Tests on concrete-part c

7/28/2019 Tests on concrete-part c

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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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Documents

Tests on concrete-part c