15. Recycling of stone slurry in industrial activities

ARTICLE IN PRESS
Building and Environment 42 (2007) 810–819
www.elsevier.com/locate/buildenv
Recycling of stone slurry in industrial activities:
Application to concrete mixtures
Nuno Almeida, Fernando Branco, José Roberto Santos
Instituto Superior Técnico, Dep. Eng. Civil e Arq., Av. Rovisco Pais,1049-001 Lisboa, Portugal
Received 2 June 2005; received in revised form 9 September 2005; accepted 27 September 2005
Abstract
To solve the problem of the waste generated by the natural stone industry, several technical solutions consider the incorporation of this
type of waste in other industrial activities as a by-product. This paper presents an overview of current solutions and the results of a
research project where natural stone slurry is used to replace fine aggregates in concrete mixtures. The concrete mechanical properties are
presented and the technical viability of this new construction material is illustrated.
r 2005 Elsevier Ltd. All rights reserved.
Keywords: Stone slurry; Microfiller; Concrete; Aggregates
1. Introduction
A high consumption level of basic raw materials by the
construction industry generates serious depletion on
mineral resources and the associated environmental damage. Concrete industry is particularly important as it is
not only responsible for consuming natural resources and
energy but also for its capacity of absorbing other
industries waste and by-products. To reduce these effects
the common practice is to substitute the more expensive
components (e.g. cement), thus neglecting affordable
components, regardless of the environmental impacts
involved in their extraction and transformation process.
As natural sources of natural fine aggregates are
becoming exhausted, it turns out urgent to develop
concrete technology capable of incorporating also ‘‘artificial’’ fine aggregates, industrial by-products or waste to
reduce the use of those natural resources.
As natural fine aggregates (sand) are used directly from
the exploration sites, some technical specifications impose
Corresponding author. Tel.: +351 218 418 340; fax: +351 218 418 339.
E-mail addresses: [email protected] (N. Almeida),
[email protected] (F. Branco), [email protected] (J.R. Santos).
0360-1323/$ - see front matter r 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.buildenv.2005.09.018
that the clay1 content on these materials must be limited in
order to be used in concrete mixtures.
The usual procedure to guarantee the fulfilment of these
specifications is to limit the quantity of material passing the
sieve of 74 mm [2]. Therefore, the rejection of very fine
materials based solely on dimensional criteria has been
common practice. However, in the light of state-of-the-art
concrete technology, this practice might be a mistake [3].
Concerning the natural stone extraction and processing
industries, there are huge amounts of waste generation,
which is continuously accumulated in open-air dumpsites
and constitute an unsolved environmental problem. For
example the total amount of stone slurry accumulated each
year, in Portugal, is estimated as 600.000 ton.2
This paper presents an overview of solutions to absorb
the stone slurry and demonstrates the technical viability for
producing white cement concrete with carbonated stone
1
Silicates present less than 2 mm, and are characterized by low stiffness,
are disintegratable, present a tendency to expand in the presence of water
[1] and are susceptible of being adsorbed by the cement particles (thus
interfering with the hydration reactions) [2]. For these reasons, clay is not
accepted to be used in concrete mixtures.
2
Estimates concerning 1998 [4]. However, there are statistics of the year
2000 [5] attesting that this quantity might be significantly higher (around
1.000.000 ton).
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slurry generated from marble and limestone processing
activities.
2. Research significance
There are records about the utilization of natural stone
since the Palaeolithic Era (500.000 B.C.) [6]. In fact, in the
history of mankind, regardless of the different civilizations,
the use of natural stone for noble purposes is widely
detected. As in other activities, the industrialization of
natural stone processing activities was inevitable, culminating its growth from the 1950s.
Actually, worldwide natural stone industry offers an
output of 68 million tons of the processed product. In 2000,
the EU alone accounted for 38.8% of the total amount,
assuming the leadership of the sector, followed by Asia,
which owed its comfortable share of 35% to the contribution of China and India [5].
Fig. 1 shows producing countries that surpassed 1
million tons, representing 73% of the total production
during 2000 [5].
According to the expected growth ratio for the sector, it
is likely that the world interchange of natural stone will
quadruplicate in the next 20 years [5].
Although available statistics concerning generated waste
are not always compliant with reality, and taking in
account that the total amount of waste generated depends
on technology availability, it is possible to estimate around
40% of the finished stones, the amount of stone slurry
generated along processing. Due to the huge amounts of
natural stone slurry generated around the world, it is then
important to incorporate this kind of waste in other
industrial activities as a by-product.
811
dependent on the raw material and on some abrading
agents or wear out debris of equipment required to process
harder stones like granite. This waste can be constituted by
calcium carbonate or silica aluminates if the original
material is marble and limestone or granite, respectively.
There are two types of natural stone processing waste:
solid and semi-liquid (slurry). Solid waste consists of stone
fragments with variable dimension which present fractures,
inadequate dimension, low commercial value or any other
factor that does not fit into its use at a technological or
economical level. Natural stone slurry results from the
physical processes such as extraction, sawing and polishing.
The equipments used on the latter activities require large
amounts of water, which plays an important role in
cooling, lubrication and cleaning of the resultant very
small particles. This mixture of water and very small
particles produces a semi-liquid substance that is generally
known as ‘‘natural stone slurry’’, due to its appearance.
This slurry is then subjected to different treatment
activities, according to the technology available in the
processing plant (e.g. sedimentation tanks can be used to
recover part of the water used in the processing activities,
thus reducing environmental impacts and improving
economic performance).
Due to its composition, this slurry presents a great
potential of being used as a by-product in mineral
consuming industries, thus reducing the environmental
impact of the natural stone industry.
3.2. Construction industry
3.1. Natural stone industry waste
The social, environmental and economic impacts of the
construction industry have been widely discussed during
the last decades. The need to find solutions towards the
reduction of consumption levels of basic raw materials
are recognized issues regarding sustainable construction.
Examples are now illustrated.
There is a huge range of natural stone varieties, which
can be grouped according to its geological and mineralogical constitutions. The waste generated from the
extracting and processing activities are almost exclusively
3.2.1. Cement industry
Recent research studies [7] concluded that there is
technical viability to incorporate massive quantities of
natural stone slurry as ‘‘raw material’’ in the production of
3. Technical solutions for the consumption of stone slurry
China
Italy
Spain
India
Portugal
Brasil
Turkey
USA
Greece
South Africa
France
0
2000
4000
6000
8000
10000
production (Mtons)
Fig. 1. Main world producers of processed natural stone during 2000 [5].
12000
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812
A - Alite
B - Belite
C - Tricalcium Aluminate
F - Ferrite
A
A+B
A+B
A+B
C F
B
Brazil and India, where red ceramic tiles are produced with
20% of stone slurry input [8].
Although limestone slurry is preferred, it is also possible
to produce red ceramic materials with granite slurry, if the
abrasive materials used in the processing are sorted [12].
3.2.3. Tiles
India also presents successful cases related to the
production of tiles containing 90% of stone slurry bonded
by 10% of resin [8].
B
3.2.4. Mortars and concrete
Technical possibilities of producing concretes and
mortars containing stone slurry have been studied with
positive results in several countries [8]. Research works in
Portugal [13,14] led to similar conclusions, demonstrating
improvements in several properties.
27
28
29
30 31
2θ angle
32
33
34
Fig. 2. Difractograms obtained from clinker produced with natural stone
slurry (above) and from the usual process (below) [7].
clinker, without any previous complex treatments. Fig. 2
compares the difractogram obtained of clinker produced
with natural stone slurry with the one produced by the
usual process.
As an example, Portuguese cement industry is responsible for the consumption of 12 million tons of raw
materials each year, about 10 million tons of which is
limestone [7]. It is even possible to refer that the Portuguese
natural stone slurry produced annually consists solely in
3.5% of the total limestone raw material needed by the
national cement industry.
As the nature of the main raw material used by the
cement industry is similar to the one of the natural stone
slurry, the technical and theoretical viabilities were
demonstrated [7,8]. Nevertheless, the solution has not yet
been generally adopted.
3.2.2. Red ceramic bricks and tiles
An European Research Project [9] concluded that it is
possible to incorporate large amounts of natural stone
slurry by substituting conventional calcium carbonate used
in the production of red ceramic bricks, without compromising the behaviour of the obtained final product [10].
The presence of this slurry in a 2–3% ratio solved the
expansion problems usually associated with structural
ceramic materials [9]. Furthermore, depending on the kind
of basic raw material used, it is possible to use up to 25%
of slurry [11].
Confirmation on the behaviour of this kind of recycled
material was also obtained from similar research done in
3.2.5. Other cement-based products
Cement-based products such as structural blocks [15],
lightweight blocks [16], soil–cement bricks [17], pavement
coatings [18] and even acoustic panels developed at an
experimental level that contained granite slurry, limestone
aggregates, cement and cork industry waste [10] are also
known applications.
3.2.6. Pavement
Stone slurry was not considered as suitable for pavement
use [20], but some laboratory tests demonstrated that it is
possible to incorporate this by-product in asphalt mixtures
as a commercial filler substitute [20]. The use of slurry in
road works is not consensual. In fact, there are researches
which attest that it is possible to use marble slurry in
roadwork layers [8] which account for 25–35% of the total
pavement thickness [19].
3.2.7. Embankment
As occurred in the pavements, opinions about the use of
stone slurry in embankments are not unanimous. Despite
the existence of bibliography referring the possibility
of using stone slurry in embankments (taking advantage
of the insulation capability of the slurry) [19] or mixed in a
25% ratio with soil [21], there are also several studies
referring to environmental impacts related with the
presence of this industrial waste in soil [13].
3.2.8. Agglomerate marble
Agglomerate marble is the designation for products that
bind pieces of natural marble together with specially
formulated polyester resin. This process allows the
reconstruction of large recycled ‘‘marble’’ blocks, similar
to the ones extracted from quarries, both in quality and
visual aspects, which can be submitted to the same
processing activities as natural stone. A research concerning the reutilization of marble slurry as a substitute of
calcium carbonate was developed for agglomerate marble
fabrication. For a total amount of slurry that reached up to
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6% of the total compounds, it was technically possible to
adopt this procedure [22].
3.2.9. Other construction materials
Research undertaken in former Yugoslavia showed that
stone slurry could be used for producing glues and paints,
achieving the required properties [23].
3.3. Other industrial activities
Apart from the construction industry, there are other
options to promote sustainable solutions for the natural
stone industry and for the recycling or reutilization of its
by-products.
3.3.1. Paper industry
There are references revealing the possibility to recycle
stone slurry in pulp production, substituting the vegetalbased raw material generally used in the paper industry [7].
Research [22] showed evidence of opportunities to
incorporate limestone and marble slurries substituting up
to 30% of the kaolin generally used as a mineral pigment.
This study showed also the feasibility of recycling slurry
in this industry with improved results concerning
physical properties, nevertheless the visual properties were
inferior [22].
3.3.2. Ceramics industry (faience)
Granite slurry can substitute 50% of the raw materials
usually used to produce floor ceramic tiles [24,25].
Additionally, other researchers addressed the possibility
of producing faiences with stone slurry [7,26].
In a particular case, it was confirmed that it was possible
to substitute calcite by marble and limestone slurry (in a
12% proportion of the total material) with no negative
repercussions on the different production phases, as well as
for the final product quality [22]. The main advantage of
this procedure was to reduce the need for special sand used
as raw material, which is one of the most expensive
materials in the mixture.
3.3.3. Agriculture soil corrective
One of the applications discovered for the stone slurry,
already tested at an experimental level, was the correction
and improved performance of soil dedicated to agriculture
exploitation, by increasing the pH level of those soils [27].
Nevertheless, some authors [7] claim that the drying
process of the slurry induces the formation of solid blocks
that are harmful for agricultural purposes and, in order for
the process to be valid, it is necessary to submit the slurry
to previous treatments that are economically unacceptable,
when compared with the traditional solutions.
Furthermore, the potential of air contamination arising
from soil revolving during agriculture activities is a reality
that can evoke concerns related to human health [7].
Experimental realizations using basalt processing byproducts for agricultural applications showed that the
813
hygroscopic properties prevented evaporation, thus retaining further humidity in the soil [9]. This solution was
studied in Catania (Italy) and it is predictable that they can
be also used in other dry areas in EU (Southeast of Spain,
Canary Islands and Greece) or other Mediterranean
countries [9].
3.3.4. Acid water treatment
Taking advantage of the capability of the slurry to
increase pH level, Soares [7] refers to the possibility of
treating acid water by means of using the stone slurry in the
process.
3.3.5. Dumpsites sealing
In a Portuguese region where dimension stone industry
assumes a relevant economic and social role, an innovative
project was developed towards the periodic sealing of
domestic solid waste cells, which formed a dumpsite, using
the large amounts of stone slurry generated by local
processing plants [28]. The project authors concluded that
the ideal humidity to be contained in the slurry for
compacting operations should be 19% [28].
Firstly, the construction of the cells should be preceded
by a watertight compacted layer with 20 cm, with the
function of avoiding infiltration of leached substances [28].
Then, according to the study, a rock fill must be done,
which is under the deposit of domestic waste accumulated
until the complete formation of a cell (with the proper care
in order to avoid accumulation of biogas). After completion, the cell is sealed with another layer of compacted
slurry [28].
The final result of the project was positive and the slurry
accomplished the functional demands, promoting impermeability, thus minimizing infiltration of water inside the
cells and reducing the existence of insects and other
undesired occurrences [28].
3.3.6. Other applications
Taking into account that very fine particles of limestone
and marble slurry present chemical and mineral nature
similar to the ground carbonated stones (calcium carbonate) used in different industrial ends, there is a whole
range of potential applications for the slurry.
Markets such as the USA consume large quantities of
these kinds of products, thus existing companies exclusively
dedicated to transportation of limestone slurry [29]. This
reality shows the competitiveness of these materials.
An independent research undertaken in Spain focused
on the fact that it was possible to insert marble and
limestone slurry in the market as calcium carbonate to be
used in sectors such as cement, paints, plastics and
polymers, paper, ceramics and glass [11].
Furthermore, it is possible to speculate that ground
marble (or marble slurry) can be used in the manufacturing
of industrial applications such as varnishes, rubber, latex
applications, vinyl compounds, PVC and foams or even in
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814
the food industry (composed food for animals, flours,
pastry, cereals, gums, etc.) [30].
According to the latter studies, other authors refer to the
possibility to apply this waste in plastics [19], rubber,
paints, siderurgy, sugar, pharmaceutics, textiles or in
articles such as soaps or candles [7].
In conclusion, the options are not exhausted once it
is realized that the possibility to use this waste as a
line marker in sports stadiums can be a business
opportunity [31].
4. Experimental programme
4.1. General procedures
An experimental programme was undertaken at the
Technical University of Lisbon—IST (Portugal) to evaluate the main mechanical properties of concrete mixtures
incorporating semi-liquid natural stone waste (slurry),
namely in concrete mixtures containing white cement.
The stone slurry generated in industrial plants was
reused as a component for concrete mixtures without being
FA1
FA2
CA1
Water absorption (%)
0.4
NP954
2594
NP954
2604
NP954
1498
NP955
0.5
NP86
0.595
NP1379
1.4
NP1379
1
NP954
2526
NP954
2551
NP954
1537
NP955
1.7
NP86
2.38
NP1379
3.2
NP1379
1.9
NP581
2576
NP581
2628
NP581
1389
NP955
3
NP86
9.51
NP1379
5.7
NP1379
Dry specific density (kg/m3)
Saturated surface dry specific
density (kg/m3)
Bulk density (kg/m3)
Microfines content (%)
Maximum size (mm)
Fineness modulus
4.2. Materials
4.2.1. Aggregates
The coarse aggregate used in concrete mixtures was
obtained from crushed limestone and the fine aggregates
were extracted from sedimentary deposits (sand). Table 1
shows the properties of coarse aggregates (CA) and fine
aggregates (FA1 and FA2), as well as the respective
specifications used for testing. Fig. 3 presents the grading
curves (determined according to NP1379).
Table 1
Properties of coarse and fine aggregates
Property
submitted to any kind of previous treatment. However, it
was realized that this procedure was only possible through
the use of high contents of superplasticizer and that it was
recommended to previously disaggregate the existing
grumes of slurry (recycling).
The light colour of the limestone and marble slurry that
was used and its very fine dimension enabled its use on
special concrete mixtures containing white cement.
The special concrete mixtures were designed with low
water/cement ratios, reduced maximum dimension of the
aggregate and higher content of cement, combined with the
use of adequate superplasticizers.
Taking these into account, eight concrete mixtures with
stone slurry (CMSS) were produced substituting 0%
(reference mixture), 5%, 10%, 15%, 20%, 34%, 67%
and 100% of the volume of fine aggregate (sand). All
concrete mixtures were set with a slump of 230710 mm
and a spread of 550710 mm, obtained by adjusting the
water/cement ratio.
4.2.2. White cement
Concrete mixtures were produced with white cement
type CEM II/B-L 32,5R (br), characterized by the
mechanical properties presented in Table 2 (determined
according to NP EN 196-1), the physical properties
presented in Table 3 (as specified by the cement producer)
and the chemical properties presented in Table 4 (cement
producer results).
100
90
percentage passing (%)
80
70
60
50
40
CA1
30
FA2
20
FA1
10
0
0.0065
0.074 0.149 0.297 0.59
1.19
2.38
4.76 6.35
sieve size (mm)
Fig. 3. Grading curve of aggregates.
9.52 12.7
19.1
25.4
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Table 2
White cement mechanical properties
Table 5
Chemical characterization of stone slurry
Age (days)
Bending (MPa)
Compression strength (MPa)
Designation
2
7
28
3.4
5.8
6.9
18.9
32.2
41.1
Lost on ignition
Insoluble residue
SiO2
Al2O3
Fe2O3
CaO
MgO
SO3
Cl
Table 3
White cement physical properties
Property
Specific density
Sieve residue
90 mm
45 mm
32 mm
Specific surface area (Blane)
Average dimension of particles
Water of normal consistency
Setting time
Initial
Final
Expansion (Le Châtelier)
Brightness Y
Whiteness index
Specification
Test result
Existence (%)
LOI
IR
43.40
0.90
0.91
3.72
0.40
54.29
0.30
0.09
0.03
2.96 g/cm3
NP EN 196-6
NP EN 196-3
NP EN 196-3
NP EN 196-3
0.1%
1.3%
6.7%
5340 cm2/g
9.4 mm
29.0%
95 min
170 min
1.0 mm
85.5%
64.8%
Table 4
White cement chemical properties
Property
Lost on ignition
Insoluble residue
SiO2
Al2O3
Fe2O3
CaO
MgO
SO3
K2O
Na2O
815
Existence (%)
LOI
IR
12.20
0.30
17.50
2.15
0.20
64.20
0.80
2.50
0.24
0.11
4.2.3. Stone slurry
The stone slurry was collected in an open-air dumpsite.
The plant responsible for generating the collected specimens processed only marble and limestone. The water
content of the different samples, at site, ranged from 1% to
2%. When collected, the dried stone slurry was composed
of dust and grumes. The grumes resulted from the
fragmentation of compacted slurry obtained in the water
recover operations performed at the processing plant. In
order to test the stone slurry, the collected samples were
reduced to dust.
Chemical tests reached the results presented in Table 5.
The high content of CaO confirmed that the original stones
were marble and limestone. It was also verified that the
slurry did not contain any organic matter, thus confirming
that it could be used in concrete mixtures.
The tested slurry had a specific density of 2.72 g/cm3.
Furthermore, by using a Easy Particle Sizer M6.10
equipment, it was possible to compare both grading curves
of cement and slurry particles (Fig. 4). The specific surface
area of the slurry particles was 7128 cm2/g and its average
size was 5.0 mm (smaller than cement particles).
The dimension of slurry particles was therefore compatible with the filling and densing of the transition zone
(measuring between 10 and 50 mm [1]) and of the capillary
pores (which range from 50 nm to 10 mm of diameter [32]),
thus being able to act as a microfiller. According to parallel
specific testing, it was concluded that the used slurry had
no hydraulic or pozzolanic activity.
The average dimension of the slurry particles was
inferior to 74 mm (which would exclude its use as an
aggregate for concrete production, according to the
conventional concrete technology approach), their chemical nature was exclusively dependent on the original
material (without clay or other deleterious materials) and
the test results showed that the slurry was fit to be used in
concrete mixtures.
4.2.4. Concrete admixtures
A new generation polymer based on modified phosphonates, with the commercial designation of Chrysofluid
Optima 100, compatible with potable water and acting as
an high activity water reducer was used. The maximum
dosage recommended by the producer (5 kg per 100 kg of
cement) was considered. This plasticizer conforms to CE
marking and NF 085 certification, whose technical
specifications are those applied in the non-harmonized
part of the NF EN 934-2. Table 6 presents more properties
of the used chemical admixtures.
4.3. Concrete mixtures proportions
Proportioning was designed by Faury’s method, and the
results are presented in Table 7 (the water/cement ratio
includes the liquid phase of the admixture).
4.4. Preparation of specimens
All eight concrete mixtures were prepared according
to a similar methodology. The studied properties were
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816
100
inferior size percentage (%)
90
80
70
60
50
40
30
White cement
20
Stone slurry
10
0
0.1
1.0
10.0
100.0
1000.0
particle size (µm)
Fig. 4. Comparison of cement and slurry particle size.
Table 6
Properties of the used superplasticizer
Nature
Liquid
Density
Colour
pH
Freezing point
Cl ions content
Na2O equivalent
Dry extract (halogen)
Dry extract (EN 480-8)
1.0670.01 g/cm3
White/yellow, slightly milky
470.5
About 3 1C
Nil to BS5075
0.3%
3071.5%
3171.5%
compressive strength at 7 and 28 days of age, splitting
tensile strength and modulus of elasticity (the latter two at
35 days of age). Compressive strength testing was undertaken upon 10 cm cubic specimens. Regarding splitting
tensile strength and modulus of elasticity, cylinders with
30 cm of height and 15 cm of diameter were cast. All
specimens were demoulded 48 h after casting. All specimens were cured in a moist room until 14 days of age, and
then transferred to regular conditions till testing.
5. Results and analysis
5.1. Test results
Table 8 presents the results obtained for the mechanical
properties and Fig. 5 plots their relative variation, when
compared with CMSS0 (mixture without stone slurry).
5.2. Compressive strength
When 5% of the initial sand content was replaced by
stone slurry (CMSS5), 10.3% higher compressive strength
after 7 days, and 7.1% higher compressive strength after 28
days were detected, when compared with CMSS0. This
increase can be related to the higher concentration of
hydrated cement compounds within the available space for
them to occupy [9]. Furthermore, by acting as microfiller,
the stone slurry promoted an accelerated formation of
hydrated compounds, thus resulting in a significant
improvement of compressive strength at earlier ages
(7 days).
In fact, the amount of slurry present in CMSS5 enabled
the very fine particles of it to act as nucleation points
[33,34]. This is related to an effect of physical nature that
ensures effective packing and larger dispersion of cement
particles, thus fomenting better hydration conditions.
Moreover, the slurry particles completed the matrix
interstices (transition zone and capillary pores) and
reduced space for free water [35,36]. The combination of
these phenomena resulted in a better bonding among the
concrete components.
CMSS10, CMSS15 and CMSS20 presented a reduction
of compressive strength ranging from 3.6% to 10.6% at 7
days of age, and from 6.7% to 8.9% at 28 days of age
(when compared to CMSS0). Lower performance of
CMSS10 could seem improbable taking into account its
water/cement ratio. However, for this extremely low water/
cement ratio, the available space for accommodating
hydrated products was insufficient, thus inhibiting chemical reactions.
Regarding higher contents of stone slurry (substitution
of more than 20% of sand), the decrease of compressive
strength values was significant. The incorporation of such
amounts of very fine material did not permit the microfiller
effect to prevail, which, in addition to a rather inappropriate grading, caused lower results.
When substituting all the sand for stone slurry
(CMSS100), test results showed 50.3 MPa at 28 days and
30.1 MPa at 7 days. While these results were acceptable by
comparison with conventional concrete, the relative
reduction amounted to 40.9% for 28 days and 50.1% for
7 days. Therefore, it is possible to conclude that full
substitution of fine aggregate for stone slurry is not reliable
when compressive strength is a critical aspect to take in
consideration.
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Table 7
CMSS mix proportions
Concrete mixture
Sand substitution (%)
CA1 (kg/m3)
FA2 (kg/m3)
FA1 (kg/m3)
Cement (kg/m3)
Slurry (kg/m3)
Water/cement ratio
CMSS0
CMSS5
CMSS10
CMSS15
CMSS20
CMSS34
CMSS67
CMSS100
0
5
10
15
20
34
67
100
1071
1080
1085
1071
1054
1037
1017
1013
473
477
479
473
465
458
225
—
253
219
182
144
103
—
—
—
401
405
406
401
395
388
381
379
—
38
77
114
152
256
489
726
0.36
0.33
0.32
0.36
0.39
0.44
0.48
0.50
Table 8
CMSS mechanical properties
Mixture
Compressive strength 7
days (MPa)
Compressive strength 28
days (MPa)
Spitting tensile strength
(MPa)
Modulus of elasticity (GPa)
CMSS0
CMSS5
CMSS10
CMSS15
CMSS20
CMSS34
CMSS67
CMSS100
60.3
66.5
55.3
58.1
53.9
41.1
36.4
30.1
85.1
91.1
79.4
79.5
77.5
60.8
58.2
50.3
4.2
4.8
4.2
4.3
4.0
3.3
3.2
3.0
40.5
43
41.4
38.8
36.9
33.5
30.7
26.7
performance variation
20%
10%
Compressive strength (7 days)
Compressive strength (28 days)
Split tensile strength
Modulus of elasticity
0%
-10%
-20%
-30%
-40%
-50%
0
10
20
30
40
50
60
70
80
90
100
substitution of fine aggregate for stone sludge (%)
Fig. 5. Variation of performance of concrete mixtures with different contents of stone slurry.
5.3. Splitting tensile strength
The benefits obtained in compressive strength property
due to the microfiller effect induced by stone slurry
particles was even further important regarding the splitting
tensile strength tests (relative increase of 14.3% detected
for CMSS5). These are coherent results, at the light of the
explanation advanced regarding the compressive strength
variation of CMSS5.
As for the compressive strength, when the substitution
level of sand surpassed 20%, the tensile splitting strength
was significantly reduced. Nevertheless, test results show
that tensile splitting strength is less sensitive to high content
of very fine particles than compressive strength. CMSS100
presented a result of 3 MPa, correspondent to a quite
acceptable reduction of 28.6% relatively to CMSS0.
5.4. Modulus of elasticity
In accordance with the analysis made concerning the
other mechanical properties, CMSS5 test results determined that this was the concrete mixture with better
behaviour in terms of modulus of elasticity (6.2% higher
than CMSS0) and that all mixtures containing less than
20% of stone slurry obtained acceptable results. CMSS10
also presented a slight improvement of 2.2% in behaviour.
In the extreme case of slurry incorporation (CMSS100), the
average of test results for the modulus of elasticity was
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N. Almeida et al. / Building and Environment 42 (2007) 810–819
26.7 GPa (34.1% less than the reference concrete mixture
CMSS0).
It is known that cement paste modulus of elasticity is
generally half the modulus of elasticity of aggregates [36].
Therefore, when introducing stone slurry (very fine
particles, with slight inferior size than cement particles),
the paste could be considered as increased, thus promoting
a negative effect on the modulus of elasticity of the
hardened concretes. This fact, in addition to the higher
water/cement ratio, could explain the lower modulus
of elasticity attained for more than 15% substitution
(inclusively).
Another reason that might explain the negative behaviour detected for more than 15% of aggregate replacement for slurry, a part from the higher water/cement ratio,
might be associated with a possible volumetric expansion
occurring among the different materials, withdrawing
aggregates (which better contributes to a higher modulus
of elasticity) from one another, thus losing some ability to
restrain deformations (further dependent on the paste).
In light of this, better behaviour of CMSS5 and CMSS10
can be explained by better grading and packing of
hardened concrete mixture, attained by reduced space
among the different particles.
6. Conclusions
Nowadays, worldwide natural stone industry offers an
output of 68 million tons of processed product. As in other
industrial activities, concerns related with the generation
and destination of waste must be addressed. Among these,
large quantities of semi-liquid wastes originated in natural
stone extraction and processing activities (stone slurry)
need to be treated through sound solutions instead of being
accumulated at open-air dumpsites.
This paper presented several technical solutions for the
incorporation of this industrial by-product in construction
materials such as cement, red ceramic bricks and tiles,
resin-based materials, mortars and concrete, agglomerate
marble, etc. or in other construction solutions ranging
from pavement to embankments and road works. Furthermore, the nature of this waste (depending mainly on its
mineralogical origin) allows other applications in a wide
range of activities like the paper industry, the ceramics
industry (faience), agriculture, water treatments and
dumpsites sealing, among others.
A research developed to evaluate the mechanical
behaviour of concrete mixtures containing stone slurry
was also undertaken. The results showed that the substitution of 5% of the sand content by stone slurry induced
higher compressive strength, higher splitting tensile
strength and higher modulus of elasticity. The feasibility
of incorporating up to 20% stone slurry in detriment of the
respective amount of fine aggregate without prejudicing
mechanical properties in a serious manner was also
determined.
In conclusion, natural stone slurry can be consumed by
several industrial activities as a by-product and can
specifically be used as a fine aggregate and/or microfiller
in concrete mixtures, inducing benefits on its mechanical
properties.
Although the technical solutions are abundant, facts like
the eventual need for expensive slurry treatments and/or
the geographical distance between the source and the
destination can compromise these solutions. Thus, it is
imperative to continue the research and the diffusion of
knowledge, hoping some of these options will prevail.
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