concrete technology questions

7/25/2019 Concrete Technology Questions

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Portland la) Cement:' PC is obtained by mixin) Portland cement clin+er5 )yps1m and

)ran1lated blast f1rnace sla) in s1itable proportions and )rindin) the mixt1re to )et a

thoro1)h and intimate mixt1re between the constit1ents. The res1ltant prod1ct is a

cement which has physical properties similar to OPC. 2t has low heat of hydration and is

relatiely better resistant to chlorides and hence can be 1sed for marine wor+s.

3) I4 the elemental !"mp"siti"n is a'aila&le, h"+ +e !an !al!#late !"mp"#n$

!"mp"siti"n?

=y 1sin) followin) e>1ations5 s1))ested by =o)1e5 we can calc1late percenta)e of main

compo1nds from the percenta)e of elemental composition.

5) What is the r"le "4 CA in the h6$rati"n pr"!ess?The reaction of C3$ with water is ery >1ic+ and iolent5 and leads to immediate

stienin) of paste5 +nown as fash set. The hydration prod1ct formed is tricalcium

aluminate hydrate,C3$6. C3$ 6 C3$6

This reaction re>1ires m1ch more water than that re>1ired for the

hydration of silicates. This ca1ses shorta)e of water and there is incomplete hydration of

silicates. To preent this Gypsum,CaO*.!!O is added to cement clin+er. ?yps1m

reacts with C3$ to form insol1ble calcium sulphaluminate ,3Cao.$l!O3.3CaO*.3"!O5

b1t eent1ally tricalcium aluminate hydrate,C3$6 is formed.

7) ist the !"mp"#n$s present in !ement a!!"r$in( t" their !"ntriti"n t"+ar$s

heat (enerati"n.The contrib1tion to heat )eneration in ,cal@) by dierent compo1nds at dierent times

is as shown:'

8) Dis!#ss the man#4a!t#rin( "4 !ement #sin( $r6 pr"!ess. Ill#strate 6"#r ans+er

+ith s!hemati! $ia(rams.

Compound At 3 days At 90 days At 13 years

C!S "# $%& $22

C2S $2 &2 "'

C! 2$2 !$$ !2&

C& *' '# $%2

C!S &,%(CaO) . ,*%(SiO2) . *,2(l2O!) . $,&!(e2O!) .

2,#"(SO!)

C2S 2,#(SiO2) . %,"&(C!S)

C! 2,*"(l2O!) . $,*'(e2O!)


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2n the dry process of man1fact1rin) of cement the raw materials are cr1shed and fed

in the correct proportions into a )rindin) mill5 where they are dried and red1ced in

si;e to a ne powder.

The dry powder5 called raw meal5 is then p1mped into a blendin) silo and nal

ad41stment is made in the proportions of the material.

Aaw meal hain) moist1re content abo1t !B is passed thro1)h a pre'heater5 1s1ally

of a s1spension type,i.e. the raw meal particles are s1spended in the risin)

)ases.ere the raw meal is heated to abo1t %00C before bein) fed into the +iln.

2n the +iln p1leri;ed coal is blown by an air blast at the lower end where the

temperat1re reaches abo1t "*00C.The mass ,raw meal then f1ses into balls5 3'!#

mm in diameter +nown as clin+er.

On exit from the +iln the clin+er is cooled and the heat bein) 1sed to the pre'heat of

the comb1stion air.

The cool clin+er which is characteristically blac+ and hard is inter)ro1nd with )yps1m

in order to preent the 1ire !0 min1tes. Th1s

the dry process re>1ires si)nicantly lesser f1el compared to the wet process.

Cr#sher

Ra+ :eal il"

ime t"ne,

;all :ill

;all :ill

R"tar6


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D1antity of coal re>1ired to prod1ce " Ton of cement is only abo1t "00 +) in case of

dry process compared to 3#0 +) for wet process.>) Dis!#ss ten t6pes "4 !ement in$i!atin( their !"mp"siti"ns, !"$al pr"'isi"ns

an$ #sa(e.

Type of

cement

Compositio

nCodal Proisions Esa)e

Ordinar

y

Portlan

d

Cemen

t

C35 C!5

C3$5 C*$&

pecication )ien in :

2 !69:"9%9 ,33 ?rade

OPC

2 %""!:"9%9 ,*3 ?rade

OPC

2 "!!69:"9%7 ,#3 ?rade

OPC&ineness:=laineFs air permeability test :

specic s1rface G !!#m!@+)

o1ndness: Ha Chatelier test : Ixpansion J"0mm

$1toclae test : Ixpansion J 0.%

percentettin) Time: Kicat test : 2nitial ettin) Time

G 30 min &inal ettin) Time J 600

minCompressie tren)th,(in:

33 ?rade *3 ?rade #3

?rade7!L"hr : "6 (pa !3 (Pa

!7 (Pa"6%L!hr : !! (pa 33 (Pa

37 (Pa67!L*hr : 33 (pa *3 (Pa

#3 (Pa

$ny ?eneral type

of constr1ction

where no special

d1rability

condition is

present

Aapid

arden

'in)

Portlan

d

Cemen

t

Contains

more C3

and Hess

C! than

OPC

pecication )ien in :2 %0*":"990&ineness:=laineFs air permeability test :

specic s1rface G 3!#m!@+)o1ndness: Ha Chatelier test : Ixpansion J

"0mm$1toclae test : Ixpansion J 0.%



min

Compressie tren)th,(in:

!*hrL30min1tes : "6 (pa7!L"hr : !7 (pa

i 2n prefabricated

concrete

constr1ction.ii Mhere formwor+

needs to be

remoed to 1se

elsewhere.iiAoad repair

wor+s.iCold weather

concrete whererapid hardenin)

red1ces chances of


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frost action

1lphat

e

Aesistin)

Portlan

d

Cemen

t

!C3$C*$&sho1ld not

exceed !#

percent

pecication )ien in :2 "!330:"9%%&ineness:=laineFs air permeability test :

specic s1rface G !!#m!@+)o1ndness: Ha Chatelier test : Ixpansion J

"0mm

$1toclae test : Ixpansion J 0.%percent

ettin) Time: Kicat test : 2nitial ettin) Time



7!L"hr : "0 (pa"6%L!hr : "6 (pa67!L*hr : 33 (pa

i 1lphate attac+

accelerated by

contin1o1s wettin)

and dryin). 2n

marine

constr1ction.ii Concrete 1sed in

basement

constr1ction where

soil is infested with

s1lphates.iii 2n sewa)e

treatment wor+

Type ofcement

Composition

Codal Proisions Esa)e

Portlan

d la)

Cement

$ mixt1re

of Portland

cement

clin+er and

blast

f1rnace

)ran1latedsla) which

is a waste

prod1ct in

ma+in) of

pi) iron.

pecication )ien in :2 *##:"9%9&ineness:=laineFs air permeability test :






7!L"hr : "6 (pa"6%L!hr : !! (pa67!L*hr : 33 (pa

How heat of

hydration so 1sed

in massconcretein)

1pers

1lphate

dCemen

t

prod1ced

by

inter)rindin) a

mixt1re of

%0 to %# B

)ran1lated

blastf1rnac

e sla)5 "0

to "#

percent

calci1m

s1lphate

pecication )ien in :2 6909:"990&ineness:=laineFs air permeability test :

specic s1rface G *00m!@+)

o1ndness: Ha Chatelier test : Ixpansion J

#mm$1toclae test : Ixpansion J 0.%




7!L"hr : "# (pa"6%L!hr : !! (pa67!L*hr : 30 (pa

i 2n marine

constr1ction.ii Concrete 1sed in

basement

constr1ction where

soil is infested with

s1lphatesiii 2n sewa)e

treatment wor+.


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and a

small

amo1nt of

Portland

cement

How

eat

Portlan

d

Cemen

t

Hower

content of

rapidly

hydratin)

compo1nd

s

pecication )ien in :2 "!600:"9%9&ineness:

=laineFs air permeability test :

specic s1rface G 3!0m!@+)o1ndness: Ha Chatelier test : Ixpansion J





7!L"hr : "0 (pa"6%L!hr : "6 (pa67!L*hr : 3# (pa

(ass concretin).

Type of

cement

Compositio


Portlan

d

Po;;ola

na

Cemen

t

Po;;olanic

material is

mixed with

portland

cement

clin+er

pecication )ien in :2 "*%9,Part":"99",


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acid5

stearic

acid etc.

&ilm )et

bro+en

whenmixin) is

done.



7!L"hr : "#.69 (pa

"6%L!hr : !".#7 (pa67!L*hr : 30.* (pa

Oil well

Cemen

t

Oil'well

cement of

classes $5

=5 C5 85 I5

&5 ? and 5

shall be

man1fact1r

edby

)rindin)

clin+er

consistin)

of hydra1lic

calci1msilicates.

pecication )ien in :2 %!!9:"9%6&ineness:=laineFs air permeability test :





min

Esed by the

petrole1m ind1stry

for cementin) )as

and oil'wells at hi)h

temperat1res and

press1res. l1rriesof s1ch cement

hae to remain

p1mpable at this

eleated temp and

press for a

s1Ncient len)th of

time and then

harden fairly

rapidly.

Type of

cement

Compositio


i)h

$l1mina

Cemen

t

The total

al1mina

content

,$l!O3shall not be

less than

3! percent

by mass.

pecication )ien in :2 6*#!:"9%9&ineness:=laineFs air permeability test :


#mmettin) Time: Kicat test : 2nitial ettin) Time



!*hrL30 min1tes : 30 (pa7!L"hr : 3# (pa

Mhere ery hi)h

rate of stren)th

deelopment is

re>1ired.

1)0"+ $" 6"# meas#re !"nsisten!6, settin( time, @neness an$ s"#n$ness "4

!ement? Ans+er in &rie4.C"nsisten!6 testP)300 )m of cement is mixed with !#B water. The paste is lled in the mo1ld,*0 mm

hei)ht of KicatFs apparat1s. $nd the s1rface of the lled paste is smoothened and


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leelled. $ s>1are needle,"0mm"0 mm attached to the pl1n)er is then lowered )ently

oer the cement paste s1rface and is released >1ic+ly. The pl1n)er pierces the cement

paste. The readin) on the attached scale is recorded. Mhen the readin) is #'7 mm from

the bottom of the mo1ld5 the amo1nt of water added is the correct percenta)e of water

for normal consistency.ettin( /ime

$fter preparin) the cement paste by addin) 0.%# times then water re>1ired to )ie a

paste of standard consistency the mo1ld is lled completely with the paste and placed

into the icat apparat1s. The test is cond1cted at room temperat1re of !7L!C. 2nitial

settin) time is the time re>1ired for the needle of the apparat1s to reach the leel of

#mm meas1red from the bottom of the mo1ld.The cement is considered to be nally set when 1pon applyin) the needle )ently to the

s1rface of test bloc+5 the needle ma+es an impression5 b1t the attachment fails to do so.Bineness8e)ree of neness of cement is the meas1re of mean si;e of )rains in it.3 methods are

)enerally 1sed for testin) neness: iee (ethod5 =lains $ir Permeability (ethod5

Ma)ner T1rbidimeter (ethod. The last two methods meas1re the s1rface area of per

)ram of cement whereas the rst one meas1res percent resid1e by wei)ht."#n$nesso1ndness of cement may be tested by He'Chatelier (ethod or by $1toclae (ethod. 2n

He'Chatelier (ethod5 a mo1ld is prepared by mixin) "00 )ram of cement with o.7% times

the water re>1ired to )ie a paste of standard consistency. (o1ld is coered with a )lass

sheet and s1bmer)ed in water at temperat1re of !7'3!C.$fter !* ho1rs 5mo1ld is ta+en

o1t and the distance separatin) the indicator point is meas1red. $fter that mo1ld is

s1bmer)ed in the boiled water for 3 ho1rs. $fter remoin) the mo1ld from water it is

cooled and the distance between the indicator points is meas1red a)ain. The dierence

between the two meas1rements represents the 1nso1ndness of the cement. 2n a1toclae

test at rst /eat cement specimen of !#mm x !#mm x !#0mm placed inside a1toclae.

Temp of a1toclae shall be raised at s1ch a rate as will brin) the )a1)e press1re of the

steam to !." (Pa in " to " h from the time the heat is t1rned on and maintained for 3

ho1rs. $fter that press1re is red1ced slowly and specimen is remoed and cooled.Chan)e in len)th of the specimen is meas1red.

11) 0"+ the @neness "4 !ement a*e!ts the pr"perties "4 !"n!rete?". The rate of hydration depends directly on the neness of the cement as ner cements

oer )reater s1rface area for hydration to ta+e place5 and for rapid deelopment of

stren)th5 hi)h neness is necessary. =1t hi)her rate of hydration means hi)her rate of

early heat eol1tion.!. 2ncreasin) the neness of cement red1ces the amo1nt of bleedin) in concrete by

increasin) the water re>1irement of concrete.

3. The wor+ability of non'air'entrained concrete is increased by increasin) the cementneness.*. The !%'day compressie stren)th Q mod1l1s of elasticity of concrete5 with or witho1t

entrained air5 increases with an increase in cement neness. The dierence in


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compressie stren)th d1e to dierence in neness of cement is considerably less at "

yearRs a)e.#. The neness of cement in


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inersely related to the permeability5 as most dama)e mechanisms inole the

di1sion of reactie ions into the concrete to attac+ either the cement paste or the

steel reinforcement.

1)What is the r"le "4 +ater re$#!in( a$mit#re in !"n!rete? Dis!#ss the

!hemistr6 &ehin$ it. Name a 4e+ !"mmer!ial +ater re$#!in( a$mit#re inmar=et.

The basic role of water red1cers is to de1irements that cannot

always be achieed ro1tinely 1sin)

conentional constit1ents and normal

mixin)5 placin)5 and c1rin) practice.

Concrete is dened as Uhi)h'

stren)th concreteF solely on the basis of

its compressie stren)th meas1red at a

)ien a)e.

$ )reater de)ree of >1ality control is

re>1ired for the s1ccessf1l prod1ction ofhi)h'performance concrete.

Aelatiely lesser de)ree of >1ality

control is re>1ired5 than that re>1ired forPC.

$ PC is not always a C. $ C is always a PC.


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17) What is the $i*eren!e &et+een se(re(ati"n an$ &lee$in(? 0"+ !an +e !"ntr"l

se(re(ati"n, &lee$in( #sin( a$$iti'esa$mit#resplasti!iers? Segregation:'

e)re)ation is dened as the separation of the constit1ent materials of concrete. There

is a considerable dierence in the si;es and specic )raities of the constit1ent

in)redients of concrete5 so there is a nat1ral tendency of the materials to fall apart.

e)re)ation may be of three types:The coarse a))re)ate separatin) o1t or settlin) down from the rest of the mix.

The paste or matrix separatin) o1t from the rest of the material.

The water5 bein) of lowest specic )raity5 separatin) o1t from the rest of the

material. Bleeding:' =leedin) is a partic1lar form of se)re)ation5 in which some of the water in

the mix tends torise to the s1rface of the freshly mixed concrete. This is ca1sed by the inability of the

solid constit1ents of the mix to hold all of the mixin) water when they settle

downwards5 water hain) the lowest specic )raity of all the mix constit1ents.

$ddities s1ch as


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1>) What is F6 ash !"n!rete?&ly'ash concrete is a special type of concrete which is made 1p of PPC5 in which the

po;;olanic material 1sed is ly-ash. &ly ash is a non'comb1sted by'prod1ct of coal'red

power plants and is collected in the electrostatic precipitator. Mhen hi)h ol1mes of


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The man1fact1re of &ly'ash concrete is less ener)y intensie5 and the raw material

1sed is cheaper. Th1s red1cin) the oerall cost. 2n


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) Dis!#ss p"st !ra!=in( &eha'i"#r "4 steel BRC. Ill#strate +ith (raph.The ber'reinforced concrete composite will carry increasin) loads after the rst crac+in)

of the matrix if the p1ll'o1t resistance of the bers at the rst crac+ is )reater than the

load at rst crac+in). $t the crac+ed section5 the matrix does not resist any tension and

the bers carry the entire load ta+en by the composite. Mith an increasin) load on the

composite5 the bers will tend to transfer the additional stress to the matrix thro1)h

bond stresses. This process of m1ltiple crac+in) will contin1e 1ntil either bers fail or the

acc1m1lated local debondin) will lead to ber p1ll'o1t.

) What is (e"-p"l6mer !"n!rete? Is it $i*erent 4r"m F6 ash !"n!rete?

?eopolymer is essentially a cement free concrete. 2t res1lts from the reaction of a

so1rce material that is rich in silica and al1mina with al+aline li>1id. Enli+e ordinary

portland@po;;olanic cements5 )eopolymers do not form calci1m'silicate'hydrates ,Cs

for matrix formation and stren)th5 b1t 1tilise the polycondensation of silica and al1mina

prec1rsors to attain str1ct1ral stren)th.

&ollowin) materials are )enerally 1sed to prod1ce ?PCCs:

"#r!e material

&ly ash5

??=5

&ine a))re)ates and

Coarse a))re)ates

Catal6ti! liH#i$ s6stem C)2t is an al+aline actiator sol1tion ,$$ for ?PCC. 2t

is a combination of sol1tions of al+ali silicates and hydroxides5 besides distilled water.

The role of $$ is to actiate the )eopolymeric so1rce materials ,containin) i and $l

s1ch as


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Aed1cin) a))re)ate@cement ratio and +eepin) w@c ratio wor+ability can be increased as

s1rface as solids,a))re)ate and cement decreases so that same amo1nt of water

increases wor+ability.

5) Dis!#ss in &rie4 re(ar$in( pr"perties "4 BA an$ CA. :enti"n I !"$e pr"'isi"ns

an$ &rie4 $etail "4 the tests.

The properties of a))re)ates arei i;e: a))re)ates hain) si;e more than *.7# mm are called coarse a))re)ates and

a))re)ates whose si;e is less than *.7# mm are +nown as ne a))re)ates.ii hape: shape of a))re)ate is an important property. 2t aects wor+ability of concrete.

Coarse a))re)ates are classied asa Ao1ndedb 2rre)1lar or partly ro1ndedc $n)1lard &la+y

iii Text1re: The relatie de)ree to which s1rface of admixt1re are polished or d1ll5

smooth or ro1)h is called text1re. 1rface text1re are classied asa ?lassyb moothc ?ran1lard Crystallinee oneycomb Q poro1s

i tren)th: it depends on the stren)th of parent roc+ to some extent. 2t is meas1red

by a))re)ate cr1shin) al1e. tren)th of a))re)ate refer to the load it can ta+e

before )ettin) cr1shed To1)hness: the property of a))re)ate to resist s1dden shoc+ or impact is called

to1)hness. 2t is meas1red by a))re)ate impact al1e test.i ardness: the property by which a))re)ates are able to resist the wear Q tear on

its s1rface is called hardness of a))re)ate. 2t is 1s1ally meas1red by Hos $n)eles

$brasion test.ii $bsorption Q (oist1re content: some a))re)ates are poro1s and absorptie which

will therefore eect the w@c ratio Q hence the wor+ability of concrete. The free

moist1re content of ne a))re)ate res1lt in b1l+in) of a))re)ate. 81e to b1l+in)

ne a))re)ate shows more ol1me which if not ta+en proper care can res1lt in a

concrete mix which is 1nder'sanded and harsh.

Testin) of a))re)ates

i $s per 2 !3%6,Part2'"9635 tests are performed to determine the


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ii To determine stren)th of concrete a))re)ate cr1shin) al1e is determined. $

)rad1ally increasin) compressie load is applied on a))re)ate passin) "!.# mm 2

siee and retained on "0 mm 2 siee. The load is increased 1pto *0 tonnes in "0

mins and then released. The material is then sieed on !.# 2 siee and the ratio

of material passin) .36 mm 2 siee to the ori)inal wt of sample is called

a))re)ate cr1shin) al1e. $))re)ate cr1shin) al1e of more than *#B is nots1ited for concrete wor+.

iii To determine resistance to s1dden shoc+ or impact a))re)ate impact test is

performed as per 2!3%6,part 2K. The test sample is selected as aboe. $fter

placin) the sample in the steel c1p the hammer wei)hin) "* +)s is allowed to fall

freely thro1)h a distance of 3%0 mm. $fter "# s1ch blow the whole of it is sieed

thro1)h !.36 mm 2 siee and the ratio of the wt of fraction passin) thro1)h the

!.36 mm siee to the total wt of sample )ies the a))re)ate impact al1e. $

a))re)ate impact al1e )reater than *#B of the wt of a))re)ates sho1ld not be1sed for concrete wor+.

i 2 !3%6,part 2K coers two methods for determinin) abrasion al1e for

a))re)ates: 8ealFs abrasion testin) Q Hos $n)eles abrasion testin) . the abrasie

char)e consists of cast iron or steel spheres approximately *% mm in dia Q

wei)hin) between 390 to **0 )m. $fter specied no of reol1tions the material is

sieed on ".7 mm 2 siee. The Aatio of material passin) tro1)h ".7 mm 2 siee

to the ori)inal wt of sample is called abrasion al1e which sho1ld not be more

than "6B for concrete a))re)ates.

7)What is the "&e!ti'e "4 !"n!rete mi $esi(n? What sh"#l$ &e the ri(ht

appr"a!h t" $esi(n a !"n!rete mi?The selection of mix proportion is simply the process of choosin) s1itable in)redient of

concrete and determinin) their relatie >1antities with the ob4ect of prod1cin) as

economically as possible concrete of certain minim1m properties notable stren)th5

d1rability and re>1ired consistency. $lso wor+ability of the mix sho1ld be 1pto the mar+

to meet the re>1irement of placin) the concrete at the site.To desi)n a concrete mix of appropriate stren)th and d1rability and of re>1ired

wor+ability one need st1dy the property of concrete in detail with special emphasis on

the rheolo)ical behaior of concrete. The properties of admixt1re sho1ld be ta+en into

acco1nt to ascertain wor+ability. $lso w@c ratio sho1ld be controlled eectiely to )et the

maxim1m compressie stren)th for a xed a))re)ate@cement ratio. /ow' a'days

porosity of concrete is controlled in an eectie manner to control stren)th and

compactness of concrete. $lso comp1ter modelin) of the properties of constit1ents of

concrete sho1ld be made to controlledY and meas1re the properties of all the materials

to prod1ce more appropriate mixes.


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8) What are the $i*erent meth"$s "4 !"n!rete mi $esi(n (enerall6 #se$? What

are the a$'anta(es an$ $isa$'anta(es "4 these meth"$s? Pr"'i$e 6"#r

"pini"n re(ar$in( appli!a&ilit6 "4 these meth"$s in $i*erent sit#ati"ns.The commonly 1sed methods of mix desi)n area Thw $C2 committee !"" methodb The 8OI methodc The 2ndian tandard recommended method ,as per 2 "0!6!'%!

d (ix desihZ)n of p1mpable concrete The $C2 committee !"" method

The adanta)es of this method are'i 2t ta+es into acco1nt the amo1nt of water content in a)).ii The eects of an)1larilities of coarse a))re)ate is re1ire more mortar than ro1nded a))re)ate.iii2t ta+es into acco1nt the fact that a denite percenta)e of air remains

entrapped which is inersely proportional to the maxim1m a))re)ate si;e. The 8OI method

This method can be 1sed for most p1rposes incl1din) road5 this method was

deeloped by the department of enironment ,E.-.5 can be 1sed for p1mpable

concrete.

The 2ndian tandard recommended method ,as per 2 "0!6!'%!

The adanta)es of this method are:'". =ased on statistical ariation5 the tar)et stren)th is xed on a conseratie

side.!. Mater absorption of ne and coarse a))re)ate is ta+en into consideration.3. 2t incorporates the stren)th of cement to eect the economy in mix desi)n.

The disadanta)e of this method are:'". /ow a days hi)h stren)th cement is aailable so the !% days stren)th

cate)ories sho1ld be reiewed.!. ?raph connectin) stren)th of cement and w@c ratio needs to be re'

established.3. The )raph connectin) !% days stren)th of cement and w@c ratio is to be

extended 1pto %0 (Pa for hi)h stren)th concrete.*. $s per reised edition of 2 *#6'!000 the mix desi)n proced1re sho1ld be

based on de)ree of wor+ability expressed in terms of sl1mp instead of

compactin) factor. This res1lts in the chan)e of al1es in estimatin)

approximate sand and water content.

(ix desi)n for p1mpable concrete$ concrete which can be p1shed thro1)h a pipe is called p1mpable concrete. 2t is

proportioned in s1ch a manner that its friction with the inner wall of the pipeline

does not become so hi)h to preent its moement at the press1re applied by the

p1mp. The content of nes is ad41sted to oer at the inner line of the pipeline

1nder press1re from the p1mp the mix does not se)re)ate or bleed.

9) What is the $i*eren!e &et+een a l"+ m"$#l#s @&er an$ a hi(h m"$#l#s @&er

#se$ t" pr"$#!e BRC?

&ibre reinforced concrete is dened as a composite material consistin) of mixt1re of

cement5 mortar of concrete and discontin1o1s5 discrete5 and 1niformly dispersed

s1itable bre. 2ts properties lar)ely on the type of bre5 bre )eometry5 bre content5


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orientation Q distrib1tion of bre5 mixin) and compaction techni>1es and si;e shape of

the a))re)ates.The mod1l1s of elasticity of the matrix m1st be m1ch lower than that of bre for eNcient

stress transfer. How mod1l1s bre s1ch as nylon and polypropylene are therefore 1nli+ely

to )ie stren)th improement b1t they helps in the absorption of lar)e ener)y and

therefore impart )reater de)ree of to1)hness and resistance to impact. i)h mod1l1s

bre s1ch as steel5 )rass and carbon impart stren)th and stiness to te composite.

>)Dis!#ss the !han(e in &eha'i"#r "4 !"n!rete ep"se$ t" $i*erent le'els "4

temperat#re #p t" 1J!.Ep to abo1t 300 C5 the concrete 1nder)oes normal thermal expansion.$boe that temperat1re5 shrin+a)e occ1rs d1e to water lossY howeer5 the a))re)ate

contin1es expandin)5 which ca1ses internal stresses.$t *#0'##0 C the cement hydrate decomposes5 yieldin) calci1m oxide.Ep to abo1t #00 C5 the ma4or str1ct1ral chan)es are carbonatation and coarsenin) of

pores.$t #73 C5 >1art; 1nder)oes rapid expansion d1e to phase transition.Calci1m carbonate decomposes at abo1t 600 C.Concrete exposed to 1p to "00 C is normally considered as healthy. The parts of a

concrete str1ct1re that is exposed to temperat1res aboe approximately 300 C

,dependent of water@cement ratio will most li+ely )et a pin+ color. Oer approximately

600 C the concrete will t1rn li)ht )rey5 and oer approximately "000 C it t1rns yellow'

brown. Es1ally5 pin+ colored concrete is considered as a dama)ed one that sho1ld be

remoed.

)What is the &asi! reH#irement "4 Re4ra!t"r6 !"n!rete "r hi(h temperat#re

resistant !"n!rete?Aefractory concrete made with hi)h al1mina cement has a )ood resistance to acid

attac+5 the chemical attac+ is increased by rin) at 900'"000C. The concrete can be

bro1)ht 1p to serice temperat1re as soon as it is hardened i.e. it does hae to be pre'

red. Aefractory hi)h'al1mina cement can withstand a considerable thermal shoc+.

1) What is !reep in !"n!rete? Creep is dened as a time'dependent deformation 1nder a constant load. The

creep deelops in a concrete rapidly at the be)innin) and )rad1ally decreases with time.

$pproximately 7#B of the 1ltimate creep in concrete occ1rs d1rin) the rst year. The

total deformation of a reinforced concrete specimen consists of the instantaneo1s

deformation5 shrin+a)e deformation5 and creep.

) Dis!#ss 4e+ salient 4eat#res "4 !reep in !"n!rete. Ill#strate 6"#r ans+er +ith

(raphs." Ender normal conditions of loadin)5 the instantaneo1s strain recorded depends on the

speed of application of the load and th1s incl1des not only the elastic strain b1t also

some creep.


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! 2t is diNc1lt to dierentiate acc1rately between the immediate elastic strain and early

creep5 b1t this is not of practical importance as it is the total strain ind1ced by the

application of load that matters.3 2f the stress is remoed after some period of time5 there is an instantaneo1s recoery

of the elastic strain and then slower recoery of some of the creep5 b1t not all. 2f the

concrete is reloaded at some later date5 instantaneo1s and creep deformations deelop

a)ain.* Creep in concrete is a post'elastic phenomena. 2n practice5 dryin) shrin+a)e and

iscoelastic behaior s1ch as creep 1s1ally ta+e place sim1ltaneo1sly. Considerin) the

ario1s combination of loadin)5 restainin)5 and h1midity conditions5 the followin) terms

are dened:2. Tr1e or =asic Creep is dened as the creep that occ1rs 1nder conditions that there is

no dryin) shrin+a)e or moist1re moement between concrete and ambient enironment.22. pecic Creep: is dened as creep strain per 1nit of applied stress:222. 8ryin) Creep: is the additional creep that occ1rs when the specimen 1nder load is

also dryin).2K. Creep CoeNcient: is dened as the ratio of creep strain to elastic coeNcient.

) What is shrin=a(e "4 !"n!rete? 0"+ !an 6"# !"ntr"l shrin=a(e "4 !"n!rete?hrin+a)e of concrete is the time'dependent strain meas1red in an 1nloaded and

1nrestrained specimen at constant temperat1re. 2t can be classied as',a Plastic hrin+a)e

hrin+a)e of this type manifests itself soon after the concrete is placed in the forms

while the concrete is still in the plastic state. Hoss of water by eaporation from the

s1rface of concrete or by the absorption by a))re)ate or s1b)rade5 is belieed to be

the reasons of plastic shrin+a)e. The loss of water res1lts in the red1ction of ol1me.

The a))re)ate particles or the reinforcement comes in the way of s1bsidence d1e to

which crac+s may appear at the s1rface or internally aro1nd the a))re)ate or

reinforcement.,b 8ryin) hrin+a)e


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in ener)y between the hi)her'ener)y shell and the lower ener)y shell may be released in

the form of an ['ray. The n1mber and ener)y of the ['rays emitted from a specimen can

be meas1red by an ener)y'dispersie spectrometer. $s the ener)y of the ['rays are

characteristic of the dierence in ener)y between the two shells5 and of the atomic

str1ct1re of the element from which they were emitted5 this allows the elemental

composition of the specimen to be meas1red.

>) Dis!#ss KAl=ali-a((re(ate Rea!ti"nL. 0"+ !an 6"# !"ntr"l KAl=ali-a((re(ate

Rea!ti"nL? The mixin) water t1rns to be a stron)ly ca1stic sol1tion d1e to sol1bility of

al+alies from the cement. The ca1stic sol1tion attac+s reactie silica of a))re)ate to

form al+ali'silica )el of 1nlimited swellin) type. Contin1o1s )rowth of silica )el exerts

stron) osmotic press1re to ca1se pattern crac+in) partic1larly in thin section li+e

paement. This phenomenon res1lts in loss of stren)th and elasticity.

$l+ali a))re)ate reaction can be controlled by:aelection of non'reactie a))re)ates. b=y 1se of low al+ali cement5 c=y the 1se of correctie admixt1re s1ch as po;;olanas. d=y controllin) oid space in concrete e=y controllin) moist1re condition and temperat1re.

3) What $" 6"# mean &6 rhe"l"(i!al pr"perties "4 !"n!rete? What is a

rhe"meter?

31) What $" 6"# mean &6 M$#ra&ilit6 "4 !"n!rete? Dis!#ss +ith eamples "4 a!i$

atta!=, !ar&"nate atta!=. 81rability of concrete is dened as its ability to resist weatherin) action5 chemical

attac+5 abrasion5 or any other process of deterioration to maintain its ori)inal form5

>1ality5 and sericeability when exposed to its intended serice enironment.$cid attac+: (ost acid sol1tions will slowly or rapidly disinte)rate portland cement concrete

dependin) 1pon the type and concentration of acid. (ost 1lnerable part of cement

hydrate is Ca,O! b1t C'' )el can also be attac+ed. Concrete can be attac+ed by

water of p al1e less than 6.#5 b1t attac+ is seere when p al1e is less than #.#. $s

the attac+ proceeds5 all cementitio1s materials leached away to)ether with any

carbonate a))re)ate. 2f acids are able to reach the reinforcin) steel thro1)h crac+s5

corrosion can occ1r.Carbonate attac+: Carbonation of concrete is a process by which CO!from the air penetrates into

concrete and reacts with calci1m hydroxide to form calci1m carbonates. Aate of

carbonation depends 1pon seeral factors li+e relatie h1midity5 )rade of concrete5

permeability of concrete etc. The hi)hest rate of carbonation occ1rs at a relatie

h1midity of between #0 to 70 percent.

3) What is lea!hin( "4 !"n!rete? Dis!#ss +ith an eample pr"'i$in( emphasis "n

!hemistr6.


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Mhen water


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3>) What $" 6"# mean &6 se!"n$ar6 h6$rati"n "4 PPC?Portland cement prod1ces calci1m silicate hydrate )el and lime by the process of

hydration. This hydration process is +nown as primary hydration.Primary ydration Aeaction:

PPC is a Portland cement blended with po;;olana. Po;;olana is a siliceo1s or siliceo1s

and al1mino1s material5 which in itself possesses little or no cementin) property. =1t in

nely diided form and in the presence of moist1re5 it chemically reacts with lime

,liberated by Portland cement at ordinary temperat1res to form compo1nds possessin)

cementitio1s properties. This process is termed as secondary hydration of PPC.econdary ydration Aeaction:

5) What is p"l6mer !"n!rete?Concrete which 1ses polymers to s1pplement or replace cement as a binder is termed as

polymer concrete. 2n polymer concrete5 thermosettin) resins are 1sed as the principal

polymer component d1e to their hi)h thermal stability and resistance to a wide ariety

of chemicals. Polymer concrete is also composed of a))re)ates that incl1de silica5

>1art;5 )ranite5 limestone5 and other hi)h >1ality material. The a))re)ate m1st be of

)ood >1ality5 free of d1st and other debris5 and dry. &ail1re of these criteria can red1ce

the bond stren)th between the polymer binder and the a))re)ate.$danta)es of polymer concrete incl1de:

a Aapid c1rin) at ambient temperat1resb i)h tensile5

concrete technology questions

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