J. and Shehata, M., “Test Methods for Evaluating
Preventive Measures for Controlling Expansion due to Alkali-silica Reaction in Concrete,” Cement and
Concrete Research, Vol. 36 (10), pp. 1842-1856, 2006.
Tremblay, C., Berube, M-A., Fournier, B., Thomas, M.D.A. and Folliard, K.J., “Use of the Accelerated
Mortar Test to Evaluate the Effectiveness of LiNO3 Against Alkali-silica Reaction Part 2: Comparison
With Results from the Concrete Prism Test,” Accepted for publication, Cement and Concrete Research,
March 2008.
21
FHWA-HIF-09-001
