SUBJECT: CONCRETE TECHNOLOGY

UNIT-1 :- INTRODUCTION

1.1 Concrete Technology: The science of concrete which deals with fundamental principles,

terminology, description and uses of concrete is called concrete technology.

1.2 Importance of concrete technology

1. It helps to understand the significance of concrete as a construction material.

2. It helps in understanding the properties of concrete in fresh and hardened state.

3. It guides the engineers to supervise the jobs performed with concrete.

4. It guides the engineer to repair and maintain the existing concrete structures.

5. It helps the engineers to understand the importance of all the concrete operations and

significance.

1.3 Definition of concrete: concrete is a binding material which is a mixture of cement, fine

aggregates, coarse aggregates and water, which is poured into moulds to obtain stone like mass.

1.4 Properties of concrete:

The characteristics or quality which deals with the study of behavior of concrete is known as

properties of concrete. Properties of concrete are divided into two stages:-

Properties of concrete in plastic stage

Properties of concrete in hardened stage

1.5 Uses of concrete in comparison to other building materials

Requirement of good concrete

The aggregates (fine and coarse) must be clean, hard and durable.

It should have good workability so that all operations can be performed satisfactory.

It should be compact and dense

It should be durable so that weathering agencies have least effect on them.

Water cement ratio should accurate.

Concrete should from homogeneous mixture.

It should be fire resistant.

It should have minimum shrinkage.

It should be impermeable.

It should be economical.

1.6 Classification of concrete

1. depending upon the binding material

2. depending upon the purpose

3. depending upon the design

1. Depending upon the binding material: Binding materials are provided in concrete to bind

the fine and coarse aggregates. Depending upon the binding material is used; the concrete can

be classified as under:

a. Cement concrete: cement is used as binding material in cement concrete. Cement binds

the fine and coarse aggregates in presence of water.

b. Lime concrete: hydraulic lime is used as a binding material in lime concrete to bind the

fine and coarse aggregates in the presence of water

2. Depending upon the purpose

a. Vacuum concrete: the cement concrete from which after entered air and excess water are

removed after placing it in position by suction with a vacuum pipe is called vacuum

concrete.

b. Air –entered-concrete: the cement concrete prepared by mixing aluminum in it is called

air –entered- concrete

c. White and colored cement: the concrete in which white is used as binding material is

called white cement

d. High –early strength: the concrete in which high early strength cement is used as a

binding material is called high-early strength.

e. Light weight concrete: the concrete prepared by using coke breeze, sinder or slab as

aggregates as light concrete

3. Depending upon the design: Based upon the design of concrete, it can be classified into

three categories:

a. Plain cement concrete (PCC): The cement concrete containing no reinforcement is

called plain cement concrete.

b. Reinforced cement concrete (RCC): The cement concrete in which the reinforcement is

embedded for taking tensile, excessive, compressive, or shearstressive.

c. Prestressed concrete: The cement concrete in which high compressive stresses are

artificially induced before its actual use is known as prestressted concrete

1.7 Advantages and Disadvantages of concrete

Advantages:

1) Concrete possesses a high compressive strength.

2) Green concrete can be easily handled and molded into any shape or size

3) It is fire resisting.

4) It is durable and requires very little maintenance.

5) The strength of concrete increases with age.

Disadvantages:

1) Concrete has very low tensile strength and hence cracks easily.

2) dead weight of concrete is very less high hence require strong shuttering

3) Concrete expands and shrinks with change in temperatures.

4) It needs more time for curing to develop strength.

5) concrete under sustained loading undergoes creep

UNIT-4 :- PROPERTIES OF CONCRETE

4.1 Properties in plastic state: Workability, Segregation, Bleeding and Harshness

Workability: workability is an important property of concrete in its plastic stage. The

diverse requirement of mix ability, stability, transportability, place ability, mobility,

compatibility and finish ability of concrete mentioned above are collectively referred to

as workability.

Harshness: Harshness is an undesirable property of concrete mix in plastic stage. The

concrete mix which causes difficulty in obtaining a smooth finish with certain amount of

toweling is known as harsh mix.

Causes of harshness:

i. It is due to excess of middle sized particles.

ii. It can be due to the deficiency of fines of fill the voids in coarse aggregates.

Prevention of harshness: Harshness can be reduced to a great extent by providing

sufficient proportion of mortar to fill the voids in coarse aggregates.

Segregation: The separation of coarse aggregates from the concrete mix in plastic stage

is termed as segregation

Causes of segregation

i. Concrete is a homogenous mixture of materials of different specific gravities .so, there is

always a tendency for the coarser and heavier particles to settle down and for lighter

particles to rise to the surface.

ii. When there is too much of water in the mix.

iii. When the aggregates are poorly graded.

Prevention of segregation

i. All the concrete operations must be strictly supervised.

ii. Optimum amount of water must be used for mixing.

Bleeding: The appearance of water, along with fine particles, on the surface of freshly

placed concrete after compaction is known as bleeding.

Causes of bleeding

i. Due to presence of excess of water.

ii. Due to deficiency of fine aggregates.

Prevention of bleeding

i. By properly designing the water cement ratio.

ii. By controlling the amount of compaction.

4.2 Factor affecting workability

Workability of a concrete mix is dependent upon following factors:-

i. Water content: Workability of a concrete is greatly affected by the amount of water

added in a mix. Workability increases with increase in water content on account of

greater lubrication. But too much water results into concretes of low strength and poor

durability.

ii. Grading of aggregates: The grading of aggregates have a considerable effect on

workability of concrete. It plays a vital role when lean concrete mix of high workability is

required. For the lean concretes, the grading should be continuous, where as for rich

mixes the grading should be coarse.

iii. Shape of aggregates: shape of aggregates have great influence on the workability of

concrete mix. Workability increases with round shaped aggregates where as angular and

rough aggregates reduce workability.

iv. Size of aggregates: Workability with increases in the size of aggregates. Large sized

particle offer less surface area as compared to surface given by smaller size particles

hence for same degree of workability, less water is required for large size aggregates and

they contribute to the improvement of workability of concrete mix.

v. Temperature: Environmental condition greatly affects the workability of concrete mix.

Among all the workability of a concrete mix is affected with change in temperature. On a

hot day, it becomes necessary to increase the water content of the mix in order to

maintain the desired workability. The amount mixing water, required to being a desired

change in workability, also increases with temperature.

vi. Porosity of aggregates: Porous and dry aggregates require more water than non porous

and saturated aggregates. For the same degree of workability, non-porous and saturated

aggregates give better workability

vii. Mixing time: Mixing of ingredient of concrete should be carried out for at least 2

minutes. As the mixing time is increased up to certain limit, the workability increases.

4.2.1 Measurement of workability: slump test, compacting factor and Vee Bee consist

meter

Concrete slump test for workability

Concrete slump test is to determine the workability or consistency of concrete mix prepared at

the laboratory or the construction site during the progress of the work.

equipment required for concrete slump test

The mould for the test is in the form of the frustum of a cone having height 30 cm, bottom

diameter 20 cm and top diameter 10 cm.

2) The tamping rod is of steel 16 mm diameter and 60cm long and rounded at one end.

1) Non porous base plate

2) Enamel tray

3) Steel rule

Procedure for Concrete Slump Test:

Clean the internal surface of the mould and apply oil.

Place the mould on a smooth horizontal non- porous base plate.

Fill the mould with the prepared concrete mix in 4 approximately equal layers.

Tamp each layer with 25 strokes of the rounded end of the tamping rod in a uniform

manner over the cross section of the mould. For the subsequent layers, the tamping

should penetrate into the underlying layer.

Clean away Remove the excess concrete and level the surface with a trowel the mortar or

water leaked out between the mould and the base plate.

Raise the mould from the concrete immediately and slowly in vertical direction.

Measure the slump as the difference between the height of the mould and that of height

point of the specimen being tested.

Slump Value Observation:

The slump (Vertical settlement) measured shall be recorded in terms of millimeters of

subsidence of the specimen during the test

Types of concrete slump test results

Collapse slump: If the concrete specimen get flatten, as soon as is lifted is known as

collapse .This type slump is difficult to measure. It occurs because excess water content

in the mix.

Shear slump: When the half of the concrete specimens slides to sideways as soon as the

mould is removed, is termed as shear slump. It is difficult to measure the slump value

precisely. This type of slump occurs in case of harsh mixes.

True slump: The even subsidence of concrete is designated as a true slump. This gives a

true value and can be measured easily. This type of slump occurs when the water is added

as per the designed water cement ratio.

Advantages of Concrete Slump Test

Slump test is very easy and simple. A non-technical person can perform it without any

problem.

It is very useful to check batch to batch or hour to hour variation in the materials which

will be fed into the mixer. Increase in slump means moisture content of aggregate has

increased unexpectedly or deficiency of fine aggregate has changed. Too high or too low

slump is an indicator of undesirable workability of concrete and mixer operator gets a

warning to find a solution to remedy the problem.

This test does not require any special costly equipment. The sample is not required to be

sent to a laboratory. It can be done in the construction area.

Slump test does not demand a long-time period to get the result. If we compare with

compressive strength test, it requires almost a month to get the result but we can obtain

slump value within some minutes.

Compaction factor test for concrete

Compaction factor test is the workability test for concrete conducted in laboratory. The

compaction factor is the ratio of weights of partially compacted to fully compacted concrete. It

was developed by Road Research Laboratory in United Kingdom and is used to determine the

workability of concrete.

Compaction factor apparatus consists of:-

• Trowels

• Hand scoop (15.2 cm long)

• A rod of steel

• Other suitable material (1.6 cm diameter, 61 cm long rounded at one end )

• A Balance.

Procedure of Compaction Factor Test on Concrete

Place the concrete sample gently in the upper hopper to its brim using the hand scoop and

level it.

Cover the cylinder.

Open the trapdoor at the bottom of the upper hopper so that concrete fall into the lower

hopper. Push the concrete sticking on its sides gently with the road.

Open the trapdoor of the lower hopper and allow the concrete to fall into the cylinder

below.

Cut of the excess of concrete above the top level of cylinder using trowels and level it.

Clean the outside of the cylinder.

Weight the cylinder with concrete to the nearest 10 g. This weight is known as the weight

of partially compacted concrete (W1).

Empty the cylinder and then refill it with the same concrete mix in layers approximately

5 cm deep, each layer being heavily rammed to obtain full compaction.

Level the top surface.

Weigh the cylinder with fully compacted. This weight is known as the weight of fully

compacted concrete (W2).

Find the weight of empty cylinder (W).

Note:

The test is sufficiently sensitive to enable difference in workability arising from the initial

process in the hydration of cement to be measured.

Each test therefore should be carried out at a constant time interval after the mixing is

completed, if strictly comparable results are to be obtained. Convenient time for releasing

the concrete from the upper hopper has been found to be two minutes after the

completion of mixing.

Calculation of Compaction Factor Value

The compaction factor is defined as the ratio of the weight of partially compacted

concrete to the weight of fully compacted concrete. It shall normally to be stated to the

nearest second decimal place.

Compaction Factor Value= (W1-W) / (W2-W)

Vee-Bee Test on Concrete

Apparatus for Vee-Bee test

The Vee-Bee test apparatus consist of a Vee-Bee consistometer as per IS: 119 – 1959, as

shown in the figure.

The apparatus consists of a vibrating table which is supported and mounted on elastic

supports.

It also consists of a sheet metal slump cone.

A weighing balance,

Cylindrical container.

A standard iron tamping rod

Trowels.

Procedure of Vee-Bee Test on Concrete

Initially the sheet metal slump cone is placed inside the cylinder container that is placed

in the consist meter. The cone is filled with four layers of concrete. Each concrete layer is

one fourth the height of the cone. Each layer after pouring is subjected to twenty-five

tamping with the standard tamping rod. The tamping is done with the rounded end of the

rod.

The strokes are distributed in uniform manner. This must be done in such a way theta the strokes

conducted for the second and the subsequent layers of concrete must penetrate the bottom layers.

Once the final layer has been placed and compacted, the concrete is struck off to make it in level

with the help of a trowel. This makes the cone to be exactly filled.

After the preparation of the concrete cone, the glass disc attached to the swivel arm is

moved and is placed on the top of the slump cone placed inside the cylindrical container.

The glass disc has to be placed such that it touches the top of the concrete level and the

reading is measured from the graduated rod.

Now the cylindrical cone is removed immediately by raising the cone slowly in the

vertical direction. The transparent disc on the top of the concrete is placed down to the

new position and the reading is determined.

Now the electrical vibrator is switched on and at the same time we have to start the stop

watch. The concrete is allowed to spread out in the cylindrical container. Until the

concrete is remolded the vibration is continued. This stage is when the surface of the

concrete becomes horizontal and the concrete surface completely adheres uniformly to

the transparent disc.

The time required for complete remolding in seconds is recorded. This time in seconds

gives us the measure of workability of the fresh concrete. This time is expressed in Vee-

Bee seconds.

Observation and Calculations in Vee-Bee Test

Initial reading from the graduated rod, before unmolding (a) in mm

The final reading on the graduated rod after removing the mold (b) in mm

Slump = a – b in mm

The time required for complete remolding in seconds

Hence the consistency of the concrete is measured in______ vee-bee seconds.

Precautions Necessary in Vee-Bee Test

The mold should be cleaned and free from moisture internally before adding the concrete

mix.

While the strokes are applied over the layers, care must be taken to apply it uniformly all

throughout the layers. This helps in having the impact of the strokes in full depth.

The removal of the slump cone should be lifted upward in such a way that the concrete

cone is not disturbed in any means.

The vee-bee tests must be conducted at a distance away from any other source of

vibration than the vibration procedure provided in the test.

When a state attains at which the transparent disc rider completely covers the concrete

and all the voids and cavities present in the concrete surface get disappeared, the

remolding of concrete is attained completely.

Disadvantages of Concrete Slump Test

It is unreliable for lean mixes. In a lean mix, a true slump may convert into shear or

collapse easily. Widely variation can be found from one sample of lean mix and it can be

a great confusion to determine the exact result.

It is not exact measurement because slump bears no unique relation to workability. Even,

for different types of aggregates, the same slump can be recorded for different

workability. We should also keep in mind that slump does not measure the ease of

compaction. The slump occurs under the self-weight of concrete only, it does not

represent behavior under various conditions like vibration, finishing, pumping or moving

through a tremie.

For a specimen, more than one shape can be resulted confusing the correct result. If shear

slump occurs, it may attain true slump in next test.

It cannot differentiate in workability of stiff mixes as it shows zero slumps. In dry range,

no difference can be detected between different mixes with different workability.

It is not suitable for concrete formed of aggregate higher than 40 mm.

UNIT-9 :- METHODS OF NON DESTRUCTIVE TESTS

9.1 Non-destructive tests

Non-destructive testing of concrete is a method to obtain the compressive strength and other

properties of concrete from the existing structures. This test provides immediate result and actual

strength and properties of concrete STRUCTURE.

9.2 Methods of Non-Destructive Testing of Concrete

1) Penetration method

2) Rebound hammers method

3) Pull out test method

4) Ultrasonic pulse velocity method

5) Radioactive methods

9.2.1 Rebound hammer test method

Rebound hammer test (Schmidt Hammer) is used to provide a convenient and rapid indication of

the compressive strength of concrete. It consists of a spring controlled mass that slides on a

plunger within a tubular housing.

The operation of rebound hammer is shown in the figure. When the plunger of rebound hammer

is pressed against the surface of concrete, a spring controlled mass with a constant energy is

made to hit concrete surface to rebound back. The extent of rebound, which is a measure of

surface hardness, is measured on a graduated scale. This measured value is designated as

Rebound Number (rebound index). A concrete with low strength and low stiffness will absorb

more energy to yield in a lower rebound value.

The rebound hammer test method is used for the following purposes:

(a) To find out the likely compressive strength of concrete with the help of suitable co-relations

between rebound index and compressive strength.

(b) To assess the uniformity of concrete.

(c) To assess the quality of concrete in relation to standard requirements.

(d) To assess the quality of one element of concrete in relation to another.

Rebound hammer test method can be used to differentiate the acceptable and questionable parts

of the structure or to compare two different structures based on strength.

Limitations of Rebound Hammer Test:

Rebound hammer has to be used against smooth and formed surface. It is not applicable

for the open textured surface, i.e. a trowelled surface. It should be rubbed smooth with an

emery stone.

For equal strengths, higher rebound number is obtained with a 7-day old concrete than

with a 28-day old.

Rebound hammer test should not be carried out on low strength concrete at early ages.

When the concrete strength is less than 7 N/mm2, the concrete surface could be damaged

by the hammer.

A correlation curve for tests performed on saturated dried concrete specimens should then

be used to estimate the compressive strength.

Though the same type of coarse aggregate is used in the concrete mix, the correlation

curves can be different if the sources of the aggregate are different.

Cement with higher alumina content can have a 100 percent higher compressive strength

than with OPC.

Cement with super sulphated content can have a compressive strength 50 percent lower

than OPC.

9.2.2 Ultrasonic pulse velocity test

An ultrasonic pulse velocity test is an in-situ, nondestructive test to check the quality of concrete

and natural rocks. In this test, the strength and quality of concrete or rock is assessed by

measuring the velocity of an ultrasonic pulse passing through a concrete structure or natural rock

formation.

Ultrasonic Testing of Concrete

• Ultrasonic pulse velocity test consists of measuring travel time, T of ultrasonic pulse of

50 to 54 kHz, produced by an electro-acoustical transducer, held in contact with one

surface of the concrete member under test and receiving the same by a similar transducer

in contact with the surface at the other end.

• With the path length L, (i.e. the distance between the two probes) and time of travel T,

the pulse velocity (V=L/T) is calculated.

• Higher the elastic modulus, density and integrity of the concrete, higher is the pulse

velocity. The ultrasonic pulse velocity depends on the density and elastic properties of the

material being tested.

The pulse velocity in concrete may be influenced by:

Path length

Lateral dimension of the specimen tested

Presence of reinforcement steel

Moisture content of the concrete

Transducer arrangement.

There are three basic ways in which the transducers may be arranged, as shown in fig. These are:

(i) Opposite faces (direct transmission)

(ii) Adjacent faces (semi-direct transmission)

(iii) Same face (indirect transmission)

Since the maximum pulse energy is transmitted at right angles to the face of the

transmitter, the direct method is the most reliable from the point of view of transit time

measurement. Also, the path is clearly defined and can be measured accurately, and this

approach should be used wherever possible for assessing concrete quality.

The semi-direct method can sometimes be used satisfactorily if the angle between the

transducers is not too great, and if the path length is not too large. The sensitivity will be

smaller, and if these requirements are not met it is possible that no clear signal will be

received because of attenuation of the transmitted pulse. The path length is also less

clearly defined due to the finite transducer size, but it is generally regarded as adequate to

take this from centre to centre of transducer faces.

The indirect method is definitely the least satisfactory, since the received signal

amplitude may be less than 3% of that for a comparable direct transmission. The received

signal is dependent upon scattering of the pulse by discontinuities and is thus highly

subject to errors. The pulse velocity will be predominantly influenced by the surface zone

concrete, which may not be representative of the body, and Copyright 1996 Chapman &

Hall the exact path length is uncertain.

UNIT-6 :-INTRODUCTION TO ADMIXTURES (CHEMICALS AND MINERALS)

FOR IMPROVING PERFORMANCE OF CONCRETE

6.1 Admixture

Fig1: Liquid admixtures, from left to right: antiwashout admixture, shrinkage reducer, water reducer, foaming agent, corrosion inhinitor, and air entraining admixture. (69795).

Admixtures are those ingredients in concrete other than Portland cement, water, and aggregates

that are added to the mixture immediately before or during mixing (Fig.1). Admixtures can be

classified by function as follows:

1. Air-entraining admixtures

2. Water-reducing admixtures

3. Plasticizers

4. Accelerating admixtures

5. Retarding admixtures

6. Hydration-control admixtures

7. Corrosion inhibitors

8. Shrinkage reducers

9. Alkali-silica reactivity inhibitors

10. Coloring admixtures

11. Miscellaneous admixtures such workability, bonding, damp proofing, permeability

reducing, grouting, gas-forming, and pumping admixtures

6.2 The major reasons for using admixtures are:

1. To reduce the cost of concrete construction

2. To achieve certain properties in concrete more effectively than by other means

3. To maintain the quality of concrete during the stages of mixing, transporting, placing, and

curing in adverse weather conditions

4. To overcome certain emergencies during concreting operations

6.3 Air- Entraining Admixtures

Used to purposely introduce and stabilize microscopic air bubbles in concrete. Air-entrainment will dramatically improve the durability of concrete exposed to cycles of freezing and thawing (Fig.2). Entrained air greatly improves concrete's resistance to surface scaling caused by chemical de-icers

Frost damage at joints of a pavement

Frost induced cracking near joints

Scaled concrete surface resulting from lack of air entrainment, use of deicers, and poor finishing and curing practices.

• The primary ingredients used in air-entraining admixtures are salts of wood resin (Vinsol resin), synthetic detergents, salts of petroleum acids, etc.

6.4 Water-Reducing Admixtures

• Used to reduce the quantity of mixing water required to produce concrete of a certain slump, reduce water-cementing materials ratio, reduce cement content, or increase slump.

• Typical water reducers reduce the water content by approximately 5% to 10%.

• Materials:

• Lignosulfonates.

• Carbohydrates.

• Hydroxylated carboxylic acids.

Fig3: Slump loss at 230C in mixture containing conventional water reducers (ASTM C 494, Type D) compared

with a control mixture (Whiting and Dziedzic1992).

Water-Reducing Admixtures

• The effectiveness of water reducers on concrete is a function of their chemical composition, concrete temperature, cement composition and fineness, cement content, and the presence of other admixtures.

Super-plasticizers (High-Range Water Reducers)

• These admixtures are added to concrete with a low-to-normal slump and water-cementing materials ratio to make high-slump flowing concrete.

• Flowing concrete is a highly fluid but workable concrete that can be placed with little or no vibration or compaction while still remaining essentially free of excessive bleeding or segregation.

Super-plasticizers (High-Range Water Reducers)

• Applications where flowing concrete is used:

1. thin-section placements,

2. areas of closely spaced and congested reinforcing steel,

3. pumped concrete to reduce pump pressure, thereby increasing lift and distance capacity,

4. areas where conventional consolidation methods are impractical or can not be used, and

5. For reducing handling costs.

Flowable concrete with high slump

Is easily placed

Even in areas of heavy reinforcing steel congestion

Low water to cement ratio concrete with low chloride permeability--- easily made with high-range water reducers- is ideal for bridge decks

Plasticized, flowing concrete is easily placed in thin sections

Superplasticizers (High-Range Water Reducers)

• Typical superplasticizers include:

– Sulfonated melamine formaldehyde condensates.

– Sulfonated naphthalene formaldehyde condensate.

– Lignosulfonates.

– Polycarboxylates.

– bleed significantly less than control concretes of equally high slump and higher water content.

– High-slump, low-water-content, plasticized concrete has less drying shrinkage than a high-slump, high-water-content conventional concrete.

– has similar or higher drying shrinkage than conventional low-slump, low-water-content concrete.

– The effectiveness of the plasticizer is increased with an increasing amount of cement and fines in the concrete.

6.5 Retarding Admixtures

• used to retard the rate of setting of concrete at high temperatures of fresh concrete (30°C or more).

• One of the most practical methods of counteracting this effect is to reduce the temperature of the concrete by cooling the mixing water or the aggregates.

• Retarders do not decrease the initial temperature of concrete.

• The bleeding rate and capacity of plastic concrete is increased with retarders.

• The typical materials used as retarders are:

• Lignin,

• Borax,

• Sugars,

• Tartaric acid and salts.

Fig4: Slump loss at various temperatures for conventional concretes prepared with and without set-retarding

admixture (Whiting and Dziedzic 1992).

Retarding Admixtures

• Retarders are used to:

1. offset the accelerating effect of hot weather on the setting of concrete,

2. delay the initial set of concrete when difficult or unusual conditions of placement occur,

3. delay the set for special finishing processes such as an exposed aggregate surface.

4. some reduction in strength at early ages (one to three days) accompanies the use of retarders.

5. The effects of these materials on the other properties of concrete, such as shrinkage, may not be predictable.

6. Therefore, acceptance tests of retarders should be made with actual job materials under anticipated job conditions.

6.6 Accelerating Admixtures

• used to accelerate strength development of concrete at an early age.

• Typical Materials are:

– Calcium chloride: most commonly used for plain concrete.

– Triethanolamine.

– Calcium formate.

– Calcium nitrate.

– Calcium nitrite.

Corrosion Inhibitors

Fig5: The damage to this concrete parking structure resulted from chloride-induced corrosion of steel

reinforcement. (50051)

Corrosion Inhibitors

• The chlorides can cause corrosion of steel reinforcement in concrete.

• Ferrous oxide and ferric oxide form on the surface of reinforcing steel in concrete.

• Ferrous oxide reacts with chlorides to form complexes that move away from the steel to form rust. The chloride ions continue to attack the steel until the passivating oxide layer is destroyed.

• Corrosion-inhibiting admixtures chemically arrest the corrosion reaction.

• Commercially available corrosion inhibitors include:

• calcium nitrite,

• sodium nitrite,

• dimethyl ethanolamine,

• amines,

• phosphates,

• ester amines.

Shrinkage-Reducing Admixtures

• Shrinkage cracks, such as shown on this bridge deck, can be reduced with the use of good concreting practices and shrinkage reducing admixtures.

6.7 Chemical Admixtures to reduce Alkali-aggregate Reactivity (ASR Inhibitors)

• Expansion of specimens made with lithium carbonate admixture

Coloring admixtures (Pigments)

• Red and blue pigments were used to color this floor