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CONCRETE
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What do we expect out of Concrete?
Desired Strength (Design strength)
Workable (Easily spread able)
Durable (Withstand for long life)
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Grades of Concrete
1. Ordinary ConcreteM10 to M20
2. Standard ConcreteM25 to M55
3. High Strength Concrete >M55
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Grades of Cement- Classified based on its 28
days comp. strengthGrade of Cement
(1) 33 Grade Cement
(2) 43 Grade Cement
(3) 53 Grade Cement
28 days CompressiveStrength
33 N/mm2
43 N/mm2
53 N/mm2
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Colour of cement
The colour of cement should be greenish-greyfor OPC and dark grey for FA based PPC.
The colour of OPC depends on its raw materialsused.
If the raw materials contain more iron, theresultant cement will be darker in colour.
As regards PPC, it is related to the type ofpozzolona admixted.
It should be noted that colour has no effect onany of the properties of cement.
The strength is dependent on the correctproportion of raw materials mixed.
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Hydration of Cement
Cement + Water =Cement
Paste
Rock like
substance
1. C3A
2. C4AF
3. C3S
4. C2S
Formed within about 24 hrs of
addition of water
Formed within a week Mainly
responsible for earlier strength of
cementFormed very slowlyResponsible
for progressive strength
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TYPES OF CEMENT
OPC Ordinary Portland Cement
33 Grade (IS:269-1989)
43 Grade (IS:8112-1989)
53 Grade (IS:12269-1987) PPC - Portland Pozzolona Cement (IS:1489)
Rapid Hardening Portland Cement (IS:8041)
Sulphate Resistant Portland Cement (IS:12330)
Portland Blast Furnace Slag Cement (IS:455)
Low Heat Portland Cement (IS:12600)
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Portland Pozzolana Cement (PPC)
Cement in which pozzolana is added with
the cement clinker.
Pozzolana is a siliceous or aluminous
material such as flyash, volcanic ash.
The % of flyash permitted by BIS is 10 to
25%.
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Age of Cement Vs Strength Cement loses its strength as it ages.
Cement age % of strength
Fresh 100
15 days 92
30 days 90
60 days 85
90 days 80
180 days 70
BIS prescribes that cement should be used within 90 daysof its production. Incase it is used at a later date then it
should be tested before use.
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Field Tests on Cement
Check that the bag displays IS mark and
number to which it confirms to.
Check the manufacturing week on the bag.
Open the bag and take a good look atcement, there should be no lumps.
Check the colour of cement. It should beuniform.
Check that an handful of cement whenthrown in a bucket of water floats forsome time and then settles down.
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CEMENT TESTS
Consistency - Vicat Apparatus
Initial Setting Time - With 1mm needle
Final Setting Time - With Annular ring
Soundness - LeChatlier/Autoclave
Fineness - Air Permeability
Compressive Strength - 50 Sq.cm. cubes
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Fine Aggregate (IS:383-1970)
Passing 4.75mm IS sieve.
Natural sand and Crushed stone fines can be
used.
Zones I to IV.
Zone I to III are preferable.
Zone I is too coarse and Zone IV is too fine.
Zone IV is not recommended for RCC works.
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Grading of Fine Aggregates
IS Sieve
Size
Percentage of Passing For
Zone I Zone II Zone III Zone IV
10mm4.75mm
2.36mm
1.18mm600
300
150
10090-100
60-95
30-7015-34
5-20
0-10
10090-100
75-100
55-9035-59
8-30
0-10
10090-100
85-100
75-10060-79
12-40
0-10
10095-100
95-100
90-10080-100
15-50
0-15
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Limits for 40mm & 20mm graded aggregate
Size of Sieve% of Passing
40mm agg. 20mm agg.
63mm 10040mm 95100 100
20mm 3070 95100
10mm 10
35 25
55
4.75mm 05 0 - 10
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Tests on Coarse Aggregate
1.Crushing Value
2.Impact Value3.Abrasion Value
4.Flakiness Index
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Water
Potable water is generally suitable formixing of concrete.
Shall be free from impurities, oils, acids,
alkalies and salts.
pH shall be between 6 to 8.
Sulphate < 400 mg/lit.
Chlorides < 2000 mg/lit. for PCC works< 500 mg/lit. for RCC works
Sea water is not permitted for mixing and
curing.
Ad i t
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AdmixturesTo accelerate initial setting cement
To retard initial setting of cementTo increase the strength of concrete
To improve the workability
To increase bond between old and new concreteTo increase bond between steel and concrete
To produce colour concrete
To inhibit corrosion of concrete
To produce non-skid surfaces
To increase resistance to chemical attack.
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Accelerators & Retarders
Accelerators Retarders
Accelerate setting of
concrete
Generally used in coldenvironment
Assist in early removal
of form work Calcium Chloride,
Calcium formate,
Calcium nitrate, Sodium
Pottasium hydroxide, etc
Delay the setting of
concrete
Generally used in hotenvironment & long haul
Results in reduction in
micro cracks Lignin, Sugars,
Tartaric acid and its
salts, etc.
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Superplasticizers (SP)
One of a class of admixtures called waterreducers that are used to lower the mix waterrequirement of concrete.
Also called as Superfludizers, super water-
reducers and high range water reducers.
Water reducer % of reduction ofwater requirement
Normal waterreducers
10 to 15%
Superplasticisers About 30%
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Classification of SP
(1) Sulphonated melamine formaldehyde(SMF)
(2)Sulphonated napthalene formaldehyde(SNF)
(3)Modified lignosulphonates (MLS)(4)Sulphonic acid esters
(5)Carbohydrate ester, etc.----------------------------------------------
Mostly available are SMF and SNF.
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Advantages of Reducing
Water Cement ratio
Increased compressive / flexural strength
Increased denseness
Reduced porosity Increased water tightness
Increased resistance to weathering
Better bond between successive layersBetter bond between concrete and
reinforcement
Less volume change from wetting and drying
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Flowing Concrete High workability permits easy and quick
placement. High workability can be achieved by
(i) Same cement with more W/C
(ii) More cement with same W/C But, both methods, lead to segregation,
excessive shrinkage, undesirable heatdevelopment, and long-term detrimental
effects. SP (0.3 0.6% by wt.)About 200mm slump.
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Without SP
With 0.30% SP
With 0.60% SP
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Necessary correction shall be made formoisture content present in aggregates.
The concrete should have aworkability such that it can be placedin the form work and compacted withminimum effort without causingsegregation or bleeding.
Compressive Strength of concrete isalmost inversely proportional to the W/C
ratio. Excess water leads to reduction in
strength of concrete.
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Curing of Concrete Curing has a strong influence on the properties
of hardened concrete such as durability,strength, and watertightness.
Adding water with cement starts the reaction,called as hydration.
Hydration produces a stone like substance thehardened cement paste.
It is necessary that water be present in theconcrete until the reaction reaches equilibrium.
Both the rate and degree of hydration, and the
resulting strength of the final concrete, dependson the curing process.
Once the water is removed, hydration ceasesand cannot be restarted.
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Methods of Curing
(Sea water should not be used for curing)
Spraying with water.
Covering with wet mat.
Covering with wet sand.Covering with waterproof paper to
prevent evaporation.
Flooding with water by building smalldams.
Steam curing
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Slump Test
Slump Value
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Slump ValueType of Structure Slump in mm
a. PCC 25b. RCC widely spaced RF 40 50(Solid Colns., Piers, Abuts.,Footing, Well steining)
c. RCC medium spaced RF 50 75(Pier, abut. Caps, box culverts,well curb, well cap, walls withtk.>300mm)
d. RCC & PSC highly congested RF 75 125(Deck slab girders, box girder,walls with tk.
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Frequency of Sampling
Qty. of Concrete(m3) No. of Samples
1- 5 1
6 15 2
16
30 3
31 50 4
51 and above 4 plus oneadditional sample
for each additional
50m3.
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Acceptance Criteria
Comp. Strength
The mean stn. determined from any
group of four consecutive samplesshould exceed the specifiedcharacteristic comp. stn. by 3 MPa
Stn. of any sample is not less thanthe specified char characteristiccomp. stn minus 3 MPa
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