Nano Concret
NANO
concrete
|
THOMAS
BRITTO(8807423228)
Thomasbritto3@gmail.com
Abstract
Nanoconcrete is one of the
most active research areas that encompass a number of disciplines including
civil engineering and construction materials, Currently, the most
active research areas dealing with cement and concrete are: understanding of the
hydration of cement particles and the use of nano-size ingredients such as titanium
oxide, silica, carbon nanojubes, and nano- sensors. if cement with
nano-size particles can be manufactured and processed, it will open up a large
number of opportunities in the field of ceramics, high strength composites etc.
it will elevate the status of Portland cement to a high tech material in
addition to its current status of most widely used construction material. The
main objective of this paper is to outline some of the applications of nanotechnology
in concrete and comparing this concrete with the ordinary concrete
Contents
1. Introduction
2. Applications Of Nanotechnology
3. Cuore Concrete Nano Silica
4. Titanium Dioxide
5. Carbon Nano Tubes
6.
Polycarboxylates
7. Nano Sensors
8. Benefits Of Nanotechnology
9. Results And Proof
10. Conclusions
11. References
INTRODUCTION:
"Nano technology is the study of the control of matter on an
atomic and molecular scale. It deals with the size 100 nanometers or smaller,
and involves developing materials or devices within that size".
A long time used material m concrete is for the
first time fully replaced by a nano maternal.
lt
is well known m physics and chemistry that a well designed and developed nano material produces better and cheaper cost results
than traditional materials.
Micro silica
has been one of the world's most widely used products for concrete for over
eighty years. Its properties allowed high compressive strength concretes; water
and chemical resistant concretes, and they have been part of many concrete
buildings that we see nowadays. Its disadvantage, though, has been its relatively high cost and contamination,
which affects the environment and the operators' health. As micro silica, as a powder, is thousand fold
thinner than cigarette smoke. Operators must take special precautions to avoid
inhaling micro silica and not to acquire silicosis, an irreversible
d.sease.hcnce to over come all tese
above ill-effects of micro silica, nanotechnology was introduced in the world
of concrete.
Nanotechnology
and Concrete
Concrete is probably unique
in construction in that it is the only material exclusive to the business and
therefore is the beneficiary of a fa.r proportion of the research and development
money from industry. The following section describes some of the most promising
applications of nanotechnology in construction that are being developed or are
even available today.
Some of the applications of nanotechnology are:
•
Cuore concrete- nano silica
•
Titanium dioxide
•
Carbon nanotubes
•
polycarboxylates
•
Nano-sensors
Cuore concrete nano-silica
Fig – Showing the mixing of nano silica in
concrete
physics,
chemistry and recent
nanotechnology advances, the challenge was fulfilled.Lab tests and production tests proved that
the nano silica did not contaminate
(because its state), but it also produced better results than micro silica, and a litre bottle of the product
was equivalent to a barrel full of micro silica, extra cement and super
plasticizing additives.Silica (SiCte)
is present in conventional concrete as part of the normal mix. However, one of
the advancements made by the study of concrete at the nanoscale is that
particle packing in concrete can be improved by using nano-silica which leads to a
densifying of the micro and nanostructure resulting in improved mechanical
properties. Nano-silica addition
to cement based
materials can also
control the degradation of the
fundamental C-S-H (calcium-silicatehydrate) reaction of concrete caused by
calcium leaching in water as well as block water penetration and therefore lead
to improvements in durability. Related to improved particle packing, high
energy milling of ordinary Portland cement (OPC) clinker and standard sand,
produces a greater particle size diminution with respect to conventional OPC
and, as a result, the compressive strength of the refined material is also 3 to
6 times higher (at different ages). Fly ash not only improves concrete
durability, strength and, importantly for sustainability, reduces the
requirement for cement, however, the curing process of concrete is slowed by
the addition of fly ash and
early stage strength is also low in comparison to normal concrete. With the addition of SiCh nanoparticles part of
the cement is replaced but the density and strength of the fly-ash concrete
improves particularly in the early stages. Research into hematite (Fe20;,) nanoparticles
added to concrete has shown that they also increase strength as
well as offering
the benefit of monitoring stress
levels through the measurement of section electrical
resistance.
Because of its innovation the nano
silica was tested for over a year in the world's largest subterranean copper
mine to prove its long term characteristics. Cuore concrete takes care of the
environment, the concrete and the operators' health. It is the first nano
product that replaced the micro sihca.Cuore concrete surpassed the expectations
of its design and gave concrete not only the high initial and final resistance
but in addition, plasticity, impermeability, minor final cost of work, and
cement savings of up to 40%. Also, it lowered the levels of environmental
contamination
In high compressive strengths concretes
(H-70), Cuore concrete is 88% more efficient than micro silica, added to
concrete and super plasticizers. ( For an average 9,43 Kg. of Cuore
concrete Nanosilica, 73Kg. of all the others additives are used).
The production cost of
is drastically lower than using the traditional production method or formulas.
The cone test shows that
It preserves the cone shape for more than one hour, (with a relation of
H2O/Cement=0.5, adding 0.5% of Nano silica
of the metric volume of the cement used, it conserved a its circle
shape of 60 cm lor two hours, with a
lost of only 5%). The nano silica has
a plasticity that has been compared to the pohcarboxilate technology. Therefore
the use of super plasticizing additives is unnecessary.
• High workability with reduced water/concrete
levels, for example: 0,2.
• Easy homogenization. The reduction of mixing
times allows concrete plants to increase their production
• Depending on the cement and the formulations used for concrete
(tests from value H-30 to H-70), shows that the material provides compressive strengths between 15 MPa and 75
MPa at 1 day; 40 MPa and 90 MPa at 28 days and 48 MPa and 120 MPa at 120 days.
• Nano silica fully complies with ISO 14001
regulations regarding the environment and health. It preserves operators of the
danger of being contaminated with silicosis and does not contaminate the
environment.
It successfully passed all the tests and since the beginning of
this year it is being commercialized in different parts of the world.
TITANIUM
DIOXIDE
Titanium dioxide itself
has no toxicity to microbe and the cell. Only after the irradiation of light
such as fluorescent or UV light, natural mineral Ti02 activates its unique
photo catalytic properties. In the presence of light and humid in the air,
titanium dioxide oxidizes, converts complex organic molecules into water and carbon
dioxide. Photo catalytic power of titanium dioxide successfully destroys
bacteria cell's wall and its membrane, and reacts with cell's components, which inhibits
bacteria's activity and ultimately results
in the death and decomposition of bacteria, thus eliminating bad odours created by a living or
decomposing bacteria and also reduces risk of bacteria spread.
The increase in patents during the last decade indicates a huge interest, especially from Japan and Europe, in the application of Ti02 as photocatalyst
in buildmu materials
Regarding the reduction of air pollution due to traffic in urban
areas, the application on pavement surfaces or on the building surfaces in
cementations materials gives optimal solutions. To increase the efficiency of
the photocatalyst, its presence at the surface of the material is crucial. It
has to be accessible by sunlight to be activated. Consequently, the pollutant
has to be absorbed on the surface and oxidized or reduced to a less harmful
element. The goal is to have as much TiC>2 as possible at the surface of the
material, without the risk of loosing it by abrasion or weathering. Up till
now, the most efficient way to apply the TiC>2 is in a thin layer
cementations material, which is placed on the surface. Application in concrete
tiles is therefore very suitable: the TiOa can be added to the weathering
layer. If the layer is slightly used, new Ti02-particles will be present at the
surface. Other
applications can be found in architectural concrete. The use of white cement with TiCh at the surface of buildings and construction
attribute to the durability of the visual aspect of the building. Due to the
photocatalytic action, the whiteness of the building will remain and dirt will
be washed away more easily due to the hydrophilic properties or will be
decomposed.
Carbon nanotubes
Carbon
nanotubes can be visualized as a modified form of graphite. Graphite is formed
from many layers of carbon atoms that are bonded in a hexagonal pattern in fiat
sheets, with weak bonds between the sheets and strong bonds within them. A CNT
can be thought of as a sheet or sheets of graphite that have been rolled up
into a tube structure. CNT can be single walled nanotubes (SWNT), as if a
single sheet had been rolled up, or multiwalled (MWNT), similar in appearance
to a number of sheets rolled together.
Schematic of a Single
Walled Nanotube
A further type of
nanoparticle, which has remarkable properties, is the carbon nanotube (CNT) and current research is
being carried out to investigate the benefits of adding CNT's to concrete. The
addition of small amounts (1 % wt) of CNT's can improve the mechanical properties of samples
consisting of the main portland cement phase and water.Oxidized multi-walled
nanotubes (MWNT's) show the best improvements both in compresstve strength (+
25 N/rnrm) and flexural strength (+ 8 N/mm2) compared to the
reference samples without the reinforcement. It is theorized the high defect
concentration on the surface of the oxidized MWNTs could lead to a better
linkage between the nanostructures and the binder thus improving the mechanical
properties of the composite rather like the deformations on reinforcing bars.
However, two problems with the addition
of carbon nanotubes to any material are the clumping together of the tubes and
the lack of cohesion between them and the matrix bulk material. Due to the
interaction between the graphene sheets of nanotubes, the tubes tend to
aggregate to form bundles or "ropes" and the ropes can
even be entangled with one another. To achieve uniform dispersion they must be
disentangled. Furthermore, due to their graphitic nature, there is not a proper
adhesion between the nanotube and the matrix causing what it is called sliding.
However, when pre-dispersing the nanotubes with gum arable an increase in the
mechanical properties is achieved, above all
in the case of single walled nanotubes (SWNT's). Additional work is needed in
order to establish the optimum values of carbon nanotubes and dispersing agents
in the mix design parameters.
The cost of adding CNT's to concrete may be prohibitive at the
moment, but work is being done to reduce their price and at such time the
benefits offered by their addition to Lementitious materials may
become more palatable.
Nano-sensors
Strain sensors are an integral part of
mueh of the lab work completed in
structuralengineering. Sensors monitor and quantify the behavior of a test
specimen, and provide insight into the reasons behind the behavior. In
concrete, strain sensors can be broken down into three main categories
•
External strain sensor
•
Strain gage sensor
•
Embedded strain gage
sensor
The most basic category is external strain sensors. These are
attached to the exterior of the specimen and typically record the strain at
that location very accurately. The disadvantage of these sensors is that the
majority of the time the critical location of the specimen is not on the
exterior of the specimen, and therefore, the readings provided by these gages
are only marginally beneficial.
The second type of strain
gage typically used in concrete is a strain gage that is Placed on the steel
reinforcement inside the concrete. These gages can be placed insidethe
concrete, so for many applications they are more useful. However, they can only
be placed in regions where there is steel reinforcement. Also, these gages
provide the strain the steel, not the strain in the concrete.
The third type of strain gage is an embedded strain sensor. These
are gages that are cast into the
concrete and provide readings of the strain in the concrete at their location.
They must be anchored or
bonded to the concrete in order to function properly. They are capable of
providing the strain in the concrete at any location and in any direction.
There arc embedded strain gages that already exist, but they are typically
large and expensi A new material has been developed that has the potential to
be used in tins applicat and this study examines the effectiveness of this
material. This experimental material is produced using a process called
electrostatic self-assembly. The process is completed by building up
alternating layers of positive and negatively charged particles. The material
is formed into a l/8-in.-thick flexible sheet that exhibits the
conductance properties of a metal. This includes changing resistance as the
length is changed. It is this property that makes the material potentially
useful as a strain sensor. If the sensor can be anchored to a specimen and the
resistance of the sensor can be accurately measured, the change in resistance
of the sensor should correspond to the strain in the specimen. The experimental
material is also very durable. It can withstand large strains and is unaffected
by the high pH that occurs in concrete. It is also produced in sheets, so the
sensors can be cut to any size or shape that is required. These properties give
this new material an advantage over existing embedded strain gages.
Immediate
benefits for the user
1)
Cessation of contamination caused by micro silica solid
particles.
2) Lower
cost per building site.
3) Concrete
with high initial and final compressive and
tensile strengths.
4) Concrete
with good workability.
5) Cessation
of super plasticizing utilization.
6)
Cessation of silicosis risk.
7)
High impermeability.
8 ) Reduction of cement using Cuore concrete Nanosilice
9) Cuore concrete nano silica on itself produces nano
cement.
10) During the moisturizing reaction of the
cement, the
silica produces CSIl
particles, the "glue" of the
concrete ensuring the cohesion of all the particles.
11) Cuore concrete has a specific surface near to l,000m2/gr
(micro silica has only 20m2/gr) and a particle size of 5nm to 250 nm.
As a consequence of its size, Cuore concrete produces nano
cristals of CSH, filling up all the micro pores and micro spaces which where
left empty in traditional concrete production. Former described function reinforces
the concrete structure on levels, thousand times smaller then in the ease of
traditional concrete production. This allows the reduction of the cement used
and gives the compression needed to reduce over 90 % of the additives used in
the production of H-70 concrete.
Cuore concrete allows to
save in between 35% and 50% of the used cement.We do stress that we recommend to change the formula of the
concrete in order to take advantage of the characteristics of the Cuore
concrete Nano silica particle.
The results are the proof
1) Resistance
to compression from 40 to 90MPa in 1 day.
2)
Resistance to compression from 70 a 10Q MPa (or more) in 28 days.
3)
Versatile: produces high resistance even with low addition (1 to
1,5 % of the cements weight) and gives self compacting characteristics with
higher proportions (2.5 %).
4)
Meets the norms of environmental protection (ISO 14001).
5)
70% less use of additives as traditional silica, super plast.cizers or traditional Fibres.
6)
Equal or minor raw material cost as in traditional production with
super plasucizers, and or fibres.
Conclusions
•
Well-dispersed
nanoparticies increase the viscosity of the liquid phase, which helps to
suspend the cement grains and aggregates, which, in turn, improves the
segregation resistance and workability of the system.
•
Nanoparticies fill the
voids between cement grains, which results in immobilization of free water
(filler effect).
•
Well-dispersed
nanoparticies act as centers of crystallization of the cement hydrates, which
accelerates the hydration.
•
Nanoparticies favor the
fomiation of small-sized crystals (such as calcium hydroxide)
•
Nanosilica participates
in the pozzolanic reactions, which results in the consumption of calcium
hydroxide and formation of an additional C-S-H.
•
Nanoparticies improve
the structure of the aggregate contact zone, which results in better bond
between aggregates and cement paste.
•
Nanoprticles improve the
toughness, shear, tensile strength
and (lexural strength of concrete.
Reference:
·
R.Z.Ma J.Wu, B.Q. Wei, Liang, and D.H. Wu, Journal Of
Materials Science, 1998, 33, 5243.
·
24, G.D., Zhan, J.D. Kuntz, J. Wan and A.K.
Mukherjee, Nature Materials, 2003, 2,38.
·
Li,
G (2004) “Properties of High-Volume Fly Ash Concrete Incorporating Nano-Si02” Cement
and Concrete Research, Vol.34, p.1043-1049
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