Admixture for use of manufactured sand in concrete
J B Jiang*, W R Grace (S) Pte Ltd, Singapore
S Loh, W R Grace (S) Pte Ltd, Singapore
S Q Zhang, W R Grace (S) Pte Ltd, Singapore
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Admixture for use of manufactured sand in concrete ~I
B Jiang*, W R Grace (S) Pte Ltd, Singapore S Loh, W R Grace (S) Pte Ltd, Singapore S Q Zhang, W R Grace (S) Pte Ltd, Singapore Abstract
Manufactured sand is purposely made of waste quarry fines through further
screening and processing. Over years, it is used increasingly as fine aggregate in
replacement of natural sand due to the environmental pressure of limited natural
source and the interest to optimise the concrete mix.
In this paper, the gradation, particle shape and surface texture of manufactured
sand from different sources, as well as effects on concrete using this kind of
material were analysed and discussed, as compared with natural river sand . An
admixture was developed particularly to overcome the problems for concrete mix
using manufactured sand in replacement of natural sand up to 100%. A
pressurized bleeding meter was used in laboratory to measure bleeding under
pressure Mpa as indicator of pumpability for concrete mix.
Test results have shown that concrete mix using manufactured sand up to 100%
with the admixture developed is able to be workable as normal concrete mix
without compromising properties of fresh and hardened concrete.
Key word : Manufactured Sand, Admixture, Concrete, Pumpability, Finishability
Introduction
It is not an unusual sight to see over-growing piles of waste product build up on a quarry site.
Typically, the waste product is rock crusher or fracture fines . Huge stockpiles of this unused or
low-value material are obviously problem for quarry site. Sometimes measured by hundreds of
thousands of cubic meters, these mountains occupy valuable quarry space and are an
environmental headache. On the other hand , available natural sand resources are becoming less
economic or totally out of reach to the concrete producer due to increasing environmental
pressure. It is of great significance to use the quarry fractures as fine aggregate in concrete
industry.
However, majority of these quarry fractures are of extremely angular, flaky or elongated shape.
Its very poor particle shape and deficiency in certain areas of a gradation make this kind of
material undesirable to concrete industry [11. It is necessary for crushing plant to improve process
technology to produce final product as fine aggregate. In this paper, manufactured sand is
defined as a purpose-made fine aggregate produced from quarry fines of certain types of rock
through further screening and processing .
263 The objective of this paper is to understand characteristics of manufactured sand and how it
affects concrete properties, and to introduce an admixture approach to overcome the challenges
arising from use of manufactured sand in concrete mix.
Characteristics of manufactured sand
Three sources of manufactured sand , designated as MS1, MS2 and MS3, were obtained to
investigate physical properties of manufactured sand . One source of natural river sand was
considered as reference.
To characterize manufactured sand , physical properties such as particle size distribution ,
fineness modulus, particle shape and texture , etc, were analyzed as compared with natural river
sand by the following tests: sieve analysis, petrographic examination and sand flow cone test.
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Sieve Size , mm
FiQure 1
Sieve analvsis of manufactured Sands
It is known that particle grading or
size distribution is an important factor
for aggregate to obtain workable
concrete with an acceptable cost.
Sieve analysis in accordance with
ASTM C 136 [2] was carried out on the
three sources of manufactured sand
as compared with natural river sand .
The particle size distribution curves
are displayed in Figure 1. The
fineness modulus and percentage of
fine particles smaller than 75 I-lm
were obtained from the sieve
analysis, and the results are given in
Table 1.
It is clearly shown in Figure 1, all of three sources of manufactured sand are out of ASTM C33
specification [3] with regard to grading, while the river sand falls within upper and lower limits.
These three sources of manufactured sand have similar size distribution, i.e., higher portion in
particle size greater than 1.25 mm and in particle size below 0.2 mm , and deficient in medium
size particles, as compared to natural river sand. The higher values of fineness modulus as
displayed in Table 1 indicate that these three sources manufactured sand can be classified as
coarse sand .
Table 1 Physical Properties of Sand
River sand
MS1
MS2
MS3
Specific gravity
2.64
2.70
2.65
2.62
Fineness modulus
Particle < 75 ~m (%)
Flow cone time (sec)
Uncompacted void(%)
2.77
1.2
30.7
36.5
3.19
3.4
48 .9
41 .9
3.52
4.6
37.6
39.8
2.96
4.8
40.0
40.8
Physical properties
The fine contents of particle below 75 I-lm in three sources of manufactured sand are higher than
in natural river sand, as shown in Table 1. But they are still under the limit of ASTM C33
specification, in which the fine content ( < 75 I-lm ) should be less than 5% and 7% for concrete
subject and not subject to abrasion respectively. Marek's [4J research indicates that the
relationship between the amount of below 75 I-lm fine content in manufactured sand and the
amount of water required to produce mortars having constant workability is fairly constant over a
range of below 75 I-lm material up to 10%, and appears to decrease at higher percentages.
Some studies [5] [6] revealed that the amount of below 75 ~m fine content of manufactured sand in
concrete could be up to 20% without decreasing the compressive strength of concrete, and the
264
little bit higher fine content may help lubricate to some extent the movement of manufactured
sand .
Another important factor for aggregate having impact on workability of concrete in its plastic state
is particle shape and surface texture because the surface condition of a particle will exert a
fractional force to resist movement within cement paste. Moreover, the importance of particle
shape and surface texture in aggregate performance increases as the particles get smaller. This
is because , the smaller a particle, the more specific surface area (ratio of surface area to volume
of a particle) it has . The higher the surface area, the more surface texture available to influence
the concrete bond and internal friction, and hence more water is required to get a fix workability.
Figure 2 displays the appearance of
the natural river sand and three
sources of manufactured sand by
petrographic examination under
microscope . Natural river sand has
round shape and smooth surface,
as shown Figure 2 (a) , which is
favorable to obtain good workability
of concrete mixture. However, as
compared to natural river sand,
(b)
(a)
manufactured sand does contain
more sharp, angular edges or flaky,
elongated particles, depending on
the source of rock and crushing
process, and these manufactured
sand particles have rougher or
coarser surface texture, as shown
in Figure 2 (b), (c) and (d). These
irregular particles of manufactured
sand with rough surface will be
(d)
(c)
more difficult to move within cement
paste than
cubical or equiFigure 2 Microscopic graphs of natural sand and
dimensional
particles .
The
manufactured sand (X 10) : (a) natural river sand, (b)
consequence is that use of
MS1, (c) MS2, and (d) MS3
manufactured sand in concrete mix
will increases water demand and
harshness, and make concrete mixture more difficult to pump and finish.
Figure 3 Sand flow cone test
apparatus
At present, the most commonly used way to measure the
influence of particle shape is a sand flow cone test [7]. The
test apparatus is shown in Figure 3. The time for a known
volume of material to flow through a fixed sized orifice (12.5
mm in this test apparatus) is recorded, and the
uncompacted void is measured . The particle shape and
surface texture both will affect the flow time and
uncompacted void of a particular sample. The less the time
required to flow through , the more workable the sand in
concrete . The higher the uncompacted void , the poorer the
gradation. Among other things, those properties will
influence internal friction characteristics and, hence, impact
on the flow time.
In details of sand flow test, 5 kg sample of each source
manufactured sand and river sand was taken, and dried. Particles retained on 4.75 mm sieve
were removed before sand flow test. Take approximately 900 ml sample, and fill in the flow cone,
remove the excess of sample. Remove the stopper at the orifice allowing sand flow through the
cone, and record the time for total sample flowing through the cone. The sample is collected in a
265
container with 700 ml volume under the orifice. Screed the surface of collected sand and remove
the excess and get weight of sand at uncompacted bulk state. Then, the uncompacted void of
sample can be calculated from its bulk density and specific gravity.
As indicated in Table 1, these three sources of manufactured sand have a flow time of 37.6 to
48.9 seconds and an uncompacted voids content of 39.8 to 41.9%, which are higher than those
of natural river sand (flow time of 30.7 seconds and uncomacted voids content of 36.5%). These
results indicate that manufactured sand is poorly shaped. In addition, the flow time of
manufactured sand is significantly different from source to source, but the uncompacted voids are
similar for these three sources of manufactured sand because they have similar gradation.
From above results and diSCUSSion, it can be summarized that manufactured sand is usually
featured with deficiency in certain medium sizes of gradation, and poor particle shape and rough
surface texture. In the next section, the effect of manufactured sand on concrete properties is
discussed, and an admixture approach for improving the properties of manufactured sand
concrete is introduced.
Effects of manufactured sand on concrete properties and admixture solution
Effects of manufactured sand on water demand, setting time, pumpability of fresh concrete
mixture and compressive strength of hardened concrete were investigated in concrete tests with
normal retarding water reducer Daratard 88, which is a normal retarding water reducer based on
lignosulphonates and hydroxylate organic compounds.
As admixture solution for improving properties of using manufactured sand in replacement of
natural river sand, a new admixture MIRA 91 has been developed, and was evaluated in concrete
tests under both lab and field conditions. It has a water reduction capacity of up to 20%, and
contains compounds to soften and lubricate concrete mixture with manufactured sand to improve
its pumpability and finishability.
For all concrete tests. crushed granite with a nominal size of 20 mm, manufactured sand MS2
and OPC cement were used. Cement content was fixed as 350 kg per cubic meter, and Initial
slump was controlled at 140 +/- 10 mm.
For evaluation of pumpability of concrete mixture, a pressurized
bleeding device, as shown in Figure 4, was used to measure the
bleeding of concrete mixture under pressure condition in
accordance with Chinese Standard JC473 [8). In procedure, take
about 3 kg sample from fresh concrete mixture. Place the sample
into the container, and compact with a rod. Apply pressure with a
manual jack. When the effective pressure in concrete mixture
increases to 3 Mpa, open the valve of outlet at the bottom of the
device, collect the bleeding water and measure the volume at time
10 seconds and 140 seconds respectively. The ratio of pressurized
bleeding Bp is given as
= VIO
B
P
Figure 4 Pressurized
bleeding device
Vl40
X 100
(1 )
where V10 and V140 are the volumes of bleeding water under
pressure of 3 Mpa for 10 seconds and 140 seconds respectively.
The pressurized bleeding rate Bp is used as indicator for evaluating pumpability of concrete mix.
The lower the value, the easier concrete mix can be pumped. The finishability of concrete
mixture was evaluated by hand-feeling of finishing operation on panel of 400 x 400 x 40 mm.
As shown in Figure 5, the water demand of concrete mix increases with the replacement level of
natural river sand by manufactured sand. When the replacement reaches 100%, 33 kg per cubic
meter extra water is required to get the fix workability for concrete mixture. Due to the increasing
water demand, the compressive strength of concrete mix using manufactured sand will
266 decreases. It can be seen in Figure 6 that the drop in compressive is as much as 37% when the
natural sand is 100% replaced by manufactured sand with normal water reducer. However,
within a limited use of 25% manufactured sand, the influence on compressive strength is
insignificant.
60 ........................................... ...................... ... . ~
260
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240
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Cement: 350 kg
Adm ixture: Daratard 88
@400 mll100kg cement
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200
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20
40
60
80
Manufactured sand
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100
o
20
60
40
80
100
(o/~
Manufactured sand(% )
Figure 5 Effect of manufactured sand on
water demand of concrete mix
Figure 6
Effect of manufactured sand
on strength of concrete
In addition. use of manufactured sand will generally shorten the setting time of concrete. As
shown in Figure 7, When the natural river sand is totally replaced by manufactured sand,
concrete mix will have about 1.5 hours shorter setting time. However, the effect on setting time
could be negligible within 40% replacement level in this case.
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60
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Manufactured Sand (%)
20
40
60
Manufactured Sand
Figure 7 Effect of manufactured sand on
setting time
80
100
(./~
Figure 8 Effect of manufactured sand
on pumpability of concrete mix
As manufactured sand usually has poor shape and surface texture, and deficits of medium size
particles, use of manufactured sand would generally impair the pumpability and finishablity of
concrete mixture[91. As shown in Figure 8, the ratio of pressurized bleeding increases almost
linearly with increasing percentage of manufactured sand in replacement of natural river sand.
The higher the ratio of pressurized bleeding, the more likely the water in concrete mixture would
be squeezed out in a short time under pressure, leading to segregation of concrete mixture and
hence to block of concrete pump. Moreover, it was felt from finishing operation on panel that
concrete mixture would become obviously harsh when manufacture sand replacement excesses
50% for MS2.
From the
concrete
impaired
approach
above results and discussion, it can be drawn out that use of manufactured sand in
mix will bring challenges for concrete producer, such as increased water demand,
pumpability, increased harshness for screeding and finishing operations, etc. One
in practice to overcome these challenges is to use partially manufactured sand with
267 blend of natural river sand and
get an acceptable workability
approach lacks of flexibility to
performance and cost reasons,
increase cement content to compensate higher water demand to
of fresh concrete and properties of hardened concrete. This
increase usage of manufactured sand in concrete due to both
and would increase drying shrinkage of concrete.
Admixture approach is to use modified admixture to overcome the negative effects brought from
use of manufactured sand, and makes use of manufactured sand up to 100% as natural sand
without compromising properties of concrete.
As mentioned previously, MIRA 91 is an admixture with enhanced water reduction and capability
of softening and lubricating fresh concrete mixture , and has developed for use of manufactured
sand in concrete mix. For comparison purpose, Daratard 88 is used in concrete mix with 100%
natural river sand, and MIRA 91 used in concrete mix with 100% manufactured sand . These two
mixes were tested under both laboratory (designated as NS-L and MS2-L) and field conditions
(designated as NS-F and MS2-F). The mix design and test results of these trials are given in
Table 2 and Table 3 respectively.
It can be seen from Table 3 that the manufactured sand mix with admixture MIRA 91 has almost
equivalent performance to the natural river sand mix with normal water reducer Daratard 88 in
terms of workability, slump retention , setting time, air content, compressive strength and the ratio
of pressurized bleeding. In addition, field trial mix with manufactured sand was finally delivered
for actual pumping and placing, and worked well at construction site. These results indicate that
the admixture MIRA 91 is able to make concrete mix with manufactured sand MS2 workable as
normal concrete mix without compromising the properties of either fresh or hardened concrete.
Table 2 Mix proportions of trial mixes
Mix
NS-L (lab trial)
MS2-L(lab trial)
NS-F (field trial)
MS2-F(field trial)
Cement
Sand
(kg)
River
815
350
350
370
805
355
(kg)
MS2
816
835
Granite
(kg)
994
995
980
980
Water Admixture (ml/100kg cement)
(kg)
MIRA91
Daratard 88
450
218
221
500
201
400
190
450
Table 3 Test results of trial mixes
Mix
Slump (mm)
NS-L
MS2-L
NS-F
MS2-F
Initial 60 min
145
100
140
105
140
140
135
125
Air
(%)
1.7
1.6
1.5
2.1
Unit
weight
(kg/3)
2218
2224
2230
2230
Compressive strength
Setting time
(Mpa)
hr:min)
3d
7d
28d
Stiffen Initial Final
26 .9
18
33
7:47
9:04 10:24
9:14 10:34 18.2
26.4
34.7
7:56
31 .5
41.8
48 .7
7:42 9:04
6:26
7:02 8:24
33.4
41 .3
49.6
5:47
Bp
(%)
19
21
25
21
Concluding remarks
Manufactured sand is featured with deficiency in medium size, and has poorer shape and surface
texture than natural river sand. Use of manufactured sand will increase water demand, and impair
pumpability and finishability of concrete mix. These effects will become more significant in lean
mix.
It is feasible to use admixture approach to overcome problems resulting from use of
manufactured sand in concrete mix. For the particular case in this paper, MIRA 91 works well in
concrete mix with 100% replacement of natural river sand by manufactured sand MS2.
268 However, as manufactured sand has great variety in properties from source to source, and
concrete mixes have different cement content from mix to mix, it is hardly to use single admixture
for all kinds of manufactured sand and concrete mix. Customised admixture approach with
particular manufactured sand would be better solution for use of manufactured sand in concrete
mix.
References
1. Barry Hudson, Better Aggregates mean less expensive concrete, Aggman , Nov. 1998.
2. ASTM C 136 - 01 , Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates ,
2001.
3. ASTM C 33-02 , Standard Specification for Concrete Aggregates, 2002
4. Marek, C. R., Importance of fine aggregate shape and grading on properties of concrete,
Vulcan Materials Company , March , 1995
5. Ahmed E and Ahmed A. EI-Kourd , Properties of concrete incorporating natural and crushed
stone very fine sand, ACI Materials Journal, Vol. 86 , N04, July 1989.
6. Ion Dumitru, Manufactured sand research in Australia - Effects of shape, texture and
gradings of manufactured sand on concrete , Aggman , May 2000 .
7. Barry Hudson , Crushing for sand as a product not a by-product , Aggman , April 1999.
8. Chinese Standard JC 473 - 2002 , Pumping Aid for Concrete, 2002.
9. Barry Hudson, Concrete Workability with high fines content sands, Aggmam , February, 1999.
269