I. JASWANTH REDDY (JASHU)

I. JASWANTH REDDY (JASHU)

1.0 INTRODUCTION

Most of the people associate GREEN concrete with concrete that is colored with

pigment.

1.1 Green Concrete Green concrete can be defined as the concrete with material as a partial or

complete replacement for cement or fine or coarse aggregates. Green concrete is taken

to mean environmentally friendly concrete.

1.2 Substitution Material The substitution material can be of waste or residual product in the manufacturing

process. The substituted materials could be a waste material that remain unused, that

may be harmful (material that contains radioactive elements).

1.3 Objective Green concrete should follow reduce, reuse and recycle technique or any two

process in the concrete technology.

The three major objective behind green concept in concrete:

1. To reduce greenhouse gas emission (carbon dioxide emission from cement industry,

as one ton of cement manufacturing process emits one ton of carbon dioxide),

2. To reduce the use of natural resources such as limestone, shale, clay, natural river

sand, natural rocks that are being consume for the development of human mankind that

are not given back to the earth,

3. Use of waste materials in concrete that also prevents the large area of land that is

used for the storage of waste materials that results in the air, land and water pollution.

This objective behind green concrete will result in the sustainable development

without destruction natural resources.

2.0 FEATURES

2.1 Carbon Dioxide emission from Concrete Cement production accounts for more than 6% of all CO2 emission which is a

major factor in the world global warming (Greenhouse gas). There have been a number

of efforts about reducing the CO2 emissions from concrete primarily through the use of

lower amounts of cement and higher amounts of Supplementary Cementitious Material

I. JASWANTH REDDY (JASHU)

(SCM) such as fly ash, blast furnace slag etc. CO2 emissions from 1 ton of concrete

produced vary between 0.05 to 0.13 tons. 95% of all CO2 emissions from a cubic meter

of concrete is from cement manufacturing. It is important to reduce CO2 emissions

through the greater use of Supplementary Cementitious Material (SCM).

2.1.1 Cement

Most of CO2 in concrete is from the cement manufacturing process. A

typical cubic meter of concrete contains about 10% cement by weight. Out of all

ingredients, cement gives out most carbon dioxide. The reaction in the process of

Cement manufacture is:

CaCO3 = CaO + CO2

2.1.2 Aggregate

Use of virgin aggregates contributes about 1% of all CO2 emissions from

a typical cubic meter of concrete. Therefore, the use of alternate aggregate is desirable.

The use of local and recycled aggregates is desirable as it can reduce transportation and

fuel cost and support sustainable development.

2.1.3 Resources

The growing shortage of natural aggregate and sand is another aspect the

construction industry must consider. Construction engineers look for viable alternatives

to natural resources. Use of recycled materials like aggregate, water is some ingredient

which should be encouraged since fresh resources are becoming increasingly scarce.

2.2 Green Concrete Green concrete mix is designed with the principle of "Particle-Packing

Optimization" to meet requirements of plastic and hardened properties. The concrete

which can fall in the category of green must have the following characteristics.

Optimizes use of available materials.

Better Performance.

Enhanced cohesion workability / consistency.

Reduced shrinkage / creep.

Durability - Better service life of concrete.

Reduced carbon footprint.

No increase in cost.

LEED India Certification.

I. JASWANTH REDDY (JASHU)

3.0 MATERIALS Green construction materials are composed of renewable, rather than non-

renewable resources. Green materials are environmentally responsible because impacts

are considered over the life of the product. Depending upon project-specific goals, green

materials may involve an evaluation of one or more of the following criteria.

Locally Available: Construction materials, components, and systems found

locally or regionally, saving energy and resources in transportation to the project

site.

Salvaged, Re-Furnished / Re-Manufactured: Includes saving a material from

disposal and renovating, repairing, restoring, or generally improving the

appearance, performance, quality, functionality, or value of a product.

Reusable / Recyclable: Select materials that can be easily dismantled and reused

or recycled at the end of their useful life.

Recycled materials that the Industry has found to perform favorably as substitutes

for conventional materials include: fly ash, granulated blast furnace slag, recycled

concrete, demolition waste, micro silica, etc.

Generation and use of recycled materials varies from place to place and from time

to time depending on the location and construction activity as well as type of

construction projects at a given site. Following materials can be considered in this

category and are discussed here.

1. Recycled Demolition Waste Aggregate

2. Recycled Concrete Aggregate

3. Blast furnace Slag

4. Manufactured Sand

5. Glass Aggregate

6. Fly ash

They are divided in cement, cementitious material, coarse and fine aggregate.

Their definitions are as usual.

I. JASWANTH REDDY (JASHU)

4.0 COARSE AGGREGATE Aggregate contents have direct and far-reaching effect on both the quality and

cost of concrete. Following source of coarse aggregate are discussed:

4.1 Fresh Local Aggregate

4.2 Recycled Demolition Waste Aggregate

4.3 Recycled Concrete Material (RCM)

4.4 Blast Furnace Slag (BFS)

4.1 Fresh Local Aggregate

Many places there are stone quarry available. Though these may not be of high

quality stone like granite, basalt, Dolomite etc. but they may be of little lower quality.

These can be used in making concrete with the help of appropriate mix design - may be

for lower characteristic strength.

4.2 Recycled Demolition Waste Aggregate Construction industry produces huge waste called demolition waste or MALWA.

The waste contributes to greenhouse gas emissions and thus waste prevention and/or its

recycling will reduce greenhouse gases and methane gas emissions etc.

Therefore, for sustainability of resources, it is necessary that all waste must be

scientifically managed. Waste Management is Collection, Transport, Processing,

Recycling or disposal of waste materials.

I. JASWANTH REDDY (JASHU)

This waste distribution shows that there is about 50% demolition waste in the

dump. In order to have sustainability of resources this demolition waste must be

recycled and used.

4.3 Recycled Concrete Material (RCM) Recycled Concrete Material (RCM), also known as crushed concrete is similar to

demolition waste. It is a reclaimed Concrete material. Primary sources of RCM are

demolition of existing concrete pavement, building slabs & foundations, bridge

structures, curb and gutter and from commercial/private facilities. This material is

crushed by mechanical means into manageable fragments. The resulting material is in

the form of Coarse Aggregate. Comprised of highly angular conglomerates of crushed

quality aggregate and hardened cement, RCM is rougher and more absorbent than its

virgin constituents.

4.4 Blast Furnace Slag (BFS) Blast furnace slag is a waste product from the manufacture of pig iron and

obtained through rapid cooling by water or quenching molten slag. Iron ore, as well as

scrap iron, is reduced to a molten state by burning coke fuel with fluxing agents of

limestone and/or dolomite.

Blast furnace slag is a nonmetallic co-product produced in the process of steel

production. BFS forms when slagging agents (e.g., iron ore, coke ash, and limestone)

are added to the iron ore to remove impurities.

I. JASWANTH REDDY (JASHU)

Air-Cooled Blast Furnace Slag (ACBFS), one of various slag products, is

available when the liquid slag is allowed to cool under atmospheric conditions. Crushed

Air-Cooled Blast Furnace Slag may be broken down as typical aggregate with the help

of processing equipment to meet gradation specifications. Thus, blast furnace slag can

be available as an aggregate as construction materials and acceptable as coarse or fine

aggregate for use in green Concrete.

5.0 FINE AGGREGATE (SAND)

Following source of Fine aggregate are normally used they are discussed here

5.1. Manufactured Sand

5.2. Recycled Glass aggregate.

5.3. Blast Furnace Slag (BFS)

5.1 Manufactured Sand for Concrete Sand is generally obtained from river bed. However, sand can also be

manufactured / produced after crushing stone from rocks.

This process is similar to getting crushed coarse aggregate. Infect after crushing

rock stone for coarse aggregate and sieving it on set of sieves between 40 - 6 mm size,

the remaining portion passing through 6 mm is called stone dust. This can also be said

to be a bi-product of manufacturing coarse aggregate.

Such product / stone dust is generally in cubical form and depend on the type of

rock being crushed and can be called manufactured sand. Cubical sand manufactured

from crushed rock is the most desirable fine material for concrete production.

It is generally accepted that particle shape depends on the rock type, breakage

energy and the type of crusher used. It is also generally accepted that the crushers most

I. JASWANTH REDDY (JASHU)

successful at producing non-flaky aggregates are autogenously (rock on rock) and

vertical-shaft impactor.

If it is produced simultaneously, it saves energy and cost, providing further

economies in the overall production cost. Here, fracture in rock generally takes place

along the rock's natural grain, producing the characteristic cubical shape and surface

texture.

5.2 Recycled Glass Aggregate Glass is formed by super cooling a molten mixture of sand (silicon dioxide), soda

ash (sodium carbonate), and/or limestone to form a rigid physical state.

Glass aggregate is a waste product of recycled mixed glass from manufacturing

and post-consumer waste. Glass aggregate, also known as glass cullet, is 100 percent

crushed material that is generally angular, flat and elongated in shape.

This fragmented material comes in variety of colors or colorless. The size varies

depending on the chemical composition and method of production / crushing.

When glass is properly crushed, this material exhibits fineness modulus &

coefficient of permeability similar to sand. It has very low water absorption.

High angularity of this material, compared to rounded sand, enhances the stability

of concrete mixes. Such material can be easily used in concrete construction as fine

aggregate and give a better cohesive mix which will save on the consumption of cement.

I. JASWANTH REDDY (JASHU)

5.3 Blast Furnace Slag (BFS) Blast furnace slag is described above under coarse aggregate. Here if blast furnace

slag may be broken down as typical fine aggregate also with the help of processing

equipment to meet gradation specifications. Thus it can be available as fine aggregate

also as construction materials and acceptable for use in green Concrete.

6.0 FLY ASH (CEMENTITIOUS MATERIALS)

6.1 Fly Ash Fly ash is a by-product produced during the operation of coal-fired power plants.

The finely divided particles from the exhaust gases are collected in electrostatic

precipitators. These particles are called Fly ash.

Gray to black represents increasing percentages of carbon, while tan color is

indicative of lime and/or calcium content. Fly ash particles are very smooth quite

spherical in shape and range in size from 0.5 m to 300 m.

Fly ash particles at 2,000x magnification (seen through Electron Microscope)

I. JASWANTH REDDY (JASHU)

6.2 Use of Fly ash Fly ash can be used as part replacement of Cement in Concrete. Finer the fly ash,

better is its reactivity and lesser is its water requirement.

Fly ash particles finer than 10 microns get adsorbed on cement particles giving a

negative charge causing dispersion of cement particle flocks, thereby releasing the water

trapped within the cement particle flocks and improves workability.

6.3 Advantages of Using Fly Ash in Concrete

Utilization of fly ash as a part replacement of cement or as a mineral

admixture in concrete saves on cement and hence the emission of CO2

Use of good quality fly ash in concrete has shown remarkable improvement

in durability of concrete, especially in aggressive environment.

Some of the technical benefits of the use of fly ash in Green Concrete are:

1. Higher ultimate strength.

2. Increased durability.

3. Improved workability.

4. Reduced bleeding.

5. Increased resistance to alkali-silica reactivity.

6. Reduced shrinkage.

7.0 MIX DESIGN The concrete mix design method for such concrete is the same as for conventional

concrete.

7.1 Objectives

Optimizes void space between aggregates by optimizing particle proportions and

packing of materials. This makes more effective use of the cement binder.

Aggregates replace excess cement paste to give improved stability, less shrinkage

and increase in strength & durability.

Less cement also generates less heat of hydration.

I. JASWANTH REDDY (JASHU)

The slump of the concrete and its flow are a function of the shape & the quantity

of the predominant size of the aggregate in the mix.

Use of more fine aggregate gives higher slump & flow. So the optimum

proportions of coarse & fine aggregate must be critically found to have the best

and dense concrete in both fresh & hardened stage of concrete.

8.0 ADVANTAGES & IMPROVEMENTS

8.1 Advantages

It will give enhanced cohesion so user friendly - easier to place, compact & finish

concrete. Some other advantages of such mix are:

Optimized mix designs mean easier handling, better consistency and easier

finishing

Reduction in shrinkage & creep

Green Concrete uses local and recycled materials in concrete.

The heat of hydration of green concrete is significantly lower than traditional

concrete

This result in a lower temperature rise in large concrete pours which is a distinct

advantage for green concrete.

I. JASWANTH REDDY (JASHU)

8.2 Improved engineering properties

Mix can result in a reduced paste volume within the concrete structure resulting

in a higher level of protection against concrete deterioration.

Higher strength per kilogram of cement

Increased durability & lower permeability

More aggregates typically mean higher Modulus of elasticity.

Concrete stiffness is an important property of concrete in a reinforced concrete

structure.