geosciences
Article
Crushed and River-Origin Sands Used as Aggregates
in Repair Mortars
Maria Stefanidou
Laboratory of Building Materials, Civil Engineering Department, Aristotle University of Thessaloniki (AUTH),
Thessaloniki 54124, Greece; [email protected]; Tel./Fax:+30-2310-995-635
Academic Editors: Carlos Alves and Jesus Martinez-Frias
Received: 21 January 2016; Accepted: 6 April 2016; Published: 13 April 2016
Abstract: The systematic analysis of mortars from monuments or historic buildings and the
simultaneous study of the construction environment show that it was common practice to use
naturally occurring sand from local rivers or streams for the production of the mortars. There are
cases though, mainly on islands, where sands of natural origin were limited, and marine or crushed
sands were used possibly after elaboration. In all cases the particle size analysis of old mortar confirms
the presence of even distribution of the granules. As regards the design of the repair mortars, there
are criteria that should be taken into consideration in order to produce materials with compatible
properties. The main properties concerning sands are the grain distribution and maximum size, the
color, the content of fines, and soluble salts. The objective of this research is the study of the physical
characteristics of the sands such as the sand equivalent, the gradation, the apparent density, the
morphology of the grains, their mineralogical composition and the influence of these properties on
the behavior of lime mortars, notably the mechanical and physical properties acquired.
Keywords: river sand; crushed sand; lime mortars; microstructure; strength
1. Introduction
Natural aggregates are the major components in building materials such as mortars. Aggregates
are much cheaper in relation to binders and economy is achieved by using as much aggregate as
possible in mortar mixtures. Also, their use improves both the volume stability and the durability
of the composite materials considerably. Their physical characteristics, and in some cases their
chemical composition, affect the properties of a mortar in both its plastic and hardened states to a
varying degree [1]. The introduction of aggregates causes structural changes and affects macroscopic
characteristics. Properties such as high porosity, inferior grading, round grains and coarse sands
provoke porosity increase and the reduction of strength of the mortars due to the formation of loose
contact zones between the aggregates and the mortar matrix [2,3]. When there is a chemical bond to
the aggregates-paste transition zone, there is a good cohesiveness and the structure is characterized by
continuity. The interlocking of the aggregate-paste forms the transition zone, which is characterized as
the “weak” phase due to the high porosity and the formation of micro-cracks and different crystal sizes
of the binder [4]. In construction, this means that stresses are transferred from one phase to another
and there is a reduction of the shrinkage phenomena in relation to the pastes without the presence of
the aggregates [5]. The incompatibility between the modulus of elasticity of the aggregate and that of
the paste affects the development of micro-cracks at the aggregate-matrix interface. However, it is well
recognized that coarse aggregate particles act as crack arresters, as they restrict the shrinkage of the
binder, so that under an increasing load, extra energy is absorbed for the formation of a new crack [6,7].
Natural aggregates are readily available and their resources are nearly infinite. Potential sources exist
in specific geologic environments and quality parameters are set by relevant regulations (EN933).
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Several
studies2016,
have
shown that aggregate behavior in mortar is influenced by composition [8,9],
size [9,10] form and texture [9,11], and the percentage of fine particles [11,12].
Several studies have shown that aggregate behavior in mortar is influenced by composition [8,9], grain
Lime-based mortars have been used for centuries as the joint material of historic monuments
size [9,10] form and texture [9,11], and the percentage of fine particles [11,12].
of masonry constructions. Such mortars consist of binders (lime or a combination of lime and
Lime-based mortars have been used for centuries as the joint material of historic monuments of
pozzolanic
materials)
and aggregates
often coarse,
in the
caseand
of masonry
masonry
constructions.
Such mortarswhich
consistare
of binders
(lime orespecially
a combination
of lime
pozzolanicwith
thick joints
[13,14].
fact thatwhich
the properties
aggregates
influence
the properties
lime thick
mortars
materials)
and The
aggregates
are often of
coarse,
especially
in the case
of masonryofwith
has been
known
antiquity
[8]. Evenofinaggregates
old mortars,
which
were designed
rather empirically,
joints
[13,14]. since
The fact
that the properties
influence
the properties
of lime mortars
has been
knownwere
sinceused
antiquity
[8]. Evensizes
in oldsuch
mortars,
which
rather
aggregates
aggregates
in different
as 0–4
mm,were
0–12designed
mm, 0–16
mmempirically,
and 0–40 mm
[2], and in
were usedso
inthat
different
sizes such
as often
0–4 mm,
0–12 mm, 0–16
mm and 0–40
mm [2],
and in
even
even gradation
the mortars
were
characterized
as “concretes”
[13,15].
Natural
aggregates
gradation
that thewere
mortars
were often
as “concretes”
Natural aggregates
used in
historic so
mortars
sourced
from characterized
rivers (usually
they were [13,15].
easily extracted)
and/or used
crushed
in
historic
mortars
were
sourced
from
rivers
(usually
they
were
easily
extracted)
and/or
crushed
aggregates (crushed rocks and crushed ceramics) [16]. Quarry sands were preferable, according
aggregates (crushed rocks and crushed ceramics) [16]. Quarry sands were preferable, according to
to classic Roman writers such as Palladius, “as it sets easily”, insisting that it must have no clay
classic Roman writers such as Palladius, “as it sets easily”, insisting that it must have no clay
content
[17]. In preparing mortars, the preferred aggregates were healthy, compact, of low porosity
content [17]. In preparing mortars, the preferred aggregates were healthy, compact, of low porosity
and smooth
gradation,
freefree
of impurities
and
ofofhigh
1).
and smooth
gradation,
of impurities
and
highstrength
strength (Figure
(Figure 1).
(a)
(b)
Figure 1. Historic mortars with (a) rounded aggregates and (b) angular aggregates.
Figure 1. Historic mortars with (a) rounded aggregates and (b) angular aggregates.
The paper presents the results of a study concerning the manufacture of mortars based on lime
The
presents
the results
ofThe
a study
concerning
the manufacture
of mortars
based
on lime
withpaper
aggregates
of different
origin.
objective
of this experimental
work is the
study of the
physical
characteristics
of three sands
including
the sandofequivalent,
the apparent
density,
morphology
of
with aggregates
of different
origin.
The objective
this experimental
work
is the the
study
of the physical
the grains,oftheir
mineralogical
composition
and the
influence of
properties
on thethe
behavior
of the of
characteristics
three
sands including
the sand
equivalent,
thethese
apparent
density,
morphology
repairtheir
mortars,
notably the composition
mechanical andand
physical
properties.
results
of the paper
could
be a of
the grains,
mineralogical
the influence
ofThe
these
properties
on the
behavior
helpful guide for restorers in order to decide upon the use of aggregates when a repair mortar
the repair mortars, notably the mechanical and physical properties. The results of the paper could
is designed.
be a helpful guide for restorers in order to decide upon the use of aggregates when a repair mortar
is designed.
2. Experimental Work
Two sands
of natural origin coded A1 and A2 and one of crushed aggregates coded N1, which
2. Experimental
Work
were of the same grain sizes (0–4 mm) that are available in the market and considered suitable for
Two
sands
of natural of
origin
coded
and
and
one of crushed
aggregates
N1, on
which
use in
the composition
mortars,
wereA1
used
in A2
order
to produce
lime mortars.
The testscoded
performed
were of
same
sizes (0–4
mm) thattheir
are gradation
available by
in the
market
and considered
suitable for use
thethe
sands
asgrain
raw materials
concerned
sieving
following
EN 933-1, mineralogical
using XRD
(Philips PW8040
diffractometer
Ni-filtered
CuKa radiation),
content
of waterin the control
composition
of mortars,
were used
in order to with
produce
lime mortars.
The tests
performed
on the
soluble
salts
with
HPLC,
determination
of
sand
equivalent
(SE)
based
on
EN933-8:1999.
The
sand
sands as raw materials concerned their gradation by sieving following EN 933-1, mineralogical control
test PW8040
quantifiesdiffractometer
the relative abundance
of sand vs.CuKa
clay and
a higher content
sand equivalent
value
using equivalent
XRD (Philips
with Ni-filtered
radiation),
of water-soluble
indicates that there is less clay-like material in a sample. Additionally, the apparent specific gravity and
salts with HPLC, determination of sand equivalent (SE) based on EN933-8:1999. The sand equivalent
the porosity of sands were measured according to EN1097:2000 and determination of the geometrical
test quantifies the relative abundance of sand vs. clay and a higher sand equivalent value indicates
characteristics of the sand grains using image analysis under a stereoscope (LEICA Wild M10) with
that there
is less
clay-like
in a sample.
Additionally,images
the apparent
gravity
and
ProgRes
program
was material
also performed.
The two-dimensional
acquired specific
were used
in order
to the
porosity
of sands
were measured
measure
the sphericity
which is according
given by: to EN1097:2000 and determination of the geometrical
characteristics of the sand grains using image analysis under a stereoscope (LEICA
Wild M10) with
4π × projected area of the particle Sphericity = Perimeter2
(1)
ProgRes program was also performed. The two-dimensional images acquired were used in order to
measure the sphericity which is given by:
4π ˆ projected area of the particle Sphericity “ Perimeter2
(1)
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For spherical
is
Geosciences
2016, 6, 23particles the value is equal to one, whereas for irregular grains the sphericity
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2016,[18].
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smaller
than one
For spherical
the mortars,
value is equal
to one,
whereas
for irregular
grains
the sphericity
is
In relation
to theparticles
produced
the lime
used
was aerial
(Type N
according
to ASTM206)
For
spherical
particles the value is equal to one, whereas for irregular grains the sphericity is
smaller
than
one
[18].
and the binder/aggregate ratio (lime/sand) was 1/3 by weight. The ratio of water/binder was
smaller
than one
[18].produced mortars, the lime used was aerial (Type N according to ASTM206)
In relation
to the
1.214 and
was kept
constant in order to study the effect of the sands on the workability of the
relation to the produced
mortars, the
lime
was aerial
to ASTM206)
and theInbinder/aggregate
ratio (lime/sand)
was
1/3used
by weight.
The(Type
ratioNofaccording
water/binder
was 1.214
mixture.
The
workability
wasratio
tested
by a flowwas
table
based
on EN1015-3:
1999.
The effects
the sands
and
thekept
binder/aggregate
1/3
by weight.
The
of
water/binder
wasof1.214
and
was
constant in order
to(lime/sand)
study the effect
of the
sands on
theratio
workability
of the mixture.
The
were tested
on
both
fresh
properties
such
as
workability,
and
in
the
hardened
state
after
curing in
and
was
kept
constant
in
order
to
study
the
effect
of
the
sands
on
the
workability
of
the
mixture.
The
workability was tested by a flow table based on EN1015-3: 1999. The effects of the sands were tested on
environment
65%
RH
and
20 ˝table
C. At
the
age
of 28
days
thestate
mechanical
and
properties
of
workability
was
tested
by
a flow
based
on
1999.
The
effects
of the
sands
were tested
on
both
fresh with
properties
such
as
workability,
and
inEN1015-3:
the
hardened
after curing
inphysical
environment
with
both fresh
properties
such
asˆ
workability,
and
in
the hardened
state after curing
in
environment
with and
the 65%
mortars
specimens
of
4
cm
4
cm
ˆ
16
cm
prisms
were
measured
based
on
EN1015-11:1999
RH and 20 °C. At the age of 28 days the mechanical and physical properties of the mortars
65% RH and 20 °C. At theAdditionally,
age of 28 days thedynamic
mechanical
and physical
properties
of thethat
mortars
RILEMCPC11.3,
modulus
of elasticity
(Edyn)
describes
specimens of 4 respectively.
cm × 4 cm × 16 cm prisms werethe
measured based
on EN1015-11:1999
and
RILEMCPC11.3,
specimens of 4 cm × 4 cm × 16 cm prisms were measured based on EN1015-11:1999 and RILEMCPC11.3,
the respectively.
stiffness of the
materials the
wasdynamic
calculated
by ultrasounds
BS1881-209:1990.
Additionally,
modulus
of elasticity based
(Edyn)on
that
describes the stiffness of the
respectively. Additionally, the dynamic modulus of elasticity (Edyn) that describes the stiffness of the
materials was calculated by ultrasounds based on BS1881-209:1990.
materials was calculated by ultrasounds based on BS1881-209:1990.
3. Results
3. Results
3. Results
3.1. Tests on Sands
3.1.3.1.
Tests
onon
Sands
Tests
Sandstested present differences in color. N1 is yellow while A2 is darker in relation
The three
sands
The
three
in
N1
is yellow
yellow
whileA2
A2with
darker
inrelation
relation
A1 as
to A1 (Figure
2).sands
Thetested
granulometry
of the three
samples
is smooth,
A1inbeing
the
finest
The three
sands
testedpresent
presentdifferences
differences
in color.
color.
N1 is
while
isisdarker
toto
A1
(Figure
2).
The
granulometry
of
the
three
samples
is
smooth,
with
A1
being
the
finest
as
Figure
3
shows,
Figure(Figure
3 shows,
and
there is a small
difference
content
fine
between
2). The
granulometry
of the three
samplesinisthe
smooth,
withof
A1the
being
thefraction
finest as (<0.2
Figuremm)
3 shows,
there
is is
a A1
small
difference
content
the
(<0.2
mm)between
between
thethree
three
sands.
A1silica
and
there
a small
difference
inthe
theparticles
contentof
ofwhereas
the fine
fine fraction
fraction
sands.
the and
three
sands.
contains
5%infine
A2 and(<0.2
N1 mm)
contain
less.the
The
sands
areA1
of
contains
5%
fine
particles
whereas
A2
N1
The sands
sandsshowed
areofofsilica
silica
composition
withwith
contains
5%
fine
particles
whereas
A2and
and
N1 contain
contain less.
The
are
composition
with
small
variations.
Their
mineralogical
examination
thatcomposition
A1
is silica with
sand
small
variations.
Their
A1 is
is silica
silicasand
sandwith
withdominant
dominantminerals
minerals
small
variations.
Theirmineralogical
mineralogicalexamination
examination showed
showed that A1
dominant minerals being quartz, opal, feldspar, calcite, magnetite and hornblende. In A2 sand, the
being
quartz,
opal,
feldspar,
In A2
A2sand,
sand,the
thepredominant
predominantminerals
minerals
are
being
quartz,
opal,
feldspar,calcite,
calcite,magnetite
magnetiteand
andhornblende.
hornblende. In
are
predominant minerals are silica, quartz, feldspar, biotite, and hornblende, while in the yellow sand
silica,quartz,
quartz,feldspar,
feldspar,biotite,
biotite, and
and hornblende,
hornblende, while
while in the
silica,
the yellow
yellow sand
sand quartz,
quartz,feldspar
feldsparand
and
quartz,
feldspar
and magnetite prevail.
magnetite
prevail.
magnetite
prevail.
(Α1)
(Α1)
(Ν1)
(Α2)
(Ν1)
(Α2)
Figure 2. Α1 (left), Ν1 (middle) and Α2 (right) under stereoscope.
Figure
2.2.A1
andΑ2
A2(right)
(right)under
under
stereoscope.
Figure
Α1(left),
(left),N1
Ν1 (middle)
(middle) and
stereoscope.
Figure 3. Gradation of the sands.
Figure 3. Gradation of the sands.
Figure 3. Gradation of the sands.
Geosciences 2016, 6, 23
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The N1 sand has a low Sand Equivalent value (S.E.) which indicates impure aggregates and
Geosciences 2016, 6, 23
4 of 6
the existence of fine clay grain sizes. Also, it is characterized by moderate absorbency in relation to
the other two materials, and it contains angular grains as the values of sphericity indicate (Table 1).
The N1 sand has a low Sand Equivalent value (S.E.) which indicates impure aggregates and the
The highest percentage of sand equivalent is presented in A1 sand, featuring material free of clayish
existence of fine clay grain sizes. Also, it is characterized by moderate absorbency in relation to the other
content. This sand has low porosity and the grains are relatively spherical. The A2 sand is fine and
two materials, and it contains angular grains as the values of sphericity indicate (Table 1). The highest
presents high water absorption. Table 2 presents the soluble salts content and it can be concluded that
percentage of sand equivalent is presented in A1 sand, featuring material free of clayish content. This
all three samples show low salt content.
sand has low porosity and the grains are relatively spherical. The A2 sand is fine and presents high
water absorption. Table 2 presents the soluble salts content and it can be concluded that all three
Table 1. Physical properties of the sands.
samples show low salt content.
Natural
App. Specific
Table(%)
1. Physical
properties
of3 )the sands.S.E.
Absorption
Gravity
(g/cm
-
Α1
Α2
Ν1
Sphericity
3)
2.36 Gravity (g/cm98.0
App. Specific
2.352.36
90.5
2.342.35
75.0
1.09
2.34
Table 2. Soluble salt content of sands (% by weight).
Table 2. Soluble salt content of sands (% by weight).
NO´
Cl´
SO4 2´
NO−
SO42−
Cl−
A1
<0.01
<0.01
Α1
<0.01
<0.01
A2
<0.01
0.04
Α2
<0.01
0.04
N1
<0.01
0.01
Ν1
<0.01
0.01
A1
0.70
Natural
Absorption
(%)
A2
1.46
0.70
N1
1.09
1.46
S.E. 0.825 Sphericity
98.0 0.791
0.825
90.5 0.723
0.791
75.0
0.723
3.2.
3.2. Mortar
Mortar Production
Production
The
The results
results regarding
regarding the
the gained
gained properties
properties of
of the
the mortars
mortars produced
produced with
with the
the three
three tested
tested sands
sands
are
listed
in
Table
3.
The
tests
have
been
performed
on
prisms
of
4
cm
ˆ
4
cmˆ
16
cm.
Six
samples
are listed in Table 3. The tests have been performed on prisms of 4 cm × 4 cm× 16 cm. Six samples
were
were
in case
eachand
casethe
and
the mean
are reported.
The mean
are generally
low (below
testedtested
in each
mean
valuesvalues
are reported.
The mean
valuesvalues
are generally
low (below
1 MPa
1compressive
MPa compressive
strength)
this
was expected
pure
lime mortars.
Nevertheless,
the mortars
strength)
but thisbut
was
expected
in purein
lime
mortars.
Nevertheless,
the mortars
with N1
with
N1
sand
present
higher
strength
and
lower
porosity
than
the
mortars
with
the
other
two This
sands.
sand present higher strength and lower porosity than the mortars with the other two sands.
is
This
is probably
duestrong
to the bonding
strong bonding
that develops
the
roughoftexture
of the grains
angular
probably
due to the
that develops
betweenbetween
the rough
texture
the angular
of
grains
of N1
sand as evidenced
by the microstructure
study
SEM (Figure
[19]. Workability
this
N1 sand
as evidenced
by the microstructure
study by
SEMby
(Figure
4) [19]. 4)
Workability
in this in
case
is
case
is
slightly
smaller
than
in
the
mortars
made
with
A1
and
A2
sands
using
the
same
quantity
of
slightly smaller than in the mortars made with A1 and A2 sands using the same quantity of water,
water,
is in agreement
with
the literature
[20].
The mortars
produced
with natural
sands present
whichwhich
is in agreement
with the
literature
[20]. The
mortars
produced
with natural
sands present
similar
similar
mechanical
and
physical
properties
in
hardened
state
and
also
similar
workability.
mechanical and physical properties in hardened state and also similar workability.
(A1)
(N1)
Figure 4.
4. Crack
Crack around
around the
the rounded
rounded grain
grain of
of mortar
mortar with
with A1
A1 sand
sand (left)
(left) and
and strong
strong cohesion
cohesion between
between
Figure
the
binder
and
rough
grain
in
a
mortar
with
N1
sand
(right).
the binder and rough grain in a mortar with N1 sand (right).
Geosciences 2016, 6, 23
5 of 6
Table 3. Mechanical and physical properties of mortars at the age of 28 days.
-
Flexure (MPa)
Compressive (MPa)
Edyn (MPa)
Porosity (%)
Workability (cm)
A1
A2
N1
0.05
0.05
0.42
0.57
0.56
0.94
407.04
387.8
1586.4
36.02
35.95
35.02
15.7
15.5
14.8
3.3. Discussion
After the completion of some physical, mineralogical and chemical tests on the three sand samples,
it can be concluded that the granulometry of the sands presented small variations, with A1 being the
finest. In all cases, the granulometry was smooth and no gap-graded cases were observed. All of them
were silica-based sands but the morphology of the grains presented differences. They were free of
soluble salts and were of similar apparent specific gravity. The sand equivalent values also presented
some variations as well indicating that N1 sand contains clayish material. Despite that, the absorption
of the N1 sand was moderate. The grains of N1 sand were angular in relation to the A1 and A2 sands,
as it is crushed sand, compared to the river origin of the other two sands.
After recording these properties, three series of lime mortars were produced with the same
binder/aggregate and binder/water proportions using the three sands as aggregates. It seems that
the properties of the aggregates influence the properties of the mortars both in fresh and in hardened
state. The water requirement is higher when aggregates with angular grains were used and it ensured
greater consistency with the binder. The contained amount of clay existing in the crushed sand does
not seem to harm the tested properties in mortars. Additionally, higher flexural and compressive
strength and lower porosity were achieved with the angular sand. Small differences were recorded
between the mortars prepared with the river sands.
4. Conclusions
Choosing natural, rounded or crushed, angular sand in repair mortars’ composition is a
multivariate decision influenced by parameters such as: the results of the analysis of the original
mortars, the properties to be imparted to the new mortar (color, texture, porosity, strength) and
the available materials. The compatibility of the repair mortars is essential for the aesthetic and
functional role they have in a conservation work. It seems that the morphology of the sand grains
affects the macroscopic properties of the mortars. Despite the higher water demand in mortars with
crushed aggregates, the strength recorded was also higher due to the strong contact zone between the
aggregates and the matrix.
In the case of river-origin sands, the two types tested in the present paper presented small
variations in relation to their mineralogy while the A1 sand presented finer and more spherical grains.
These properties resulted in a more workable mortar which presented sufficient mechanical and
physical properties when hardened.
Conflicts of Interest: The author declare no conflict of interest.
References
1.
2.
3.
4.
5.
Jackson, N.; Dhir, R.K. Concrete—aggregate. In Civil Engineering Materials, 5th ed.; Jackson, N., Dhir, R.K.,
Eds.; Macmillan: Basingstoke, UK, 1996; pp. 179–181.
Stefanidou, M.; Papayianni, I. The role of aggregates on the structure and properties of lime mortars.
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