Concrete book cement bleeding

Introduction: Cement Concrete is composite product obtained by mixing cement, water and an
inert matrix of sand and gravel or crushed stone. When the aggregate is mixed together with the
dry cement and water, they form a fluid mass that is easily mouldable into any shape. The cement
reacts chemically with the water and other ingredients to form a hard matrix, which binds all the
materials

together

into

a

durable

stone-like

material,

The ingredients of concrete fall into two groups namely:(a) active ingredients: cement and water

which

hardens

over

time.

(b) inactive ingredients: Fine and coarse aggregate
Famous concrete structures include the Hoover Dam, the Panama Canal and the Roman
Pantheon. The earliest large-scale users of concrete technology were the ancient Romans, and
concrete was widely used in the Roman Empire. The Colosseum in Rome was built largely of
concrete, and the concrete dome of the Pantheon is the world's largest unreinforced concrete
dome. Today, large concrete structures (for example, dams and multi-storey car parks) are
usually made with reinforced concrete.
Today, concrete is the most widely used man-made material (measured by tonnage).

History
The word concrete comes from the Latin word "concretus" (meaning compact or condensed), the
perfect passive participle of "concrescere", from "con-" (together) and "crescere" (to grow).
Perhaps the earliest known occurrence of cement was twelve million years ago.
On a human time-scale, small usages of concrete go back for thousands of years. The ancient
Nabatea culture was using materials roughly analogous to concrete at least eight thousand years
ago, some structures of which survive to this day.
German archaeologist Heinrich Schliemann found concrete floors, which were made of lime and
pebbles, in the royal palace of Tiryns, Greece, which dates roughly to 1400-1200 BC. Lime
mortars were used in Greece, Crete, and Cyprus in 800 BC. The Assyrian Jerwan Aqueduct (688
BC) made use of waterproof concrete. Concrete was used for construction in many ancient
structures. Aggregate: The inert filler material that makes up the bulk of concrete. Usually sand,
gravel, and rocks. Fibers and reinforcing bars are not considered aggregate.
Terminology
Bleeding: An undesirable process of mix water separating from the fresh cement paste or
concrete while it is being placed or consolidated.
Cement: This word is used colloquially to mean several very different things: the dry unreacted
powder that comes in a sack, the sticky fluid stuff formed just after water is added, and the
rocklike substance that forms later on. As noted above, people also tend to use it to refer to

concrete. Obviously this won’t work for people who want to have technical discussions. For our
purposes, the word cement used by itself refers to the dry unreacted powder.
Cement paste: Cement (see above) that has been mixed with water. Usually the term implies
that it has already become hard (see Fresh).
Concrete: A mixture of sand, gravel, and rocks held together by cement paste. The world’s most
widely-used man-made material.
Curing/Hardening: Essentially interchangeable terms that mean the process of continued
strength gain after the cement paste has set due to chemical reactions between cement and
water.
Fresh: Refers to cement paste or concrete that has been recently mixed and is still fluid. This is
what those big trucks with the rotating container on the back are full of. (These are often called
“cement mixers” but now you know why they should be called “concrete mixers”).
Hardened: Refers to cement paste or concrete that has gained enough strength to bear some
load.
Heat of hydration: Like most spontaneous chemical reactions, the hydration reactions between
cement and water are exothermic, meaning that they release heat. Large volumes of concrete
can warm up considerably during the first few days after mixing when hydration is rapid. This is
generally a bad thing, for reasons that will be discussed.
Hydration: The chemical reactions between cement and water. Hydration is what causes cement
paste to first set and then harden.
Hydration products: The new solid phases that are formed by hydration.
Mature: Refers to cement paste or concrete that has reached close to its full strength and is
reacting very slowly, if at all. An age of 28 days is a very rough rule of thumb for reaching
maturity.
Mortar: A mixture of cement paste and sand used in thin layers to hold together bricks or stones.
Technically, mortar is just a specific type of concrete with a small maximum aggregate size.
Placing: The process of transferring fresh concrete from the mixer to the formwork that defines
its final location and shape

Segregation: An undesirable process of the aggregate particles becoming unevenly distributed
within the fresh cement paste while the concrete is being placed or consolidated.
Set: The transition from fresh cement paste to hardened cement paste. The terms “initial set”
and “final set” refer to specific times when the paste becomes no longer workable and completely
rigid, respectively. “Setting” is the process by which this occurs.
Application of Cement Concrete:Roads
bricks/blocks
Beams
sewer pipes
Canals
Dams
Caskets
Tombs
swimming pools
Canoes
Tunnels
holding tanks
flower pots & planters

Sidewalks
Bridges
Foundations
water mains
missile silos
Churches
Monuments
indoor furniture
airport runways
Barges
parking garages
Chimneys
bath tubs

houses
walls
floors
containment of nuclear waste
solidification of hazardous wastes
garden ornaments
subways
patio bricks
sculptures
grave vaults

Composition of concrete
There are many types of concrete available, created by varying the proportions of the main
ingredients below. In this way or by substitution for the cementations and aggregate phases, the
finished product can be tailored to its application with varying strength, density, or chemical and

thermal

resistance

properties.

The main ingredients of the cement concrete are listed below:1) Cement – The Glue in Concrete
The responsible for bonding, the word cement by itself only to mean the dry unreacted
powder. Once water is added, it becomes cement paste - the glue that holds concrete together.
This is justified because vastly more Portland cement is used throughout the world than all other
types of cement combined. The name "Portland cement" arose in the 1820s because one of the
early developers of modern calcium silicate cements, and Englishman named Joseph Aspdin,
thought that the hardened paste bore a resemblance to Portland limestone, a commonly used
building stone quarried on the Isle of Portland. Giving a man-made building material a name that
connotes the hardness and durability of stone was of course a shrewd marketing move.
The Cement used shall be any of the following and the type selected should be appropriate for
the intended use(As per IS 456:2000)
a) 33 Grade ordinary Portland cement conforming to IS 269
b) 43 Grade ordinary Portland cement conforming to IS 8112
c) 33 Grade ordinary Portland cement conforming to IS 12269
d) Rapid hardening Portland cement conforming to IS 8041

e) Portland slag cement conforming to IS 455

f) Portland pozzolana cement (fly ash based) conforming to IS 1489 (Part 1)
g) Portland Pozzolana cement (Calcined clay based) conforming to IS 1489 (Part-2)
h) Hydrophobic cement conforming to IS 8043
i)

Low heat Portland cement conforming to IS 12600

Components of Cement
Comparison of Chemical and Physical Characteristics
Siliceous
Calcareous
Portland (ASTM C618 Class (ASTM C618 Class Slag
Cement F)
C)
Cement
Fly Ash
Fly Ash

Property

Silica
Fume

SiO2 content (%) 21

52

35

35

85–97

Al2O3
(%)

content

5

23

18

12

—

Fe2O3
(%)

content

3

11

6

1

—

CaO content (%) 62

5

21

40

<1

Specific surfaceb
370
(m2/kg)

420

420

400

15,000–
30,000

Specific gravity

2.38

2.65

2.94

2.22

Cement
replacement

Cement
replacement

Cement
Property
replacement enhancer

General
in concrete

3.15

use Primary
binder

a

Values shown are approximate: those of a specific material may vary.

b

Specific surface measurements for silica fume by nitrogen adsorption (BET) method,
others by air permeability method (Blaine).

Aggregates: Aggregate should be as per with the requirement of

IS 383. As far possible

preference shall be given to natural aggregate.
a.

Other types of aggregate such as slag and cursed over burnt bricks or tile which may be

found suitable with regard to strength durability of concrete and freedom from harmful effects may
be used for plain concrete members but such aggregate should be used not contain more then
0.5 percent of sulphates as So, and should not absorb more than 10 percent of their own mass
of water.

b. Heavy weight aggregates or light weight aggregates such as bloated aggregates and sintered
fly ash aggregate may also be used provided the engineer in charge is satisfied with the data on
the properties of concrete made with them.
Size of Aggregate :
a.) The nominal maximum size of coarse aggregate should be as large as possible within the
limits specified but in no case greater than one-fourth of the minimum thickness of the member,
provided that the concrete can be placed without difficulty so as to surround all reinforcement
thoroughly and fill the corners of the form.
b)The nominal maximum size of coarse aggregate should be as large as possible within the limits
specified but in no case greater that one fourth of the minimum thickness of the members
provided that the concrete can be placed without difficulty so as to surround all reinforcement
thoroughly and fill the corners of the form. For most work 20mm aggregate is suitable where there
is no restriction to the flow of concrete into section 40mm or larger size may be permitted in
concrete elements with thin sections closely spaced or small cover. Consideration should be
given to the use to 10mm nominal maximum size. Plums above 160mm and up to any reasonable
size may be used in plain concrete work up to a maximum limit of 20 percent by volume of
concrete when specifically permitted by the engineer in charge. The plums shall be distributed
evenly and shall be not closer than 150 mm from the surface
c)

For heavily reinforced concrete members as in the case of the ribs of main beams the

nominal maximum size of the aggregate should usually be restricted to 5 mm less that the
minimum clear distance between the main bars or 5mm whichever is smaller.
d)

Coarse and fine aggregate shall be batched separately All-in aggregate shall be used

only where specifically permitted by the engineer in charge.
e)

Construction of Pavement Quality Concrete (PQM) nominal size of 31.5 Mineral

Admixture
a)

Pozzolana materials conforming to relevant indian standard may be used with the

permission of the engineer in charge provided uniform blending with cement is ensured
b)

Fly ash conforming to Grade 1 to IS 3812 may be used as part replacement of ordinary

Portland cement provided uniform blending with cement is ensured
c)

Silica fume conforming to a standard approved by the deciding authority may be used as

part replacement of cement provided uniform with the cement is ensured.

d)

Rice husk ash giving required performance and uniformity characteristics may be used

with the approval of the deciding authority.
Metakaoline having fineness between 700 to 900 m 2/kg may be used as pozzolanic

e)

material in concrete.
f)

Ground granulated blast furnace slag obtained by grinding granulated blast furnace slag

conforming to IS 12089 may be used as part replacement of ordinary Portland cements provided
uniform blending with cement is ensued.
g)

Other types of aggregates such as slag and crushed overburnt bricks or tile, which may

be found suitable with regard to strength durability of concrete and freedom from harmful effects
may be used for plain concrete members but such aggregates should not contain more than 0.5
percent of sulphates should as So and should not absorb more than 10 percent of their own
mass of water.
Chemical admixtures
Chemical admixtures are materials in the form of powder or fluids that are added to the concrete
to give it certain characteristics not obtainable with plain concrete mixes. In normal use,
admixture dosages are less than 5% by mass of cement and are added to the concrete at the
time of batching/mixing. (See the section on Concrete Production, below.)The common types of
admixtures] are as follows.


Accelerators speed up the hydration (hardening) of the concrete. Typical materials used
are

CaCl

2, Ca(NO3)2 and NaNO3. However, use of chlorides may cause corrosion in steel
reinforcing and is prohibited in some countries, so that nitrates may be favored.
Accelerating admixtures are especially useful for modifying the properties of concrete in
cold weather.


Retarders slow the hydration of concrete and are used in large or difficult pours where
partial setting before the pour is complete is undesirable. Typical polyol retarders are
sugar, sucrose, sodium gluconate, glucose, citric acid, and tartaric acid.



Air entraining agents add and entrain tiny air bubbles in the concrete, which reduces
damage during freeze-thaw cycles, increasing durability. However, entrained air entails a
trade off with strength, as each 1% of air may decrease compressive strength 5%. If too
much air becomes trapped in the concrete as a result of the mixing process, Defoamers
can be used to encourage the air bubble to agglomerate, rise to the surface of the wet
concrete and then disperse.



Plasticizers increase the workability of plastic or "fresh" concrete, allowing it be placed
more easily, with less consolidating effort. A typical plasticizer is lignosulfonate.
Plasticizers can be used to reduce the water content of a concrete while maintaining
workability and are sometimes called water-reducers due to this use. Such treatment
improves its strength and durability characteristics.



Superplasticizers (also called high-range water-reducers) are a class of plasticizers that
have fewer deleterious effects and can be used to increase workability more than is
practical with traditional plasticizers. Compounds used as superplasticizers include
sulfonated naphthalene formaldehyde condensate, sulfonated melamine formaldehyde
condensate, acetone formaldehyde condensate and polycarboxylate ethers.



Pigments can be used to change the color of concrete, for aesthetics.



Corrosion inhibitors are used to minimize the corrosion of steel and steel bars in
concrete.



Bonding agents are used to create a bond between old and new concrete (typically a
type of polymer) with wide temperature tolerance and corrosion resistance.



Pumping aids improve pumpability, thicken the paste and reduce separation and
bleeding.

Water – The Activator in Concrete
Water is then mixed with this dry /aggregate blend, which produces a semi-liquid that workers
can shape (typically by pouring it into a form). The concrete solidifies and hardens through a
chemical process called hydration. Hydration involves many different reactions, often occurring at
the same time. As the reactions proceed, the products of the cement hydration process gradually
bond together the individual sand and gravel particles and other components of the concrete to
form a solid mass.
Reaction:
Cement chemist notation C3S + H → C-S-H + CH
Standard notation: Ca3SiO5 + H2O → (CaO)·(SiO2)·(H2O)(gel) + Ca(OH)2
Balanced: 2Ca3SiO5 + 7H2O → 3(CaO)·2(SiO2)·4(H2O)(gel) + 3Ca(OH)2
The water reacts with the cement, which bonds the other components together, creating a robust
stone-like material.
Effects of Water Cement Ratio :Another important issue associated with the mix water is the amount that is added in relation to
the amount of cement. This important parameter is called the water/cement ratio, or "w/c", and it

always refers to the weights of water and cement.. Although there are many aspects of the
concrete mix design and the curing process that affect the final properties of the concrete, the w/c
is probably the most important. If the w/c is too low, the concrete will be stiff and clumpy and will
be difficult to place. However, the lower the w/c, the stronger and more durable the final concrete.
This is easy to understand when one realizes that any space in the fresh concrete that is
originally occupied by the mix water will end up as porosity in the hardened concrete. Porosity
lowers the intrinsic strength and makes it easier for the concrete to corrode, crack, and spall. For
this reason, the w/c should be a low as possible, meaning just high enough so that the concrete
can be placed properly. This will depend on many factors, such as the amount, size, and shape of
the aggregate , the fineness of the cement, the type of form or mold the concrete is being placed
into, and the type of reinforcement.
A lower water-to-cement ratio yields a stronger, more durable concrete, whereas more water
gives a freer-flowing concrete with a higher slump. Impure water used to make concrete can
cause problems when setting or in causing premature failure of the structure.
Due to increase in water cement ratio, effect on properties of concrete has been illustrated in
following table:-

Mix
Proportion

WaterCement
Ratio

Age
(day)

1:2:4
1:2:4
1:2:4
1:2:4
1:2:4
1:2:4
1:2:4
1:2:4
1:2:4
1:2:4
1:2:4
1:2:4
1:2:4
1:2:4
1:2:4

0.55
0.60
0.65
0.70
0.80
0.55
0.60
0.65
0.70
0.80
0.55
0.60
0.65
0.70
0.80

7
7
7
7
7
14
14
14
14
14
28
28
28
28
28

Weight
of
Cube
(g)
8100
7850
7799
7499
7401
8300
8000
7897
7600
7450
8397
8100
8000
7698
7600

Density
of
Cube
(g/cm3)
2.400
2.326
2.311
2.222
2.193
2.459
2.370
2.340
2.252
2.207
2.488
2.400
2.370
2.281
2.252

Crushi
ng
Load
(KN)
245
238
237
218
207
360
323
305
290
281
450
390
385
367
360

Compressive
Strength
(N/mm2)
10.89
10.58
10.53
9.69
9.20
16.00
14.36
13.56
12.89
12.49
20.00
17.33
17.11
16.31
16.00

TYPES OF CONCRETE WITH APPLICATIONS
Types of concrete with applications for different structural components like beams, columns,
slabs,
foundations
are
explained
here.
Special
concrete
with
uses.

Light weight concrete
One of the main advantages of conventional concrete is the self weight of concrete. Density of
normal concrete is of the order of 2200 to 2600. This self weight will make it to some extend an
uneconomical structural material.
1. Self weight of light weight concrete varies from 300 to 1850 kg/m3.
2. It helps reduce the dead load, increase the progress of building and lowers the hauling
and handling cost.

3. The weight of building on foundation is an important factor in the design , particularly in
case of weak soil and tall structures. In framed structure , the beam and column have to
carry load of wall and floor. If these wall and floor are made of light weight concrete it will
result in considerable economy.
4. Light weight concrete have low thermal conductivity.( In extreme climatic condition where
air condition is to installed the use of light weight concrete with low thermal conductivity is
advantageous from the point of thermal comfort and low power consumption.
5. Only method for making concrete light by inclusion of air. This is achieved by a) replacing
original mineral aggregate by light weight aggregate, b) By introducing gas or air bubble
in mortar c) By omitting sand fraction from concrete. This is called no – fine concrete. No
fine concrete is made up of only coarse aggregate , cement and water.These type of
concrete is used for load bearing cast in situ external walls for building. They are also
used for temporary structures because of low initial cost and can be reused as
aggregate.
6. Light weight aggregate include pumice, saw dust rice husk, thermocole beads, formed
slag. Etc
7. Light weight concrete aggregate exhibit high fire resistance.
8. Structural lightweight aggregate’s cellular structure provides internal curing through water
entrainment which is especially beneficial for high-performance concrete
9. lightweight aggregate has better thermal properties, better fire ratings,

reduced

shrinkage, excellent freezing and thawing durability, improved contact between aggregate
and cement matrix, less micro-cracking as a result of better elastic compatibility, more
blast resistant, and has better shock and sound absorption, High-Performance lightweight
aggregate concrete also has less cracking, improved skid resistance and is readily
placed by the concrete pumping method
High density concrete
1. The density of high density concrete varies from 3360 kg/m3 to 3840 kg/m3.They can
however be produced with density upto 5820 kg/m3 using iron as both fine and coarse
aggregate.
2. Heavyweight concrete uses heavy natural aggregates such as barites or magnetite or
manufactured aggregates such as iron or lead shot. The density achieved will depend on
the type of aggregate used. Typically using barites the density will be in the region of
3,500kg/m3, which is 45% greater than that of normal concrete, while with magnetite the
density will be 3,900kg/m 3, or 60% greater than normal concrete. Very heavy concretes can

be achieved with iron or lead shot as aggregate, is 5,900kg/m 3 and 8,900kg/m3
respectively.
1. They are mainly used in the construction of radiation shields (medical or nuclear).
Offshore, heavyweight concrete is used for ballasting for pipelines and similar structures
2. The ideal property of normal and high density concrete are high modulus of elasticity ,
low thermal expansion , and creep deformation
3. Because of high density of concrete there will be tendency for segregation. To avoid this
pre placed aggregate method of concreting is adopted.
4. High Modulus of Elasticity, Low thermal Expansion ,Low elasticity and creep deformation
are ideal properties.
5. The high density. Concrete is used in construction of radiation shields. They are effective
and economic construction material for permanent shielding purpose.
6. Most of the aggregate specific gravity is more than 3.5
Mass concrete
Mass concrete is defined in ACI as “any volume of concrete with dimensions large enough to
require that measures be taken to cope with generation of heat from hydration of the cement and
attendant volume change to minimize cracking.” The design of mass concrete structures is
generally based on durability, economy, and thermal action, with strength often being a
secondary, rather than a primary, concern. The one characteristic that distinguishes mass
concrete from other concrete work is thermal behavior. Because the cement-water reaction is
exothermic by nature, the temperature rise within a large concrete mass, where the heat is not
quickly dissipated, can be quite high. Significant tensile stresses and strains may result from the
restrained volume change associated with a decline in temperature as heat of hydration is
dissipated. Measures should be taken where cracking due to thermal behavior may cause a loss
of structural integrity and monolithic action, excessive seepage and shortening of the service life
of the structure, or be aesthetically objectionable. Many of the principles in mass concrete
practice can also be applied to general concrete work, whereby economic and other benefits may
be realized. Mass concreting practices were developed largely from concrete dam construction,
where temperature-related cracking was first identified. Temperature-related cracking has also
been experienced in other thick-section concrete structures, including mat foundations, pile caps,
bridge piers, thick walls, and tunnel linings
Ready-mix Concrete

Ready-mix concrete has cement, aggregates, water

and

other

ingredients,

which

are

weigh-batched at a centrally located plant. This is then delivered to the construction site
in truck mounted transit mixers and can be used straight away without any further treatment. This
results in a precise mixture, allowing specialty concrete mixtures to be developed and
implemented on construction sites. Ready-mix concrete is sometimes preferred over on-site
concrete mixing because of the precision of the mixture and reduced worksite confusion.
However, using a pre-determined concrete mixture reduces flexibility, both in the supply chain
and in the actual components of the concrete. Ready Mixed Concrete, or RMC as it is popularly
called, refers to concrete that is specifically manufactured for delivery to the customer’s
construction site in a freshly mixed and plastic or unhardened state. Concrete itself is a mixture of
Portland cement, water and aggregates comprising sand and gravel or crushed stone. In
traditional work sites, each of these materials is procured separately and mixed in specified
proportions at site to make concrete. Ready Mixed Concrete is bought and sold by volume –
usually expressed in cubic meters. Ready Mixed Concrete is manufactured under computercontrolled operations and transported and placed at site using sophisticated equipment and
methods. RMC assures its customers numerous benefits.
Advantages of Ready mix Concrete over Site mix Concrete


A centralised concrete batching plant can serve a wide area.



The plants are located in areas zoned for industrial use, and yet the delivery trucks can
service residential districts or inner cities.



Better quality concrete is produced.



Elimination of storage space for basic materials at site.



Elimination of procurement / hiring of plant and machinery



Wastage of basic materials is avoided.



Labor associated with production of concrete is eliminated.



Time required is greatly reduced.



Noise and dust pollution at site is reduced.

Disadvantages of Ready-Mix Concrete


The materials are batched at a central plant, and the mixing begins at that plant, so the
traveling time from the plant to the site is critical over longer distances. Some sites are
just too far away, though this is usually a commercial rather than technical issue.



Access roads and site access have to be able to carry the weight of the truck and load.
Concrete is approx. 2.5tonne per m². This problem can be overcome by utilizing so-called

‘minimix’ companies, using smaller 4m³ capacity mixers able to access more restricted
sites.


Concrete’s limited time span between mixing and going-off means that ready-mix should
be placed within 2 hours of batching at the plant. Concrete is still usable after this point
but may not conform to relevant specifications.

Polymer concrete
Concrete is porous. The porosity is due to air voids , water voids or due to inherent property of gel
structures. On account of porosity strength of concrete is reduced , reduction of porosity result in
increase in strength of concrete. The impregnation of monomer and subsequent polymerization is
the latest technique adopted to reduce inherent porosity of concrete and increase strength and
other properties of concrete
There are mainly 4 types of polymer concrete
1. Polymer impregnated concrete
2. Polymer cement concrete
3. Polymer concrete
4. Partially impregnated and surface coated polymer concrete.
Polymer impregnated concrete
It is a precast conventional concrete cured and dried in oven or by dielectric heating from which
the air in the open cell is removed by vacuum. Then a low viscosity monomer is diffused through
the open cell and polymerized by using radiation, application of heat or by chemical initiation.
Mainly the following type of monomers are used
Methyl methacrlylate(MMA)
1. Acrylonitrile
2. t- butyl styrene
3. Other thermoplastic monomer

4. The amount of monomer that can be loaded into a concrete specimen is limited by the amount
of water and air that has occupied the total void space.
5. PIC require cast in situ structures
Polymer cement concrete
Polymer cement concrete is made by mixing cement, aggregate, water and monomer. Such
plastic mixture is cast in moulds , cured dried and polymerized. The monomer that are used in
PCC are
1. Polyster- styrene
2. Epoxy-styrene
3. Furans
4. Vinyldene chloride
PCC produced in this way have been disappointing. In many cases material poorer than ordinary
concrete is obtained.This is because organic material are incompatable with aqueous systems
and some times interfere with the alkaline cement hydration process. Russians developed a
superior polymer by incorporation of furfuryl alcohol and aniline hydrochloride in the wet mix. This
material is dense and non shrinking and to have high corrosion resistance, low permeability and
high resistance to vibration and axial extension .PCC can be cast in situ for field application.
Polymer concrete
Polymer concrete is an aggregate bound with a polymer binder instead of Portland cement as in
conventional concrete. The main technique in producing PC is to minimize void volume in the
aggregate mass so as to reduce the quantity of polymer needed for binding the aggregate. This is
achieved by properly grading and mixing the aggregate to attain maximum density and minimum
voids
Shotcrete
It is defined as a mortar conveyed through a hose and pneumatically projected at high velocity on
to a surface. There are mainly two different methods namely wet mix and dry mix process. In wet
mix process the material is conveyed after mixing with water. Shotcrete is a process where
concrete is projected or "shot" under pressure using a feeder or "gun" onto a surface to form

structural shapes including walls, floors, and roofs. The surface can be wood, steel, polystyrene,
or any other surface that concrete can be projected onto. The surface can be trowelled smooth
while the concrete is still wet. The properties of both wet and dry process shotcrete can be further
enhanced through the addition of many different additives or admixtures .
a) Wet method – All ingredients, including water, are thoroughly mixed and introduced into the
delivery equipment. Wet material is pumped to the nozzle where compressed air is added to
provide high velocity for placement and consolidation of the material onto the receiving surface.
b) Dry method – Pre-blended dry or damp materials are placed into the delivery equipment.
Compressed air conveys material through a hose at high velocity to the nozzle, where water is
added. Material is consolidated on the receiving surface by the high-impact velocity.

c) Advantages
Shotcrete has high strength, durability, low permeability, excellent bond and limitless shape
possibilities. These properties allow shotcrete to be used in most cases as a structural material.
Although the hardened properties of shotcrete are similar to conventional cast-in-place concrete,
the nature of the placement process provides additional benefits, such as excellent bond with
most substrates and instant or rapid capabilities, particularly on complex forms or shapes. In
addition to building homes, shotcrete can also be used to build pools
Pre packed concrete
In constructions where the reinforcement is very complicated or where certain arrangements like
pipe, opening or other arrangements are incorporated this type of concreting is adopted. One of
the methods is concrete process in which mortar is made in a high speed double drum and
grouting is done by pouring on prepacked aggregate. This is mainly adopted for pavement slabs
Vacuum concrete
Concrete poured into a framework that is fitted with a vacuum mat to remove water not required
for setting of the cement; in this framework, concrete attains its 28-day strength in 10
days and has a 25% higher crushing strength. The elastic and shrinkage deformations
are considerably greater than for normal-weight concrete. Specialty Concretes
Pervious concrete

Pervious concrete is a mix of specially graded coarse aggregate, cement, water and little-to-no
fine aggregates. This concrete is also known as "no-fines" or porous concrete. Mixing the
ingredients in a carefully controlled process creates a paste that coats and bonds the aggregate
particles. The hardened concrete contains interconnected air voids totalling approximately 15 to
25 percent. Water runs through the voids in the pavement to the soil underneath. Air entrainment
admixtures are often used in freeze–thaw climates to minimize the possibility of frost damage.

Nano concrete is created by High-energy mixing (HEM) of cement, sand and water using a
specific consumed power of 30 - 600 watt/kg for a net specific energy consumption of at least 5
kJ/kg of the mix. A plasticizer or a superplasticizer is then added to the activated mixture which
can later be mixed with aggregates in a conventional concrete mixer. In the HEM process sand
provides dissipation of energy and increases shear stresses on the surface of cement particles.
The quasi-laminar flow of the mixture characterized with Reynolds number less than 800 is
necessary to provide more effective energy absorption. This results in the increased volume of
water interacting with cement and acceleration of Calcium Silicate Hydrate (C-S-H) colloid
creation. The initial natural process of cement hydration with formation of colloidal globules about
5 nm in diameter[50] after 3-5 min of HEM spreads out over the entire volume of cement – water
matrix. HEM is the "bottom-up" approach in Nanotechnology of concrete. The liquid activated
mixture is used by itself for casting small architectural details and decorative items, or foamed
(expanded) for lightweight concrete. HEM Nano concrete hardens in low and subzero
temperature conditions and possesses an increased volume of gel, which drastically reduces
capillarity in solid and porous materials.
Microbial concrete
Bacteria such as Bacillus pasteurii, Bacillus pseudofirmus, Bacillus cohnii, Sporosarcina pasteuri,
and Arthrobacter crystallopoietes increase the compression strength of concrete through their
biomass. Not all bacteria increase the strength of concrete significantly with their biomass.
Bacillus sp. CT-5. can reduce corrosion of reinforcement in reinforced concrete by up to four
times. Sporosarcina pasteurii reduces water and chloride permeability. B. pasteurii increases
resistance to acid. Bacillus pasteurii and B. sphaericuscan induce calcium carbonate precipitation
in the surface of cracks, adding compression strength.

Pumped concrete

Pumped concrete must be designed to that it can be easily conveyed by pressure through a rigid
pipe of flexible hose for discharge directly into the desired area. Pozzocrete use can greatly
improve concrete flow characteristics making it much easier to pump, while enhancing the quality
of the concrete and controlling costs.
REQUIREMENT OF CONCRETE MIX
The designer must be aware of the need to improve the grade and maintain uniformity of the
various materials used in the pumped mix in order to achieve greater homogeneity of the total
mix. Three mix proportioning methods frequently used to produce pump able concrete are :
Maximum Density of Combined Materials
Maximum Density – Least Voids
Minimum Voids – Minimum Area
Mixes must be designed with several factors in mind:
1. Pumped concrete must be more fluid with enough fine material and water to fill internal voids.
2. Since the surface area and void content of fine material below 300 microns control the liquid
under pressure, there must be a high quantity of fine material in a normal mix. Generally
speaking, the finer the material, the greater the control.
3. Coarse aggregate grading should be continuous, and often the sand content must be
increased by up to five percent at the expense of the coarser aggregate so as to balance the 500
micron fraction against the finer solids.
Pozzocrete Effective
Unfortunately, adding extra water and fine aggregate leads to a weaker concrete. The usual
remedies for this are either to increase the cement content, which is costly, or to use chemical
admixtures, which can also be costly and may lead to segregation in marginal mixes. There is
another and far more effective alternative:
POZZOCRETE
There are many advantages to including POZZOCRETE in concrete mixes to be pumped. Among
them are :

1. Particle Size. Pozzocrete meets IS 3812 Specification with 66% passing the 325 (45-micron)
sieve and these fine particles are ideal for void filling. Just a small deficiency in the mix fines can
often prevent successful pumping.
2. Particle Shape. Microscopic examination shows most Pozzocrete particles are spherical and
act like miniature ball bearings aiding the movement of the concrete by reducing frictional losses
in the pump and pining. Studies have shown that Pozzocrete can be twice as effective as cement
in improving workability and, therefore, improve pumping characteristics.
Pozzolanic Activity:
his chemical reaction combines the Pozzocrete particles with the calcium hydroxide liberated
through the hydration of cement to form additional cementitious compounds which increase
concrete strength.
Water Requirement:
Excess water in pumped mixes resulting in over six inch slumps will often cause material
segregation and result in line blockage. As in conventionally placed mixes, pumped concrete
mixes with excessive water also contribute to lower strength, increased bleeding and shrinkage.
The use of Pozzocrete in pumped or conventionally placed mixes can reduce the water
requirement by 2% to 10% for any given slump.
Sand/Coarse Aggregate Ratio:
In pumped mixes, the inclusion of liberal quantities of coarse aggregate can be very beneficial
because it reduces the total aggregate surface area, thereby increasing the effectiveness of the
available cementitious paste. This approach is in keeping with the “minimum voids, minimum
area” proportioning method. As aggregate size increases, so does the optimum quantity of
coarse aggregate. Unfortunately, this process is frequently reversed in pump mixes, and sand
would be substituted for coarse aggregate to make pumping easier. When that happens, there is
a need to increase costly cementitious material to compensate for strength loss. However, if
Pozzocrete is utilized, its unique workability and pump ability properties permit a better balance of
sand to coarse aggregate resulting in a more economical, pump able 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.
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
Procedure for Mix Design
1. Determine the mean target strength f t from the specified characteristic compressive strength at 28day fck and the level of quality control , This equation is for building work .For Bridge work take
the target strength as per table 1700-5 MORT&H Specifications. For road work the design mix is
based on flexure strength as per IRC 44.
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 empirical 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.

Concrete production

Concrete plant facility showing a Concrete mixer being filled from the ingredient silos.
Concrete production is the process of mixing together the various ingredients—water, aggregate,
cement, and any additives—to produce concrete. Concrete production is time-sensitive. Once the
ingredients are mixed, workers must put the concrete in place before it hardens. In modern
usage, most concrete production takes place in a large type of industrial facility called a concrete
plant, or often a batch plant.
In general usage, concrete plants come in two main types, ready mix plants and central mix
plants. A ready mix plant mixes supply the required grade of concrete as per customer
requirement and supplied by transit mixer loaders by giving necessary dose of retarders , while a
central mix plant mixes all the ingredients including water. A central mix plant offers more
accurate control of the concrete quality through better measurements of the amount of water
added, but must be placed closer to the work site where the concrete will be used, since
hydration begins at the plant.
A concrete plant consists of large torage hoppers for various reactive ingredients like cement,
storage for bulk ingredients like aggregate and water, mechanisms for the addition of various
additives and amendments, machinery to accurately weigh, move, and mix some or all of those
ingredients, and facilities to dispense the mixed concrete, often to a concrete mixer truck.

Modern concrete is usually prepared as a viscous fluid, so that it may be poured into forms, which
are containers erected in the field to give the concrete its desired shape. There are many different
ways in which concrete formwork can be prepared, such as Slip forming and Steel plate
construction. Alternatively, concrete can be mixed into dryer, non-fluid forms and used in factory
settings to manufacture Precast concrete products.
There is a wide variety of equipment for processing concrete, from hand tools to heavy industrial
machinery. Whichever equipment builders use, however, the objective is to produce the desired
building material; ingredients must be properly mixed, placed, shaped, and retained within time
constraints. Once the mix is where it should be, the curing process must be controlled to ensure
that the concrete attains the desired attributes. During concrete preparation, various technical
details may affect the quality and nature of the product.
Mixing concrete
Thorough mixing is essential for the production of uniform, high-quality concrete. For this reason
equipment and methods should be capable of effectively mixing concrete materials containing the
largest specified aggregate to produce uniform mixtures of the lowest slump practical for the
work.
Separate paste mixing has shown that the mixing of cement and water into a paste before
combining these materials with aggregates can increase the compressive strength of the resulting
concrete. The paste is generally mixed in a high-speed, shear-type mixer at a w/c (water to
cement ratio) of 0.30 to 0.45 by mass. The cement paste premix may include admixtures such as
accelerators or retarders, superplasticizers, pigments, or silica fume. The premixed paste is then
blended with aggregates and any remaining batch water and final mixing is completed in
conventional concrete mixing equipment.
Placing Of Concrete

Placing is the ability of a fresh (plastic) concrete mix to fill the form/mold properly with the desired
work (vibration) and without reducing the concrete's quality. Placing depends on workability of
concrete (water content, aggregate ,shape and size distribution, cementitious content and age
,level of hydration) and can be modified by adding chemical admixtures, like superplasticizer.
Raising the water content or adding chemical admixtures increases concrete workability.
Excessive water leads to increased bleeding (surface water) and/or segregation of aggregates
(when the cement and aggregates start to separate), with the resulting concrete having reduced
quality. The use of an aggregate with an undesirable gradation can result in a very harsh mix
design with a very low slump, which cannot readily be made more workable by addition of
reasonable amounts of water.
Workability can be measured by the concrete slump test, a simplistic measure of the plasticity of
a fresh batch of concrete following the ASTM C 143 or EN 12350-2 test standards. Slump is
normally measured by filling an "Abrams cone" with a sample from a fresh batch of concrete. The
cone is placed with the wide end down onto a level, non-absorptive surface. It is then filled in
three layers of equal volume, with each layer being tamped with a steel rod to consolidate the
layer. When the cone is carefully lifted off, the enclosed material slumps a certain amount, owing
to gravity. A relatively dry sample slumps very little, having a slump value of one or two inches (25
or 50 mm) out of one foot (305 mm). A relatively wet concrete sample may slump as much as
eight inches. Workability can also be measured by the flow table test.
Slump can be increased by addition of chemical admixtures such as plasticizer or superplasticizer
without changing the water-cement ratio.Some other admixtures, especially air-entraining
admixture, can increase the slump of a mix.
High-flow concrete, like self-consolidating concrete, is tested by other flow-measuring methods.
One of these methods includes placing the cone on the narrow end and observing how the mix
flows through the cone while it is gradually lifted.
After mixing, concrete is a fluid and can be pumped to the location where needed.
Curing

A concrete slab ponded while curing.
In all but the least critical applications, care must be taken to properly cure concrete, to achieve
best strength and hardness. This happens after the concrete has been placed. Cement requires a
moist, controlled environment to gain strength and harden fully. The cement paste hardens over
time, initially setting and becoming rigid though very weak and gaining in strength in the weeks
following. In around 4 weeks, typically over 90% of the final strength is reached, though
strengthening may continue for decades. The conversion of calcium hydroxide in the concrete
into calcium carbonate from absorption of CO2 over several decades further strengthens the
concrete and makes it more resistant to damage. However, this reaction, called carbonation,
lowers the pH of the cement pore solution and can cause the reinforcement bars to corrode.
Hydration and hardening of concrete during the first three days is critical. Abnormally fast drying
and shrinkage due to factors such as evaporation from wind during placement may lead to
increased tensile stresses at a time when it has not yet gained sufficient strength, resulting in
greater shrinkage cracking. The early strength of the concrete can be increased if it is kept damp
during the curing process. Minimizing stress prior to curing minimizes cracking. High-earlystrength concrete is designed to hydrate faster, often by increased use of cement that increases
shrinkage and cracking. The strength of concrete changes (increases) for up to three years. It
depends on cross-section dimension of elements and conditions of structure exploitation.
During this period concrete must be kept under controlled temperature and humid atmosphere. In
practice, this is achieved by spraying or ponding the concrete surface with water, thereby
protecting the concrete mass from ill effects of ambient conditions. The picture to the right shows
one of many ways to achieve this, ponding – submerging setting concrete in water and wrapping
in plastic to contain the water in the mix. Additional common curing methods include wet burlap
and/or plastic sheeting covering the fresh concrete, or by spraying on a water-impermeable
temporary curing membrane.

Properly curing concrete leads to increased strength and lower permeability and avoids cracking
where the surface dries out prematurely. Care must also be taken to avoid freezing or
overheating due to the exothermic setting of cement. Improper curing can cause scaling,
reduced strength, poor abrasion resistance and cracking.
TESTS FOR CONCRETE QUALITY CHECKING
Tests for checking quality of concrete should be done for the following possible purposes:
1. To detect the variation of quality of concrete being supplied for a given specification.
2. To establish whether the concrete has attained a sufficient strength or concrete has set
sufficiently for stripping, stressing, de-propping, opening to traffic etc.
3. To establish whether the concrete has gained sufficient strength for the intended purpose.
There are so many tests available for testing different qualities of concrete. Different tests give
results for their respective quality of concrete. Thus it is not possible to conduct all the tests as it
involves cost and time. Thus, it is very important to be sure about purpose of quality tests for
concrete. The most important test for quality check of concrete is to detect the variation of
concrete quality with the given specification and mix design during concrete mixing and
placement. It will ensure that right quality of concrete is being placed at site and with checks for
concrete placement in place, the quality of constructed concrete members will be as desired.

Following are the lists of various tests conducted for Concrete Quality:
Tests on hardened concrete:



Compressive strength (cylinder, cube, core)



Tensile strength: Direct tension



Modulus of rupture



Indirect (splitting) Test



Density



Shrinkage



Creep



Modulus of elasticity



Absorption



Permeability Tests on Concrete



Freeze/thaw resistance



Resistance to aggressive chemicals



Resistance to abrasion



Bond to reinforcement



Analysis for cement content and proportions



In situ tests: Schmidt Hammer, Concrete pull-out, break-off, cones etc.



Ultrasonic, nuclear.

Tests on fresh concrete:


Workability Tests (slump test and others)



Bleeding



Air content



Setting time



Segregation resistance



Unit weight



Wet analysis



Temperature



Heat generation

Of these many tests for concrete quality, in practice well over 90% of all routine tests on concrete
are concentrated on compression tests and slump tests. It is also desirable to conduct fresh
concrete temperature and hardened concrete density determination tests.

The reasons for the selection of compressive strength test and slump test in practice for
quality control testing of concrete are:
1. All or most other properties of concrete are related to its compressive strength.
2. Compressive strength test is the easiest, most economical or most accurately determinable
test.
3. Compressive strength testing is the best means available to determine the variability of
concrete.
4. Slump tests also checks for variation of construction materials in mix, mainly water-cement
ratio.
5. Slump test is easy and fast to determine quality of concrete before placement based on
recommended slump values for the type of construction.
6. Slump test is most economical because it is done at site and does not require any laboratory or
expensive testing machine.
7. Slump tests is done before the placement of concrete, so the quality of control is high as
rejected mix can be discarded before pouring into the structural member. So, dismantling or
repair of defective concrete members can be avoided. VEE-BEE TEST

To determine the workability of fresh concrete by using a Vee-Bee consistometer as per IS: 1199
–

1959.

The

apparatus

used

is

Vee-Bee

consistometer.

Procedure to determine workability of fresh concrete by Vee-Bee consistometer.
i) A conventional slump test is performed, placing the slump cone inside the cylindrical part of the
consistometer.
ii) The glass disc attached to the swivel arm is turned and placed on the top of the concrete in the
pot.
iii) The electrical vibrator is switched on and a stop-watch is started, simultaneously.
iv) Vibration is continued till the conical shape of the concrete disappears and the concrete
assumes

a

cylindrical

shape.

v) When the concrete fully assumes a cylindrical shape, the stop-watch is switched off
immediately. The time is noted.The consistency of the concrete should be expressed in VBdegrees, which is equal to the time in seconds recorded above.
COMPACTING FACTOR
Compacting factor of fresh concrete is done to determine the workability of fresh concrete by
compacting factor test as per IS: 1199 – 1959. The apparatus used is Compacting factor
apparatus.
Procedure to determine workability of fresh concrete by compacting factor test.
i)

The

sample

ii)

The

trap-door

of

concrete
is

opened

is
so

placed
that

in
the

the

upper

concrete

hopper

falls

into

up

to

the

the

lower

brim.
hopper.

iii) The trap-door of the lower hopper is opened and the concrete is allowed to fall into the
cylinder.
iv) The excess concrete remaining above the top level of the cylinder is then cut off with the help
of

plane

blades.

v) The concrete in the cylinder is weighed. This is known as weight of partially compacted
concrete.
vi) The cylinder is filled with a fresh sample of concrete and vibrated to obtain full compaction.
The concrete in the cylinder is weighed again. This weight is known as the weight of fully
compacted

concrete.

Compacting factor = (Weight of partially compacted concrete)/(Weight of fully compacted
concrete)

AGGREGATE IMPACT VALUE

This test is done to determine the aggregate impact value of coarse aggregates as per IS: 2386
(Part IV) – 1963. The apparatus used for determining aggregate impact value of coarse
aggregates is Impact testing machine conforming to IS: 2386 (Part IV)- 1963,IS Sieves of sizes –
12.5mm, 10mm and 2.36mm, A cylindrical metal measure of 75mm dia. and 50mm depth, A
tamping rod of 10mm circular cross section and 230mm length, rounded at one end and Oven.
Preparation of Sample
i) The test sample should conform to the following grading:
– Passing through 12.5mm IS Sieve – 100%
– Retention on 10mm IS Sieve – 100%
ii) The sample should be oven-dried for 4hrs. at a temperature of 100 to 110 oC and cooled.
iii) The measure should be about one-third full with the prepared aggregates and tamped with 25
strokes of the tamping rod.
A further similar quantity of aggregates should be added and a further tamping of 25 strokes
given. The measure should finally be filled to overflow, tamped 25 times and the surplus
aggregates struck off, using a tamping rod as a straight edge. The net weight of the aggregates in
the measure should be determined to the nearest gram (Weight ‘A’).

Procedure to determine Aggregate Impact Value
i) The cup of the impact testing machine should be fixed firmly in position on the base of the
machine and the whole of the test sample placed in it and compacted by 25 strokes of the
tamping rod.
ii) The hammer should be raised to 380mm above the upper surface of the aggregates in the cup
and allowed to fall freely onto the aggregates. The test sample should be subjected to a total of
15 such blows, each being delivered at an interval of not less than one second.
Reporting of Results
i) The sample should be removed and sieved through a 2.36mm IS Sieve. The fraction passing
through should be weighed (Weight ‘B’). The fraction retained on the sieve should also be
weighed (Weight ‘C’) and if the total weight (B+C) is less than the initial weight (A) by more than
one gram, the result should be discarded and a fresh test done.
ii) The ratio of the weight of the fines formed to the total sample weight should be expressed as a
percentage.
iii) Two such tests should be carried out and the mean of the results should be reported

Aggregate impact value = (B/A) x 100%.
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

The procedure of making the test cubes is as follows: –

design

mix.

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

4.

Assemble

hardened
the

cube

concrete
mold

correctly

and
and

superfluous

ensure

all

water

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.
Checking Quality of Fine Aggregates

For checking the quality of fine aggregates, a field test was conducted in which the sand was
placed in a flask containing water. The sand was allowed to settle for some time and then after

few hours the reading of the silt or other impurity layer is takenIf that reading is less than 5% of
the total sand that is put in the flask, then we accept the sand but if it is more than 5% the sand is
rejected.