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MICROSILICA AND NANO SILICA ON CONCRETE PROPERTIES
CONTENTS
1. INTRODUCTION 1
2. INVESTIGATIONS MADE ON MECHANICAL
3. PROPERTIES OF MICROSILICA CONCRETE 4
2.1 EXPERIMENTAL PROGRAMME 5
2.1.1 MATERIALS USED 5
2.1.2 CASTING AND CURING 7
2.1.3 TEST RESULTS 8
2.1.4 COMPRESSIVE STRENGTH TEST 8
2.1.5 SPLITTING TENSILE STRENGTH TEST 9
2.1.6 FLEXURAL STRENGTH TEST 10
3. INVESTIGATIONS MADE ON APPLICATION OF 13
NANO SILICA
3.1 PRODUCTION METHOD OF NANO SILICA 13
3.2 EFFECT OF NANO SILICA 14
3.3 APPLICATION OF NANO SILICA 16
4. INVESTIGATIONS MADE ON THE INFLUENCE OF 17
MICRO AND NANO SILICA ON CONCRETE
PERFORMANCE
4.1 MATERIALS USED AND TEST CONDUCTED 18
4.1 COMPRESSIVE STRENGTH 19
4.2 ELECTRICAL RESISTANCE 20
5. CONCLUSIONS 21
6. REFERENCES 23
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MICROSILICA AND NANO SILICA ON CONCRETE PROPERTIES
1. INTRODUCTION:
The construction industry uses concrete to a large extent. About 14 bln ton were used in
concrete is used in infrastructure and in buildings. It is composed of granular materials of different
sizes and the size range of the composed solid mix covers wide intervals. The overall grading of the
mix, containing particles from 300 nm to 32 mm determines the mix properties of the concrete. The
properties in fresh state (flow properties and workability) are for instance governed by the particle
size distribution (PSD), but also the properties of the concrete in hardened state, such as strength
and durability, are affected by the mix grading and resulting particle packing. One way to further
improve the packing is to increase the solid size range, e.g. by including particles with sizes below
300 nm. Possible materials which are currently available are limestone and silica fines likes silica
flavor (Sf), silica fume (SF) and nano-silica (nS). However, these products are synthesized in a
rather complex way, resulting in high purity and complex processes that make them non-feasible for
the construction industry.
In this new century, the technology of nano-structured material is developing at an
astonishing speed and will be applied extensively with many materials. Although cement is a
common building material, its main hydrate C–S–H gel is a natural nano-structured material [Qing,
Y., Zenan, Z., Deyu, K., Rongshen, C., 2007]. The mechanical and durability properties of concrete
are mainly dependent on the gradually refining structure of hardened cement paste and the gradually
improving paste–aggregate interface. Microsilica (silica fume) belongs to the category of highly
pozzolanic materials because it consists essentially of silica in non-crystalline form with a high
specific surface and thus exhibits great pozzolanic activity [Qing, Y., Zenan, Z., Deyu, K.,
Rongshen, C., 2007; Mitchell DRG, Hinczak I, Day RA., 1998]. A new pozzolanic material [Skarp,
U., and Sarkar, S.L, 2000. Collepardi, M., Ogoumah Olagot, J.J., , Skarp, U. and Troli, R ,2002
Collepardi, M., Collepardi, S., Skarp, U., Troli, R, 2002] produced synthetically, in form of water
emulsion of ultra-fine amorphous colloidal silica (UFACS), is available on the market and it
appears to be potentially better than silica fume for the higher content of amorphous silica (> 99%)
and the reduced size of its spherical particles (1-50 nm). Water permeability resistance and 28-days
compressive strength of concrete were improved by using nanosilica [Ji, T., 2005]. Addition of
nanosilica into high-strength concrete leads to an increase of both short-term strength and long-term
strength [Li,G., 2004]. In the present work, try have been done to assess the simultaneous effect of
nano and micro silica on concrete performances.
Microsilica is a mineral admixture composed of very fine solid glassy spheres of
silicondioxide (SiO2). Most microsilica particlesvare less than 1 micron (0.00004 inch) in
diameter,generally 50 to 100 times finer than average cement or fly ash particles.Frequently called
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MICROSILICA AND NANO SILICA ON CONCRETE PROPERTIES
condensed silica fume, microsilicais a by- product of the industrial manufacture of ferrosiliconand
metallic silicon in high-temperature electricarc furnaces. The ferrosilicon or silicon product is
drawnoff as a liquid from the bottom of the furnace. Vapor risingfrom the 2000-degree-C furnace
bed is oxidized, and as it cools condenses into particles which are trapped in huge cloth bags.
Processing the condensed fume to remove impurities and control particle size yields microsilica.
Microsilica in concrete contributes to strength and durability two ways:
As a pozzolan, microsilica provides a more uniform distribution and a greater volume of
hydration products.
As a filler, microsilica decreases the average size of
pores in the cement paste.
Mi c ro s i l i c a’s effectiveness as a pozzolan and a filler depends largely on its composition
and particle size which in turn depend on the design of the furnace and the composition of the raw
materials with which the furnaceis charged. At present there are no U.S. standard specifications for
the material or its applications. Dosages of microsilica used in concrete have typically been in the
range of 5 to 20 percent by weight of cement, but percentages as high as 40 have been reported.
Used as an admixture, microsilica can improve the p ro p e rties of both fresh and hardened
concrete. Used as a partial replacement for cement, microsilica can substitute for energy-consuming
cement without sacrifice of quality.
Now a days high performance concrete refers to the concrete that has uniaxial
compressive strength greater than normal concrete at same region. than the normal strength concrete
obtained in a particular region. This definition does not include a numerical value for compressive
strength indicating a transfer from a normal strength concrete to high strength concrete. In 1950’s,
concrete with a compressive strength of M35 MPa was considered as high strength concrete. In the
1990’s concrete with a compressive strength greater than 110MPa was used in developed countries.
However this numerical value (110MPa) could be considerably lower depending on the
characteristics of the local materials used for these concrete products. Report of ACI committee 363
in 1979 defined high-strength concrete as having compressive strength more than 41.37 MPa
(6000Psi).
High-strength and High-performance concrete are being widely used throughout the
world and to produce them it is necessary to reduce the water/binder ratio and increase the
binder content. High-strength concrete means good abrasion, impact and cavitation
resistance. Using High-strength concrete in structures today would result in economical
advantages. Most applications of high strength concrete to date have been in high-rise
buildings, long span bridges and some special structures. Major application of high strength
concrete in tall structures have been in columns and shear walls, which resulted in decreased
DEPT. OF CIVIL ENGINEERING, U.V.C.E. Page 3
MICROSILICA AND NANO SILICA ON CONCRETE PROPERTIES
dead weight of the structures and increase in the amount of the rental floor space in the
lower stories.
2. According to the investigations made by V. Bhikshma∗a, K. Nitturkarb and Y.
Venkatesham(Department of Civil Engineering, University College of Engineering, Osmania
University (UCE,OU) , Hyderabad, India
Department of Civil Engineering, MVSR Engineering College Hyderabad, India
Department of Civil Engineering, UCE, OU, Hyderabad, India) respectively following results were
obtained. Their reports includes following contents:
In future, high range water reducing admixtures (super plasticiser) will open up new
possibilities for use of these materials as a part of cementing materials in concrete to
produce very high strengths, as some of them are more finer than cement. The brief
literature on the study has been presented in following text.
Hooton [1] investigated on influence of silica fume replacement of cement on physical
properties and resistance to sulphate attack, freezing and thawing, and alkali-silica
reactivity. He reported that the maximum 28-day compressive strength was obtained at 15% silica
fume replacement level at a w/b ratio of 0.35 with variable dosages of HRWRA. Prasad et al. [2]
has undertaken an investigation to study the effect of cement replacement with micro silica in the
production of High-strength concrete. Yogendran etal.[3] investigated on silica fume in High-
strength concrete at a constant water-binder ratio (w/b) of 0.34 and replacement percentages of 0 to
25, with varying dosages of HRWRA.The maximum 28-day compressive strength was obtained at
15% replacement level. Lewis [4] presented a broad overview on the production of micro silica,
effects of standardization of micro silica concrete-both in the fresh and hardened state. Bhanja., and
Gupta [5] reported and directed towards developing a better understanding of the isolated
contributions of silica fume concrete and determining its optimum content. Their study intended to
determine the contribution of silica fume on concrete over a wide range of w/c ratio ranging from
0.26 to 0.42 and cement replacement percentages from 0 to 30.
Tiwari and Momin [6] presented a research study carried out to improve the early age
compressive strength of Portland slag cement (PSC) with the help of silica fume. Silica fume from
three sources- one imported and two indigenous were used in various proportions to study their
effect on various properties of PSC.Venkatesh Babu and Natesan [7] Investigated on physico-
mechanical properties of High-performance concrete (HPC) mixes, with different replacement levels
of cement with condensed silica fume (CSF) of grade 960-D. Keeping some of the important points
of literature.
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MICROSILICA AND NANO SILICA ON CONCRETE PROPERTIES
High-strength concrete of grades M40 and M50, the replacement levels of cement by
silicafume are selected as 0%, 3%, 6%, 9%, 12% and 15% for standard sizes of cubes, cylinders and
prisms for testing.
2.1 EXPERIMENTAL PROGRAMME
The experimental program was designed to compare the mechanical properties i.e,
compressive strength, flexural strength and splitting tensile strength of high strength concrete with
M40 and M50 grade of concrete and with different replacement levels of ordinary Portland cement
(ultra tech cement 53 grade) with silica fume or micro silica of 920-D.
The program consists of casting and testing a total of 144 specimens. The specimens of
standard cubes (150mmX150mmX150mm), standard cylinders of (150mm Dia X 300mm height)
and standard prisms of (100mmX100mmX500mm) were cast with and with out silica fume.
Universal testing machine was used to test all the specimens. In first series the specimens were cast
with M40 grade concrete with different replacement levels of cement as 0%, 3%, 6%, 9%, 12% and
15% with silica fume. And in the second series the same levels of replacement with M50 grade of
concrete were cast.
2.1.1 Materials Used
Ordinary Portland cement (Ultra tech cement) of 53 grade conforming to IS: 12269 and
locally available natural sand were used. Specific gravity and fineness modulus were found to be
2.53 and 2.73 respectively. Crushed granite stone chips (angular) of maximum size 20mm were used.
Specific gravity and fineness modulus were found to be 2.60 and 7.61 respectively. Potable water
was used for mixing and curing.
Silica fume (Grade 920-D) was obtained from “Elkem India private limited”, Mumbai,
India.
Super plasticizer by trade name Conplast SP-430 manufactured at Bangalore was used as
water reducing agent to achieve the required workability. It is available in brown liquid instantly
dispensable in water.
Physical properties of cement as per IS 4031 (Part-II)-1988, and silica fume as per IS 4031
(Part-II)-1999, tested at National Council for Cement and Building Materials. The experimental
program was designed to compare the mechanical properties i.e, compressive strength, flexural
strength and splitting tensile strength of high strength concrete with M40 and M50 grade of concrete
and with different replacement levels of ordinary Portland cement (ultra tech cement 53 grade) with
silica fume or micro silica of 920-D.
The program consists of casting and testing a total of 144 specimens. The specimens of
standard cubes (150mmX150mmX150mm), standard cylinders of (150mm Dia X 300mm height)
and standard prisms of (100mmX100mmX500mm) were cast with and with out silica fume.
Universal testing machine was used to test all the specimens. In first series the specimens were cast
DEPT. OF CIVIL ENGINEERING, U.V.C.E. Page 5
MICROSILICA AND NANO SILICA ON CONCRETE PROPERTIES
with M40 grade concrete with different replacement levels of cement as 0%, 3%, 6%, 9%, 12% and
15% with silica fume. And in the second series the same levels of replacement with M50 grade of
concrete were cast.
Physical properties of cement as per IS 4031 (Part-II)-1988, and silica fume as per IS4031
(Part-II)-1999, tested at National Council for Cement and Building Materials Hyderabad India, are
presented in Table 1.
Hyderabad India, are presented in Table 1.
Table 1. Physical properties of cement and silica fume
Designation Specific
gravity
Cement 3.15
Silica fume 2.27
Chemical properties of cement (as per IS 12269) and silica fume (as per ASTMC-99) tested
at Indian Institute of Chemical Technology, Hyderabad, India are presented in Table 2 and Table 3,
respectively.
Table 2. Chemical properties of cement
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Table 3. Chemical properties of silica fume
Characteristics Specifications Result
(%by mass)
SiO2 % min 85.0 88.7
Moisture content % max 3.0 0.7
Loss on ignition
975c
% max 6.0 1.8
Carbon % max 2.5 0.9
>45 micron % max 10 0.2
Bulk density 500-700
Kg/m3
670
Two concrete mixes were designed to a compressive strengths of 40MPa and 50MPa with a
water-cementitious ratio of 0.36 and 0.30 respectively, as per IS code. In both the cases, the
Portland cement was replaced with silica fume by 0%, 3%,6%, 9%, 12%, and 15%. The water
reducing agent Conplast SP-430, 600 ml per 50kg of cement was added, to get thedesired
workability. The proportions of constituent materials i.e., cementitious material
(cement and silica fume), aggregates (coarse and fine), water and chemical admixture (super
-plasticizer) for two mixes are presented in Table 4.
Table 4. Proportions of Constituent materials of M40 and M50 Grade Concrete
Proportions of constituent
Grade of mix materials
DEPT. OF CIVIL ENGINEERING, U.V.C.E. Page 7
Characteristics Result (%by mass)
Loss on ignition 1.95
Silica as (SiO2) 23.5
Alumina as (Al2O3) 4.42
Iron as (Fe2O3) 11.38
MICROSILICA AND NANO SILICA ON CONCRETE PROPERTIES
w/c ratio C F.A C.A
M40 0.36 1 0.92 2.82
M50 0.30 1 0.65 1.90
2.1.2 Casting and Curing of Test Specimens
The specimens of Standard cubes (150mm×150mm×150mm) 6 No.s, Standard prisms
(100mmX100mmX500mm) 6No.s and Standard cylinders (150mm diameterX300mm height) 6 No.s
were cast per a day, for 6 days. In all 72 specimens, cement was replaced by silica fume (RS-0, RS-3,
RS-6, RS-9, RS-12 and RS-15) with M40 mix case and 72 specimens with M50 mix case were cast.
Measured quantities of coarse aggregate and fine aggregate were spread out over
animpervious concrete floor. The dry ordinary Portland cement (ultra tech) and silica fume were
spread out on the aggregate and mixed thoroughly in dry state turning the mixture over and over
until uniformity of color was achieved. Water was measured exactly by weight, and super plasticiser
Conplast SP-430 (600ml per 50kg) was added to the water, 75% quantity of water was added to the
dry mix and it was thoroughly mixed to obtain homogeneous concrete. The time of mixing shall be
in 10-15 minutes.
2.1.3 TEST RESULTS:
The present investigation reports a part of a comprehensive study intended to determine the
contribution of silica fume on concrete mixes M40 and M50 with a w/c ratio of 0.36 and0.30 and
cement replacement levels from 0 to 15.
The optimum silica fume replacement level and strength improvement of high strength
concrete have been determined. The workability tests are presented in Table 5.
Table 5. Slump and compaction factor values of M40 and M50 grade concrete
M40 M50
Silica fume % Slump(mm) Slump(mm)
RS-3 45 40
RS-6 43 38
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RS-9 41 37
RS-12 38 35
RS-15 35 32
2.1.4 Compressive Strength of Concrete
The test was carried out conforming to IS 516-1959 to obtain compressive strength of M40
and M50 grade of concrete. The compressive strength of High-strength concrete with OPC and silica
fume concrete at the age of 28 days is presented in Table 6. There is a significant improvement in the
strength of concrete because of the high pozzolanic nature of the silica fume and its void filling
ability. The compressive strength of the two mixes M40 and M50 at 28-days age, with replacement
of cement by silica fume (920-D) was increased gradually up to an optimum replacement level of
12% and then decreased. The maximum 28-day cube compressive strength of M40 grade with 12%
of silica fume was 61.20MPa, and of M50 grade with 12% silica fume was 68.66MPa.
The compressive strength of M40 grade concrete with partial replacement of 12% cement
by silica fume shows 16.37% greater, and of M50 grade with 12% replacement shows 20% greater,
than the controlled concrete.
The maximum compressive strength of concrete in combination with silica fume depends
on three parameters namely the replacement level, water cement ratio and chemical admixture. The
chemical admixture dosage plays a vital role in concrete to achieve the required workability at lower
w/c ratio.
Table 6. Twenty eight days compressive strength of concrete
Silica fume % Compressive strength( M P a )
M40 M50
RS-0 52.59 57.18
RS-3 54.18 57.63
RS-6 58.22 62.08
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MICROSILICA AND NANO SILICA ON CONCRETE PROPERTIES
RS-9 60.74 62.81
RS-12 61.20 68.66
RS-15 58.50 63.50
Note: RS-Replacement of silica fume by weight of cement
2.1.5 Splitting Tensile Strength of Concrete
The test was carried out according to IS 5816- 1999 to obtain the splitting tensile strength of
M40 and M50 grade concrete. The test results of both the mixes were presented in the Table7
Table 7. Twenty eight days splitting tensile strength of concrete
Silica fume % Flexural strength ( MPa)
M40 M50
RS-3 5.11 5.14
RS-6 5.41 5.39
RS-9 5.78 5.7
RS-12 5.82 5.85
RS-15 5.58 5.68
As replacement level increases there is an increase in splitting tensile strength for both
M40 and M50 grades of concrete up to 12% replacement level, and beyond that level there is a
decrease in splitting tensile strength. The splitting tensile strength at 28-days age of curing of M40
and M50grade of concrete was 4.17MPa and 3.80MPa respectively. The splitting tensile strength of
both grades at 12% replacement, increased by about 36.06% and 20.63% respectively, when
compared to that of conventional concrete.
2.1.6Flexural Strength of Concrete
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The tests were carried out conforming to IS 516-1959 to obtain the flexural strength of M40
and M50 grade concrete. Three standard prism specimens were cast for each replacement level and
tested under two-point loading. The experimental results of flexural strength with OPC for both the
mix cases are shown in Table 8.
Table 8. Twenty eight days flexural strength of concrete
Silica fume %
Flexural strength ( MPa)
M40 M50
RS-0 5 5.06
RS-3 5.11 5.14
RS-6 5.41 5.39
RS-9 5.78 5.7
RS-12 5.82 5.85
RS-15 5.58 5.68
The flexural strength at the age of 28- days of silica fume concrete continuously increased
with respect to controlled concrete and reached a maximum value of 12% replacement level for both
M40 and M50 grades concrete respectively. The maximum 28-day flexural strength of M40 and
M50 grades of concrete with 12% replacement of silica fume was 5.82MPa and 5.85MPa
respectively.
It can be concluded that the ultra-fine silica fume particles, which consist mainly of
amorphous silica, enhance the concrete strength by both pozzolanic and physical actions. The
results of the present investigation indicate that the percentage of silica fume contributing to the
mechanical properties is comparable or even more significant than that ofcontrol concrete.
The material used silica fume, slump and testing setup are presented in plates 1-5.
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MICROSILICA AND NANO SILICA ON CONCRETE PROPERTIES
Typical stress-strain curves for M40 and M50 grades of concrete are presented in Figure 1-
The flexural strength at the age of 28- days of silica fume concrete continuously increased with
respect to controlled concrete and reached a maximum value of 12% replacement level for both M40 and
M50 grades concrete respectively.
The maximum 28-day flexural strength of M40 and M50 grades of concrete with 12% replacement
of silica fume was 5.82MPa and 5.85MPa respectively.
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MICROSILICA AND NANO SILICA ON CONCRETE PROPERTIES
3. According to the investigations made by G.QUERCIA AND H.J.H. BROUWERS
(Materials Innovation Institute – M2i and 2Eindhoven University of Technology
Building and Physics, P.O. box 513, 5600 MB Eindhoven, The Netherlands) a special
type of nano-silica a new nano-silica is produced from olivine. This nS, as well as
commercially available nS, will be applied and tested. In addition, a mix design tool used for
self compacting concrete (SCC) will be modified to take into account particles in the size
range of 10 to 50 nm. The following results were obtained according to their studies and it is
as follows:
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3.1 Production method of nS:
Nowadays there are different methods to produce nanosilica concrete. One of the
production methods is water route method at room temperature. In this process the starting materials
(mainly Na2SiO4 and organometallics like TMOS/TEOS) are added in a solvent, and then the pH of
the solution is changed, reaching the precipitation of silica gel. The produced gel is aged and filtered
to become a xerogel . This xerogel is dried and burned or dispersed again with stabilized agent (Na,
K, NH3, etc.) to produce a concentrated dispersion (20 to 40% solid content) suitable for use in
concrete industry .
An alternative production method is based on vaporization of silica between 1500 to 2000°C
by reducing quartz (SiO2) in an electric arc furnace. Furthermore, nS is produced as a byproduct of
the manufacture of silicon metals and ferro-silicon alloys, where it is collected by subsequent
condensation to fine particles in a cyclone. Nano-silica produced bythis method is a very fine
powder consisting of spherical particles or microspheres with a main diameter of 150 nm with high
specific surface area (15 to 25 m2/g).
Estevez et al. developed a biological method to produce a narrow and bimodal distribution
of nS from the digested humus of California red worms (between 55nm to 245nm depending of
calcination temperature). By means of this method, nanoparticles having a spherical shape with
88% process efficiency can be obtained. These particles were produced by feeding worms with rice
husk, biological waste material that contain 22% of SiO2.
Finally, nS can also be produced by precipitation method. In this method, nS is
precipitated from a solution at temperatures between 50 to 100 °C (precipitated silica). It was first
developed by Iller in 1954. This method uses different precursors like sodium silicates (Na2SiO3),
burned rice husk ash (RHA), semi-burned rice straw ash (SBRSA), magnesium silicate and others .
In addition, nano-silica (nS) is being developed via an alternative production route.
Basically, olivine and sulphuric acid are combined, whereby precipitated silica with extreme
fineness but agglomerate form is synthesized (nano-size with particles between 6 to 30 nm), and
even cheaper than contemporary micro-silica. The feasibility of this process has been proven in two
preceding PhD theses and published data .Currently, parallel PhD project ocuses on the process to
produce nS on industrial scale in large quantities for concrete production. Furthermore, the
combination of raw materials and process parameters on production will be examined.
3.2 Effect of nS addition in concrete and mortars: In concrete, the micro-silica (Sf
and SF) works on two levels. The first one is the chemical effect: the pozzolanic reaction of silica
with calcium hydroxide forms more CSH-gel at final stages. The second function is physical one,
because micro-silica is about 100 times smaller than cement. Micro-silica can fill the remaining
voids in the young and partially hydrated cement paste, increasing its final density. Some
researchers found that the addition of 1 kg of micro-silica permits a reduction of about 4 kg of
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MICROSILICA AND NANO SILICA ON CONCRETE PROPERTIES
cement, and this can be higher if nS is used. Another possibility is to maintain the cement content at
a constant level but optimizing particle packing by using stone waste material to obtain a broad
PSD. Optimizing the PSD will increase the properties (strength, durability) of the concrete due to
the acceleration effect of nS in cement paste. Nano-silica addition in cement paste and concrete can
result in different effects. The accelerating effect in cement paste is well reported in the literature.
The main mechanism of this working principle is related to the high surface area of nS, because it
works as nucleation site for the precipitation of CSH gel.
However, according to Bjornstrom et al. it has not yet been determined whether the more
rapid hydration of cement in the presence of nS is due to its chemical reactivity upon dissolution
(pozzolanic activity) or to their considerable surface activity. Also the accelerating effect of nS
addition was established indirectly by measuring the viscosity change (rheology) of cement paste
and mortars. The viscosity test results shown that cement paste and mortar with nS addition needs
more water in order to keep the workability of the mixtures constant, also concluded that nS
exhibits stronger tendency for adsorption of ionic species in the aqueous medium and the formation
of agglomerates is expected. In the latter case, it is necessary to use a dispersing additive or
plasticizer to minimize this effect.
Ji studied the effect of nS addition on concrete water permeability and
microstructure. Different concrete mixes were evaluated incorporating nS particles of 10 to 20 nm
(s.s.a. of 160 m2/g), fly ash, gravel and plasticizer to obtain the same slump time as for normal
concrete and nS concrete. The test results show that nS can improve the microstructure and reduce
the water permeability of hardened concrete. Lin et al. demonstrated the effect of nS addition on
permeability of eco-concrete. They have shown with a mercury porosimetry test that the relative
permeability and pores sizes decrease with nS addition (1 and 2% bwoc). Decreasing permeability
in concrete with high fly ash content (50%) and similar nS concentrations (2% of nS power) was
reported by. Microstructural analysis of concrete by different electronic microscope techniques
(SEM, ESEM, TEM and others) revealed that the microstructure of the nS concrete is more uniform
and compact than for normal concrete. Ji demonstrated that nS can react with Ca(OH)2 crystals,
and reduce the size and amount of them, thus making the interfacial transition zone (ITZ) of
aggregates and binding cement paste denser. The nS particles fill the voids of the CSH-gel structure
and act as nucleus to tightly bond with CSH-gel particles. This means that nS application reduces
the calcium leaching rate of cement pastes and therefore increasing their durability .
The most reported effect of nS addition is the impact on the mechanical properties of
concrete and mortars. As it was explained before, the nS addition increases density, reduces
porosity, and improves the bond between cement matrix and aggregates. This produces concrete that
shows higher compressive and flexural strength. Also, it was observed that the nS effect depends on
the nature and production method (colloidal or dry powder). Even though the beneficial effect of nS
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addition is reported, its concentration will be controlled at a maximum level of 5% to 10% bwoc,
depending on the author or reference. At high nS concentrations the autogenous shrinkage due to
self-desiccation increases, consequently resulting in higher Cracking potential. To avoid this effect,
high concentration of super plasticizer and water has to be added and appropriate curing methods
have to be applied.
The program consists of casting and testing a total of 144 specimens. The specimens
of standard cubes (150mmX150mmX150mm), standard cylinders of (150mm Dia X 300mm height)
and standard prisms of (100mmX100mmX500mm) were cast with and with out silica fume.
Universal testing machine was used to test all the specimens. In first series the specimens were cast
with M40 grade concrete with different replacement levels of cement as 0%, 3%, 6%, 9%, 12% and
15% with silica fume. And in the second series the same levels of replacement with M50 grade of
concrete were cast.
3.3 Applications of nS
At present Sf, SF and nS, because of their price, are only used in the so-called high
performance concretes (HPC), eco-concretes and self compacting concretes (SSC). For the last types
of special concretes (eco-concrete and SCC), the application of these materials is a necessity. Also,
some explorative applications of nS in high performance well cementing slurries, specialized mortars
for rock-matching grouting, and gypsum particleboard [39] can be found, but nS is not used in
practice yet. The application of these concretes can be anywhere, both in infrastructure and in
buildings.
Nano-silica is applied in HPC and SCC concrete mainly as an anti-bleeding agent. It is also
added to increase the cohesiveness of concrete and to reduce the segregation tendency. Some
researchers found that the addition of colloidal ns (range 0 to 2% bwoc) causes a slight reduction in
the strength development of concretes with ground limestone, but does not affect the compressive
strength of mixtures with fly ash or ground fly ash (GFA). Similarly, Sari et al. used colloidal nS
(2% bwoc) to produce HPC concrete with compressive strength of 85 MPa, anti-bleeding properties,
high workability and short demolding times (10 h). Another application of nS well documented and
referred in several technical publications, is the use as additive in eco-concrete mixtures and tiles.
Eco-concretes are mixtures where cement is replaced by waste materials mainly sludge ash,
incinerated sludge ash, fly ash or others supplementary waste materials. One of the problems of these
mixtures is their low compressive strength and long setting period. This disadvantage is solved by
adding nS to eco-concrete mixes to obtain an accelerated setting and higher compressive strength.
Roddy et al. applied particulate nS in oil well cementing slurries in two specific ranges of particles
sizes, one between 5 to 50 nm, and a second between 5 and 30 nm. Also they used nS dry powders in
encapsulated form and concentrations of 5 to 15% bwoc. The respective test results for the slurries
demonstrate that the inclusion of nS reduces the setting time and increases the strength (compressive,
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tensile, Young’s modulus and Poisson’s ratio) of the resulting cement in relation with other silica
components (amorphous 2.5 to 50 μm, crystalline 5 to 10 μm and colloidal suspension 20 nm types
silica) that were tested.
4. According to investigations made by M.Nilli, A.Ehsani and K.Shabani Civil Eng.,
Dept., Bu-Ali Sina University, Hamedan, I.R. Iran Eng., Research Institute of Jahad-
Agriculture Ministry, Tehran, I.R. Iran had conducted experiments by adding both
nanosilica and microsilica as partial replacement to cement by varying their percentages.
Experimental details and the various materials used in the experiment is as follows:
The mechanical and durability properties of concrete are mainly dependent on the gradually
refining structure of hardened cement paste and the gradually improving paste–aggregate interface.
Microsilica (silica fume) belongs to the category of highly pozzolanic materials because it consists
essentially of silica in non-crystalline form with a high specific surface and thus exhibits great
pozzolanic activity [Qing, Y., Zenan, Z., Deyu, K., Rongshen, C., 2007; Mitchell DRG, Hinczak I,
Day RA., 1998]. A new pozzolanic material [Skarp, U., and Sarkar, S.L, 2000. Collepardi, M.,
Ogoumah Olagot, J.J., , Skarp, U. and Troli, R ,2002 Collepardi, M., Collepardi, S., Skarp, U.,
Troli, R, 2002] produced synthetically, in form of water emulsion of ultra-fine amorphous colloidal
silica (UFACS), is available on the market and it appears to be potentially better than silica fume for
the higher content of amorphous silica (> 99%) and the reduced size of its spherical particles (1-50
nm). Water permeability resistance and 28-days compressive strength of concrete were improved by
using nanosilica [Ji, T., 2005]. Addition of nanosilica into high-strength concrete leads to an
increase of both short-term strength and long-term strength [Li,G., 2004]. In the present work, try
have been done to assess the simultaneous effect of nano and micro silica on concrete performances.
4.1 MATERIALS AND TESTING PROGRAM
Crushed stone, with 19 mm maximum nominal size, in two ranges of 5-10 and 10-19 with
relative density at saturated surface dry of 2.61 were used. Fineness modulus of sand and relative
density were 3.24 and of 2.56 respectively. Water absorption of fine and coarse aggregate is 3.09%
and 2%, respectively. Portland cement type 2, with a specific gravity of 3.11 and 3750 cm2/gr
surface area was used. A commercial carboxylic type plasticizer, (Gelenium 110M, BASF Co.), was
used to adjust workability of the fresh concrete. Silica fume, made by Semnan Ferro Alley factory
(IFC Co.), was used at 0%, 3%, 4.5%, 6% and 7.5% (by weight) as partial replacement of cement.
Colloidal nanosilica, made by Akzo Nobel Chemicals GmbH (Cembinder® 8) was also used at 0%,
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1.5%, 3% and 4.5% (by weight) as partial replacement of cement. The characteristics of
cementitious materials are given in Table 1. Mix proportions of the concrete mixtures and results of
fresh concrete slump tests are given in Table 2. Water-cementitious material (w/cm) ratio of all
mixtures is constant and equal to 0.45. The colloidal nanosilica was mixed with Superplasticizer and
half of the mixing water. A pan mixer was used and the mixing procedures are as follows. At the
beginning, sand, cement, half of the mixing water and half of the admixture content were mixed for
1 minute. Then, the remaining water and admixture and also coarse aggregate were added into the
mixture and mixed for 2 minutes. Cube specimens (100×100×100 mm) were used for determination
of compressive strength development, electrical resistance development and capillary absorption.
The casting specimens were remolded after 24 hours and then were cured in water. Testing ages
were 3, 7, 28 and 91 days. Electrical resistance was measured via copper plates which were installed
in top and bottom of the saturated concrete specimen at the ages of testing. Capillary absorption test
was performed according to RILEM TC, CPC 11.2 (1982).
Table 1. Chemical Composition and Physical Properties of
Cementitious Material
Material Chemical composition
(%) and Physical properties
Cement Al2O3, 4.75; SiO2,
26.58; P2O3, 0.26; SO3, 7.74;
K2O, 0.76; CaO, 55.75; TiO2,
0.24; Cr2O3, 335ppm; MnO,
0.13; FeO, 3.83; SrO, 665ppm;
As2O3<144 ppm; CuO,
185ppm;
Microsilica SiO2, 85-95; C, 0.6-1.5;
Fe2O3, 0.4-2; CaO, 2-2.3;
Al2O3, 0.5-1.7; MgO, 0.1-0.9;
Colloidal Nanosilica Average primary particle
size: 50-60 nm; Specific surface
area (BET): 80 m2/g;
Solid content (SiO2-
content): 50 wt %; density: 1.4
g/cm3; Ph: 9.5; Viscosity: <15
cPS
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4.2 EXPERIMENTAL RESULTS
4.2.1 Compressive strength
Fig. 1 shows the compressive strength development of concrete mixtures. The results show
that increasing in nanosilica content ,1.5% to 4.5% by weight, leads to an increase of compressive
strength at all stages. The results also indicate that the specimens which contain both nano and
micro silica, due to the high pozzolanic activity, have higher compressive strength than reference
ones. However, large quantities of nanosilica in the mixtures, due to agglomerate effect, don't lead
to increase compressive strength. As it is shown the highest compressive strength at the age of 28
days is corresponding to SF6, NS1.5 mixture.
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The above figure represents the compressive strength obtained after 3 days , 7 days, 28 days and 91
days of water curing. The results show that increasing in nanosilica content from 1.5% to 4.5% by
weight, leads to an increase of compressive strength at all stages. It is found that for SF-6% and Ns-
1.5% 28 days compressive strength was found to be greater than other combination.
4.2.2 Electrical resistivity
The electrical resistance development of the specimens which was measured at the ages of 3,
7, 28 and 91 days is illustrated in Fig. 2. As it is shown, a considerable increase in electric resistance
of later ages of 91 days, compare to the early age result is observed. This is, of course, due to
hydration progress which occurred in the later ages. Similar to compressive strength results, the
maximum electrical resistance, at the ages of 28 days, is attained in the mixture that contains 6%
and 1.5% microsilica and nanosilica, respectively.
The resistivity of concrete is strongly dependent on the concrete quality and on the exposure
conditions. In concrete material with high electrical resistivity the corrosion process will be slow
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compared to concrete with low resistivity in which the current can easily pass between anode and
cathode areas [Song, H. W., Saraswathy, V., 2007].
CONCLUSIONS
1. According to V. Bhikshma∗a, K. Nitturkarb and Y. Venkatesham
(Department of Civil Engineering, University College of Engineering, Osmania University
(UCE,OU) , Hyderabad, India
Department of Civil Engineering, MVSR Engineering College Hyderabad, India
Department of Civil Engineering, UCE, OU, Hyderabad, India)
Cement replacement upto 12% with silica fume leads to increase in compressive
strength, splitting tensile strength and flexural strength, for both M40 and M50 grades. Beyond 12%
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there is a decrease in compressive strength, tensile strength and flexural strength for 28 days curing
period.
It is observed that the compressive strength, splitting tensile strength and flexural
strength of M40 grade concrete is increased by 16.37%, 36.06% and 16.40% respectively, and for
M50 grade concrete 20.20%, 20.63% and 15.61% respectively over controlled concrete.
There is an increase in Young’s modulus of concrete as silica fume content increases.
This increase is again up to a replacement level of 12%. The Young’s modulus at this replacement
level is Ec=32.19GPa, for M40 grade concrete which is 28.06% higher than conventional concrete.
There is a decrease in workability as the replacement level increases, and hence water
consumption will be more for higher replacements.
The ratio of cube strength to cylinder is found as 1.22 and 1.24 respectively for M40
and M50 grades, where as for the conventional concrete is1.20.
.The maximum replacement level of silica fume is 12% for M40 and M50 grades of
concrete.
2. According to G.QUERCIA AND H.J.H. BROUWERS (Materials Innovation Institute – M2i
and 2Eindhoven University of Technology Building and Physics, P.O. box 513, 5600 MB Eindhoven,
The Netherlands) A new nano-silica (nS) can be produced in high quantities and for low prices that
allows for a mass application in concrete. It may replace cement in the mix, which is the most costly
and environmentally unfriendly component in concrete. The use of nS makes concrete financially
more attractive and reduces the CO2 footprint of the produced concrete products. The nS will also
increase the product properties of the concrete: the workability and the properties in hardened state,
enabling the development of high performance concretes for extreme constructions.
3. According to M. Nili, A. Ehsani , and K. Shabani (Civil Eng., Dept., Bu-Ali Sina
University, Hamedan, I.R. Iran Eng., Research Institute of Jahad-Agriculture Ministry,
Tehran, I.R. Iran)
The highest compressive strength at the ages of 7 and 28 days was attained when the
mixtures contain 6% microsilica and 1.5% nanosilica.
A considerable increase in electric resistant of nano-micro silica specimens was
observed compare to reference ones and the highest value was corresponding to the specimens
which contain totally 7.5% nano and micro silica.
In general we can conclude that microsilica and nano-silica replace cement in some percentages
resuts in improved compressive strength, to quite an extent tensile strength is also improved. We
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can also notice that incorporation of colloidal nano-silica and microsilica as partial replacements
of cement have got advantageous effect on overall concrete performance.
REFERENCES:
1. M. Nili, A. Ehsani , and K. Shabani, “ Influence of Nano-SiO2 and Microsilica on Concrete
Performance” proceedings of Second International conference on Sustainable Construction
Materials and technologies on June 28-30,2010.
2. G.QUERCIA AND H.J.H. BROUWERS “Application of nano-silica (nS) in concrete mixtures”
presented in 8th fib Symposium in Kgs. Lyngby, Denmark on June 20 – 23, 2010.
3. V. Bhikshma, K. Nitturkar and Y. Venkatesham “Investigation on Mechanical Properties of High
Strength Silica Fume Concrete” ASIAN JOURNAL OF CIVIL ENGINEERING (BUILDING AND
HOUSING) VOL. 10, NO. 3 (2009) PAGES 335-346
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