Concrete & types

8/18/2019 Concrete & types

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CONCRETE


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Defnitions Shotcrete

It is that type of mortar or concrete which is conveyed through a hose

(flexible tube) and pneumatically projected at high velocity. Pozzolanic cement

It comes from the name of the village Pozzuoli, near Vesuvius, where the volcanicash was first found. The Pozzolanic cement is the term used to describe thecements obtained by simple grinding of natural materials at normal temperature.

Portland cement A cement consisting of Portland cement with not more than 5 of other inorganic

materials. It usually originates from limestone. It is a fine powder produced bygrinding Portland cement clin!er "more than #$%, a limited amount of calciumsulfate "which controls the set time% and up to 5 minor constituents

ydraulic cement They consists mainly of silicates and aluminates of lime and can be broadly

classified as natural cements, Portland cements and high Alumina cements. !lended "ement

A cement consisting of Portland cement and two or more appropriate inorganicmaterials which contribute to the strength gaining properties of the cement with orwithout other constituents, processing additions and functional additions is calledblended cement. "#S$% " &&'*+a%

"ivil engineers are concerned with the calcareous cements.


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As per A&T'

"&',*+ or

" '*'*+a

types of cementare given in

table.

Types o Cement


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Compound Composition odierent type o OPC


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Types o Cement

-rdinary Portland cement ($ypeI) (sed in general concrete construction where there is no

e)posure to sulphates in soil or ground water. /0 &*& 1

&**2.

%odified "ement ($ypeII) The rate of gain of strength is similar to *P+.

The rate of heat development is higher than a low heat cement.

It has improved performance and durability.


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Types o Cement

3apid hardening Portland cement ($ypeIII) It is used where high early strength is reuired or where

formwor! is reuired for reuse or where uic!construction is reuired.

-igh early strength cause high rate of heat development. -igher "4S content "more than 55 up to $% and finer

grinding of clin!er cause increase rate of strengthgaining.

It should not be used for mass construction wor!s "/am%or for large structural sections. &etting time of *P+ and rapid hardening cement is

same i.e. not less than 05 minutes.


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Types o Cement

5ow heat Portland cement ($ypeI0) /ue to low thermal conductivity of concrete the rise in

temperature in the interior of concrete mass can leadto serious crac!ing.

In this types of cement the rate of gain of temperatureis low and limited to 15$ 23g "4$ cal3g% at days and1#$ 23g "$ cal3g% at 1 days.

6ow content of +7& and +7 A results in a slower

development of strength. #S$% "&',*+ covers the detail of low heat cements.


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Types o Cement

Sulfate resisting "ement ($ype0) +alcium aluminates in cement can react with sulfate salt

which will increase the volume and cause disintegration of

concrete.

8here &ulfate attac! is suspected "i.e. shore areas,

underground areas% &9 cements are suitable.

"4# content must be low 7.5 as per !S +,,2 1 &**&

#S$% "&',*+ covers the detail of &ulfate resisting+ements.


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Types o Cement

6hite cement and Pigments These cements contain very low Iron *)ide "less than

$.7 by mass of clin!er% and 'anganese *)ide. +hina

clay with +hal! or limestone is generally used.

8hite cement satisfy the !S &2 1 &**&

Pigments used for different colours in cement li!e :

Iron o)ides can produce ;ellow, 9ed


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Types o Cement

#ntibacterial "ement It?s a Portland cement interground with a antibacterial agent which

prevents microbiological fermentation. (sed in food processing plants, swimming pools etc.

ydrophobic "ement It is a special type of cement and it can be stored for a long time

under unfavorable conditions. -ydrophobic properties are due to the formation of an water=

repellent film around each particle of cement. This cement is obtained if -P" is grinding with $.> to $.0 of

*leic acid, stearic acid or Pentachlorophenol. -ilwell cements

It is used for grout or slurry to be pumped to depth of thousandsmeters "Temperature >5$=7$$o@ and >$$'pa pressure%


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Types o Cement

igh #lumina "ement It gain strength at a very high rate i.e $

strength in 10 hours.

ood to resist sulfate attac!s It contains about 0$ alumina and lime>5 of

ferrous and ferric o)ides 5 slica small amount of

magnesia

9aw material are limestone and bau)ite


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Batching & mixing oconcrete


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Batching y !o"ume #$%T C'()*+,-

In volumetric batching, ingredients of concrete aremi)ed by volume.


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Buc.et or measuringingredients o concrete

> ? = 4 D

1 ? = $

D


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Batching y /eight

It is more accurate method of batching.

Each ingredient of concrete is weighted and mi)ed.

8eighting coarse aggregate is a laborious wor!.


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ixing o concrete

-and mi)ing 'achine mi)ing

In hand mi)ing first aggregate is deposited on aplatform then fine aggregate "sand% is added finallycement is spreaded on the dump of materials.

/iagonal parts of material is mi)ed and processes isrepeated for 7 to 0 times until a uniform mi)ture is

achieved. 8ater is added preferably by shower or by ma!ing a

ditch in the material.

'i)ing Platform


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achine mixing

+oncrete mi)ers used on building sites must

conform !S &4,' 1&*+

&everal types of concrete mi)ers are available li!e

>. Pan mi)ers or forced action mi)ers "P%1. /rum mi)ers

>. Tilting mi)ers "T%

1. Bon tilting type mi)ers "BT%

7. 9eversing /rum mi)ers

7. &pecialized mi)ers "+olloidal mi)er%


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Ti"ting mixers #T-

The mi)ingchamber iscalled /rum.

It consists ofa bowl

shaped drumhaving vanesinside.

@ordischarging

concretedrum can betilted.


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Ti"ting mixers #T-

It can be with

or without

hopper.


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Non ti"ting mixer #Re!ersingdrum mixer-

A)is of

mi)er is

always

horizontal


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Truc. mixers

They are

used when

concrete is

reuired to

transport to a

long distance

They wor!

with a centralbatching

plant.


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%pecia"i0ed mixers #Co""oida"mixer- They are used for shotcreting.

+olloidal mi)ers are used for mortar mi)ing.

+ement and water is mi)ed at a speed of

1$$$ rev3min then sand is added.

Pre mi)ing of cement and water allow better

hydration


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Continuous ixers

#S$% " 78'*+ discuss reuirements for

continuous mi)ing and volumetric batching.

(sing a modern continuous mi)er Placing,

compaction and finishing can all be achievedin >5 minutes.


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Time o ixing

Time of mi)ing is infect number of revolutions ofmi)er GGGGGG

enerally 1$ revolution with optimum speed aresufficient.

'i)ing time and uniformity got a relationship "Shalonand Reinitz % shown in graph.

&trength of concrete increases with mi)ing time asshown by Abrams tests up to 1 minutes and afterthis time slight decrease in strength is observed.

'inimum time of mi)ing is specified by the mi)ermanufacturer::: min mi)ing time for a ,.'m4 or& yd4 mi)er is I minute ::. Add >5 seconds foreach additional &yd4. it is given by #S$% " *+*+

and #"I 4,+38*


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Transportation o concrete

+oncrete can be transported from the

mi)ing place to its final placement position

by following means

>. 8heel barrows

1. +hutes

7. Truc!s

0.


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Testing o concrete

+oncrete testing can broadly classified in to twomaFor divisions.

reen concrete Tests. 8or!ability tests

&. Slump test1. +ompacting factor test

7. A&T' flow test

0. 9emoulding test

5. Vebe Test

4. @low test

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