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Concrete is the material of present as well as future. The wide use of it in structures, from
buildings to factories, from bridges to airports, makes it one of the most investigated material of the 21st century. Due to the rapid population explosion and the technology boom to cater to
these needs, there is an urgent need to improve the strength and durability of concrete. Out of
the various materials used in the production of concrete, cement plays a major role due its size
and adhesive property. So, to produce concrete with improved properties, the mechanism of
cement hydration has to be studied properly and better substitutes to it have to be suggested.
Different materials known as supplementary cementations materials or SCMs are added to
concrete improve its properties. Nano Silica and steel slag are replacement of materials in
concrete. Of the various technologies in use, Nano-technology looks to be a promising approach
in improving the properties of concrete.
The use of concrete is increasing day by day, so our natural resources get depleted
due to the production of concrete. “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". Nano concrete 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 Nano-tubes, 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.
A long time used material concrete is for the first time fully replaced by a nano maternal.
It is well known 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 operator’s 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
hence to overcome all this above ill-effect of micro silica, nanotechnology was introduced in the
world of concrete.
Nano silica is typically a highly effective pozzolanic material. It normally consists of very fine vitreous particles approximately 1000 times smaller than the average cement particles. It has
proven to be an excellent admixture for cement to improve strength and durability and decrease
permeability Nano Silica reduces the setting time and increases the strength (compressive,
tensile) of resulting cement in relation with other silica components that were tested Nano-silica
is obtained by direct synthesis of silica sol or by crystallization of Nano-sized crystals of quartz.
Fig 1.3: Nano silica
Nano silica is a new Pozzolonic material which is available in water in both solid and liquid
form. In the concrete industry, Nano silica is one of the most famous materials that determine
viscosity and filling state of the concrete. Nano-silica in particular has found wide usage in
construction field because of its high reactivity and very large specific surface area, which
results in a high degree of pozzolonic activity. Nano-silica, further accelerates the dissolution of
C3S and formation of C–S–H with its activity being inversely proportional to the size, and also
provides nucleation sites for C–S–H .Even small additions (0.6 wt. % binder) of NS is very
efficient for the improvement in mechanical properties of cement-based materials. This is
especially pronounced at early ages and for concretes with regular strength grade.
Adding Nano particles in concrete could maintain its strength during physical and chemical
reactions and also compress the particles. From the Nano-indentation studies, it was observed
that the Nano-silica addition significantly alters the proportions of low stiffness and high
stiffness (C–S–H) modification effects of colloidal Nano Silica on cement hydration and its gel
Importance of Nano Silica (NS) Nano Silica (NS) can contribute to efficient 'Particle Packing' in concretes by densifying the
micro and nanostructure leading to improved mechanical and durability properties. NS can
control degradation (through blocking of water entry on account of pore refinement) of the
fundamental binder system of hydrated cement i.e., C-S-H gel caused usually due to calcium
leaching out when immersed in water. NS improves behavior of freshly mixed cement concretes
by imparting segregation resistance and by enhancing both workability and cohesion of the
matrix. Nanotechnology increases the durability of concrete. In other words, it decrease
carbonation risk, penetration of chlorine and so forth.
Benefits of Nano Silica ▲ Low maintenance.
▲ Reduces the thermal transfer rate.
▲ Increases the sound absorption of acoustic absorber.
▲ Increases the reflectivity of glass.
▲ Improves segregation resistance.
▲ Fix micro-cracking.
▲ Low life-cycle cost
Applications of Nano Silica
Application of concrete can be anywhere, both in infrastructure and in buildings. Following are
major applications of NS.
▲ It is added to increase the cohesiveness of concrete.
▲ It is also used to reduce the segregation tendency.
▲ It can be used to produce HPC concrete with high compressive strength, anti-bleeding
properties and high workability.
▲ Nano-silica is used as additive in eco-concrete mixtures.
▲ Nano-silica is applied in HPC and SCC concrete mainly as an anti-bleeding agent.
some explorative applications of NS in high performance well cementing slurries, specialized
mortars for rock-matching grouting and gypsum particleboard can be found, but NS is not used
in practice yet.
1.3. STEEL SLAG:
Global warming and environmental destruction has come forward as a major issue in the
recent years. Started alarming in engineers mind, especially in civil engineers mind. Looking
forward for finding out the solution of these issues and also the use of more and more
environmental- friendly materials in every Industry particularly construction industry is a
paramount importance. Civil engineers start thinking about concrete, which is more dominant
product to be used by civil engineers to make it environmental friendly. One of its part is natural
aggregates which are becoming increasingly scarce, their production and shipment is becoming
difficult for us. Concrete mixture contains supplementary cementations material and admixtures
which forms part of the cementations component. These materials are majority byproducts from
other processes, out of all these materials one of the useful byproduct material is Steel slag. Steel
slag is previously used as aggregate in hot mix asphalt surface applications, but needs to update for additional work to determine the feasibility of utilizing this industrial by-product more wisely
as a replacement for both fine and coarse aggregates in a conventional concrete mixture. The
primary aim of study was to evaluate the Fresh, Hardened, and Durability properties of concrete
made with steel slag aggregates. This study presents result of experimental investigations carried
out to evaluate effects of replacing coarse aggregate with that of slag on various concrete
The Steel slag, a byproduct of steel making, is produced during the separation of molten steel
from impurities in steel making furnaces. This can be used as aggregate in concrete. Steel slag
aggregate generally exhibit a propensity to expand because of the presence of free lime and
magnesium oxides that have not reacted with the silicate structure and that can hydrated and
expand in humid environments. This potentially expansive nature (volume changes up to 10
percent or more attributable to the hydration of calcium and magnesium oxides) could cause
difficulties with products containing steel slag, and is one reason why steel slag aggregate are not used in concrete construction. Steel slag is currently used as aggregate in hot mix asphalt surface
applications, but there is a need for some additional work to determine the feasibility of utilizing
this industrial by-product more wisely as a replacement for both fine and coarse aggregates in a
conventional concrete mixture. Most of the volume of concrete is aggregates. Replacing all or
some portion of natural aggregates with steel slag would lead to considerable environmental
benefits. Steel slag has high specific gravity, high abrasion value than naturally available
aggregate apart from the drawbacks like more water absorption, high alkalis.
Steel slag, a by-product of steel making, is produced during the separation of the molten steel
from impurities in steel-making furnaces. The slag occurs as a molten liquid melt and is a
complex solution of silicates and oxides that solidifies upon cooling. Virtually all steel is now
made in integrated steel plants using a version of the basic oxygen process or in specialty steel
plants (mini-mills) using an electric arc furnace process. The open hearth furnace process is no
longer used. In the basic oxygen process, hot liquid blast furnace metal, scrap, and fluxes, which
consist of lime (CaO) and dolomitic lime (CaO.MgO or "dolime"), are charged to a converter
(furnace). A lance is lowered into the converter and high-pressure oxygen is injected. The
oxygen combines with and removes the impurities in the charge. These impurities consist of
carbon as gaseous carbon monoxide, and silicon, manganese, phosphorus and some iron as liquid
oxides, which combine with lime and dolime to form the steel slag. At the end of the refining
operation, the liquid steel is tapped (poured) into a ladle while the steel slag is retained in the
vessel and subsequently tapped into a separate slag pot. There are many grades of steel that can be produced, and the properties of the steel slag can change significantly with each grade.
Grades of steel can be classified as high, medium, and low, depending on the carbon content of
the steel. High-grade steels have high carbon content. To reduce the amount of carbon in the
steel, greater oxygen levels are required in the steel-making process. This also requires the
addition of increased levels of lime and dolime (flux) for the removal of impurities from the steel
and increased slag formation. There are several different types of steel slag produced during the
steel-making process. These different types are referred to as furnace or tap slag, raker slag,
synthetic or ladle slags, and pit or cleanout slag. Figure 18-1 presents a diagram of the general
flow and production of different slags in a modern steel plant. The steel slag produced during the
primary stage of steel production is referred to as furnace slag or tap slag. This is the major
source of steel slag aggregate. After being tapped from the furnace, the molten steel is
transferred in a ladle for further refining to remove additional impurities still contained within
the steel. This operation is called ladle refining because it is completed within the transfer ladle.
During ladle refining, additional steel slags are generated by again adding fluxes to the ladle to
melt. These slags are combined with any carryover of furnace slag and assist in absorbing
deoxidation products (inclusions), heat insulation, and protection of ladle refractories. The steel
slags produced at this stage of steel making are generally referred to as raker and ladle slags. Pit
slag and clean out slag are other types of slag commonly found in steel-making operations. They
usually consist of the steel slag that falls on the floor of the plant at various stages of operation,
or slag that is removed from the ladle after tapping. Because the ladle refining stage usually
involves comparatively high flux additions, the properties of these synthetic slags are quite
different from those of the furnace slag and are generally unsuitable for processing as steel slag
aggregates. These different slags must be segregated from furnace slag to avoid contamination of
the slag aggregate produced. In addition to slag recovery, the liquid furnace slag and ladle slags
are generally processed to recover the ferrous metals. This metals recovery operation (using
magnetic separator on conveyor and/or crane electromagnet) is important to the steelmaker as
the metals can then be reused within the steel plant as blast furnace feed material for the
production of iron.