UNIT I-CONCRETE TECHNOLOGY
Cements – Grade of cements - manufacture of cement – concrete chemicals and
Applications –Mix design concept – mix design as per BIS & ACI methods – manufacturing
of concrete –Batching – mixing – transporting – placing – compaction of concrete – curing
and finishing.Testing of fresh and hardened concrete – quality of concrete - Non –
destructive testing.
1.1 CEMENTS.
A cement is a binder, a substance that sets and hardens independently, and can bind other
materials together. The word "cement" traces to the Romans, who used the term opus
caementicium to describe masonry resembling modern concrete that was made from crushed
rock with burnt lime as binder. The volcanic ash and pulverized brick additives that were added to
the burnt lime to obtain a hydraulic binder were later referred to as cementum, cimentum, cäment
and cement.
Cement used in construction is characterized as hydraulic or non-hydraulic. Hydraulic
cements (e.g., Portland cement) harden because of hydration chemical reactions that occur
independently of the mixture's water content; they can harden even underwater or when
constantly exposed to wet weather. The chemical reaction that results when the anhydrous
cement powder is mixed with water produces hydrates that are not water-soluble. Non-hydraulic
cements (e.g., lime and gypsum plaster) must be kept dry in order to retain their strength.
The most important use of cement is the production of mortar and concrete—the bonding of
natural or artificial aggregates to form a strong building material that is durable in the face of
normal environmental effects.
1.2 GRADE OF CEMENT
The Bureau of Indian Standards came forward to grade the ordinary portland cement into
grade 33 cement, grade 43 cement and grade 53 cement. This grading closely followed the U.K.
grading which was 32.5, 42.5 and 52.5 as well as 62.5, some of Indian companies are also trying
to make and persuade the Bureau of Indian Standards to introduce grade 63.
These higher grades of cements are specifically introduced to cater to the needs of the
industry engaged in the construction of long span bridges, high rise structures and other
structures of gigantic magnitude requiring high grades of concretes. With the cement then
available. It was very difficult to design a mix for obtaining concrete of grade 4.5 and above
commonly used in such structures. Hence, Bureau of Indian Standards classified ordinary
portland cement into the above 3 grades that is now available in the market
1.2.A) TYPES OF CEMENT/

Ordinary Portland cement
OPC33,OPC43 and OPC53 grade

Rapid hardening cement

Extra rapid hardening cement

Sulphate resisting cement

Portland slag cement

Quick setting cement

Low heat cement

Portland pazzolona cement

Air entraining cement

Colored cement

White cement

Hydrophobic cement

Masonry cement

expansive cement

Oil well cement

Redi set cemnt

Concrete sleeper grade cement

High alumina cement

Very high strength cement
1.3 MANUFACTURING OF CEMENT
Raw materials used


Calcareous
Argillaceous
Calcareous materials used are
o
o
o
o
o
Cement rock
Lime stone
Marl
Chalk
Marine shell
Argillaceous materials used are
o
o
o
o
Clay
shale
slate
blast furnace slag
Process manufacturing cement

Dry process

Wet process
Dry process
General
Adopted when the raw materials are quite hard
The process is slow an the product is costly
Process
Lime stone and clay are ground to fine powder separately and are mixed together
Water is added to make a thick paste which contains 14% of moisture
The paste format are dried and off charged into a rotary kiln
The product obtained often calcinations in rotary kiln
The clinker I obtained as a result of incipient fusion and sintering at a temp about 1400◦c to 1500◦
c
The clinker is cooled to preserve the meta stable compounds and there solid solutions
Dispersion of one solid with another solid which made the clinker again heated
Clinker is again cooled and grounded in tube mills where 2-3% gypsum is added
The purpose of adding gypsum is to coat the cement particle by interfering the process of
hydration of cement particles
The flow diagram of dry process
Wet process
The operations are

Mixing

Burning

Grinding
Process
The crushed raw materials are fed in to a ball mill and a little water is added
The steel balls in the ball mill pulverized the raw material which form a slurry with water
The slurry is passed through storage tanks where the proportioning of compound is adjusted to
ensure desired chemical composition
The corrected slurry having moisture about 40%,is then fed into rotary kiln
Where it loses moisture and form on to lumps
These are finally burned at 1500◦ to 1600 ◦c
It becomes clinker at this stage, the clinker is cooled and then grounded in tube mills
While grinding the clinker 3% gypsum I added this is stored in silos and packed
1.4 CONCRETE CHEMICALS AND APPLICATIONS
Water-reducing admixture / Plasticizers:
These admixtures are used for following purposes:
1. To achieve a higher strength by decreasing the water cement ratio at the same
workability as an admixture free mix.
2. To achieve the same workability by decreasing the cement content so as to reduce the
heat of hydration in mass concrete.
3. To increase the workability so as to ease placing in accessible locations
4. Water reduction more than 5% but less than 12%
Actions involved:
1. Dispersion:
Surface active agents alter the physic chemical forces at the interface. They are adsorbed on the
cement particles, giving them a negative charge which leads to repulsion between the particles.
Electrostatic forces are developed causing disintegration and the free water become available for
workability.
2. Lubrication:
As these agents are organic by nature, thus they lubricate the mix reducing the friction and
increasing the workability.
3. Retardation:
A thin layer is formed over the cement particles protecting them from hydration and increasing the
setting time. Most normal plasticizers give some retardation, 30–90 minutes
Super Plasticizers:

These are more recent and more effective type of water reducing admixtures also known
as high range water reducer
The commonly used Super Plasticizers are as follows:
Sulphonated melamine formaldehyde condensates (SMF)
Give 16–25%+ water reduction. SMF gives little or no retardation, which makes them very
effective at low temperatures or where early strength is most critical.
However, at higher temperatures, they lose workability relatively quickly. SMF generally give a
good finish and are colorless, giving no staining in white concrete.
They are therefore often used where appearance is important.
Sulphonated naphthalene formaldehyde condensates (SNF)
Typically give 16–25%+ water reduction. They tend to increase the entrapment of larger, unstable
air bubbles. This can improve cohesion but may lead to more surface defects.
Retardation is more than with SMF but will still not normally exceed 90 minutes. SNF is a very
cost-effective.
Polycarboxylate ether super plasticizers (PCE)
Typically give 20–35%+ water reduction. They are relatively expensive per liter but are very
powerful so a lower dose (or more dilute solution) is normally used.
In general the dosage levels are usually higher than with conventional water reducers, and the
possible undesirable side effects are reduced because they do not markedly lower the surface
tension of the water.
Accelerators:
An admixture which, when added to concrete, mortar, or grout, increases the rate of hydration of
hydraulic cement, shortens the time of set in concrete, or increases the rate of hardening or
strength development.
Accelerating admixtures can be divided into groups based on their performance and application:
1. Set Accelerating Admixtures,
Reduce the time for the mix to change from the plastic to the hardened state.
Set accelerators have relatively limited use, mainly to produce an early set.
2. Hardening Accelerators,
Which increase the strength at 24 hours by at least 120% at 20ºC and at 5ºC by at least 130% at
48 hours. Hardening accelerators find use where early stripping of shuttering or very early access
to pavements is required.
They are often used in combination with a high range water reducer, especially in cold conditions.
.
Set Retarders:
The function of retarder is to delay or extend the setting time of cement paste in concrete. These
are helpful for concrete that has to be transported to long distance, and helpful in placing the
concrete at high temperatures.
When water is first added to cement there is a rapid initial hydration reaction, after which there is
little formation of further hydrates for typically 2–3 hours.
The exact time depends mainly on the cement type and the temperature. This is called the
dormant period when the concrete is plastic and can be placed.
At the end of the dormant period, the hydration rate increases and a lot of calcium silicate hydrate
and calcium hydroxide is formed relatively quickly. This corresponds to the setting time of the
concrete.
Retarding admixtures delay the end of the dormant period and the start of setting and hardening.
This is useful when used with plasticizers to give workability retention. Used on their own,
retarders allow later vibration of the concrete to prevent the formation of cold joints between
layers of concrete placed with a significant delay between them.
The mechanism of set retards is based on absorption. The large admixture anions and molecules
are absorbed on the surface of cement particles, which hinders further reactions between cement
and water i.e. retards setting.
Air Entrained Admixtures:
An addition for hydraulic cement or an admixture for concrete or mortar which causes air, usually
in small quantity, to be incorporated in the form of minute bubbles in the concrete or mortar during
mixing, usually to increase its workability and frost resistance.
Air-entraining admixtures are surfactants that change the surface tension of the water.
Traditionally, they were based on fatty acid salts or vinsol resin but these have largely been
replaced by synthetic surfactants or blends of surfactants to give improved stability and void
characteristics to the entrained air.
Air entrainment is used to produce a number of effects in both the plastic and the hardened
concrete. These include:
• Resistance to freeze–thaw action in the hardened concrete.
• Increased cohesion, reducing the tendency to bleed and segregation in the plastic concrete.
• Compaction of low workability mixes including semi-dry concrete.
• Stability of extruded concrete.
1.5 CONCRETE MIX DESIGN CONCEPT
Concrete Mix Design
Introduction
The process of selecting suitable ingredients of concrete and determining their relative amounts
with the objective of producing a concrete of the required, strength, durability, and workability as
economically as possible, is termed the concrete mix design. The proportioning of ingredient of
concrete is governed by the required performance of concrete in 2 states, namely the plastic and
the hardened states. If the plastic concrete is not workable, it cannot be properly placed and
compacted. The property of workability, therefore, becomes of vital importance.
The compressive strength of hardened concrete which is generally considered to be an index of
its other properties, depends upon many factors, e.g. quality and quantity of cement, water and
aggregates; batching and mixing; placing, compaction and curing. The cost of concrete is made
up of the cost of materials, plant and labour. The variations in the cost of materials arise from the
fact that the cement is several times costly than the aggregate, thus the aim is to produce as lean
a mix as possible. From technical point of view the rich mixes may lead to high shrinkage and
cracking in the structural concrete, and to evolution of high heat of hydration in mass concrete
which may cause cracking.
The actual cost of concrete is related to the cost of materials required for producing a minimum
mean strength called characteristic strength that is specified by the designer of the structure. This
depends on the quality control measures, but there is no doubt that the quality control adds to the
cost of concrete. The extent of quality control is often an economic compromise, and depends on
the size and type of job. The cost of labour depends on the workability of mix, e.g., a concrete mix
of inadequate workability may result in a high cost of labour to obtain a degree of compaction with
available equipment.
Requirements of concrete mix design
The requirements which form the basis of selection and proportioning of mix ingredients
are :
a ) The minimum compressive strength required from structural consideration
b) The adequate workability necessary for full compaction with the compacting equipment
available.
c) Maximum water-cement ratio and/or maximum cement content to give adequate
durability for the particular site conditions
d) Maximum cement content to avoid shrinkage cracking due to temperature cycle in
mass concrete.
Types of Mixes
1. Nominal Mixes
In the past the specifications for concrete prescribed the proportions of cement, fine and
coarse aggregates. These mixes of fixed cement-aggregate ratio which ensures
adequate strength are termed nominal mixes. These offer simplicity and under normal
circumstances, have a margin of strength above that specified. However, due to the
variability of mix ingredients the nominal concrete for a given workability varies widely in
strength.
2. Standard mixes
The nominal mixes of fixed cement-aggregate ratio (by volume) vary widely in strength and may
result in under- or over-rich mixes. For this reason, the minimum compressive strength has been
included in many specifications. These mixes are termed standard mixes.
IS 456-2000 has designated the concrete mixes into a number of grades as M10, M15, M20,
M25, M30, M35 and M40. In this designation the letter M refers to the mix and the number to the
specified 28 day cube strength of mix in N/mm 2. The mixes of grades M10, M15, M20 and M25
correspond approximately to the mix proportions (1:3:6), (1:2:4), (1:1.5:3) and (1:1:2)
respectively.
3. Designed Mixes
In these mixes the performance of the concrete is specified by the designer but the mix
proportions are determined by the producer of concrete, except that the minimum cement content
can be laid down. This is most rational approach to the selection of mix proportions with specific
materials in mind possessing more or less unique characteristics. The approach results in the
production of concrete with the appropriate properties most economically. However, the designed
mix does not serve as a guide since this does not guarantee the correct mix proportions for the
prescribed performance.
For the concrete with undemanding performance nominal or standard mixes (prescribed in the
codes by quantities of dry ingredients per cubic meter and by slump) may be used only for very
small jobs, when the 28-day strength of concrete does not exceed 30 N/mm 2. No control testing is
necessary reliance being placed on the masses of the ingredients.
Factors affecting the choice of mix proportions
The various factors affecting the mix design are:
1. Compressive strength
It is one of the most important properties of concrete and influences many other describable
properties of the hardened concrete. The mean compressive strength required at a specific age,
usually 28 days, determines the nominal water-cement ratio of the mix. The other factor affecting
the strength of concrete at a given age and cured at a prescribed temperature is the degree of
compaction. According to Abraham’s law the strength of fully compacted concrete is inversely
proportional to the water-cement ratio.
2. Workability
The degree of workability required depends on three factors. These are the size of the section to
be concreted, the amount of reinforcement, and the method of compaction to be used. For the
narrow and complicated section with numerous corners or inaccessible parts, the concrete must
have a high workability so that full compaction can be achieved with a reasonable amount of
effort. This also applies to the embedded steel sections. The desired workability depends on the
compacting equipment available at the site.
3. Durability
The durability of concrete is its resistance to the aggressive environmental conditions. High
strength concrete is generally more durable than low strength concrete. In the situations when the
high strength is not necessary but the conditions of exposure are such that high durability is vital,
the durability requirement will determine the water-cement ratio to be used.
4. Maximum nominal size of aggregate
In general, larger the maximum size of aggregate, smaller is the cement requirement for a
particular water-cement ratio, because the workability of concrete increases with increase in
maximum size of the aggregate. However, the compressive strength tends to increase with the
decrease in size of aggregate.
IS 456:2000 and IS 1343:1980 recommend that the nominal size of the aggregate should be as
large as possible.
5. Grading and type of aggregate
The grading of aggregate influences the mix proportions for a specified workability and watercement ratio. Coarser the grading leaner will be mix which can be used. Very lean mix is not
desirable since it does not contain enough finer material to make the concrete cohesive.
The type of aggregate influences strongly the aggregate-cement ratio for the desired workability
and stipulated water cement ratio. An important feature of a satisfactory aggregate is the
uniformity of the grading which can be achieved by mixing different size fractions.
6. Quality Control
The degree of control can be estimated statistically by the variations in test results. The variation
in strength results from the variations in the properties of the mix ingredients and lack of control of
accuracy in batching, mixing, placing, curing and testing. The lower the difference between the
mean and minimum strengths of the mix lower will be the cement-content required. The factor
controlling this difference is termed as quality control.
1.6 MIX DESIGN AS PER BIS & ACI METHODS
Mix Proportion designations
The common method of expressing the proportions of ingredients of a concrete mix is in the
terms of parts or ratios of cement, fine and coarse aggregates. For e.g., a concrete mix of
proportions 1:2:4 means that cement, fine and coarse aggregate are in the ratio 1:2:4 or the mix
contains one part of cement, two parts of fine aggregate and four parts of coarse aggregate. The
proportions are either by volume or by mass. The water-cement ratio is usually expressed in
mass
Factors to be considered for mix design
ð The grade designation giving the characteristic strength requirement of concrete.
ð The type of cement influences the rate of development of compressive strength of concrete.
ð Maximum nominal size of aggregates to be used in concrete may be as large as possible within the
limits prescribed by IS 456:2000.
ð The cement content is to be limited from shrinkage, cracking and creep.
ð The workability of concrete for satisfactory placing and compaction is related to the size and shape
of section, quantity and spacing of reinforcement and technique used for transportation, placing
and compaction.
1.6.1 BIS METHOD
Procedure
1. Determine the mean target strength f t from the specified characteristic compressive strength at 28day fck and the level of quality control.
ft = fck + 1.65 S
where S is the standard deviation obtained from the Table of approximate contents given after the
design mix.
2. Obtain the water cement ratio for the desired mean target using the emperical relationship between
compressive strength and water cement ratio so chosen is checked against the limiting water
cement ratio. The water cement ratio so chosen is checked against the limiting water cement ratio
for the requirements of durability given in table and adopts the lower of the two values.
3. Estimate the amount of entrapped air for maximum nominal size of the aggregate from the table.
4. Select the water content, for the required workability and maximum size of aggregates (for
aggregates in saturated surface dry condition) from table.
5. Determine the percentage of fine aggregate in total aggregate by absolute volume from table for
the concrete using crushed coarse aggregate.
6. Adjust the values of water content and percentage of sand as provided in the table for any
difference in workability, water cement ratio, grading of fine aggregate and for rounded aggregate
the values are given in table.
7. Calculate the cement content form the water-cement ratio and the final water content as arrived
after adjustment. Check the cement against the minimum cement content from the requirements
of the durability, and greater of the two values is adopted.
8. From the quantities of water and cement per unit volume of concrete and the percentage of sand
already determined in steps 6 and 7 above, calculate the content of coarse and fine aggregates
per unit volume of concrete from the following relations:
where V = absolute volume of concrete
= gross volume (1m3) minus the volume of entrapped air
Sc = specific gravity of cement
W = Mass of water per cubic metre of concrete, kg
C = mass of cement per cubic metre of concrete, kg
p = ratio of fine aggregate to total aggregate by absolute volume
fa, Ca = total masses of fine and coarse aggregates, per cubic metre of concrete,
respectively, kg, and
Sfa, Sca = specific gravities of saturated surface dry fine and coarse aggregates,
respectively
9. Determine the concrete mix proportions for the first trial mix.
10. Prepare the concrete using the calculated proportions and cast three cubes of 150 mm size and
test them wet after 28-days moist curing and check for the strength.
11. Prepare trial mixes with suitable adjustments till the final mix proportions are arrived at.
1.6.2 American Concrete Institute Method of Mix Design 11.3 (ACI Concrete Mix Design)
This method of proportioning was first published in 1944 by ACI committee 613. In 1954 the
method was revised to include, among other modifications, the use of entrained air. In 1970, the
method of ACI mix design became the responsibility of ACI committee 211. We shall now deal
with the latest ACI Committee 211.1 method.
It has the advantages of simplicity in that it:
1.
2.
3.
4.
Applies equally well
With more or less identical procedure to rounded or angular aggregate
To regular or light weight aggregates
To air entrained or non-air-entrained concretes.
1.7 MANUFACTURING OF CONCRETE
Introduction
Production of concrete requires meticulous care at every stage
The ingredients of good and bad concrete are same but good rules are not
Observed it may become bad
Manufacturing of concrete includes the following stages
1. Batching
2. Mixing
3. Transporting
4. Placing
5. Compacting
6. Curing
7. Finishing
1.8 Batching
The measurement of materials for making concrete is known as batching.
Methods of batching
 Volume batching
 Weigh batching
Volume batching
The required ingredients of conc. Are measured by volume basis
o
Volume batching is done by various types of gauge boxes
o
The gauge boxes are made with comparatively deeper with narrow surface
o
Some times bottomless gauge boxes are used but it should be avoided
Volume batching is not a good practice because of the difficulties it offers to granular
material.
Some of the sand in loose condition weighs much less than the same volume of dry
compacted soil.
For un important concrete or any small job concrete may be batched by volume.
Weigh batching
It is the correct method of measuring materials for concrete.
Use of weight system in batching ,facilitates accuracy flexibility and simplicity
The different types of weigh batching are there, they are used based on the different
situation.
In small works the weighing arrangement consist of two weighing buckets connected to the
levers of spring loaded dials which indicates the load,
The weighing buckets are mounted on a central spindle about which they rotate
On large works the weigh bucket type of weighing equipment used ,the materials are fed from
the over head storage hopper and it discharges by gravity.
1.9 Mixing
Thorough mixing of materials is essential for the production of uniform concrete
The mixing should ensure that the mass becomes homogeneous uniform in color and
consistency.

Types of mixing
Hand mixing
Machine mixing
Hand mixing
It is practiced for small scale un important concrete works
Hand mixing should be done over a impervious concrete or brick floor sufficiently large size
take one bag of cement .
Spread out and measure d out fine aggregates and course aggregate in alternative layers.
Pour he cement on the top of it and mix them dry by showel, turning the mixture over and
over again until the uniformity of color is achieved.
The uniform mixture is spread out in the thickness of about 20 cm
The water is taken and sprinkled over the mixture and simultaneously turned over
The operation is continued till such time a good uniform homogeneous concrete is obtained
Machine mixing
Mixing of concrete almost invariably carried ot by machine ,for reinforced concrete work
medium or large scale concrete works .
Machine mixing is not only efficient it is also economical when quantity of concrete to be
produced is large
Type of mixer for mixing concrete


Batch mixer
Continuous mixer
Batch mixer
Batch mixer produce concrete batch by batch with time interval
This is used in normal concrete work
Batch mixers are two types
 Pan type
 Drum type
Drum types are further classified into tilting ,non tilting and forced action type
The capacity of batch mixer depends on the proportion of the mix
For 1:2:4 ideal mixer 200 liters
For 1:3:6 ideal mixer 280 liters
Mixing time
Concrete mixers are generally designed to run at a speed of 15 to 20 revolutions per minute
For proper mixing it is seen that about 25to 30 revolutions are required in a well designed
mixer
It is important that a mixer should not stop in between concreting operations for this
requirement concrete mixer must be kept maintained
1.10 Transporting of concrete
Concrete can be imported by variety of methods and equipments
Methods adopted for transportation of concrete

]

Mortar pan

Crane, bucket and rope way

Truck mixers and dumpers
Wheel barrow

Belt conveyors

Chute

Skip and hoist

Transit mixer

Pump and pipe line

Helicopter
Mortar pan

This case concrete is carried out in small quantities

This method exposes greater surface area of concrete for drying conditions

This results a geat loss of water particularly in hot weather

Mortar pan must be wetted to start with and must be kept clean
Wheel barrow

Used for transporting concrete in ground level.

This method is employed for hauling concrete in longer distance in case of concrete road
construction.

If the distance is long or ground is rough it is likely that the concrete get segregated due
to vibration
To avoid this, wheel barrows are provided with pneumatic wheel.

Crane bucket and rope way
This is one of the right way for transporting concrete above the ground level
Crane can handle concrete in high rise construction project and are becoming familiar sites in big
cities
Rope way buckets of various sizes are used
Rope way method is adopted for
Concrete works in valley
Construction work of the pier in the river
For dam construction
Truck mixer and dumpers
For large concrete works particularly for concrete to be placed at ground level
These are ordinary open steel tipping lorries
Dumpers having 2-3 cubic meter capacity
Belt conveyors also can be used for
Chutes
Provided for transporting concrete from ground to lower level
The surface should have same slope not flatter than 1 vertical to 2 and a1/2 horizontal
Skip and hoist
Adopted method for transporting concrete vertically for 3 to 4 floors
Mortar pan with staging and human ladder is used for transporting concrete
Transit mixer
This is the equipment for transporting concrete over a big distance particularky ready mix
concrete
They are truck mounted having a capacity of 4 to 7 m3
The speed of rotation of truck mixer is 4to16 rev/min
A small concrete pump is also mounted on the truck carrying transit mixer
Pumps and pipe lines
Universally accepted method
Starts with the suction stroke for suck the concrete inside the pipe
It has a piston which moves forward and backward to have suction and delivery of concrete

Choosing a correct pump involves

Length of horizontal pipe

Length of vertical pipe

Number of bends

Diameter of pipe line

Length of flexible hose

Change in line diameter

Slump of concrete
1.11 Placing of concrete
Concrete must be placed in a systematic manner to yield optimum results
Some situation where we used provide concrete
Placing concrete within earth mould
Placing concrete with large earth mould or timber plank form work
Placing concrete in layers with in timber or steel shutter
Placing concrete with in usual form work
Placing concrete under water
Placing concrete within earth mould
Concrete is invariably as foundation bed below the walls and columns
Before placing concrete
All loose earth must be removed
Roots of trees must be cut
If surface is dry must be made just damp
If it is too wet or rain soaked the water slush must be removed
Placing concrete with large earth mould or timber plank form work
For construction of road slabs,air field slabs and ground floor slabs in building conc os placed in
this method
The ground surface must be free from loose earth pool of water ,grass or roots or leaves
The earth must be compacted well
Poly ethylene film is used in between conc ground to avoid absorption of moisture
Concrete is laid alternative layers to give enough scope for shrinkage
Placing concrete in layers with in timber or steel shutter
This can be used in the following cases
Dam construction
Construction of concrete abutments
Raft for a high rise building
The thickness of layers depend on
Method of compaction
Size of vibrator
Frequency of vibrator used
It is good for laying 15 to 30 cm thick layer of concrete ,for mass concrete it may varie from 35 to
45 cm
Its better to leave the top of the layer rough so that succeeding layer can have the good bond
Placing concrete with in usual form work
This can be adopt for Column ,beam and floors
Rules that should be followed while placing the concrete

Check the reinforcements are correctly tied and placed

Check the reinforcement is having appropriate cover

The joints between plywood’s or sheets properly plugged

Mould releasing agent should be applied
The concrete must be placed very care fully a small quantity at a time so that they will not block
the entry of subsequent concrete
Placing concrete under water
Concrete is often required to be placed under water or I a trench filled with slurry
In such a cases use of bottom slurry buckets or termic pipes are used
In the bottom bucket concrete is taken through water in a water tight box or bucket reaching final
place of deposition
The bottom is made to open by some mechanism and the whole concrete is dumped slowly.
1.12 Compaction of concrete
Compaction of concrete is the process adopted for expelling the entrapped air from the concrete
Method for compacting concrete

Hand compaction

Compaction by vibrator

Compaction by pressure and jolting

Compaction by spinning
Hand compaction
Adopted in case of unimportant concrete
This can be adopted when mechanical mean cannot be used
It consist of



Roding
Ramming
Tamping
Roding
Poking the concrete with about 2m long 16 mm dia rod to poke the concrete reinforcement
Ramming
Should be done with care
Permitted in unreinforced foundation concrete in ground floor construction
Tamping
The thickness of conc should be comparatively less
Consist of beating the op surface by wooden cross beam
The section of wooden beam is about 10x10 cm
Compaction by vibrators
We can place the concrete economically when compared to hand compaction
The use of vibrators may be essential for the production of good concrete

Type of vibrators

Internal vibrator

Formwork vibrator

Table vibrator

Platform vibrator

Surface vibrator

Vibratory rollers
Compaction by pressure and jolting

This is one of the effective method of compacting dry concrete

Often used for compacting hollow block ,cavity blocks concrete blocks

The stiff concrete is vibrated pressed and also given jolts
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With the combined action of the three the stiff conc gets compacted to an dense form to
give good strength and volume
Compaction by spinning
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This is one of the recent method of the compacting concrete
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This is adopted for fabrication of concrete pipes
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The plastic concrete when at every high speed get well compacted by centrifugal force
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Potential products such as spun pipes are compacted by spinning process
Vibratory rollers
One of the recent methods of compacting very lean or dry concrete
The concrete compacted by rollers can be called as roller concrete
1.13 TESTING OF FRESH AND HARDENED CONCRETE
Concrete Slump Test
This test is performed to check the consistency of freshly made concrete.
The slump test is done to make sure a concrete mix is workable.
The measured slump must be within a set range, or tolerance, from the target slump.
Workability of concrete is mainly affected by consistency i.e. wetter mixes will be more workable
than drier mixes, but concrete of the same consistency may vary in workability.
It can also be defined as the relative plasticity of freshly mixed concrete as indicative of its
workability.
Tools and apparatus used for slump test (equipment):
1.
2.
3.
4.
5.
Standard slump cone (100 mm top diameter x 200 mm bottom diameter x 300 mm high)
Small scoop
Bullet-nosed rod (600 mm long x 16 mm diameter)
Rule
Slump plate (500 mm x 500 mm)
Procedure of slump test for concrete:
 Clean the cone. Dampen with water and place on the slump plate. The slump plate should be
clean, firm, level and non-absorbent. Collect a sample of concrete to perform the slum test
.
 Stand firmly on the footpieces and fill 1/3 the volume of the cone with the sample. Compact
the concrete by 'rodding' 25 times. Rodding means to push a steel rod in and out of the
concrete to compact it into the cylinder, or slump cone. Always rod in a definite pattern,
working from outside into the middle.
 Now fill to 2/3 and again rod 25 times, just into the top of the first layer.
 Fill to overflowing, rodding again this time just into the top of the second layer. Top up the
cone till it overflows.
 Level off the surface with the steel rod using a rolling action. Clean any concrete from around
the base and top of the cone, push down on the handles and step off the footpieces.
 Carefully lift the cone straight up making sure not to move the sample.
Turn the cone upside down and place the rod across the up-turned cone.
Take several measurements and report the average distance to the top of the sample.If the
sample fails by being outside the tolerance (ie the slump is too high or too low), another must be
taken. If this also fails the remainder of the batch should be rejected.
Compression Test
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The compression test shows the compressive strength of hardened concrete.
The compression test shows the best possible strength concrete can reach in perfect
conditions.
The compression test measures concrete strength in the hardened state. Testing should
always be done carefully. Wrong test results can be costly.
The testing is done in a laboratory off-site. The only work done on-site is to make a
concrete cylinder for the compression test.
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The strength is measured in Megapascals (MPa) and is commonly specified as a
characteristic strength of concrete measured at 28 days after mixing.
The compressive strength is a measure of the concrete’s ability to resist loads which tend
to crush it.
Apparatus for compression test
Cylinders (100 mm diameter x 200 mm high or 150 mm diameter x 300 mm high) (The small
cylinders are normally used for most testing due to their lighter weight)
1.
2.
3.
4.
Small scoop
Bullet-nosed rod (600 mm x 16 mm)
Steel float
Steel plate
Procedure for compression test of concrete
 Clean the cylinder mould and coat the inside lightly with form oil, then place on a clean, level
and firm surface, ie the steel plate. Collect a sample.
 Fill 1/2 the volume of the mould with concrete then compact by rodding 25 times. Cylinders
may also be compacted by vibrating using a vibrating table.
 Fill the cone to overflowing and rod 25 times into the top of the first layer, then top up the
mould till overflowing.
 Level off the top with the steel float and clean any concrete from around the mould.
 Cap, clearly tag the cylinder and put it in a cool dry place to set for at least 24 hours.
 After the mould is removed the cylinder is sent to the laboratory where it is cured and crushed
to test compressive strength
1.14 QUALITY OF CONCRETE
Test conducted on site for quality control
Slump test
This is a site test to determine the workability of the ready mixed concrete just before its placing
to final position inside the formwork, and is always conducted by the supervisor on site. However
in mid of concreting process , should the site supervisor visually finds that the green concrete
becomes dry or the placement of concrete has been interrupted , a re-test on the remaining
concrete should be conducted in particular of the pour for congested reinforcement area . The
procedure of test in brief is as follows: 1. Ensure the standard Slump Cone and associated equipment are clean before test and free
from hardened concrete.
2. Wet the Slump Cone and drain away the superfluous water.
3. Request the mixer or concrete truck to well mix the concrete for additional 5 minutes.
4. Place the Slump Cone on one side ( i.e. not in middle ) of the base plate on leveled ground and
stand with feet on the foot-pieces of cone .
5. Using a scoop and fill the cone with sampled concrete in 3 equal layers, each of about 100mm
thick.
6. Compact each layer of concrete in turn exactly 25 times with a Slump Rod, allowing the rod
just passes into the underlying layer.
7. While tamping the top layer, top up the cone with a slight surcharge of concrete after the
tamping operation.
8. Level the top by a “sawing and rolling” motion of the Slump Rod across the cone.
9. With feet are still firmly on the foot-pieces, wipe the cone and base plate clean and remove any
leaked concrete from bottom edge of the Slump Cone.
10. Leave the foot-pieces and lift the cone carefully in a vertical up motion in a few seconds time.
11. Invert the cone on other side and next to the mound of concrete.
12. Lay the Slump Rod across the inverted cone such that it passes above the slumped concrete
at its highest point.
13. Measure the distance between the underside of rod and the highest point of concrete to the
nearest 5mm.
14. This reading is the amount that the sampled concrete has slumped.
15. If the concrete does not show an acceptable slump, repeat the test with another sample.
16. If the repeated test still does not show an acceptable slump, record this fact in the report, or
reject that load of concrete.
Compression test
The Compression Test is a laboratory test to determine the characteristic strength of the concrete
but the making of test cubes is sometimes carried out by the supervisor on site. This cube test
result is very important to the acceptance of insitu concrete work since it demonstrates the
strength of the design mix.
The procedure of making the test cubes is as follows: 1. 150 mm standard cube mold is to be used for concrete mix and 100 mm standard cube
mold is to be used for grout mix.
2. Arrange adequate numbers of required cube molds to site in respect with the sampling
sequence for the proposed pour.
3. Make sure the apparatus and associated equipment ( see Fig 7 – 6 ) are clean before
test and free from hardened concrete and superfluous water .
4. Assemble the cube mold correctly and ensure all nuts are tightened.
5. Apply a light coat of proprietary mold oil on the internal faces of the mold.
6. Place the mold on level firm ground and fill with sampled concrete to a layer of about
50 mm thick.
7. Compact the layer of concrete thoroughly by tamping the whole surface area with the
Standard Tamping Bar. (Note that no less than 35 tamps / layer for 150 mm mold and no
less than 25 tamps / layer for 100 mm mold).
8. Repeat Steps 5 & 6 until the mold is all filled. (Note that 3 layers to be proceeded for
150 mm mold and 2 layers for 100 mm mold).
9. Remove the surplus concrete after the mold is fully filled and trowel the top surface
flush with the mold.
10. Mark the cube surface with an identification number (say simply 1, 2, 3, etc) with a
nail or match stick and record these numbers in respect with the concrete truck and
location of pour where the sampled concrete is obtained.
11. Cover the cube surface with a piece of damp cloth or polythene sheeting and keep
the cube in a place free from vibration for about 24 hours to allow initial set .
12. Strip off the mold pieces in about 24 hours after the respective pour is cast. Press the
concrete surface with the thumb to see any denting to ensure the concrete is sufficiently
hardened, or otherwise de-molding has to be delayed for one more day and this
occurrence should be stated clearly in the Test Report.
13. Mark the test cube a reference number with waterproof felt pen on the molded side, in
respect with the previous identification number.
14. Place the cube and submerge in a clean water bath or preferably a thermostatically
controlled curing tank until it is delivered to the accredited laboratory for testing.
1.15 NONDESTRUCTIVE TESTING
Nondestructive testing (NDT) is a wide group of analysis techniques used in science and
industry to evaluate the properties of a material, component or system without causing
damage.[1] Because NDT does not permanently alter the article being inspected, it is a highly-
valuable technique that can save both money and time in product evaluation, troubleshooting,
and research. Common NDT methods include ultrasonic, magnetic-particle, liquid penetrant,
radiographic, remote visual inspection (RVI) and eddy-current testing.NDT is a commonlyused tool in forensic engineering, mechanical engineering, electrical engineering, civil
engineering, systems engineering, aeronautical engineering, medicine, and art.
N D T - METHODS
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VISUAL INSPECTION
REBOUND HAMMER
ULTRASONIC PULSE VELOCITY METER
PENETRATION RESISTANCE
PULL OUT STRENGTH
COVER METER
CARBONATION DEPTH
CORROSION MAPPING
MATURITY METER
PERMEABILITY TEST
RADIOGRAPHY
REBOUND HAMMER
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MOST COMMON NDT METHOD
DEVELOPED IN 1948
MEASURES REBOUND HARDNESS OF CONCRETE
NO THEORETICAL RELATIONSHIP AVAILABLE FOR ASSESSMENT OF STRENGTH
EMPIRICAL RELATIONSHIP BETWEEN REBOUND HARDNESS AND STRENGTH
DEVELOPED
CONDUCT ON SMOOTH AND UNIFORM FACE
AVOID ROUGH SPOTS, HONEY COMBS
AVOID TROWELLED SURFACES
THIN SECTIONS (< 100 mm) SHOULD BE BACKED UP TO AVOID DEFLECTIONS
TAKE ATLEAST 15 REBOUND READINGS IN ANY ONE TEST
CALCULATE THE MEAN
COMPARE DEVIATION OF READINGS FROM THE MEAN
TEST IS CONSIDERED RELIABLE IF THE DEVIATION OF TEN READINGS IS NOT
MORE THAN THE FOLLOWING:
REBOUND VALUE 15
30
45
DEVIATION
3
3.5
2.5
 USE BEST 10 READINGS FOR CALCULATING THE MEAN
 DETERMINE COMPRESSIVE STRENGTH BY REFERRING TO REBOUND NUMBER
VS STRENGTH CHARTS AGAINST THE MEAN VALUE
 BEST ACCURACY ACHIEVEABLE IS WITHIN + 20%
PULSE VELOCITY METHOD
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DEVELOPED IN 1940s
BASED UPON PROPOGATION OF ULTRASONIC WAVES IN ELASTIC MEDIUM
MEASURES VELOCITY OF PROPOGATION OF ULTRASONIC WAVES
VELOCITY RELATED TO THE DENSITY OF THE MEDIUM V=(E/p)1/2
STRENGTH IS DEDUCED FROM THE DENSITY OF THE MEDIUM
 FREQUENCY OF WAVES USED - 20 - 150 kHz
 TYPES OF TESTING METHOD
 DIRECT TRANSMISSION
 SEMI DIRECT TRANSMISSION
 SURFACE TRANSMISSION
 DIRECT TRANSMISSION METHOD IS THE BEST BUT IT REQUIRES ACCESS TO
TWO OPPOSITE SIDES OF CONCRETE MEMBER
LIMITATIONS OF N D T
ALL NDT METHODS ARE INDIRECT
CORELATION BETWEEN MEASURED PARAMETER AND CONCRETE STRENGTH IS
NEVER EXACT.
EFFECTIVENESS OF NDT REDUCES WITH HETEROGENEITY OF THE MATERIAL
RESULTS ARE DEPENDENT ON TOO MANY PARAMETERS
NORMALLY ACHIEVEABLE LEVEL OF ACCURACY IS + 25%
INTERPRETATION OF RESULTS REQUIRE INTUITIVE JUDGEMENT