Materials Characterization
Structural properties of quartz and their potential role for ASR
Maarten A.T.M. Broekmans*
Geological Survey of Norway, Department of Mineral Resources, N-7491 Trondheim, Norway
Received 30 August 2004; accepted 31 August 2004
Abstract
Quartz is the predominant silica polymorph in alkali-reactive aggregate materials. Being a major constituent of the Earth’s
crust as well, quartz is stable under a broad range of conditions including pressure, temperature, fluids present, postdeformation,
etc. The conditions under which a particular quartz was formed are reflected in its qualities, including the crystal structural
details and its (trace) element composition. However, current testing methods to determine the alkali–silica reaction expansion
potential of aggregate materials do not address these qualities directly. To gain an idea which qualities affect the dissolution
behavior of quartz under ASR conditions, it might be useful to first consider the geological conditions, and apply these to
concrete.
D 2004 Elsevier Inc. All rights reserved.
Keywords: Quartz dissolution; Crystal structure; Crystal chemistry; ASR
1. Introduction
Three constituents are essential to the alkali-silica
reaction (ASR): alkalies and silica as reagents and
moisture (both as a reagent and a transport medium).
The alkalies are supplied by the cement paste or,
under certain circumstances, can be derived from the
aggregate material, and the water is mostly provided
by dexposure conditionsT, i.e., meteoric or otherwise.
Considered in their pure state, these constituents
behave consistently when reacting to form a silica
1044-5803/$ - see front matter D 2004 Elsevier Inc. All rights reserved.
doi:10.1016/j.matchar.2004.08.010
* Tel.: +47 7390 4152; fax: +47 7392 1620.
E-mail address: [email protected]
(M.A.T.M. Broekmans).
gel, regardless of their origin. The mechanism of silica
dissolution is not so much controlled by the alkali
species Na and K, but rather by water molecules and
dissolved OH-ions breaking silica bonds, which then
later recombine with alkali. Of course, differences in
concrete composition and local microenvironment
sensu lato do affect the alkali-reaction (i.e., silica
dissolution) conditions.
Already back in 1955, Ralph Iler published the first
edition of bThe colloid chemistry of silica and
silicatesQ [1], a monograph that, over the years, has
become famous, if not monolithic. It provides an
excellent introduction to the chemistry of silica
dissolution. However, since the publication of the first
edition and the subsequent expanded and updated
53 (2004) 129–140
M.A.T.M. Broekmans / Materials Characterization 53 (2004) 129–140130
second edition in 1974, much more data on quartz
and silica have become available. The 1994 compiled
review volume edited by Heaney et al. [2] covers the
behavior of silica under elevated geological con-
ditions as well as its physical properties, and capita
selecta from its application as an industrial material.
The book bStructure and imperfections in amorphous
and crystalline silicaQ [3] contains a valuable se-
lection of papers dealing with just that, from an
industrial point of view. Silica dissolution under
ambient weathering conditions is extensively treated
in Ref. [4].
Aggregate materials as used in concrete are of
diverse geological origin, and consequently, so is
the quartz they contain, having formed under
diverse conditions, essentially different for each
rock type with respect to their specific combination
of pressure, temperature and fluid history. To begin
with, it may be convenient to lump a mineral
formed under broadly variable conditions under one
single general denominator. Using combined min-
eralogical and geochemical techniques, however, it
is possible to identify different properties and
qualities of quartz from different geological envi-
ronments, potentially affecting its alkali-reactivity
potential.
Many publications have been dedicated to the
relationship between the nature and reactivity of
aggregate [e.g., Refs. [5–7], and references therein].
However, the different properties and qualities of
quartz sensu stricto with respect to its ASR-potential
seem to have received only little attention from a more
fundamental point of view. It is therefore useful to
review the mineralogical and geochemical properties
and qualities that possibly affect the dissolution of
quartz.
2. Silica dissolution controls
2.1. General
Parameters controlling quartz dissolution have
been well studied by many researchers. Recent
reviews are given in Refs. [4,8], and new contribu-
tions are frequently published in international jour-
nals. The key point in the alkali-silica reaction is the
hydrous dissolution of silica in the presence of
dissolved Na and K at high pH (N13), as is common
in OPC concrete.
The properties and qualities of the silica and its
environment may affect its solubility under the given
conditions. These will be discussed below in separate
paragraphs, with special emphasis on ambient pres-
sure (P)–temperature (T) conditions.
2.2. Equilibrium dissolution
The dissolution reaction of silica can be repre-
sented by the equation:
ð1Þ
However, the true nature of the silica in dissolution
is not simply H4SiO4 (aq), of which notation is
merely used for convenience, but rather depends on
solution properties such as pH, time, etc. [1,9]. Due
to dimerization and polymerization of the dissolved
silica upon ageing, the ratio SiO2:H2O trends
towards less than 1:2. However, if H-bonded waters
are counted in, the balance goes the other way.
Reaction Eq. (1) is an equilibrium reaction with a
constant K written as:
K ¼ aH4SiO4
aSiO2d a2H2O
ð2Þ
The principal shape of this equilibrium equation is
independent of the dissolving silica polymorph, even
when its solubility differs. A general rule of thumb is:
the lower the activity (or alternatively DGf8) of the
silica, the lower the solubility. This means that,
though the shape of Eq. (2) for quartz is the same
for all silica polymorphs, the respective a-values are
different [4]. It also means that a plotted graph of such
equations for each polymorph in essence will have the
same shape, but will be shifted along the vertical axis.
From thermodynamic data as experimentally con-
firmed by laboratory experiments, it appears that
quartz is the least soluble polymorph, glassy silica the
most soluble, whilst other are intermediate [10]. Apart
from the differences attributed to a different bulk
crystal structure, a higher lattice integrity with fewer
defects also affects silica solubility. Thus, the con-
centration of the dissolved species strongly depends
M.A.T.M. Broekmans / Materials Characterization 53 (2004) 129–140 131
on the whole nature of the solid silica with which the
solution is in equilibrium.
2.3. Effects of solution pH
Silica is an amphoteric material, which means that it
dissolves at extreme pH values in strongly acidic or
strongly alkaline conditions, and less around neutral
pH. At high pH in a basic environment, dissolved silica
as H4SiO4 behaves like a weak acid. From pH 9 and
upwards, silica dissolves according to the equation:
SiO2 þ 2H2O W H3SiO�4 þ Hþ ð3Þ
The predominant species in solution is no longer
H4SiO4 (aq), but the deprotonized variant of that. At
higher pH values, stepwise deprotonization runs to
final completion according to equation:
H3SiO�4 W SiO4�
4 þ 3Hþ at pHN12; ð4Þ
with equilibrium constant for each increment similar to
the model of Eq. (2). Eqs. (1), (3), and (4), in fact,
represent a scheme of subsequent reactions with
incrementally increasing deprotonization ((3) and (4))
that develop when pure silica dissolves in water at
pHN12.
If the final concentration of dissolved silica is high
enough, then it will polymerize to form H6Si4O72�
complexes, merely an effect of solution ageing and
not of pH. However, the speciation of freshly
dissolved silica does depend on pH.
3. Silica crystal structural features
3.1. Natural silica polymorphs
Some 12% of the volume of the entire earth’s crust
is made of the dpureT oxide SiO2, representing a
weight of ~3.2�1021 kg. In total, some nine silica
polymorphs are known to exist, each of the compo-
sition SiO2 but each with its own unique crystal
structure different from all others. Best known are a-
quartz, h-quartz, tridymite, cristobalite on the high-T
side, and coesite and stishovite on the high-P side.
Very recently, a completely new silica phase that
appears to be stable at extreme pressures beyond
stishovite stability was identified [11].
Lechatelierite is an amorphous silica glass from
fused sand found in fulgurites, and keatite is
crystalline but has as yet only been synthesized in
the laboratory [13]. The polymorph moganite has
officially been acknowledged by the Commission on
New Minerals and Mineral Names of the International
Mineralogical Association (CNMMN/IMA), but is
nevertheless still a matter of dispute among scientists.
A monograph on quartz varieties and their natural
appearances (and including some other silica poly-
morphs) was written by Rykart [12].
Most of the silica in the earth’s crust occurs as the
polymorph a-quartz, due to its large stability region in
the P,T-field [13]. Other polymorphs are in principle
thermodynamically unstable in the quartz P,T-region,
but may nevertheless persist due to the very sluggish
reconstructive phase transformations to quartz. An
extensive review on the crystal structures and other
properties of micro- and noncrystalline silica poly-
morphs can be found in Ref. [14].
3.2. Crystal structure of a-quartz
The crystal structure of quartz can be represented
as a 3D framework of [SiO4]-tetrahedra. Each
tetrahedron is built of four isometric triangles with
608 corners, with one O-atom at all four apices and the
Si-atom placed in its center of gravity. Adjacent
tetrahedra share their apical oxygen, reducing the O-
content of the bulk material to SiO2.
The [SiO4]-tetrahedra are arranged in sixfold rings,
where the top apex of tetrahedron 6 shares its oxygen
with the bottom apex of tetrahedron 1, forming a helix
that can be either left- or right-handed. Thus, quartz is
a chiral material with l (levus; left-handed) and d
(dexter; right-handed) enantiomorphs. At room tem-
perature and pressure conditions, the symmetry of
these six-fold rings is reduced from hexagonal to (di-)
trigonal as three of the six angles are wider than the
three other angles in the same ring. This arrangement
is called a-quartz and is the most stable polymorph
under ambient conditions.
3.3. Phase transformations of silica
Despite a-quartz being the most ubiquitous silica
polymorph, other polymorphs might be important in
specific environments and bear importance for con-
M.A.T.M. Broekmans / Materials Characterization 53 (2004) 129–140132
crete materials science. It is therefore interesting to
take a closer look at these, beginning with the P,T-
diagram for silica.
At room temperature, increasing pressure will
transform a-quartz to coesite above 1.9 GPa (19
kbar) and to stishovite above 7.6 GPa (76 kbar). Both
polymorphs immediately reverse to a-quartz when
pressure is released, so neither of these polymorphs
exists metastably at ambient conditions. The com-
pressive yield strength of highest performance con-
cretes produced and tested under laboratory
conditions is on the order of a few hundred MPa
and of modern bulk concrete in practice under 100
MPa. Together with a safety strength margin of 50%
the concrete that modern structures are designed with,
and in older days double that value, mechanical
stresses will be considerably lower than 100 MPa in
daily practice. Thus, the coesite and stishovite silica
polymorphs can be safely neglected in an ambient
concrete environment.
At ambient pressure, a-quartz will transform to h-quartz above 573 8C, changing its crystal structure
from di-trigonal to hexagonal by shifting the tetrahe-
dra to more symmetric places in the sixfold ring by an
intricate set of rotations. This also results in a stepwise
volume change of around 10% at the transformation
temperature: expansive upon heating, shrinking upon
cooling. This type of transformation is called dis-
placive as it merely comprises tilting of tetrahedra
affecting bond angles. Therefore, transformation is
rapid and reversible. A commensurate intermediate
phase is known to exist at temperatures near the a–htransition, but its treatment here is beyond the scope
of this paper [13].
Further heating will result in the h-quartz trans-
forming into tridymite above 867 8C and into
cristobalite above 1470 8C. Finally, cristobalite melts
at 1713 8C. Although formally a melt, molten silica is
extremely viscous and does not even need a container
as it will not flow. The melt’s viscosity can be
attributed to its extreme polymerization, as it still
represents a 3D silica network.
Upon cooling, the melt crystallizes as cristobalite,
which then transforms to tridymite below 1470 8C, incontrast to the heating trajectory. Further cooling does
not result in a transformation to h-quartz below 867
8C, but instead immediately to a-quartz at 573 8C,provided the cooling is done slow enough to allow the
lattice reconstructions to take place. If quenched,
silica glass, cristobalite, and/or tridymite will persist
down to ambient temperatures.
Neither the crystal structure of tridymite nor that of
cristobalite can be constructed from the h-quartzstructure by rotation of the [SiO4]-tetrahedra. Instead,
O–Si–O bonds have to be broken and mended
requiring a relatively high activation energy, making
this type of phase transformation reconstructive and
hence sluggish, so much so even that some phases are
skipped. Adding a fluxing agent such as, e.g., sodium
tungstate significantly speeds up reconstructive phase
transformations in silica [15].
Remarkably, 3D-network polymorphs tridymite
and cristobalite also crystallize under authigenic
(near-ambient) conditions in amorphous opal-A,
transforming it to opal-CT. Similarly, devitrification
of silica glass also leads to the formation of
cristobalite/tridymite intergrowths (eventually dstuffedderivativesT) like the dsnowflakesT in natural obsidian
[16], or spots in Medieval stained glass [17].
Intermediate crystallization into metastable cristoba-
lite/tridymite before recrystallization to a stable silica
phase (mostly a-quartz) is preferred due to the close
resemblance of their crystal structures to that of glassy
silica, requiring a smaller activation energy for the
(re-) construction of the crystal structure [18].
A number of SiO2 species are of particular
interest with respect to the alkali–silica reaction,
including opal, chert, and chalcedony [5,7]. Apply-
ing the appropriate nomenclature to fine grained
silica varieties is a complicated matter, as are their
respective crystal structures [14]. It is proposed that
only moganite is a polymorph sensu stricto [19], and
that agate, chert, flint, chalcedony, etc., are instead
rather to be regarded as rock names [20]. The crystal
structure of moganite can be described as being
derived from a-quartz by lamellar Brazil twinning,
polysynthetic at unit cell scale [13]. The moganite
structure has been applied to the domain structure of
chalcedony as a three dimensional construct of
quartz and moganite domains of variable size and
degree of (mis-) orientation. As per today, moganite
has not yet been mentioned as participant in a
deleterious alkali-silica reaction [e.g., Refs. [21–24]],
whereas it has been demonstrated to be a common
constituent in selected chert and other fine-grained
silica varieties from all over the globe [25]. Porous
M.A.T.M. Broekmans / Materials Characterization 53 (2004) 129–140 133
chert is listed as a severe ASR hazard in the
Netherlands, Belgium, Germany, and Denmark,
among other countries.
The silica polymorphs tridymite, cristobalite, and
moganite are thermodynamically less stable than
quartz to various degrees, and hence more prone to
dissolution and/or alkali reactivity than quartz. If the
solubility rate of quartz in pH-neutral water at 25 8C is
set at unity, then cristobalite dissolves 2.05 times as
fast, tridymite 2.71 times [8], and moganite at pH 3.5
even 7.4 times [26]. The respective volume of quartz
and moganite and the degree of misorientation
between domains are thought to affect the dissolution
of this type of silica, and may also explain the
variations in reference values for the solubility of
chalcedony [18].
Although the speciation of dissolved silica depends
on pH (and ageing), the concentration of the dissolved
species also depends on the nature of the solid silica
with which the solution is in equilibrium. All this
implies that, although the template of equilibrium Eq.
(2) will not change, the effective concentration of
dissolved silica will, depending on the actual poly-
morph and its degree of crystallinity.
3.4. Effect of the quality of the crystal lattice
The exact definition of a grain boundary differs
with the boundary type. In general terms, a grain
boundary is defined as a btwo-dimensional lattice
defect that introduces a misorientation with no long-
range stress fieldQ. In this respect, a high-angle
misorientation is, in fact, a plane between two
individual grains with differently oriented lattices, in
contrast to a low-angle misorientation that is to be
regarded as a defect within one single crystal [27].
Thus, a grain boundary is comparatively low in stress.
Within a certain volume embedding a structure
imperfection in quartz, the crystal structure is distorted
and deviates from the proper structure, more easily
accommodating foreign ions than an undistorted
structure. Consequently, aggressive agents have an
easier job breaking the stressed bonds in and near
imperfections than elsewhere, whence the solubility of
quartz also reflects its structural perfection.
The above provides the basis for the supposedly
increased alkali-solubility of deformed quartz as
compared to defect-free quartz [see, e.g., Ref. [6]].
Experimental mortar bar expansion testing on heavily
deformed rocks (Norwegian mylonites) confirmed
these are violently alkali-reactive indeed [66]. Thus,
there seems to be more to the alkali-reactivity of
deformed quartz in mylonite than merely undulous
extinction [e.g., Ref. [6]] and a strongly oriented grain
fabric.
Twin planes also represent a discontinuity in a
crystal structure, albeit for a totally different reason. In
quartz, Dauphine twins are most common followed by
Brazil twins [28,29]. Less-common twin modes are
summarized in Refs. [30,31]. The structures of both
twin individuals are differently oriented by a crystallo-
graphical symmetry operation, such as, e.g., a
rotation, a mirror or a glide plane, or a combination.
The difference in orientation results in a distortion of
the interface’s crystal structure. For instance, in
Dauphine-twinned quartz, the twin interface acquires
a distorted h-quartz structure with stressed interatomic
bonds, as a kind of average of the two di-trigonal
individuals. Other twinning modes may have different
interface structures, with different amounts of bond-
stress [13]. The thermodynamic stability of the silica
at a twin interface is reduced relative to bulk material.
Hence, twin interfaces are in principle more prone to
attack in aggressive environments, including high pH.
In natural quartz, Dauphine-twinning occurs at all
sizes down to the transmission electron microscopy
scale [e.g., Ref. [32]]. Dauphine twinning can also be
mechanically induced by applying oriented stress. As
Dauphine twinning is optically inactive, it remains
invisible in petrographic microscopy. Thus, its macro-
scopic identification in quartz oscillator plates and
thin sections is traditionally done using etching
techniques, giving good but mainly qualitative results
[28,31]. Etching techniques have long been known
but have a major disadvantage in that they often use
health-hazardous chemicals [e.g., Ref. [33]]. In con-
trast, electron backscatter diffraction mapping is a far
safer alternative that provides quantitative data on
twinning and domain building as well as (mis-)
orientation at the same time.
High-temperature experiments in the transmission
electron microscope have demonstrated that Dauphine
twins disappear above the a-h transition temperature
at 573 8C, conforming to expectation from crystal-
symmetry points of view. However, when the sample
is cooled through the transition temperature, the
M.A.T.M. Broekmans / Materials Characterization 53 (2004) 129–140134
original Dauphine twin pattern reemerged. Repeated
thermal cycling resulted in only minor changes [34].
Early high-temperature experiments on quartz oscil-
lator plates back in the 1940’s gave very similar
results on the macroscopic scale [28]. Amazingly, it
was also found that even sustained heating for 14 days
to temperatures up to 1000 8C could not eliminate
initial/natural Dauphine twinning. In an additional
experiment, synthetic Dauphine twins were induced
mechanically on quartz plates already containing
natural twins. The natural Dauphine twins were as
persistent as previously observed. However, the
synthetic Dauphine twins did disappear, even after
short heating to only 600 8C, providing a great
contrast to their natural counterparts.
From similar experimental results on anorthite, it
has been speculated that this memory-effect might be
attributed to foreign ions present at the location of the
twin interfaces. The deviations from the structure at
the twin interface may accommodate foreign species
that effectively pin the twin boundary and cause it to
reemerge at its original position [35]. Dry heating only
slowly moves these species away from their initial
positions, explaining why the original twin pattern is
so persistent and with only minimal change. On a
much larger size scale, interspersed small mica grains
have been proven to be effective in pinning grain
boundaries in quartzite [27].
The deformation inflicted on the quartz lattice by
polishing may result in the formation of a surface
layer with an amorphous, noncrystalline structure,
until a depth of a few hundred Angstrom, called the
Beilby layer after its discoverer [36]. Beilby layers
have been identified in a variety of materials,
including oxides (i.e., gem materials), and were
originally thought to be caused by polish-induced
flow of the top surface. The original theory of Beilby
layer formation was dismissed in the 1980s [37].
Amorphous Beilby layers also form when material is
being crushed. Analysis by A-differential thermal
analysis (DTA) of quartz ground in a ball mill for
20 h clearly showed that the material was not
completely amorphous and still had a relic a–h phase
transition near 573 8C, although peak broadening
already occurred after 1 h. However, in similar
experiments with a regular DTA (i.e., non-A), evenextended milling for 400 h could not remove
completely the transition peak [38].
Beilby layers are known to affect the surface
reactivity of silica with respect to its toxicity in
respiratory issues; bulk silica is less harmful. Beilby
layers on silica powder can be removed by acid
etching or simply by ageing in a wet environment
[39]. Therefore, the surface of freshly crushed
aggregate could be expected to be more reactive in
a similar way.
3.5. Effect of foreign species in the solid silica
Despite being known as one of the purest mineral
species in nature, quartz usually contains a small
amount of foreign species, including hydrous species.
The helical crystal structure of quartz proper is very
rigid and does not easily accommodate ions of
deviating size or charge, limiting replacement to
minor amounts at specific locations. The most
common substituents for tetravalent Si4+ are trivalent
Al3+ and Fe3+, leaving uncompensated charges in the
structure. To maintain electrical balance, small mono-
valent cations such as H+, Li+, Na+, and/or K+ enter
the quartz structure in interstitial spaces, not at
original Si-locations [40]. Alternatively, two Si4+
can be substituted by one Al3+ plus one P5+, some-
times dubbed the berlinite replacement. Berlinite is a-
AlPO4 which is iso-structural with quartz. Substitu-
tions with other elements (Ti4+, Mg2+, etc.) have also
been reported [31,41–43].
As the Al3+ and/or Fe3+ substituents are bonded in
the quartz structure, they are rather immobile under
ambient conditions. In contrast, interstitial charge
compensating ions are rather mobile and can be
exchanged for other species by electrochemical treat-
ment [44], in particular, through the helical channels
in the quartz structure that run parallel to the c-axis.
This effect was described for the first time almost 120
years ago, in the late 1880s, by the brothers Jacques
and Pierre Curie and contemporaneous researchers
[Ref. [45], and references therein].
Alternatively, silicon in quartz can be substituted
by four H+ for one Si4+ [40]. All four H+-s are each
bonded to their own O2�, thus in fact making up four
hydroxyls filling an Si4+ vacancy. This entire arrange-
ment is called a silanol group. In larger structural
vacant volumes, additional water molecules may
become H-bonded to the silanol groups, forming
nano-inclusions of essentially bonded water mole-
M.A.T.M. Broekmans / Materials Characterization 53 (2004) 129–140 135
cules. Due to the bonding, the freezing temperature of
the water is considerably reduced, by tens of degrees
centigrade. In natural quartz, silanol groups are
common at dislocations, in previous cracks healed
under elevated conditions as demonstrated experi-
mentally by Bakker [46], and in neogenic quartz in
compacted sandstone as demonstrated from geolog-
ical practice [47]. Silanol groups may become an
active color center after activation, e.g., by the
electron beam in cathodoluminescence. They make
quartz luminesce in the far red, with intensity
increasing after prolonged beam exposure.
3.6. Effect of silica grain size
Grain size is in itself not a fundamental material
property. Nevertheless, the grain size of quartz does
affect its solubility, because of the increasing surface
area with diminishing grain size. If more area is
available for dissolution, then the material will
dissolve in a shorter time. In addition, the small
(quartz) grains need to be accessible for the solvent,
requiring porosity and permeability of the aggregate
grain to facilitate (chemical) communication. For
instance, very fine grained silica will react delete-
riously in porous chert, whereas it will not do so in
nonporous chert, also for porous and dense parts
within one single chert grain. In addition, the
logarithmic plot of NBRI-expansion vs. mean quartz
grain size in Norwegian mylonites is suggestive of an
davailable surface areaT-related relationship [48].
Quartz solubility increases significantly at grain
sizes below ~0.1 Am due to an inflection point
occurring in the particle’s free Gibbs energy DGf
[4]. Quartz particles with a convex curvature (i.e.,
spheres) have a measurably higher solubility. As a
result, the finest quartz particles sub ~0.1 Am will
dissolve, whereas larger particles will grow. This
process of overall grain coarsening has long been
known as Oswald ripening. In contrast, quartz with a
concave curvature experience decreased solubility.
Consequently, voids in fine-grained porous chert will
fill with newly precipitated quartz, becoming more
equidimensional and clotting initial permeability.
Related to the above discussion on grain size and
enhanced solubility is the definition of grain bounda-
ries. A grain boundary can be defined as a certain
misorientation angle between two separate volumes in
the same crystal structure, essentially a planar array of
dislocations. Two volumes separated by a low-angle
dislocation array are considered as one crystal struc-
tural entity; if separated by a high-angle boundary
instead, they consist of two contiguous individuals.
Arbitrarily, the distinction between low- and high-
angle is put at 108–158. Alternatively, a nonplanar
Dauphine twin interface and planar arrangements like
a Brazil twin interface or deformation lamellae can
also be regarded as a grain boundary [27].
3.7. Catalytic effects of coexisting minerals
In the last few decades, more and more articles
have appeared describing the catalytic action of
certain minerals upon dissolution reactions/rates.
Biotite has been documented to promote the formation
of sillimanite at elevated conditions [49], and of
hydrogarnet at lower grade conditions [50]. Phyllosi-
licates, clay minerals, and zeolites have proven
catalytic properties on the most diverse chemical
processes [51,52], and it has even been postulated that
clay minerals could be closely involved with the
origin of life [53].
Several minerals are known to affect the pH of
pore solutions. In 1983, Boles and Johnson [54]
published results from an elegantly simple experiment
demonstrating that fine-grained muscovite suspended
in water affected the final pH of the suspension
differently than biotite did. Depending on mineral
composition and detailed crystal structure (in the
experiment mentioned above: dioctahedral vs. triocta-
hedral mica), phyllosilicates may either spawn H+ into
the solution or absorb it from, in both cases altering
the pH. In addition, alkalies rather easily leach from
the sides of phyllosilicate flakes into the pore water by
incongruent dissolution.
The effect of phyllosilicates on quartz solubility
has previously been described for muscovite in
sandstone. Upon compaction of sand into sandstone
under diagenetic conditions, single flakes of musco-
vite appear to penetrate deeply into quartz grains
sideways, without kinking or even bending. The
quartz grains, in particular, are of detrital origin and
not neogenic precipitates, as confirmed by cathodo-
luminescence. A simple calculation using published
E-module data for mica precludes mechanical intru-
sion into quartz, simply due to lack of strength of the
M.A.T.M. Broekmans / Materials Characterization 53 (2004) 129–140136
mica. Thus, the only way to penetrate into quartz is
to dissolve away the quartz at the side of the mica
flake [55].
Adjacent quartz grains in the same sandstone
material often have a serrated interface, whereas,
thermodynamically, a smooth boundary would be
more advantageous. Element maps of K, Al, and Si at
high magnification correlate directly with a back-
scatter image of the same area suggesting the presence
of clay minerals (e.g., kaolinite, smectite) at the
interface, but the mineral grains themselves proved
beyond resolution of the scanning electron micro-
scope used [55]. Such (serrated) grain boundaries are
described as having denhanced visibilityT under a lightoptical microscope. Independently, a similar observa-
tion on grain boundaries had been made in alkali-
reactive sand-/siltstone in Dutch concrete [56,57].
Both penetration of mica into detrital quartz and the
formation of serrated grain boundaries are attributed
to the catalytic action of mica and/or clay phyllosili-
cates [58].
4. Comparison with quartz in the concrete
environment
4.1. Geological vs. ambient conditions
Conditions in the earth’s crust range from ambient
up to roughly 1.5 GPa and 1200 8C, whereas ambient
conditions in concrete structures may range up to ~30
MPa at temperatures ranging from around �20 to +30
8C in a temperate climate, although extreme values
may be substantially different. Under ambient con-
ditions, some minerals initially formed under higher-
grade geological conditions deeper in the earth’s crust
will dissolve and reprecipitate in another assemblage.
Under ambient conditions, dissolved species are
transported by liquid water, resulting in the local
depletion of particular chemical species and enrich-
ment elsewhere. Transport of locally dissolved matter
necessarily also affects porosity and permeability of
the rock.
4.2. Silica gel composition
The true chemical composition of silica gel from
laboratory, natural, or concrete systems cannot be
represented by H4SiO4, although such is often done
for brevity. As explained above, the solubility of
quartz (and silica in general) is influenced by other
species in solution, each with a specific affinity for the
quartz, dissolved or solid. The more outspoken the
affinity of a given species, the more firmly that
species attaches itself to the quartz [4].
Real-life compositions of alkali–silica gel typically
contain significant amounts of Na+, K+, and Ca2+,
whereas microscopic observations on the mineralogy
of the alkali–silica reaction and its products suggests
that Al3+, SO42�, CO3
2�, and possibly also Mg2+ and
Fe2+/3+ play an important role [59]. The alkali–silica
gel reaction product may, in an advanced stage of
deleterious ASR, be extruded along cracks, even
outside the concrete. Element species with a high gel-
affinity will be transported along with the extruded
gel, whereas other species reside with the residual
material and behave immobile [60].
4.3. Silica particle size, aggregate porosity, and fluid
access
Although grain size in itself is not a fundamental
material property of quartz, it does affect its solubility,
especially in combination with porosity and perme-
ability of the aggregate grain. Thus, aggregate grains
containing quartz with a small initial grain size and/or
coarse-grained quartz that suffered extensive grain
size reduction and/or subgraining due to geological
deformation (e.g., load compaction, mylonitization)
will be more prone to develop a deleterious ASR due
to an increase in available surface, provided that the
increased surface is sufficiently accessible for the pore
solution. In addition, quartz solubility is higher for
grain sizes below ~0.1 Am for a fundamentally
different reason.
Nota bene: referring to optics theory, the resolving
power of a modern light optical microscope is limited
to around ~1 Am, under optimum conditions with very
thin (submicron) samples, and using oil immersion. In
20- to 30-Am thin petrographic sections, studied in air
with a cover glass mounted (standard thickness: 0.17
mm=170 Am), optical resolution is typically reduced
to 3–5 Am [78]. Per geological definition, siltstones
have a grain size ranging from 63 Am down to 2 Am.
Cherts have an average observed grain size of 8–10
Am [18]. Thus, in a typical petrographic thin section
M.A.T.M. Broekmans / Materials Characterization 53 (2004) 129–140 137
of chert or fine-grained siltstone, several quartz grains
will be stacked on top of each other, blurring view and
reducing resolution. Grains that eventually would
enjoy enhanced solubility due to their small enough
grain size are completely beyond optical resolution.
The discussion of grain size and subgraining is
obviously related to the phenomenon of undulous (or
dwavyT) extinction. Extinction angles may vary con-
siderably within a single quartz grain, up to 108–158or more between its extremities, and obviously also
depending on its size [6]. According to the (arbitrary)
criterion of 108–158 described above, an undulous
grain must contain several low-angle boundaries
separating domains with a slightly different orienta-
tion, effectively reducing overall grain size. Fluid
access is facilitated along the angular misfit between
adjacent domains separated by a planar dislocation
array. There, fluids may have an easy job attacking the
dislocation-rich subgrain walls (compare Refs.
[40,46,61]).
Not all twin modes are optically active and/or may
be easily overlooked, especially in fine grained
material like chert or siltstone. The interfaces between
twin individuals in a-quartz do not have a proper
quartz structure but a deformed one, sometimes
actually closer to h-quartz. Foreign species tend to
favor the deformed interface structure, inducing dtwinmemoryT by pinning twin boundaries [28,35].
Chemical impurities and foreign ions, including
water and silanol groups, tend to associate with
dislocations, vacancies and other structural irregular-
ities in quartz, providing easy access for attack by
chemical and/or physical forces [62]. The effect of
lattice defects and grain boundaries has recently been
addressed in general terms by Wigum [48]. He
recognizes the impact of the problem in proper
characterization of aggregate materials and he devel-
oped a point-counting method for application to
mylonites. Whether, and if, and to what extent the
method works for other rock types has not been
verified.
4.4. Identification and characterization of silica
According to ASR literature and field experience,
quartz is by far the most occurring silica polymorph in
confirmed alkali-reactive aggregate materials. In most
studies, the reactive species is mostly only identified
as quartz (eventually in chert, siltstone, or other rock
types), but only rarely characterized in detail by
mineralogical or geochemical methods in terms of
crystal structure, the presence of domain building and
twinning, and/or its chemical composition [e.g., Refs.
[63,64]]. Whereas identification of quartz by petrog-
raphy is straightforward and mostly occurs by face-
factor, quartz qualities affecting its solubility and
susceptibility for deleterious ASR have to be assessed
with more intricate analytical methods, especially in
fine-grained materials. That includes the presence of
moganite that appears to be more prominent in fine
grained silica varieties [13,25].
Quartz containing Norwegian felsic mylonites
have been reported to be violently alkali-reactive
[65,66]. Although a correlation of total quartz area
versus accelerated expansion testing was demonstra-
ted [48], the fundamental reason for the increased
quartz solubility remained unaddressed. Several
crystal structural and compositional options exist that
can increase quartz solubility, which, in principle,
also could affect quartz crystallinity, including dis-
location density. However, the Normin2000 project
[67] puts blastomylonites that have enjoyed
dequilibrium recrystallizationT after their deformation
in the same alkali-reactive category. The recrystalli-
zation changes the strongly oriented fabric into a
more equiangular fabric, also reducing the dislocation
density. As a result, the quartz has smooth extinction
as opposed to undulous in a non-recrystallized
mylonite, suggesting a decrease in reactivity potential
[compare Ref. [6]]. Recently, two regular Norwegian
mylonites (i.e., non-recrystallized) were found to
behave inertly in repeated accelerated mortar bar
experiments [68], despite their true mylonite texture
and fabric.
A similar thing occurs with sand-/siltstones that,
according to the current Norwegian regulations,
classify as potentially alkali-reactive, without any
further specification. However, recent long-term field
experience shows that some sandstones apparently do
not react deleteriously, despite their classification. In
contrast, Dutch sand-/siltstone is regarded as nonalkali
reactive according to the latest regulations (unless
containing chert fragments, chalcedony or opal), but
field experience has actually confirmed that some
grains do react [69]. Geologically speaking, sand-
stones display a broad variation in composition,
M.A.T.M. Broekmans / Materials Characterization 53 (2004) 129–140138
structure, texture, and other properties; however, that
is not reflected in the Dutch and/or Norwegian ASR
classification.
Apparently, classifying a rock as potentially alkali-
reactive by simply applying nomenclature is not quite
good enough as innocuous rocks may be included as
well, obviously an undesirable situation. Therefore,
proper characterization of silica species in potentially
and actually alkali-reactive aggregate must also
include these aspects.
4.5. Catalytic actions of coexisting minerals
The presence of some nonsilica minerals has been
tied to the occurrence of ASR in several cases, e.g.,
phlogopite [70], dawsonite [59,71], and basalt rock
[72,73]. The possible active contribution of mica to
deleterious ASR in Dutch sand-/siltstone has been
suggested, describing bell-shaped areas of increased
porosity at the edges of detrital muscovite grains
[56,57]. In thin sections, the grain boundaries in such
sand-/siltstones appear optically enhanced, matching
descriptions in sedimentology literature on catalytic
action of detrital mica [55,58].
Catalytic or other (inter-) action of minerals has
not too often been demonstrated in natural rock
systems, and not at all for ASR or other causes of
concrete deterioration. Such interaction can for
instance consist of incongruent dissolution preferently
releasing alkalies [e.g., Refs. [74,75]], or a truly
catalytic action affecting pore water pH [Ref. [54];
also see Ref. [76]]. Recently, it was observed that
portlandite occurred intimately intergrown with and
within frayed biotite flakes in Dutch concrete [77],
strongly suggesting a pH-dependent relationship
present in concrete, at least during the precipitation
of portlandite [see also Ref. [50]].
5. Conclusions
There are a great number of qualities and properties
about quartz as a material that may affect its undesired
dissolution under ASR conditions. Some of them are
quite obvious and relatively easy to assess, but most
of quartzTs intricacies are more difficult to character-
ize as they require specific instrumentation. Detailed
and thorough analysis of alkali-reactive silicas from
different origins with a range of techniques and
methods will be needed to understand why some
silica is alkali-reactive and why others are not, what
their differences are, in order to be able to develop
reliable (and preferably quick) testing procedures.
References
[1] Iler RK. The colloid chemistry of silica and silicates, 1st
edition. Ithaca (NY)7 Cornell Univ. Press; 1955. p. 324.
[2] Heaney PJ, Prewitt CT, Gibbs GV, editors. Silica: physical
behavior, geochemistry and materials applications. Reviews in
Mineralogy, vol. 29. Washington (DC)7 Mineralogical Society
of America; 1994. p. 606.
[3] Devine RAB, Duraud JP, Dooryhee E, editors. Structure and
imperfections in amorphous and crystalline silicon dioxide.
Chichester (UK)7 John Wiley & Sons; 2000. p. 505.
[4] Dove PM. Kinetic and thermodynamic controls on silica
reactivity in weathering environments. In: White AF, Brantley
SL, editors. Chemical weathering rates of silicate minerals.
Reviews in Mineralogy, vol. 31. Washington (DC)7 Minera-
logical Society of America; 1995. p. 235–90.
[5] Fookes PG. An introduction to the influence of natural
aggregates on the performance and durability of concrete.
Q J Eng Geol 1980;13:207–29.
[6] Dolar-Mantuani L. Handbook of concrete aggregates—a
petrographic and technological evaluation. New York (NY)7
Noyes Publications; 1983.
[7] French WJ. Concrete petrography: a review. Q J Eng Geol
1991;24:17–48.
[8] Dove PM, Rimstidt JD. Silica–water interactions. In: Heaney
CT, Prewitt CT, Gibbs GV, editors. Silica. Reviews in
Mineralogy, vol. 29. Washington (DC)7 Mineralogical Society
of America; 1994. p. 259–308.
[9] Lieftink DJ. The preparation and characterization of silica
from acid treatment of olivine. PhD thesis. Utrecht, NL:
University of Utrecht, Faculty of Chemistry; 1997. 177.
[10] Robie RA, Hemingway BS, Fischer R. Thermodynamic
properties of minerals and related substances at 298.15 K
and 1 bar (105 Pascals) and at higher pressures and higher
temperatures. US Geol Surv Bull 1978;1452:456.
[11] Luo SN, Tschauner O, Asimov PD, Ahrens TJ. A new dense
silica polymorph: a new possible link between tetrahedrally
and octahedrally coordinated silica. Am Mineral 2004;
89:455–61.
[12] Rykart R. Quarz-Monographie, 2nd edition. Thun (Swit-
zerland)7 Ott Verlag; 1995. p. 462.
[13] Heaney PJ. Structure and chemistry of the low-pressure silica
polymorphs. In: Heaney PJ, Prewitt CT, Gibbs GV, editors.
Silica: physical behavior, geochemistry and materials applica-
tions. Reviews in Mineralogy, vol. 29. Washington (DC)7
Mineralogical Society of America; 1994. p. 1–40.
[14] Graetsch H. Structural characteristics of opaline and micro-
crystalline silica minerals. In: Heaney PJ, Prewitt CT, Gibbs
GV, editors. Silica: physical behavior, geochemistry and
M.A.T.M. Broekmans / Materials Characterization 53 (2004) 129–140 139
materials applications. Reviews in Mineralogy, vol. 29.
Washington (DC)7 Mineralogical Society of America; 1994.
p. 209–32.
[15] Kqhnel RA, Verkroost TW, Chaudry MA. Thermal behavior
of amorphous silica. In: Rodrıguez-Clemente R, Tardy Y,
editors. Proceedings of the Conference on Geochemistry
and Mineral Formation in the Earth Surface. Madrid, Spain,
p. 863–75.
[16] Fiore S, Huertas FJ, Tazaki K, Huertas F, Linares J. A low
temperature alteration of a rhyolitic obsidian. Eur J Mineral
1999;11:455–69.
[17] Garcia-Valles M, Gimeno-Torrente D, Martınez-Manent S,
Fernandez-Turiel JL. Medieval stained glass in a Mediterra-
nean climate: typology, weathering and glass decay, and
associated biomineralization processes and products. Am
Mineral 2003;88:1996–2006.
[18] Knauth LP. Petrogenesis of chert. In: Heaney PJ, Prewitt CT,
Gibbs GV, editors. Silica. Physical behavior, geochemistry
and materials applications. Reviews in Mineralogy, vol. 29.
Washington (DC)7 Mineralogical Society of America; 1994.
p. 233–58.
[19] Flfrke OW, Jones JB, Schmincke HU. A new microcrystalline
silica from Gran Canaria. Zeitschrift fqr Kristallographie
1976;143:156–65.
[20] Flfrke OW, Graetsch H, Martin B, Rfller K, Wirth R.
Nomenclature of micro- and non-crystalline silica minerals,
based on structure and microstructure. Neues Jahrb Mineral
Abh 1991;163:19–42.
[21] Diamond S. Alkali aggregate reactions in concrete: an
annotated bibliography, 1939–1991. Strategic highway
research program report (SHRP/C/UWP-92/601). Washington
(DC)7 National Research Council; 1991. p. 470.
[22] Poole AB, editor. Proceedings of the 9th International
Conference on Alkali-Aggregate Reaction in Concrete, West-
minster/London, UK, p. 1130.
[23] Shayan A, editor. Proceedings of the 10th International
Conference on Alkali-Aggregate Reaction in Concrete, Mel-
bourne, Australia, p. 1063.
[24] Berube MA, Fourier B, Durand B, editors. Proceedings of the
11th International Conference on Alkali-Aggregate Reaction
in Concrete, Quebec City, PQ, Canada, p. 1406.
[25] Heaney PJ, Post JE. The widespread distribution of a novel
silica polymorph in microcrystalline quartz varieties. Science
1992;255:441–3.
[26] Gıslason SR, Heaney PJ, Oelkers EH, Schott J. Kinetic and
thermodynamic properties of moganite, a novel silica poly-
morph. Geochim Cosmochim Acta 1997;61:1193–204.
[27] Poirier JP. Creep of crystals: high-temperature deformation
processes in metals ceramics and minerals. Cambridge (UK)7
Cambridge University Press; 1985. p. 260.
[28] Frondel C. Secondary Dauphine twinning in quartz. Am
Mineral 1945;30:447–61.
[29] Friedlaender C. Morphologische Feststellung von R-L-
Verzwillingung an alpinen Quarzkristallen. Schweiz Mineral
Petrogr Mitt 1948;28:71–83.
[30] Gault HR. The frequency of twin types in quartz crystals. Am
Mineral 1949;34:142–62.
[31] Friedlaender C. Untersuchung qber die Eignung alpiner
Quarze fqr piezoelektrische Zwecke. Beitr7ge zur Geologie
der Schweiz, Geotechnische Serie, Lieferung 1951;29:98.
[32] Heaney PJ, Veblen DR. Observations of the a–h phase
transition in quartz: a review of imaging and diffraction
studies and some new results. Am Mineral 1991;76:1018–32.
[33] Meyer O, Penfield SL. Results obtained by etching a sphere of
quartz with hydrofluoric acid. Transactions 1890;8:158–65.
[34] Heaney PJ, Veblen DR. Observation and kinetic analysis of a
memory effect at the a–h quartz transition. Am Mineral
1991;76:1459–66.
[35] Hayward SA, Salje EKH. Twin memory and twin amnesia in
anorthoclase. Mineral Mag 2000;64:195–200.
[36] Beilby GT. Aggregation and flow of solids. London (UK)7
MacMillan & Co; 1912.
[37] Crowcroft PJ. Demise of the Beilby–Bowden theory of
polishing. J Gemol 1981;17(7):459–65.
[38] Moore GSM. The a–h inversion in quartz and the effects of
structural damage. Phase Transit 1986;7:25–40.
[39] Goldschmidt DF. Health effects of silica dust exposure. In:
Heaney PJ, Prewitt CT, Gibbs GV, editors. Silica. Physical
behavior, geochemistry and materials applications. Reviews in
Mineralogy, vol. 29. Washington (DC)7 Mineralogical Society
of America; 1994. p. 545–606.
[40] Kronenberg AK. Hydrogen speciation and chemical weaken-
ing of quartz. In: Heaney PJ, Prewitt CT, Gibbs GV, editors.
Silica. Physical behavior, geochemistry and materials applica-
tions. Reviews in Mineralogy, vol. 29. Washington (DC)7
Mineralogical Society of America; 1994. p. 123–76.
[41] Bambauer HU. Spurenelementgehalte und g-Farbzentren in
Quarzen aus Zerrkluften der Schweizer Alpen. Schweiz
Mineral Petrogr Mitt 1961;41:335–69.
[42] Bambauer HU, Brunner GO, Laves F. Wasserstoff-Gehalte in
Quarzen aus Zerrklqften der Schweitzer Alpen und die
Deutung ihrer regionalen Abh7ngigkeit. Schweiz Mineral
Petrogr Mitt 1962;42:221–36.
[43] Smith JV, Steele IM. Chemical substitution in the silica
polymorphs. Neues Jahrb Mineral, Geol Palaontol, Monatsh
1984;1984:137–44.
[44] Kats A. Hydrogen in alpha-quartz, parts 1 and 2. Philips Res
Rep 1962;17(133–195):201–79.
[45] Kronenberg AK, Kirby SH. Ionic conductivity of quartz: DC
time dependence and transition in charge carriers. Am Mineral
1990;72:739–47.
[46] Bakker RJ. On modifications of fluid inclusions in quartz. PhD
thesis. Utrecht, NL: University of Utrecht, Geologica Ultra-
iectina 94, 1992, 189.
[47] Kronenberg AK, Wolf GH. Fourier transform infrared
spectroscopy determinations of intragranular water content
in quartz-bearing rocks: implications for hydrolytic weakening
in the laboratory and within the earth. Tectonophysics
1990;172:255–71.
[48] Wigum BJ. Examination of microstructural features of
Norwegian cataclastic rocks and their use for predicting
alkali-reactivity in concrete. Eng Geol 1995;40:195–214.
[49] Foster CT. The role of biotite as a catalyst in reaction me-
chanisms that form sillimanite. Can Mineral 1991;29:943–63.
M.A.T.M. Broekmans / Materials Characterization 53 (2004) 129–140140
[50] Nijland TG, Verschure RH, Maijer C. Catalytic effect of
biotite: formation of hydrogarnet lenses. Comptes Rendues de
l’Academie des Sciences Paris 1994;318-II:501–6.
[51] Vogels RJMJ. Non-hydrothermally synthesized trioctahedral
smectites. Preparation, characterisation and catalytic properties
of synthetic clay minerals. PhD thesis. Utrecht, NL: University
of Utrecht, Faculty of Chemistry; 1995. 191.
[52] Titulaer M. Porous structure and particle size of silica
and hydrotalcite catalyst precursors. PhD thesis. Utrecht,
NL: University of Utrecht, Geologica Ultraiectina 99,
1993. 268.
[53] Cairns-Smith AG, Hartman H. Clay minerals and the origin
of life. Cambridge (UK)7 Cambridge University Press; 1986.
p. 193.
[54] Boles JR, Johnson KS. Influence of mica surfaces on pore-
water pH. Chem Geol 1983;43:303–17.
[55] Bjbrkum PA. How important is pressure in causing dissolution
of quartz in sandstones? J Sediment Res 1996;66:147–54.
[56] Broekmans MATM, Jansen JBH. ASR in impure sandstone:
mineralogy and chemistry. In: Sveinsdottir EL, editor. Pro-
ceedings of the 6th Euroseminar on Microscopy Applied to
Building Materials, Reykjavik, Iceland, p. 161–76.
[57] Broekmans MATM, Jansen JBH. Silica dissolution in impure
sandstone: application to concrete. In: Vriend SP, Zijlstra JJP,
editors. Proceedings of the Conference on Geochemical
Engineering: Current Applications and Future Trends. J
Geochem Explor, Special, vol. 62, p. 311–8.
[58] Oelkers EH, Bjbrkum PA, Murphy WM. A petrographic and
computational investigation of quartz cementation and poros-
ity reduction in North Sea sandstones. Am J Sci 1996;296:
420–52.
[59] Thaulow N, Jakobsen UH, Clark B. Composition of alkali
silica gel and ettringite in concrete railroad ties: SEM-EDX and
X-ray diffraction analyses. Cem Concr Res 1996;26:309–18.
[60] Taylor HFW. Cement chemistry, 2nd ed. London (UK)7
Thomas Telford; 1997. p. 459.
[61] Heggie MI. A molecular water pump in quartz dislocations.
Nature 1992;355:337–9.
[62] Bloss FD. Crystallography and crystal chemistry, 2nd ed.
Washington (DC)7 Mineralogical Society of America; 1994.
p. 545.
[63] Buurman P, Van der Plas L. The genesis of Belgian and Dutch
flints and cherts. Geol Mijnb 1971;50:9–28.
[64] Rayment PL. The relationship between flint microstructure
and alkali–silica reactivity. In: Poole AB, editor. Proceedings
of the 9th International Conference on Alkali-Aggregate
Reaction in Concrete, London, UK, vol. 2, p. 843–50.
[65] Jensen V. Alkali aggregate reaction in southern Norway.
Doctor technicae thesis. Trondheim, Norway: Technical
University of Trondheim; 1993. 262.
[66] Wigum BJ. Alkali-aggregate reactions in concrete: properties,
classification and testing of Norwegian cataclastic rocks.
Doctor Ingenibr thesis. Trondheim, Norway: Norwegian
University of Technology and Science; 1995. 227.
[67] Normin 2000. Alkalireaksjoner i betong. Hovedprosjektrap-
port, Norges Forskningsr3d, Trondheim, 2000. pp. 166 +
bildeatlas: pp. 14.
[68] Wigum BJ, Hagelia P, Haugen M, Broekmans MATM. Alkali
aggregate reactivity of Norwegian aggregates assessed by
quantitative petrography. In: Berube MA, Fournier B, Durand
B, editors. Proceedings of the 11th International Conference
on Alkali-Aggregate Reaction in Concrete, Quebec City,
Canada, p. 533–42.
[69] Heijnen WMM, Larbi JA, Siemes AJH. Alkali–silica reaction
in the Netherlands. In: Shayan A, editor. Proceedings of the
10th International Conference on Alkali-aggregate Reaction in
Concrete, Melbourne, Australia, vol. 1, p. 109–16.
[70] Grattan-Bellew PE, Beaudoin JJ. Effect of phlogopite mica on
alkali-aggregate expansion in concrete. Cem Concr Res
1980;10:789–97.
[71] Gillot JE, Rogers CA. Alkali-aggregate reaction and internal
release of alkalis. Mag Concr Res 1994;46:99–112.
[72] St. John DA, Goguel RL. Pore solution/aggregate
enhancement of alkalies in hardened concrete. In: Poole
AB, editor. Proceedings of the 9th International Confer-
ence on Alkali-Aggregate Reaction in Concrete, London,
UK, vol. 2, p. 894–901.
[73] Goguel R. Alkali release by volcanic aggregates in concrete.
Cem Concr Res 1995;25:841–52.
[74] Pokrovski VA, Helgeson HC. Unified description of incon-
gruent reactions and mineral solubilities as a function of bulk
composition and solution pH in hydrothermal systems. Can
Mineral 1991;29:909–42.
[75] Constantiner D, Diamond S. Alkali release from feldspars into
pore solutions. Cem Concr Res 2003;33:549–54.
[76] Aplin AC. The composition of authigenic clay minerals in
recent sediments. In: Manning DAC, Hall PL, Hughes CR,
editors. Geochemistry of clay–pore fluid interactions. The
Mineralogical Society Series, vol. 4. Dordrecht (NL)7 Kluwer
Academic Publishers; 1992. p. 81–106.
[77] Nijland TG. personal communication, 1998.
[78] St. John DA, Poole AB, Sims I. Concrete petrography, 1st
edition. London7 Arnold Publishers; 1998. p. 474.
Top Related