3.Properties of Hardened Concrete

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3. Properties of Hardened coConcrete technology and masonry structures


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3.1.1. Deformation of hardened conc

to calculate the deformation and deflection of structural members, we have t

the relation between stress and strain.

concrete behaves nearly elastically when load is first applied.

However, under sustained loading, concrete exhibits creep,

i.e. the strain increases with time under a constant stress, even at very low

normal environmental conditions of temperature and humidity.


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3.1.2. Modulus of elasticity

oncrete shows nonlinear and

behavior, i.e. a permanent deformatio

after removal of load as shown

"he slope #modulus of elasticity.

"he elastic modulus of concrete in comp

$c %&'''

Figure :stress and strain diagram for concrete


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"ypes of modulus of elasticity of concrete

(tatic modulus of elasticity

). *nitial tangent modulus of elasticity #at origin

+. "angent modulus of elasticity # at any point

. (ecant modulus of elasticity # slope of line connecting a specified point andorigin

D. hord modulus of elasticity: found out with refenrence to the chord

Dynamic modulus of elasticity

lexural modulus of elasticity


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Dynamic modulus of elasticity

Static modulus of elasticity does not truly represent the elastic beconcrete.

modulus of elasticity from # non!destructive testing of concrete.

"he modulus of elasticity can be determined by sub-ecting the concrete

longitudinal vibration at their natural freuency.

involves the determination of either resonant freuencythrough a spec

or pulse velocity travelling through the concrete. +y making use of theparameters modulus of elasticity can be calculated from the following

Ed % Kn2L2p where : where Edis the dynamic modulus of elasticit

constant, nis the resonant freuency/ 0 is the length of specimen/ an

density of concrete.


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!ltrasonic pulse elocity e"uipment #nding dynamic modulus of elasticity


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3.2.1 creep

*t is 2the time!dependent

part of the strain resulting

from stress

"his is also known as plastic

flow or time yield

increase in strain under sustained constant

stress after taking into account other time

dependent deformations not associated with

stress.Time


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Factors a$ecting creep

C%&&'

S(%&)*(+

Sti$erthe a

+igher the olumeof a

+igher the modulus of e

-o,er ,ater cement ra

+ence decreases in ,ater cem

Creep is smaller ,hen concrete is cu


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Shrinage

Caused by loss of ,ater by eaporation or by hydration of

Contraction of concrete due to loss of moisture is called sh

(ypes

/. 'lastic shrinage

0. /utogenous shrinage

C. Drying shrinage

D. Carbonation shrinage

&. (hermal shrinage


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-oss of,ater &aporation

/bsorptionby

aggregate

'lastic shrinage

hile the cement paste is plastic it undergoes olumetric c,ater due to loss of ,ater

/ complete preention of eaporation immediately after careduces

preention

Coering,ith

polyethylene

oring atnight


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/utogenous shrinage

&en ,hen no moisture moement to or from the set concpossible autogenous shrinage occurs

(his is caused by loss of ,ater used up in hydration

f there is a continuous supply of ,ater to the concrete durconcrete e4pands due to absorption of ,ater by the cemenprocess is no,n as s,elling


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Drying shrinage

ithdra,al of ,ater form hardened concrete stored in unscauses drying shrinage

Since hydration of cement is an eerlasting process 5 the dshrinage is also an eer lasting process

Simply the shrinage taen place after the concrete has sehardened


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(hermal shrinage

6olumetric change due to decrease in temperatures

&4ample can be taen as a roof slab or road paement e4pthe day and undergoes thermal shrinage during night


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Factors in7uencing shrinage

Depends on the relatie humidity

ater cement ratio


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Fatigue of concrete

Static fatigue or creep rupture : failure occurs under a sus8or a slo,ly increasing load9 near5 but belo, the strength

Fatigue :failure occurs under cyclic or repeated loading

%epeated loadings can be seen in many structures for e4amroads5 air #eld paement


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Fatigue failure

Concrete specimen subected toalterations of compressie stress

Stress strain cure :concaeto,ards the strain a4is: linear :concae to,ards the stress a4is

Stress strain cure of under cyclic compres

loading


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&$ect of porosity


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&$ect of porosity

(he hydrated cement contains : solid product of hydration ,hich is held physically or is adsorbed on the large surfacehydrates this ,ater is called gel ,ater also called gel pores

6olume of solid products of hydration < 8olume of dry cem,ater 9

oids or capillary pores

= the residual space taes the form of oids or capillary po 'orosity depends upon ,ater?cement ratio and degree of h


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'orosity erses compressie st

Porosity 4log scale5 ! per cent


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&$ect of ,ater?cement ratio

/bram@s la, A

=for any gien condition of test the strength of ,ell compa,ith good ,orability depends upon the BC cement ratio the mi4 is ,orable>. +e presented his classic la, in the fo

S

here 4 ,aterBcement ratio by olume and / and 0 are

S compressie strength of concrete

= ,hich simply says that the strength is inersely proportionacement ratio


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&$ect of aggregate siEe

0arger si6e larger strength7 7

8es upto some extent

+ut as larger maximum si6e gives lower surface area for developments of

is responsible for the lower strength of the concrete

(econdly bigger aggregate si6e causes a more heterogeneity in the concre

prevent the uniform distribution of load when stressed


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Durability of concrete

t is the ability to resist ,eathering action5 chemical attacany other process of deterioration

Durable concrete ,ill retain its original form5 "uality and se,hen e4posed to its enironment

=no material is inherently8 naturally 9 durable>


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&nironmental related causes oconcrete durability problems

(emperature

Moisture

'hysical factor

Chemical factor

0iological factors


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Cracks in concrete

0l d t


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0leed at

Top of Slab

Inhibited by Fly ash


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'lastic shrinage occurs ,hen the concretebleed ,ater too "uicly from its surface antherefore dries rapidly


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'lastic settlement : Settlement ,hile thconcrete is still settling. (his happens,hen the concrete coer oer thereinforcement is too small5 or the mi4contains too many #nes or the mi4 is toslo, in releasing its bleed ,ater.t cracoccur ,hen concrete is


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(hermal cracing

Surface Disintegrati


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Surface Disintegrati

Dusting

mproperB-ac of Curing

+igh Surface BC

Carbonation

Fresh /ir

Spallin


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Spallin

mproper curing

%apid eaporation

Sealing surfaceprematurely

(oo lo, ,Bc ratio

/ggregate Contamination

FreeEing

Plastic Shrinkage Crack


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PlasticShrinkageCrack

Occur when rate of evaporation

exceeds rate of bleed

CraEin


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CraEin

mproper Curing

%apid surfacedrying

erGFinishing

(oo long a delay from#nal tro,eling to

application of curingcompound

+igh BC ratio

=0lessing> Surface

mproperly Designed Structural Cracs


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mproperly Designed Structural Cracs


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=Hour dreams are lie the cement. f you,ater it ,ith actions5 it becomes a hardconcrete mass. 0ut if you leae it e4poseand un,atered5 the air ,ill easily blo, ita,ayI>J sraelmore/yior
http://www.goodreads.com/author/show/7023141.Israelmore_Ayivorhttp://www.goodreads.com/author/show/7023141.Israelmore_Ayivorhttp://www.goodreads.com/author/show/7023141.Israelmore_Ayivorhttp://www.goodreads.com/author/show/7023141.Israelmore_Ayivorhttp://www.goodreads.com/author/show/7023141.Israelmore_Ayivor


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3.Properties of Hardened Concrete

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