MALA NAGARAJU SUPPORTING, Thesis for Geology
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MALA NAGARAJU SUPPORTING, Thesis for Geology

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INTRODUCTION

1.1 GENERAL

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.

1.4 Nano-silica

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

property.

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.

▲ Corrosion-resistance.

▲ 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

properties.

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.

ORIGIN

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.

Figure 1

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