Download - Clase 04 - Mezclas Concreto y Refuerzo
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Fundamentals
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Lecture Goals
Concrete Mixing and Proportioning
Concrete Properties
Steel Reinforcement
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Concrete Mixing and
ProportioningConcrete: Composite material composed of
portland cement, fine aggregate (sand),coarse aggregate (gravel/stone), and water;with or withot other additives!
"#dration: Chemical process in which thecement powder reacts with water and thensets and hardens into a solid mass, $onding
the aggregates together
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Concrete Mixing and
Proportioning
"eat of "#dration: "eat is released dring theh#dration process!
%n large concrete masses heat is dissipatedslowl# temperatre rises and
volme expansion later coolingcases contraction! &se specialmeasres to control crac'ing!
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Concrete Mixing andProportioning! Proportioning: oal is to achieve mix with
*de+ate strengthProper wor'a$ilit# for placement
ow cost
ow Cost:
Minimi-e amont of cement
ood gradation of aggregates (decreasesvoids and cement paste re+ired)
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Concrete Mixing and
Proportioning
.aterCement Ratio (./C)
%ncreased ./C: %mproves plasticit# andflidit# of the mix!
%ncreased ./C: Reslts in decreasedstrength de to larger volme of voids incement paste de to free water!
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Concrete Mixing and
Proportioning .aterCement Ratio (./C) (cont!!)
Complete h#dration of cement re+ires./C 0 1!23!
4eed water to wet aggregate srfaces,
provide mo$ilit# of water dringh#dration and to provide wor'a$ilit#!
5#pical ./C 6 1!711!81
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Concrete Mixing and
Proportioning .ater/Concrete ta$le
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Concrete Mixing and
Proportioning
Proportions have $een given $# volme orweight of cement to sand to gravel (ie!:2:7) with ./C specified separatel#
4ow cstomar# to specif# per 97 l$! ag ofcement: wt! f water, sand < gravel
atch +antit#: wt! per c$ic #ard of each
component
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Concrete Mixing and
Proportioning
2! *ggregates =1=3> of volme of hardened concrete Remainder 6 hardened cement paste,
ncom$ined water, air voids
More densel# pac'ed aggregate give $etterStrength
.eather resistance (dra$ilit#)
?conomical
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Concrete Mixing and
Proportioning
2! *ggregates @ine aggregate: sand (passes throgh a
4o! 7 sieve; 7 openings per inch)
Coarse aggregate: gravel
ood gradation:2A si-e grops of sand
Several si-e grops of gravel
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Concrete Mixing and
Proportioning
Maximm si-e of coarse aggregate in RCstrctres: Mst fit into forms and $etweenreinforcing $ars:(4SR1, C!A!A!2)
/3 narrowest form dimension
/A depth of sla$
A/7 minimm distance $etweenreinforcement $ars
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Concrete Mixing and
Proportioning
*ggregate Strength
Strong aggregates: +art-ite, felsite
.ea' aggregates: sandstone, mar$le%ntermediate strength: limestone, granite
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Concrete Mixing and
Proportioning
Balit#
.or'a$ilit#
?conomical
In the design of concrete mixes, three principal
requirements for concrete are of importance:
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Concrete Mixing and
Proportioning
Balit#of concrete is measred $# itsstrength and dra$ilit#! 5he principal factorsaffecting the strength of concrete , assming
a sond aggregates, ./C ratio, and theextent to which h#dration has progressed!ra$ilit# of concrete is the a$ilit# of theconcrete to resist disintegration de to
free-ing and thawing and chemical attac'!
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Concrete Mixing and
Proportioning
.or'a$ilit#of concrete ma# $e defined as acomposite characteristic indicative of the easewith which the mass of plastic material ma#deposited in its final place withot
segregation dring placement, and its a$ilit#
to conform to fine forming detail!
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Concrete Mixing and
Proportioning
?conomicalta'es into accont effective seof materials, effective operation, and ease ofhandling! 5he cost of prodcing good +alit#
concrete is an important consideration in theoverall cost of the constrction proDect!
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Concrete Mixing and
Proportioning5he inflence of ingredients on properties
of concrete!
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Concrete Mixing and
ProportioningA! .or'a$ilit#
.or'a$ilit# measred $# slmp test
1. Layer 1: Fill 1/3 full. 25 stokes
2. Layer 2: Fill 2/3 full. 25 stokes3. Layer 3: Fill full. 25 stokes
4. Lift cone and measure slump (typically 2-6 in.)
1 2 3 4
12slump
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Concrete Mixing and
ProportioningSlump test - The measurement of the consistency of the
mix is done with the slump-cone test. The recommend
consistency for various classes of concrete structures .
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Concrete Mixing and
Proportioning
7! *dmixtres*pplications:
%mprove wor'a$ilit#
*ccelerate or retard setting andhardening
*id in cring
%mprove dra$ilit#
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Concrete Mixing and
Proportioning7! *dmixtres
Air-Entrainment: *dd air voids with $$$les
"elp with free-e/thaw c#cles, wor'a$ilit#, etc!
ecreases densit#: redces strength, $t alsodecreases ./C
Superplasticizers: increase wor'a$ilit# $#chemicall# releasing water from fine aggregates!
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Concrete Mixing and
Proportioning3! 5#pes of Cement
5#pe %: eneral Prpose
5#pe %%: ower heat of h#dration than5#pe %
5#pe %%%: "igh ?arl# Strength
"igher heat of h#dration
+ic'er strength (= da#s vs! 2E da#s for5#pe %)
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Concrete Mixing and
Proportioning3! 5#pes of Cement
5#pe %F: ow "eat of "#dration
radall# heats p, less distortion
(massive strctres)! 5#pe F: Slfate Resisting
@or footings, $asements, sewers, etc!exposed to soils with slfates!
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Concrete Mixing and
ProportioningFailure Mechanism of Concrete
Shrinkage Microcracks
are the initial shrinkage
cracks due tocarbonation shrinkage,
hydration shrinkage, and
drying shrinkage.
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Concrete Mixing and
ProportioningFailure Mechanism of Concrete
Bond Microcracks areextensions of shrinkage
microcracks, as the
compression stress fieldincreases, the shrinkage
microcracks widen but
do not propagates intothe matrix. Occur at 15-
20 % ultimate strength of
concrete.
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Concrete Mixing and
ProportioningFailure Mechanism of Concrete
Matrix Microcracks - aremicrocracks that occur in
the matrix. The propagate
from 20% fc. Occur up to30-45 % ultimate strength
of concrete. Matrix
microcracks start bridge oneanother at 75%. Aggregate
microcracks occur just
before failure (90%).
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Concrete Properties! &niaxial Stress verss Strain ehavior inCompression
c
Ec
o u
0.45fc
fcfc 12
6
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Concrete PropertiesThe standard strength test generally uses a cylindrical
sample. It is tested after 28 days to test for strength, fc.The concrete will continue to harden with time and for a
normal Portland cement will increase with time as follows:
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Concrete Properties Compressive Strength, fGc
4ormall# se 2Eda# strength for designstrength
PoissonGs Ratio,
0 1!3 to 1!21&sall# se = 1!=
c
Ec
o u
0.45fc
fcfc
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Concrete Properties Modls of ?lasticit#, ?c
Corresponds to secant modls at 1!73 fGc
4SR1 (Sec! C!E!3!):
where w 6 nit weight (Hg/mA)
771 Hg/mAI wc I2381 Hg/mA
@or normal weight concrete
(wc 2711 Hg/mA)
1 . 5( ) 0 . 0 4 3 '
c cE M P a w f=
( ) 4 7 0 0 'c cE M P a f=
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Concrete Properties Concrete strain at max! compressive stress,
o@or t#pical crves in compression
o varies $etween 1!1131!11A
@or normal strength concrete, o 0 1!112
Ec
o u
0.45fc
fc
fc
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Concrete Properties Maximm sea$le strain,
4SR1: 6 1!11A (C!1!2!A)&sed for flexral and axial compression
Ec
o u
0.45fc
fc
fc
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Concrete PropertiesTypical Concrete Stress-Strain Curves in Compression
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Concrete PropertiesTypes of compression failure
There are three modesof failure.
[a] Under axial
compression concretefails in shear.
[b] the separation of the specimen into columnar pieces by
what is known as splitting or columnar fracture.
[c] Combination of shear and splitting failure.
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Concrete Properties2! 5ensile Strength 5ensile strength 0 E> to 3> of fGc Modls of Rptre, f
r @or deflection calclations, se:
5est:
2
6
bh
M
I
Mcfr ==
0 . 6 2 ' ( )
( 1 0 , . 8 . 6 )
r cf f M P a
N S R C
=
NSR-10Eq. 9-10
P
frMmax = P/2*a
unreinforced
concrete beam
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Concrete Properties2! 5ensile Strength (cont!)
Splitting 5ensile Strength, fct Split C#linder 5est
P
Concrete CylinderPoissons
Effect
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Steel Reinforcement
! eneral
StandardReinforcing arMar'ings
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Steel Reinforcement! eneral
Most common t#pes for nonprestressedmem$ers: hotrolled deformed $ars
welded wire fa$ric
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Steel Reinforcement*reas, .eights, imensions
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Steel Reinforcement2! 5#pes
*S5M *83 Standard Specification foreformed and Plainillet Steel ars
rade 81: f# 6 81 'si, JA to JE
most common in $ildings and $ridges
rade 71: f# 6 71 'si, JA to J8
most dctile
rade =3: f# 6 =3 'si, J8 to JE
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Steel Reinforcement
2! 5#pes
*S5M *88 RailSteel ars*S5M *8= *xleSteel ars
*S5M *=18 ow*llo#Steel ars
more dctile R81 steel
min! length of #ield platea 6 sh/# 6 3
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Steel Reinforcement
A! Stress verss Strain
StressStrain crve
for varios t#pes ofsteel reinforcement$ar!
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Steel Reinforcement ?s 6 %nitial tangent
modls 6 29,111 'si(all grades)
NoteR71 has a longer#ield platea
Stress
Strain
0.20
GR 40
GR 60 (less ductile)
Es1