Clase 04 - Mezclas Concreto y Refuerzo

7/24/2019 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!


5/44

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)


6/44

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!


7/44

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


8/44

Concrete Mixing and

Proportioning .ater/Concrete ta$le


9/44

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


10/44

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


12/44

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!


19/44

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!


23/44

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 %)


24/44

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!


25/44

Concrete Mixing and

ProportioningFailure Mechanism of Concrete

Shrinkage Microcracks

are the initial shrinkage

cracks due tocarbonation shrinkage,

hydration shrinkage, and

drying shrinkage.


26/44

Concrete Mixing and


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.


27/44

Concrete Mixing and


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


29/44

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:


30/44

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


31/44

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=


32/44

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


35/44

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.


36/44

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


37/44

Concrete Properties2! 5ensile Strength (cont!)

Splitting 5ensile Strength, fct Split C#linder 5est

P

Concrete CylinderPoissons

Effect


38/44

Steel Reinforcement

! eneral

StandardReinforcing arMar'ings


39/44

Steel Reinforcement! eneral

Most common t#pes for nonprestressedmem$ers: hotrolled deformed $ars

welded wire fa$ric


40/44

Steel Reinforcement*reas, .eights, imensions


41/44

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


42/44

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!


44/44

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

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Clase 04 - Mezclas Concreto y Refuerzo