Sand Gradation Influence on Masonry Mortar Properties
By Tim Conway and William Behie, Manager, Quality Assurance and R&D, and Masonry Specialist,
respectively, Holcim (US) Inc.
In the United States and elsewhere, masonry
mortars are specified per American Society for
Testing and Materials (ASTM) C 270, Specification
for Mortar for Unit Masonry. ASTM C 270 provides
two options for specifying mortar: proportion
or property. If each ingredient meets its own
specification, either approach is possible.
Mortar properties are influenced by aggregate—
masonry sand. Although sand would seem to be a
constant, its characteristics vary geographically and
over time. This is normal and expected. For instance, it is not uncommon
#50 Sieve
for sand gradation to fall a little outside
the range allowed by ASTM C 144,
100
Figure 1. Mortar
90
Specification for Aggregate for Masonry
80
Percent passing
is proportioned
by volume and
sand should be
measured in a
damp, loose
70
min
max
ideal
no #50
double #50
60
50
40
30
waiver allows for that sand to be used
(and tested) to meet certain required
10
0
(IMG12185)
gradation requirements of C 144, a
provided the mortar is proportioned
20
condition.
Mortar. When sand does not satisfy
8
16
30
50
100
200
Seive size
Pan
properties, shown here in Table 1.
Table 2 shows gradation limits for
natural sand, both the range (“allow-
Figure 2. A series of sand gradation curves for
an ASTM C 144 material showing maximum,
minimum, “ideal,” and #50 modified sands.
able percent passing”) and an “ideal”
gradation—defined for this study as one that falls in
the middle of the gradation curves. See Standard
C 144 for the manufactured sand gradation.
Vol. 16, No. 1
Summer 2006
Modifying the Gradation
Contents
The purpose of the study was to determine the
Sand Gradation Influence on Masonry Mortar Properties
air, water requirement for cubes, water retention,
Announcements
effect of each size fraction on mortar properties of
Water to make cubes
255
the impact on entrained air; a Type S was chosen for conve-
250
Milliliters of water
and compressive strength. Masonry cement was used to evaluate
245
nience in producing a C 270 Type S mortar. Proportions were
240
typical 1 part cement to 3 parts sand. Although bond strength,
235
230
permeability, and workability were not studied, it is expected
225
220
that these properties would also be affected.
215
210
A commercially available masonry sand from Summerfield,
205
d
6
0
n
0
6
0
n
0
#8
00 100
00 200
#8
an
#3
pa
#5
#1 e #1
#3
pa
#5
#1
#2
#
#
No uble No
ls
l
No uble
No uble
No uble No
le
No uble
ea
ub
o
ub
Do
Id
o
o
Do
Do
D
Do
D
D
Sand
Figure 3. Effect of gradation on water content to make cubes.
the midpoint of ASTM C 144 on each sieve. One size fraction
was systematically removed from the ideal gradation and other
sizes were adjusted to maintain the 1440-g sample size to determine how the mortar was affected by each size. In the same
Air
14
manner, the ideal gradation quantity of each size fraction was
12
doubled. These gradation variations are large, particularly from a
10
Percent
South Carolina was used for this study. It was regraded to fall in
single source. Smaller variations would be expected to have less
8
effect on mortar properties.
6
4
The gradations for the ideal and both #50 modified sands are
2
shown in Fig. 2. The two red lines show the maximum and
Id
ea
ls
an
d
N
o
#
8
D
ou
bl
e
#8
N
o
#1
D
6
ou
bl
e
#1
6
N
o
#3
D
0
ou
bl
e
#3
0
N
o
#5
D
0
ou
bl
e
#5
0
N
o
#1
D
00
ou
bl
e
#1
00
N
o
#2
D
00
ou
bl
e
#2
00
N
o
pa
D
n
ou
bl
e
pa
n
0
Sand
minimum allowable gradation limits; the green line is the ideal
grading; the yellow line has all the #50 material removed; and
the blue line represents a doubling of the #50 material.
Figure 4. Effect of gradation on air content.
Water retention
ASTM C 270 Mortar Properties
Percent
100
95
The #30 and #50 particles have the greatest impact on mortar
90
properties studied, probably in part because these two sieves have
85
the largest amount of material retained on them. The +50 mesh, for
80
75
instance, is 35% of the total mass of the sand with the ideal grada-
70
tion. Removing all of it, then doubling it, changed the proportion
65
of that size fraction from 0% to 70%—a very large change.
Id
ea
ls
an
d
N
o
#8
D
ou
bl
e
#8
N
o
#1
D
ou
6
bl
e
#1
6
N
o
#
D
ou 30
bl
e
#3
0
N
o
#5
D
ou
0
bl
e
#5
0
N
o
#
D
ou 100
bl
e
#1
00
N
o
#
D
ou 200
bl
e
#2
00
N
o
pa
D
ou
n
bl
e
pa
n
60
Sand
normal, and high amounts of each sieve fraction. The middle
Figure 5. Effect of sand gradation on water retention of mortar.
bar in each grouping is the test result using the sand graded to
Strength, psi
28-day strength
the midpoint mass of all the fractions.
4000
Cube water content: Fig. 3 shows the effects of the sand changes
3500
on the water needed for the correct flow of mortar to make cubes.
3000
Situations that lead to a greater proportion of fines increase the
2500
water demand: for instance, doubling the #50 mesh material or
2000
removing all of the #8 or #16 material.
1500
1000
Air content: Fig. 4 shows that the #50 sieve has the biggest
500
impact on air content on both sides of ideal. Still, changes in
0
6
0
n
0
d
6
0
n
0
#8
00
00
00
00
#8
#1
#5
pa
#3
#1
#5
pa
#3
an
#1
#2
#1
#2
No uble
ls
o
o
No uble
No uble
No uble
No uble
le
le
N
N
ea
b
b
o
d
u
u
D
I
Do
Do
Do
Do
Do
Do
Sand
Figure 6. Effect of sand gradation on compressive strength.
2
In Figures 3-6, the data can be viewed as groups of three: low,
Masonry Today / Summer 2006
gradation did not cause any test to fail C 270.
Water retention: As in the other graphs, the middle bar in each
series in Fig. 5 represents the ideal sand gradation. In almost
Table 1. C 270 Mortar Property Table*
Mortar
Type
28-day compressive
strength, psi (MPa)
Cement-lime or
mortar cement
M
S
N
O
2500
1800
750
350
(17.2)
(12.4)
(5.2)
(2.4)
Masonry cement
M
S
N
O
2500
1800
750
350
(17.2)
(12.4)
(5.2)
(2.4)
Water retention,
min. %
}
}
Air content,
max. %
Aggregate ratio
75
12
12
14**
14**
2-1/4 to 3-1/2 times the
cementitious materials
75
18
18
20†
20†
2-1/4 to 3-1/2 times the
cementitious materials
Cumulative weight
retained
Batch weight, grams
* Adapted from ASTM.
** If structural reinforcement is present, the maximum air content shall be 12%.
† If structural reinforcement is present, the maximum air content shall be 18%.
Table 2. C 144 “Ideal” Natural Sand Gradation and Allowable Limits
Screen
Allowable %
passing
Ideal %
passing
4
100
100
8
95–100
97.50
2.50
36.00
36.0
16
70–100
85.00
15.00
216.00
180.0
30
40–75
57.50
42.50
612.00
396.0
50
10–35
22.50
77.50
1116.00
504.0
100
2–15
8.50
91.50
1317.60
201.6
200
0–5
2.50
97.50
1404.00
86.4
0.00
100.00
1440.00
36.0
Pan
Cumulative %
retained
0
Total
1440
every case, removing or doubling the material on each sieve
is removed entirely or doubled). For the Type S mortar used
lowers the water retention. This implies that having some amount
here, changes in sand gradation did not cause any strength test
of material in each size fraction—in other words, a well graded
to fail C 270.
sand—is favorable to water retention. Two of the tests did fall
just short of passing water retention (75% minimum): the double
Conclusions
#50 mesh test and the removal of the #200 mesh material.
It's helpful to have an idea how the gradation of sand for mortar
Compressive strength: Similar trends occur for both the 7-day
impacts the desired properties. When a sand does not conform
and 28-day compressive strength results. Only the 28-day strength
to C 144, mortar made with it must be tested to show it has the
is shown in Fig. 6. Note again that most of the variations have
required C 270 properties. This study demonstrates that many
little impact on strength. The #50 sieve exhibits the widest
of the properties can be expected to meet C 270, even when
variation in strength on both sides of ideal (whether the material
gradations are outside the range allowed by C 144. Specific results
Masonry Today / Summer 2006
3
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of mortar properties given in this article pertain to this sand and cement
combination. In addition, and perhaps more broadly:
• The amount of each size fraction can vary widely and still be at or near
gradation allowed by C 144 (changes to the #50 and #30 mesh material
affect grading the most): see Fig. 2.
• Water demand (for cubes) increases when finer material is increased
substantially (doubling the #50) or when coarser material is removed
(no #8, no #16): see Fig. 3.
• Well graded sands lead to mortars with better water retention: see Fig. 5.
TMS
The Masonry Society is holding its 2006 Annual Meeting and Business Meetings in
Atlanta, Georgia, October 12–17. Among the technical programs, social events, and
recreational activities planned, two seminars offer educational opportunities:
Design of Masonry Structures to the 2005 MSJC and the IBC 2006
The Role of Masonry in Sustainable Design and LEEDTM
See www.masonrysociety.org for more information
ASTM C 12 75th Anniversary
MASONRY
Today
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Regency Atlanta, Georgia. The fall meeting of C 12 is set for December 5–7, 2006.
Direct all correspondence to:
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See www.astm.org for more information
© 2006 Portland Cement Association
All rights reserved
PL389.01
Jamie Farny, Editor
[email protected]