Concrete Technology

2.  The final stage of concrete making process –
hardened concrete.
 Important properties – Strength , Durability,
Impermeability, Stability
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3.  Strength is of 4 types – compressive, tensile,
flexural and bond strength.
 Most valuable property of concrete.
 Most cases strength is having direct influence
on load carrying capacity of PCC and RCC.
 Strength can be easily determined compare to
other properties of concrete
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5.  Test specimen size – Lesser the cube size –
higher is strength – cube expected to give
15% of higher strength compare to cylinder.
 Size of aggregates used
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6.  Testing machine used – results may vary –
errors in centering the cubes, inaccurate
calibration etc.
 Moisture content in specimen – dry cubes –
dry shrinkage and bond failure – test the
cubes immediately removed from curing to
maintain the uniformity.

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7.  W/C ratio – main factor affecting compressive
strength – inversely proportional – increase in
W/C ratio by 0.01 – decrease in strength by 1
to 1.5 Mpa.
 Quality of cement – finer the grinding –
greater the early strength.
 Storage of cement – strength decreases due
to hydration. – 15% in 3 months.
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8.  Properties and proportion of concrete
ingredients.
 Method of mixing and compacting.
 Method of curing.
 Age of concrete.
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9.  Characteristic Strength – strength below
which not more than 5% of the test results
are expected to fall.
 Compressive Strength – strength of concrete
against crushing due to direct compressive
load.
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10.  Tensile Strength – strength of concrete in
tension.
 Flexural strength – strength of concrete in
bending.
 Bond Strength.
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11.  Ratio of optimum quantity of water added to
cement to obtain the desired consistency and
workability of concrete mix.
 Reduction in water – reduces strength.
 Excess water – separation of coarse aggregates –
slurry will escape through form work – leads to
honey comb.
 For proper workability – W/C ratio – 0.4 to 0.6.
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12.  The Strength of concrete only depends upon
W/C ratio provided the mix is workable
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 Strength inversely proportional to W/C ratio.
 For achieving same strength – higher W/C
ratio for hand compaction and less for
vibration.
 At low W/C ratio –not valued - compaction is
not possible.

14.  Gel /space ratio – ratio of solid products of
hydration and space available for these
hydration products.
 Higher gel/space ratio – reduces porosity –
increases strength.
 Higher W/C ratio – reduces gel/space ratio –
reduces strength.
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16.  Compressive Strength Test
 Split Tensile Test
 Flexural Test
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17.  Equipments – 150 mm3 cube, cylinder –
150mm (H) 300 mm (D), standard tamping
rod, CTM.
 Prepare specimen.
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18.  Clean the surface of CTM and specimen.
 Apply load continuously and gradually.
 The maximum load applied to the specimen
is noted.
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21.  Measurement of direct tension is difficult.
 So flexural tensile strength at failure or
modulus of rupture is determined.
 There are two tests
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22.  Specimen subject to compression load in
UTM.
 Load increased gradually – fails by splitting
along vertical diameter.
 Portion below load – compression – portion
corresponding to depth subjected to tensile
stresses.
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25.  Also called Modulus Rupture Test.
 Specimen size = 150mm X 150mm X 700mm.
 Placed in UTM on two rollers at C/C distance 600mm.
 Apply load by means of two similar rollers.
 Load applied continuously.
 Fracture load, type of failure and appearance is
noted.
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29.  Time – dependent deformation under
constant.
 Creep develops rapidly at the beginning and
gradually decreases with time.
 Creep also called as time yield.
 Creep depends – stress in concrete, age of
loading, duration of loading, type aggregate,
W/C ratio.
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30.  Aggregates – Stronger the aggregates- lesser the
creep.
 W/C ratio – Creep increases with increase in W/C
ratio.
 Creep decreases with age of concrete.
 Increase moisture content increases creep.
 Higher the strength – lesser creep.
 Creep increases with rate of loading
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31.  Creep decreases with increase in thickness of
concrete member.
 Creep increases with increase in temperature.
 Presence of reinforcement in compression
zone decreases the creep.
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32.  Increases deflection in RCC beam.
 Creep relieves stress concentration induced
by shrinkage, temperature changes,
movement of supports in beam column
junction and SIS.
 Creep reduces stress in prestress concrete.
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35.  The volumetric reduction in concrete is called
shrinkage.
 Caused mainly because of loss of water due
to hydration and carbonation.
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36.  Plastic
 Drying
 Autogeneous
 Carbonation
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37.  Loss of water by evaporation from freshly
placed concrete while the cement paste in
plastic state is called plastic shrinkage.
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38.  Higher W/C ratio
 Improper vibration
 Badly proportioned concrete
 Rapid drying
 More cement content
 Greater bleeding
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39.  By reducing loss of moisture from concrete.
 Usage of aluminium powder.
 Revibrate the concrete in control manner.
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40.  The shrinkage that takes place after the
concrete has set and hardened is called dry
shrinkage.
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41.  W/C ratio
 Cement content
 Relative humidity
 Type of aggregate, its size and shape
 Type of cement
 Type of admixtures
 Curing method
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42.  Maintaining humidity
 Adopting low W/C ratio
 Using steam curing
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43.  W/C ratio: Shrinkage directly varies with W/C
ratio.
 Composition and fineness of cement: High
early strength and low heat cement – more
shrinkage – finer the cement – greater the
expansion under moist condition.
 Relative humidity: Atmospheric humidity
directly affects the concrete by means of
humidity.
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44.  Type, amount and gradation of aggregate: smaller
the aggregate – higher shrinkage and vise – versa.
 Type of cement: the rapid hardening cement- higher
shrinkage than other cements – Cement deficient in
gypsum exhibit higher shrinkage.
 Admixture: admixture that increases water
requirement increases shrinkage and vice –versa.
 Storage and curing condition: Shrinkage takes place
over long period. Some part of the long term
shrinkage may be due to carbonation.
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45.  Property of concrete by virtue of which it is
capable of resisting the disintegration and
decay
 A durable concrete is the one which retains
its original form, quality and serviceability
when exposed to its service environment.
 Depending on different environment,
durability of concrete varies.
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46.  Durable concrete – long term resistant – wear
and tear, chemical attack, polluted
atmosphere.
 Durability increases the life of the concrete.
 Durable concrete – do not require special care
– no repair and maintenance.
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47.  Sulphates attacks – hydrated calcium
aluminate to from ettringite -reacts with
free calcium ions to form gypsum.
 These compounds causes expansion of
concrete.
 Expansion leads to cracking – further
penetration – continues till complete
disintegration of concrete.
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48.  Sulphate attack accelerates – alternating wetting
and drying – marine structures – zone of tidal
variations.
 Sulphate attacked caused – by sulphate salts in
soil – Ammonium sulphate in agriculture soil by
fertilizers – Hydrogen sulphate by decay of
organic matter.
 Sulphate attack – whitish appearance – damage
starts from edges or corners followed by cracking
and spalling.
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50.  Use sulphate resisting cement.
 Use of Pozzolona
 Quality of Concrete
 Use of air – entrainment
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51.  Use of high – alumina cement
 High pressure steam curing
 Use of polyethylene sheet
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52.  Due to high alkalinity – protective oxide film
is formed around reinforcement.
 This film can lost due carbonation or
presence of chlorides.
 Chloride causes – corrosion.
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54.  Process of penetration of carbon dioxide from
air into concrete and reacts with calcium
hydroxide to form calcium carbonates.
 Carbonation reduces pH of concrete.
 As pH reduces to 9 , concrete gets
carbonated on the surface.
 Carbonated concrete – no protection to
reinforcement.
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55.  Permeability – carbonation is higher in
permeable concrete.
 Stronger concrete – lower the carbonation.
 Depth of cover plays a major role in
protecting reinforcement from corrosion.
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56.  The cover provided should be according to
code of practice.
 The cement content should not be <
300kg/m3.
 The W/C ratio should preferably be not > 0.4.
 The aggregates and water should be free
from deleterious substances.
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57.  The quality control of concreting should be
good.
 Good curing starts immediately after the
concrete hardens and to be continued for
specified minimum period.
 Removal of form works must be according to
the provisions of code
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58.  NDT – quick and performed both in
laboratory and in-situ with convenience
 In NDT – specimen- not subjected to failure,
undisturbed, unharmed
 NDT – on both green and hardened concrete
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59.  Penetration Test
 Pull out Test
 Rebound Hammer Test
 Ultrasonic Pulse velocity Test
 Core Extraction Test
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76.  This test is used to determine the compressive strength of a
concrete core, which has usually been extracted from an
existing structure.
 The value of compressive strength can then be used in
conjunction with other measured properties to assess the
condition of the concrete.
 Using a masonry saw, the core is first trimmed to the correct
test length, which varies upon the standard being adopted.
 Following trimming, the core will have its ends either
ground perfectly flat, or be capped in a material to produce
a smooth bearing surface.

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77.  After the prescribed curing has taken place, the
specimen is then crushed to failure noting the
maximum load achieved.
 From the values of load and dimensions, the
compressive strength of the core can be calculated.
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