3. cement replacement materials lecture

7/28/2019 3. Cement Replacement Materials Lecture

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Cement Replacement

Materials

Concrete Technology


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Learning Outcome

To evaluate the properties of concreteconstituent materials.


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What are cement replacement

materials? Cement replacement materials (CRM) are some

kind of mineral admixtures.

Mineral admixtures are finely divided siliceous

materials which are added to concrete in relatively

large amounts, generally in the range 20 to 70

percent by mass of the total cementitious material.


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Why CRM?

The concrete industry is the largestconsumer of virgin materials such assand, gravel, crushed rock, and freshwater.

It is consuming Portland and modifiedPortland cements at an annual rate ofabout 1.6 billion metric tons.

The cement production consumes vastamounts of limestone and clay besidesbeing energy-intensive.


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Why CRM?

Obviously, large amounts of energy and materials, in

addition to financial resources, are wasted when

structures deteriorate or fail prematurely which, in fact,

has been the case with many recently built reinforcedconcrete bridge decks, parking garages, and marine

structures throughout the world.

Traditionally, most concrete structures are designed

for a service life of 50 years.

With the advent of high-performance concrete

mixtures, some structures are now being designed and

built for a service life of 100 years.


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Why CRM?

In the long run, sustainable development of the

concrete industry will not take place until we are

able to make even more dramatic improvements in

our resource productivity.

In this context, it should be noted that the Factor

Ten Club, a group of scientists, economists and

business people have made a declaration that,

within one generation, nations can achieve atenfold increase in their resource productivity

through a 90% reduction in the use of energy and

materials.


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Major effects of CRM on

properties of concrete


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Types and Classification

Natural materials

Natural materials have been processed for the sole

purpose of producing a pozzolan. Processing usuallyinvolves crushing, grinding, and size separation; in

some cases it may also involve thermal activation.


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Industrial by-products

By-product materials are not the primary products of the

industry producing them. Industrial byproducts may or may not

require any processing. Some of the byproducts are:

Fly ash (pulverized fuel ash) FA or PFA is the ash from

pulverized coal used to fire in power stations

Ground granulated blast furnace slag (ggbs); slag from scum

formed in iron smelting in a blast furnace, ground to a powder

Condensed silica fume; sometimes called micro-silica;

very fine particles of silica condensed from waste gases given

off in production of silicon metal


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Natural Pozzolan

Except diatomaceous earth, all natural pozzolan are

derived from volcanic rocks and minerals. Duringexplosive volcanic eruptions quick cooling of the

magma, which is composed mainly of aluminosilicates

results in the formation of glass or vitreous phases

with disordered structure.

Agricultural wastes

Rice husk ask

Oil palm ash


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What does it mean by pozzolanic

materials?A pozzolanic material is one which

contains active silica (SiO2) and is not

cementitious in it but will, in a finely dividedform and in presence of moisture,

chemically reacts with calcium hydroxide at

ordinary temperatures to form cementitious

compoundsPozzolanic reaction (Secondary reaction)

S + CH + H C- S - H


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Pozzolanic Reactivity Index

The applicability of pozzolanic materials used

as admixtures in cement technology is

determined by the so-called pozzolanicactivity.

This pozzolanic activity is strongly related to

the amount of active components, such as

SiO2 and Al2O3 available in reaction withcalcium hydroxide formed as a result of

calcium silicate hydrolysis .


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Pozzolanic Reactivity Index

The calcium silicates, as it is commonly known, arethe main constituents of Portland cement. Pozzolanicactivity of materials depends generally on the activesilica content.

In cement paste this active silica dissolves andprecipitates in the form of calcium silicate hydrate, so-called CSH phase.

Thus the calcium hydroxide content in cement pastedecreases, as a result of calcium ions consumption byadditional silica.

Cement pastes produced with pozzolanic admixturesshow fairly good strength, long-term durability andcorrosion resistance.


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Determination of pozzolanic

reactivity indexDirect Methods

They are based on the measurement of

the amount of lime reacted Compressive strength

Thermal method

Accelerated chemical method

Indirect Method

Conductometric technique


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Fly Ash, FA


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Fly Ash: Classification


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Low Calcium Fly Ash


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High Calcium Fly Ash


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Fly Ash Microstructure


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Fly Ash Particle Size


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Ground granulated blast

furnace slag, GGBS


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Ground granulated blast

furnace slag, GGBS


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Silica fume


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Silica fume


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Rice husk ash, RHA


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Rice husk ash, RHA


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Metakaolin


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Thank You

3. cement replacement materials lecture

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