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INTRODUCTION

QUESTIONS & ANSWERS

I. WATER REDUCING ADMIXTURES: 1. BACKGROUND AND DEFINITIONS.

2. THE CHEMISTRY OF WATER REDUCING ADMIXTURES.

3. THE EFFECTS OF WRA ON THE WATER- CEMENT SYSTEM.

4. THE EFFECT OF WRA ON THE PROPERTIES OF ( PLASTIC

&HARDENED ) CONCRETE.

5. APPLICATIONS OF WRA .

II. ACCELERATORS 1. BACKGROUND AND DEFINITIONS .

2. THE CHEMISTRY OF ACCELERATORS .

3. THE EFFECTS OF ACCELERATORS ON THE WATER- CEMENT

SYSTEM.

4. THE EFFECT OF ACCELERATORS ON THE PROPERTIES OF (

PLASTIC &HARDENED ) CONCRETE .

5. APPLICATIONS OF ACCELERATORS

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III. CONCRETE WATER PROOFERS : 1. BACKGROUND AND DEFINITIONS.

2. THE CHEMISTRY OF WATERPROOFERS.

3. THE EFFECTS OF WATERPROOFERS ON THE WATER-

CEMENT SYSTEM.

4. THE EFFECT OF WATERPROOFERS ON THE PROPERTIES

OF ( PLASTIC &HARDENED ) CONCRETE.

5. APPLICATIONS OF WATERPROOFERS .

IV. AIR – ENTERAINING AGENTS 1. BACKGROUND AND DEFINITIONS .

2. THE CHEMISTRY OF AIR-ENTERAINED AGENTS.

3. THE EFFECTS OF AIR-ENTERAINED AGENTS ON THE

WATER- CEMENT SYSTEM.

4. THE EFFECT OF AIR-ENTERAINED AGENTS ON THE

PROPERTIES OF ( PLASTIC & HARDENED ) CONCRETE .

5. APPLICATIONS OF AIR-ENTERAINED AGENTS

V. SPECIFICATIONS & STANDARDS FOR CHEMICAL

ADMIXTURES.

VI. REFERENCES.

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The chemical admixtures business has shown remarkable

growth world wide and has become a major chemical business

with annual turnover of 600 million $ until 1981 and raised to

2 billion $ at 2002.

The increase in the use of admixtures has been reflected in a

greater interest in admixture materials and technology from all

sectors of industry .

The purpose of this guide is to compile into it the available data

on admixtures in order to satisfy the demand of civil engineer ,

consultant . supplier as well as manufacturer .

The types of admixtures of admixtures include in this guide are

water-reducing agents (super plasticizers & retarders ) ,water

proofers , accelerators and air entraining agents .

The practical use of admixtures is a variety of applications as

ready mixed & site batched .etc. are included.

International standards and specifications are to provided.

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QUESTIONS

&

ANSWERS

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Although the terms cement and concrete often are

used interchangeably, cement is actually an

ingredient of concrete. Concrete is basically a

mixture of aggregates, water, admixtures and

cement. The aggregates are sand and gravel or

crushed stone.

Chemical admixtures, like those produced by Axim

are a critical part of the formulation of concrete.

Admixtures can alter the chemical reaction of cement and water

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What is the difference between

cement and concrete ?

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PORTLAND CEMENT is not a brand name, but the

generic term for the type of cement used in virtually

all concrete, just as stainless is a type of steel and

sterling a type of silver. Cement comprises from 10

to 15 percent of the concrete mix, by volume.

Through a process called hydration, the cement

and water harden and bind the aggregates into a

rocklike mass. This hardening process continues for

years meaning that concrete gets stronger as it gets

older.

So, there is no such thing as a cement sidewalk, or a

cement mixer; the proper terms are concrete

sidewalk and concrete mixer

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Admixtures enhance the properties of concrete or

mortar in the plastic state and improve durability in

the hardened state. Admixtures increase the

efficiency of cementitious materials and/or improve

the economy of the concrete mix.

What are the different types of Chemical

Admixtures?

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Why do you use Admixtures in concrete?

Admixtures are defined in following categories:

Air Entraining Agent.

Water Reducers.

Mid-Range Water Reducers.

Superplasticizers or High Range Water Reducers.

Corrosion Inhibitors.

Set Retarders.

Set Accelerators (Chloride / Non Chloride)

An air-entraining agent is a liquid chemical admixture

used to create bubbles that will provide adequate

freeze-thaw protection in concrete by generating 5

to 7 percent of the volume with air of properly sized

and properly spaced bubbles. Air-entraining

admixtures are surfactants, soaps or detergents,

primarily used to generate microscopic size bubbles

that render hardened concrete resistant to the

effects of freezing and thawing. It is also used to

improve the workability/placeability of fresh

concrete.

• Air entraining admixtures meet ASTM C- 260.

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What is an Air Entraining Agent?

A Water-Reducing Admixture is an admixture that

either increase slump of freshly mixed concrete or

mortar without increasing water content or maintain

slump with a reduced amount of water—the effect

being due to factors other than air entrainment.

It is a product that can be used as a water reducer,

plasticizer, workability agent or surface active agent

Water Reducer: a product that will require less

water to maintain in a given slump, results in

reduced w/c ratio and adds improved strength and

durability

Plasticizer: a liquid or dry material that will

facilitate the handling and/or processing of the final

product into which it is blended.

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What is a Water Reducer Admixtures?

Workability agent: normally a liquid material that

will produce a more homogenous mix and will

enhance the placement of concrete

Surface active agent: any compound that reduces

surface tension when dissolved in water—by

reducing the interfacial tension between a liquid

and a solid

Water-Reducing Admixture can, increase strength,

reduce cement and/or all mineral admixtures,

facilitate placeability, improve finishability, maintain

freeze-resistant concrete and increase profitability

and productivity.

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Accelerators are used to reduce the set time of

concrete and increase early strength gain. Although

the mechanism is not fully understood, it is believed

that accelerating admixture increases the reactivity

and hydration of C3S and C2S. The reaction is

catalytic in nature, forming CSH (calcium silica

hydrate) gel and increasing rate of reaction. This

results with increased reaction of Hydrates,

especially at early ages.

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What are Accelerators?

What are Retarders?

Retarders are admixtures that cause a decrease in

the rate of cement hydration and lengthen the time

of setting. Retarders remove the tendency of some

cement to exhibit false set and counter the

accelerating effect of high temperatures. They

improve the workability and the finishability in hot

weather and increase the transporting distance of

the ready-mixed concrete. Retarders help to reduce

the possibility of early dry-shrink cracking and

reduce the maximum temperature rise in mass

concreting, by extending the heat-dissipation

period.

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What are Superplasticizers or High Range

Water Reducers?

Superplasticizers are liquid chemical admixtures

used in concrete because of its ability to perform as

a highly effective wetting agent. Superplasticizers

increase water reduction to achieve low

water/cement ratios, increase strength gain,

increases slump for ease of placement and creates

a denser and more durable concrete.

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Why does concrete crack?

Concrete, like all other materials, will slightly

change in volume when it dries out. In typical

concrete this change amounts to about 500

millionths. Translated into dimensions-this is about

1/16 of an inch in 10 feet (.4 cm in 3 meters). The

reason that contractors put joints in concrete

pavements and floors is to allow the concrete to

crack in a neat, straight line at the joint when the

volume of the concrete changes due to shrinkage.

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Why test concrete?

Concrete is tested to ensure that the material that

was specified and bought is the same material

delivered to the job site. There are a dozen different

test methods for freshly mixed concrete and at least

another dozen tests for hardened concrete, not

including test methods unique to organizations like

the Army Corps of Engineers, the Federal Highway

Administration and state departments of

transportation.

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What are the most common tests for fresh

concrete? Slump, air content, unit weight and compressive

strength tests are the most common tests. Slump is a

measure of consistency, or relative ability of the

concrete to flow. If the concrete can't flow because the

consistency or slump is too low, there are potential

problems with proper consolidation. If the concrete

won't stop flowing because the slump is too high, there

are potential problems with mortar loss through the

formwork, excessive formwork pressures, finishing

delays and segregation.

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Air content measures the total air content in a sample

of fresh concrete, but does not indicate what the final

in-place air content will be, because a certain amount

of air is lost in transportation, consolidating,

placement and finishing.

Three field tests are widely specified: the pressure

meter and volumetric method are ASTM standards

and the Chace Indicator is an AASHTO procedure.

Unit weight measures the weight of a known volume

of fresh concrete.

Compressive strength is tested by pouring cylinders

of fresh concrete and measuring the force needed to

break the concrete cylinders at proscribed intervals

as they harden.

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According to Building Code Requirements for

Reinforced Concrete (ACI 318), as long as no

single test is more than 500 psi below the design

strength and the average of three consecutive tests

equals or exceeds the design strength then the

concrete is acceptable. If the strength tests don't

meet these criteria, steps must be taken to raise the

average.

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How do you control the strength of

concrete?

The easiest way to add strength is to add Cement.

The factor that most predominantly influences

concrete strength is the ratio of water to cement in

the cement paste that binds the aggregates

together. The higher this ratio is, the weaker the

concrete will be and vice versa. Every desirable

physical property that you can measure will be

adversely affected by adding more water. You can

reduce the water/cement ratio by adding Water

Reducing Admixtures or Superplasticizers.

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What is alkali-silica reactivity (ASR)? Alkali-silica reactivity is an expansive reaction between

reactive forms of silica in aggregates and potassium

and sodium alkalis, mostly from cement, but also from

aggregates, pozzolans, admixtures and mixing water.

External sources of alkali from soil, deicers and

industrial processes can also contribute to reactivity.

The reaction forms an alkali-silica gel that swells as it

draws water from the surrounding cement paste,

thereby inducing pressure, expansion and cracking of

the aggregate and surrounding paste. This often

results in map-pattern cracks, sometimes referred to

as alligator pattern cracking. ASR can be avoided

through 1) proper aggregate selection, 2) use of

blended cements, 3) use of proper pozzolanic

materials 4) contaminant-free mixing water and 5)

adding Lithium-Based Admixtures.

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How much does concrete weigh? Fresh concrete weighs about 3900 pounds per cubic

yard using normal weight aggregates. It weighs about

3500 to 3700 pounds per cubic yard when cured.

What is Portland Cement? Portland cement is hydraulic cement produced by

pulverizing clinker consisting essentially of hydraulic

calcium silicates, usually containing one or more of

the forms of calcium sulfate as an interground

addition. Portland cement was first patented in 1824

and is named after the natural limestone quarried on

the Isle of Portland in the English Channel.

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What are the different types of Cement? ASTM C150 (AASHTO M 85)

I. Normal

II. Normal, air-entraining

III. Moderate sulfate resistance

IV. Moderate sulfate resistance, air-entraining

V. High early strength

VI. High early strength, air-entraining

VII. Low heat of hydration

VIII.High sulfate resistance

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What is Fly Ash? Fly Ash is a pozzolan. A pozzolan is a siliceous and/ or

siliceous and aluminous material which in itself is not

cementitious but will, in the presence of moisture and

temperature > 40°F (> 5C), combine with calcium

hydroxide to form cementitious compounds. The

major use of fly ash is as a partial replacement for

cement in concrete. The amount of cement replaced

depends on the fly ash type, the fly ash quality, the

application and the atmospheric conditions.

What is Blast Furnace Slag? It's non-metallic element and consists essentially of

silicates and aluminosilicates of calcium, and of other

bases. It's developed in a molten condition

simultaneously with iron in a blast furnace. Blast

Furnace Slag is cementitious and pozzolanic. It

improves concrete performance

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What is Silica Fume? Silica fume is a by-product resulting from the reduction of

high purity quartz with coal in an electric arc furnace in

the manufacture of ferro silicon and silicon metal.

Silica fume, which has a high content of amorphous

(uncrystallized) silicon dioxide and consists of very

fine spherical particles, is collected by filtering gases

escaping from the electric arc furnaces. Silica fume

helps to improve the compressive strength and to

reduce the permeability of concrete by two methods:

Micro-Filling: Silica fume is an ultra fine material that fills concrete voids and capillary channels.

Pozzolanic Reaction: Silica fume reacts with calcium hydroxide forming more calcium silicate

hydrate gel.

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What is Self Consolodating Concrete? Self Consolidating Concrete (SCC) is concrete that

can flow around reinforcement and consolidate within

formwork under its own weight without additional

effort, while retaining its homogeneity. SCC is different

from traditional concrete and it has high fluidity,

stability and deformability. It has an improved surface

finish and greater durability. SCC was developed in

the late 1980s by Prof. Hajime Okamura at the

University of Tokyo in Japan. AXIM has been a leader

in North America in the development and mix design

of SCC.

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The benefits of SCC include:

Faster pouring rates (+100%)

Labor reduction (-50%)

Reduced post stripping work (-90%)

Increased form life span (+100%)

Improved surface finish

Allow casting of complex shapes

Improved durability

Safer working environment (BRITE-EURAM

project BRPR-CT96-0366)

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WATER

REDUCING

AGENTS

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The water reducing admixtures are the group of products

which has the ability to produce concrete of a given

workability as measured by slump at a lower water-

cement ratio than that of a control concrete without

admixtures.

The earliest known used material was made in 1932 ,

where polymerized naphthalene formaldhyde sulphonate

salts are used . During the mid 1930s – 1940s, the use of

lignosulphonates are increased until 1950s. The hydroxyl

– carboxylic salts were developed. Materials as glucose ,

hydroxylated polymers are used in North America .

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The ( WRA ) allow the reduction of w / c ratio at a given

workability without affecting the setting of the concrete , this

effect can be utilized in three ways :

By addition of (WRA ) with a reduction in the W/C ratio, a

concrete having the same workability as the control concrete

can be obtained, with unconfined compressive strengths at

all ages which exceed those of the control.

If the ( WRA ) is added directly to a concrete as a part of

the gauging water with no other changes to the mix

proportions, a concrete with similar strength development

characteristics is obtained, yet having a greater workability

than the control concrete.

A concrete with similar workability and strength

development characteristics can be obtained at a lower

cement content than a control concrete without affecting the

durability or engineering properties of the concrete.

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The accelerating WRA , whilst possessing the water

reducing capability , give higher strength during the early

hydration period.

The retarding WRA are often of similar chemical

composition to the normal WRA but used a higher

dosage to extend the period of time of workable concrete

for transport , handling & placing .

The air entraining WRA process the ability to entrain

microscopic air bubbles into the cement paste whilst

allowing a reduction in the W/C ratio greater than that

which would be obtained by the air entrainment itself.

They are available in the normal and retarding forms.

The super plasticizers are an extension the WRA they

are formulated from materials which allow much greater

addition to be made ( up to 10 times more )without

producing adverse side effects .they give extreme

workability , considerable reduction in W/C ratio and

very high strength .

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Only five chemical materials form the basis of Water

Reducing Agent (WRA) lignosulphonate hydroxyl

carboxylic acid, hydroxylated polymers formaldehyde

naphthalene sulphonate, formaldehyde melamine

sulphonate salts .

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2.1. LIGNOSULPHONATES: It is a waste liquor formed as a by-product from the process

of paper making pulp from wood . It is a complex mixture of

lignin , carbohydrates (sugar ) and sulphonates by

neutralization , precipitation and fermentation processes

produce a range of lignosulphonates

Commercial lignosulphonates are calcium or sodium based

with sugar of ( 1 – 30 %)

In the formulation of lignosulphonate the following comments

are relevant :

The less pure types entrain air into the concrete , this can be

desirable to enhance durability or cohesion, but is often an

unwanted side effect .thus in the production of normal

WRA and super plasticizers. A small quantity of an air –

detraining agent is added as tri-butyl phosphate (1%), di-

butyl phthalate, borate ester, silicon derivatives and water in

soluble alcohols.

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The lignosulphonate and the air-draining agents added

as tri-butyl phosphate (1%), di-butyl phthalate, borate

ester , silicon derivatives and insoluble alcohols ,

The lignosulphonate and the sugar present do have a

retarding effect on the hydration of cement . Incase of

the higher sugar content , this is utilized to produce

(retarders ). A 15% of tri-ethanol amine is used as an

accelerators to compensate the retarding effect of the

lignosulphonate.

The accelerating WRA are simply calcium chloride or

calcium format with lignosulphonate . typically , 33%

calcium chloride AND 4% calcium lignosulphonate by

weight in water would be used .

Air – entraining WRA can be based on impure ligno-

sulphonates , where only 2-3 % additional air is

required , However this air may not be of the amount,

type & stability required, Therefore the addition of

surfactants as alkyl-aryl sulphonates & fatty acid soaps

are made.

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2.2. HYDROXYCARBOXYLIC ACIDS They are organic chemicals produced from feed stocks

generally , the sodium salt is used approximately 30 %

solution of the salt is used at low dosage as normal WRA

and at high dosage as WRA and retarder and if blended

with calcium chloride it procedures accelerator WRA also

air entraining agent can be added.

The hydroxcarboxylic acid are not used in super–plasticizers

because of its considerable retarding influence at high

dosage .

2.3. HYDROXYLATED POLYMER They are derived from natural polysaccharide as corn

starch .

They do impart a retardation , which can be overcome by

adding small of calcium chloride or tri-ethanol amines .

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2.4. NAPHTHALENE FORMALDHYDE

SULPHONIC ACID SALTS The material is produced from naphthalene by oleum

Sulphonation. Subsequent reaction with fomaldhyde leads to

polymerization and the sulphonic acid is neutralized with

sodiumhydroxide.

The commercial type leads to air entrainment , so it is

necessary to add air – detraining agents such as tri-butyl

phosphate and di-butyl phthalate.

This type is used to produce the super plasticizer because it

is possible add large amounts to increase workability &

reduce w/c ratio .

2.5. MELAMINE FORMALDHYDE SULPHONATE SALTS

It is prepared by normal resinification.

It is used as sole ingredient in super plasticizers and also it

can be blended with lignosulphonates and hydroxyl-carboxylic

acids.

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The WRA operate by chemically reacting through their

acidic and hydroxyl functional groups with

predominantly the early hydration products of C3A

and C3S to form a monomolecular layer of admixture

at the water –cement interface . This layer will be

associated with a sheath of water molecules to form

a total barrier which will prevent close approach of

cement hydration particles and reduce the Vander

Waals forces of attraction . thus the interparticle

friction is reduced so that the energy required to

induce follow into the system is reduced

An alternative is that the adsorbed molecules retain

their ionic nature resulting in initial repulsion of the

particles .

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The presence of WRA at the surface depending

on the force between the admixture and the

surface will impose an additional barrier to the

diffusion of hydration products , therefore

increasing the length of dormancy period.

The introduction of competitive material for sites ,

particularly on the ( C3A) phase , the reaction of

(C3A ) and gypsum are slightly modified at early

stages , although the overall products of reaction

are similar.

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Concrete passes through a number of stages the initial plastic state subsequent to the mixing process and the later plastic state when the concrete may be transported , handled and placed , the hardened state usually at 28 days and the subsequent hardened state is during the life of the structure .

4.1. PLASTIC CONCRETE

4.1.1. AIR ENTRAINMENT Where the (WRA ) has been added to produce a

concrete of high workability , for those materials which result in an increase the air content , approx. 1% or more , will result the presence of entrained air will reduce the density in the plastic stage.

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4.1.2. WORKABILITY

The hydroxyl carboxylic type is superior to the ligno-sulphonates in increasing the value of slump (workability).

The higher dosage of WRA or super plasticizer the increasing in workability is more dramatic. In addition, a considerable retardation is obtained a case of WRA.

4.1.3. WATER REDUCTION :

The amount of water reduction depend on some factors as aggregate/cement ratio , where ligno-sulphonates are preferred than hydro-carboxylic acid and hydroxylated polymers types for the lower cement content (high aggregate / cement ) ratio .

The WRA are most effective at an aggregate / cement ratio between ( 6.5 – 7.0 ).

Another factor affecting water reduction is designed workability since the higher the required workability , the greater is the reduction in w/c ratio at the presence of WRA.

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4.1.4. SETTING CHARACTERISTICS OF FRESH CONCRETE The WRA will extend the time available for transport ,

placing and finishing of concrete.

4.1.5. THE STABILITY OF FRESH CONCRETE The stability of concrete mix is ( cohesion ) which is used

to describe its ability to maintain a homogenous appearance under stress.

Lack of cohesion leads to segregation of the mixture into layers Relevant to their densities.

Another term is related to stability is bleeding which is movement of water to the surface of fresh concrete .

When a WRA is used to produce a high strength concrete with a low w/c ratio , the concrete appears to be cohesive.

It is possible to achieve high workability without a loss in cohesion by the use of WRA.

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4.1.6. MIX CONSIDERATIONS : There is no necessity to make change to the mix

design from that produced of concrete of low initial low slump when WRA are used.

No change in mix designed if WRA are used to decrease W / C ratio.

Type of aggregates do not affect the performance of the WRA.

Change of cement type affect the performance of WRA as in ( sulphate resistant cement ) with low C3A , an increase in retardation occur also expansive properties with cements in the presence of WRA are reduced.

Pozzolans as fly ash and silica fume are behave normally with WRA.

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4.2. HARDENED CONCRETE

4.2.1. STRUCTURAL DESIGN PARAMETERS: The most important properties of concrete used in

calculations for load – bearing applications are the compressive strength , the tensile strength and the modulus.

The permeability or the porosity of concrete used in water retaining structures is also important and to be considered.

4.2.2. COMPRESSIVE STRENGTH The compressive strength at 28 days of concrete

containing WRA is a function of W / C ratio. No special considerations has to be taken into account for design purposes as far as 28 day compressive strength is concerned .

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4.2.3. TENSILE STRENGTH WRA will not alter the relationship between the

compressive strength and the tensile & the flexural strengths.

4.2.4. MODULUS OF ELASTICITY : There is no apparent difference between concrete

containing (WRA ) and control concrete.

4.2.5. PERMEABILITY OR POROSITY : The permeability is a guide to concrete durability

Gross porosity is due to continuous passages in the concrete , due to poor compaction or cracks which can be minimized by the use of WRA.

WRA can reduced the W/C ratio so ensuring that the permeability is kept minimum thus concrete with W/C ratio of 0.4 will be almost impermeable.

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4.2.4. MODULUS OF ELASTICITY :

There is no apparent difference between concrete

containing (WRA ) and control concrete.

4.2.5. PERMEABILITY OR POROSITY :

The permeability is a guide to concrete durability

Gross porosity is due to continuous passages in

the concrete , due to poor compaction or cracks

which can be minimized by the use of WRA .

WRA can reduced the W/C ratio so ensuring that

the permeability is kept minimum thus concrete

with W/C ratio of 0.4 will be almost impermeable .

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4.2.6. DURABILITY ASPECTS

The durability of concrete is the ability of material to maintain its structural integrity , protective capacity and aesthetic qualities over a prolonged period of time .

Concrete durability can be considered in terms of the following properties .

4.2.6.1. RESISTANCE TO AGGRESSIVE LIQUIDS

It is recognized that the lower the W / C ratio and the use of WRA leads to an improvement in sulfate resistance and sea water attack. .

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4.2.6.2. RESISTANCE TO FREEZE – THAW CYCLING :

Concrete is damaged by free – thaw conditions due

to the expansion of water in the voids on freezing to

form ice , this leads to loss of strength , loss of

modulus , unacceptable view and possibility of

corrosion .

W/C ratio reduction will be beneficial in enhancing

the durability under these conditions .

The use of WRA enhance resistance to freeze .

thaw cycling ,specially in the presence of pozzolan

because the substitution of the cement by

pozzolan resulted in a reduction in freeze-thaw

resistance.

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4.2.6.3. PROTECTION OF STEEL REINFORCEMENT One of the prime function of concrete in load-bearing

structure is to protect steel reinforcement incorporated

to increase the tensile strength . If exposed to air and

water steel rust result in expansive force so that the

concrete fails in tension causing breaking of concrete .

WRA help to reduce W/C ratio to prevent the ingress

of water and minimum cover over the steel is specified.

Some factors should be considered when studying the

role of concrete protection to steel reinforcement

including concrete permeability , chemical attack on

the reinforcement and reinforcement bond .

WRA as lignosulphonate enhance the passivation of

the steel and counteract the effect of calcium chloride .

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4.2.6.4. GAIN IN COMPRESSIVE STRENGTH

Testing for strength at ages to 50 years , indicates

that the use of WRA have no significant effect on

loss of strength or decrease in the gain strength .

4.2.6.5. VOLUME DEFORMATION:

The volume deformation of concrete is shrinkage,

which occurs under drying conditions, and creep

which is the additional deformation obtained under

an applied stress.

Shrinkage and swelling and creep properties are

increased by the addition of WRA .

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5. APPLICATIONS OF WRA

Ready mixed concrete .

High strength concrete ( precast & pre-stressed).

Large pours and retarded concrete .

Slip forming .

High workability mix .

Piling

Tilt –up construction .

Pumping.

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Concrete accelerators increase the rate of hardening of cement and concrete mixes.

The major material used is calcium chloride since 1885 and mainly in cold weather.

Chloride-free accelerators are replaced calcium chloride in reinforced concrete to avoid steel corrosion.

This category includes calcium chloride ,calcium formate and tri – ethanol amine.

2.1. CALCIUM CHLORIDE : It is produced as by –product of solvay process

for sodium carbonate production . for use as an accelerator it is supplied as a 33-35 % solution.

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2.2. CALCIUM FORMATE : It is a by-product in the manufacturing of polyhydric

alcohol.

It is obtained as a fine powder and used as an accelerators in The same form since it is low soluble in water (15%).

2.3. TRI-ETHANOL AMINE : It is produced from reaction of ammonia and ethylene

oxide it is oily ,water soluble liquid .

It is used normally with other admixture formulation

3.1. RHEOLOGICAL EFFECT :

Most accelerators don not significantly alter the

rheological of cement paste at early stages . the quicker

stiffness of accelerated pastes will result in higher

viscosities at a later age .

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3.2. CHEMICAL EFFECTS :

3.2.1. CALCIUM SALTS :

There does not appear to any reaction between

calcium chloride and C2S OR C3S .

Calcium chloride react with C3A and gypsum to

form calcium tri-sulpho aluminate ( ettringite )

and calcium aluminate .

The reactions occurring with calcium nitrate ,

formate, thiosulphate are the same as calcium

chloride .

3.2.2. TRI-ETHANOL AMINE :

It is not effective when used a lone , but it is

used as an ingredient in some admixture mixes

In the presence of ( TEA ) the reaction between

C3A and gypsum is accelerated

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3.3. EFFECTS ON CEMENT HYDRATION :

Calcium chloride is a more effective accelerators

than the others .

All the materials accelerate reaction of C2S and

C3S phase hydrations.

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4.1. PLASTIC CONCRETE

Accelerators have no effect on the workability , air content , mix stability or W/R ratio .

The only properties of plastic concrete which are affected the heat evolution and setting time.

4.1.1. EFFECT ON HEAT EVOLUTION : The heat evolution of concrete mixes containing

accelerators is increased than mixes with no admixture .

4.1.2. EFFECT SETTING TIME : Accelerators reduce both initial and setting time.

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4.2. HARDENED CONCRETE:

4.2.1. COMPRESSIVE STRENGTH :

The compressive strength of concrete containing

an accelerator will have a higher 28 days

compressive strength than that of plain concrete

with the same composition. The difference is

greater at lower temperatures .

4.2.2. FLEXURAL, TENSILE STRENGTH & MODULUS OF ELASTICITY :

No effect on all the three properties .

4.2.3. DURABILITY ASPECTS : Since the degree of hydration in the case of

accelerator addition will be increased and the

larger volume of hydration initially increased and

the larger volume of hydration products leads to

reduce the permeability ,

The porosity of concrete is increased at later ages .

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The resistance of concrete containing

accelerators to the attack by aqueous sulphate

is reduced .

concrete containing accelerators develops

strength more rapidly and therefore has a

greater resistance to freeze . thaw cycles this will

be reduced at later ages .

In will design compacted concrete , the addition

of up to 1.5 % calcium chloride (accelerators ) by

the weight of cement can be used without

corrosion of steel reinforcement , but excessive

dosage of calcium chloride with concrete of high

porosity can lead to corrosion. other types of

accelerators as calcium formate does not have

an effect on the steel .

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The use of accelerators shorter the set time and

increase the early strength of concrete .

The benefits of an increase in strength gain are,to

permit earlier removable of forms , to reduce

curing period , to compensate time when the

strength may used , to advance the time when the

structure may be used and to compensate for

the slower hydration of cement at low

temperatures .

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P R O K E M

WATER

PROOFERS

61

Concrete waterproofers are integral admixtures

which alter the surface of concrete to be a water

repellent or less wettable .

This water repellency is effective in preventing

water from entering the surface when pressure is

small as rain fall .

In water – retaining structures or basements the

hydrostatic pressure is high , so these materials

are not be beneficial

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These materials are able to form a thin hydrophobic

layer within the pores, voids and on the surface of

concrete in one of three ways:

Reaction with cement hydration products such

as liquid fatty acids (Oleic acids, Capric ). Stearic

acid can be added directly to the mix in powder

form or as an emulsion in water. Butyl stearate is

also added as an emulsion.

Materials which coalesce on contact with cement

hydration products as wax exulsions ( wax with

melting point 57 – 60°C are used with emulsifying

agents based on Sorbitan mono stearates).

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Finally divided hydrophobic materials as calcium

and aluminum stearates is widely used in the

precast concrete industry. Inert materials such

as hydrocarbon resins and coal tar pitches in

fine powder form are claimed to maintain their

ability to produce hydrophobic surfaces. They

would typically be ground to pass the 200

micron sieve.

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Wax emulsions cause considerable reduction in

bleeding .

Waterproofers do not have any effect on the setting

charcteristic of the hydration products of cements.

Waterproofed concrete should not show significant

uptake of surface water in condition of rain, but on

prolonged exposure some wetting occur because of

the defects in hydrophobic layer and the presence

of voids.

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4.1. PLASTIC CONCRETE

Waterproofers admixtures have no affect on the

properties of plastic concrete as workability and

mix design .

4.2. HARDENED CONCRETE

Waterproofers admixtures do not affect the strength

of concrete at 28 days unless a WRA are used , wax

emulsions give a slight air entraining approximate

4% by volume .

There are no indicator that wateproofers would alter

the stiffness of concrete (modulus of elasticity ).

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It is necessary to add sufficient amount of

waterproofers so that the absorption of surface

is reduced.

Volume change as shrinkage is not affected on

single drying but under drying and wetting cycling

the shrinkage will reduced.

No improvement in resistance to attack by

aggressive gases and liquids are obtained.

Watertight concrete .

Architectural concrete.

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P R O K E M

AIR

ENTRAINING

AGENTS

68

The air-entraining admixtures are organic materials

in liquid from which when added to the gauging

water entrain a controlled amount of air in a

uniform microscopic bubbles, this is not entrapped

air which is often present in concrete in irregular

shaped cavities due to inadequate compaction or

flaky aggregates .

Since 1939, an air – entrained concrete was

produced for more durable roads because it was

found that (4-10%) by volume air entrainment

make the concrete withstand freeze –thaw cycling .

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The presence of a small amounts of entrained air (2

– 4 %) by volumes leads to improvement in

cohesion and stability .

A reduction in sand content can be made when air

is entrained without loss of cohesion and this leads

to reduction in W/C ratio to minimize the effect on

compressive strength .

Air entrainment can be increased up to 30% by

volume , to lower the density, enhance the thermal

insulation properties or to produce a light weight

concrete in conjunction with light weight aggregates.

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Different chemical surfactants are suitable as :

Fatty acids salts.

Alky - Aryl Sulphonates (anionic).

Phenol ethoxylates (non-ionic ).

Abietic and pimeric acid salts (anionic).

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The air entrained admixtures increase the

viscosity of the cement pastes.

An increase in the w/c ratio of the cement pastes

leads to greater air entrained and decrease in the

specific surface area of bubbles.

The effect of temperature is not great on the air

entraining capacity in a cement paste.

The air entraining admixtures does not affect the

hydration product of cement .

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4.1. PLASTIC CONCRETE Most air entraining agents are formulated to give

(3-6 %) by volume air. The greater the quantity of air-entraining agent added , the larger will be the volume of air entrained.

1% of entrained air will be lost by mixing for up to 30 minutes.

The fineness of cement is a major factor in deter-mining the quantity of air – entraining agent required to incorporate a given amount of air .

The amount of entrained air decreased with increasing the cement content .

Increase in alkali content minimize the amount of air – entraining agent .

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More workable mix entrain more air than a less

workable mix. For very workable mix ( slump >

180 mm ) the air will be lost before placing

The higher the temperature of concrete , the lower

the air content .

Coarse aggregates does not affect the amount

of air -entrained .

The amount of air – entrained increases with an

increase in fine aggregates (sand ) content .

The addition of (WRA) as lignosulphonates gives

a reduction of 50 – 60 % in the quantity of air-

entraining agent .

In order to minimize air losses, air-entrained

concrete should be compacted with minimum

vibration .

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The presence of air-content results in an increase

in the workability of concrete.

Reduction in water concrete is dependent on the

amount of air –entrained and the cement content.

When fine fillers as fly ashes is included in the

mixed design , the amount of air – entraining must

be increased.

A reduction of 50- 69 % in the quantity of air-

entrained agent can be in case the mix. Contains

WRA.

In order to minimize air losses , air – entrained

concrete should be compacted with minimum

vibration ( 5 – 15 minutes ) is enough.

The presence of air-entraining agents results in

an increase in the workability of concrete . An

increase in slump from 12 mm to 50 mm.

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The presence of air –entraining agent makes the

concrete more cohesive, reduce the segregation

and bleeding allows a reduction in fine aggregates

4.2. HARDENED CONCRETE The entrainment of air in concrete leads to a

reduction in both compressive and flexural

strength .

The entrainment of air in concrete does not alter

the relation between compressive strength and

modulus of elasticity of plain concrete .

The permeability of concrete to aqueous liquid

is reduced and the resistance to attack by

sulphate solutions is improved by the addition of

air-entraining agents .

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The resistance of concrete to freeze-thaw cycling in the presence of air-entraining agent is improved particularly in the presence of de-icing salts .

The air-entrained concrete should provided a better reinforcement protection on the long term .

Air-entrained concrete has tendency to lose moisture under dry conditions , which means that air-entrained concrete should develop strength more than plain concrete .

Air entrainment do not increase drying shrinkage of concrete.

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Hydraulic structure such as dams , tunnels and

canals .

Aircraft ways & carriage ways .

Precast concrete and light weight concrete.

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:

The manufacture must supply the following

information :

Identification of admixture by name , type

Details of acceptance and uniformity .

Details of any certification

Recommended dosage ( normal & maximum )

Effects of both under and over dosage .

Effect on air content , setting or color of

concrete .

Instructions for transport & storage .

Instructions for use and safety .

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Physical state .

Chloride content.

Sugar content .

Composition including type of main active

ingredient .

Any known in compatibility with other

concrete constituents

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Standards conditions stipulations about labelling

The following items to be marked :

Quantity .

Maximum storage life .

Identify of production lot ( batch number , date and location of manufacturer

Endorsement of conformity to standard as approval .

Number of relevant standard .

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Standards now require admixtures to meet

performance requirement in concrete . The

following characteristics must determined :

Water reduction or water content .

Air content .

Bleeding .

Setting time .

Compressive strength .

Tensile strength .

Shrinkage .

Freeze –thaw resistance .

Consistency ( at same W/C ratio ) .

The cost of testing should be balanced against the benefit of increased assurance.

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CHEMICAL ADMIXTURES FOR CONCRETE,

3RD EDITION.

AMERICAN SOCIETY FOR TESTNG AND

MATERIALS.

CANDIAN STANDARDS ASSOCIATION

BRITISH STANDARDS INSTITUTION .

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