Development of Strength and Fracture Properties of Latex ...loading spt:elra, Bridge deek...
Transcript of Development of Strength and Fracture Properties of Latex ...loading spt:elra, Bridge deek...
Development of Strength and Fracture
Properties of Latex Modified Concrete
Abslract
This paper reports latex modified
concrete (LMC) .~Irength and fracture
properties at ages ranging from 5 hours
and 28 days. The development of strength,
defonnability and fracture properties were
sligthly different from eonveotional con
crete. Test results indica[e a significant
improvement in reducing and bridging
microcracks,; especially in the prepeak load
region. The load deflection relationship
was obsered: to he highLy linear up to 0.93
of peak lop-d. Fracture toughness and
deformabiE!y increased significantly.
Fracture energy varies from 2.3 to l33.1
N/m, depending on age, and La some degree,
-~~--
SuvimoJ Su,liaranich '
.Tames R. Lundy 2
on notch depth ratio. However, the postpeak
hehavior was quite similar to convenrional
concrete. In the range studied. notch depth
appears to have less effect. compared to
nonnal concrete. The crack mouth opening
displacement control method provided
consistent values which may henefit olher
researchers.
Keyword:
Early llge perfonnance, styrene
butadiene. latex modified concrete.
mierocracb, strength development.
dcformabillty. fracture energy. characteristic
length, prepeak, posfpeak, strain softening,
cmocL
1, Associate; Professor. Civil Engineering Depanment, Faculty of Engineering, Kasetsart
UOlversity, Ph. D. student at College of Engineering, Oregon State University,
2. College of Engineering, Oregon State University, Corvallis. Oregon 9733l.
Introduction
OeteriQf;ltion of the infru~trueturc
may be due to environmental eondilions.
age, material degradation and/or increased
loading spt:elra, Bridge deek deterioration
is one major coneern beeause it affeets
the serviee life, maintenance costs, useT
eonvenience. and safety. Therefore, good
performing repair materials and cost-effec
tive application of these materials are of
interest.
These repair materials serve two
purposes. First. effeelive materials and
effieiem teehniques reciuce public incon
venienef', and, as a result. user costs.
Secondly, materials thaI reduce rhe bridge
deek pcnneability also provide a protection
system against <:lggres~ive solution seepage.
The second funetion is believed to delay
the corrosion of reinforcing steel, a major
factor in bridge deek deterioration.
Impermeability and dumbility are
two important faetors whieh are used to
judge the effeetivenes~ of ~ bridge deck
overlays. Low permeability materials that
provide a more effective proteetion system
against the ingress of aggressive solutions
are of interest.
Improved eoncrete propertics.
particul:.l1"ly lower pcnnc<:lbility, can be
achieved by adding admixtnres such as
latex to modify the concrete matriees (l , 5),
Latex modified concrete is the most eom
man overlay material used for bridge decks
during the last decade (l). Many highway
ageneies eontinue to use this material and
reeonize it~ heneficial qualities..'\lthough
these modified materials generally perfonn
well. distress eontinues to be reported.
Often, dislrt:sses are reported soon after
eonstruction.
The most eommonly reported early
age dislres~es. cracking and delamination.
pennit the ingress of moisture or aggressive
solutions into the substrate. These actions
may contribute to olher snbseqnent dis
tresses. Therefore. 10 avoid or minimIze
these distresses and achieve better long
term performance. a smdy is necessary to
investigate and understand the material
pror~nies and mcchani~r.1s involv~.
To study the meehanisms involved.
it has been recognized that models based on
fracture mechanics, sueh as the cohesive
cri.lck model, provide a better description of
eraek development in a composite material
like concrele, eompared to the conventional
stress criterial which assumes an immediate
drop to zero stres.s after peak stress (2). In
order to apply [he eohesive erack model to
study early age crack propagation, some
fraeture parameters are needed.
The investigation of maleria.l
properties reported in this paper is a part of
a study illvolving early age perfoffimnce of
laL~x modified concrete bridge deck over
lays. A test program and subsequent rcsults
for strength development, deformability
and fractnre energy of LMC provide Lhe
necessary information for further sludy,
LlJ1:YUJ'U - n'i'nlJ1P'1lJ
Material: Latex Modified concrete
(LMC)
Polym~rs were first introdueed to
hydrautic-eeme~t system" in 1923 because
of an increased need for durable eom;truction
material. In lnL1, Lefebure, using conven
tional concrete mixture proportioning, pro
duced lcllex modified concrete (LMC) and
latex modified 'mortar (LMM) (1). LMC.
defined by the :ACT committee 548. is the
mIxture of Portiand cement. fine and coares
aggrcgates combined wilh orgamc polymers
that are dispcrsed in "",."uer at the timc of
mlXlng(l).
After WWll, natural latex \I,/as
replaced with ;scvcral types of chemkal
polymers, bolh thermoplastic (vinyl-type)
and clastomeric: (styrene- butadiene copoly
mcr) based. Th¢se materials were developed
and commerdalized to modify thc structure
of concrete sys~ms, Some improved latexes
such as ~tyrene: butadiene have been widely
used in the l,;oocrcle industry, especi<.llly in
bridge deck overlays. This m<.lteriat has been
widely reporteu as providing s;ltisfaetory
protective/preventive systems for bridge
decks due to its excellent properties espe
cially lower permability and improved
bond str~ngth.
Styrene butadicne, an elastomcric
polymcr, is the copolymerized product of
two monomers, styrene and butadiene.
Latex is typic~l1y included in concrete in
the form of a coUoidal suspension polymer
1f'11n'i''i'lJ'1\1'i' lJn. l19
in water. This polymer latex, usually a
milky-white fluid, eontains small, spherical,
eopolymer particles that vary in size from
about 0.05-5.0 !-1m in diameter. The emul
sion polymerization of l<.ltex modifies the
conerete Slrueture system through two
processes, cemcnt hydration and film for
mation. Ohama modelled and cle;lrly
cxplained these processes in three steps (l).
The wide size variation of polymer
particles results in an effectivc void-fill
ill and a closely-packed system of film
formation. The closely-packed polymer
particles fonn a continuous film on the
surface of the ccment gel-unhydrated
cement particle mixturc. This film will
rctain internal moiqure and enhance curing.
The continuous mau·ix. also bridges some
capillary pores and microcracks. The resul1
is <.l dmslic improvement in some concrCle
plOperties such as tensile strength. flexural
strenglh and permeability (1, .d, 5).
Although a cleal modification
model of the interface zone betwcen
aggregate and cement pastc does not exist. is
likely that the microcracks in this zone, in
LMC. arc effectively bridged by lhe pore
filling and the interfacl' zone is improved
hy the bonding effect (3), Thc.'ie re!iulrs are
reported to reduce microcrack intensity
in concrete subjectd 10 every load level,
even before <.lny load is applied. However,
sudden increased microcrack intensity is
still reported as in convcntional conCrete
in spite of latex modification (3).
The typical LMC pore structure
differs from those of conventional concrete
(Ll). The hardened LMC contains a relatively
small number of single pores. Pores with
radii of 0.2 fJm. or more are signifieantly
rcclucc:c.. Huwl;:wr smaller radii pores (s
75nm.) are increased. (5, 6, 7). The total
porosily tenris to deerease by a~ mueh as
50°/" as the polymer-cement rario (piC)
increases (5).
The effeel.~ of filling large voids
and sealing with polymer reduces gas and
water vapor transmission. This phenomenon
increases material re~islance to liquid
intrusion. Pcnncabiliry tends Iu cUlllilJue
deeren~ing nfter the initjeal 28 dny cunng
period as a function of age (8, 'I),
Typical LMC mIXes eontain
about 5-l0 percent latex solids and have
wlc ratios of about 0.30-0.LlO. The latex to
cement ratios. ranging between 5-20%.
strongly affeet [he mixture properties; nor
mally 15% is used.
Experiment
Little information is nvailabJe in
the literature on em'ly age properties of
modified concrete. Some properties of
LMC have never been sludied. particnlarly
fracture energy and flexural eurvature at
initi<:l1 cracking. However, 10 order to apply
fracture mechanics 10 failure behavior, if is
necessary 10 determine values for these
parameters. Therefore, and experiment i~
requisite 10 georcrate Ihe fracture parameters
from the test results. These parameters will
be used as input to predict the outcome of
erack propagation and crack mouth opening
displaeement (cmod) in the applieaation
phase of lhe study.
Experimental Program
Sinee there are no standard tests
available for early age eoncrete, especially
for modified eoncreLe, some standard test
methods and specimen preparation teeh
niques for eonventional concrete were
used, whenever possible. However, dne to
Ine chamcteristics of the m",teri<:ll and tne
limitations of the avaLiable equipment, the
specimen sizes in this stndy differ slightly
from ASTM standards or RILEM recom
mendations. Sizes similar to those used in
olher studies ("10, "11) were ehosen TO provide
comparative re~;n1ts_
Material
The laboratory work was COIl
ducted on specimens using a mix similar to
thJt used by the Oregon Department of
Transportation (22). The wi" proportions
and material properlies are shown in Tables
1 lnd 2
P0I11and cement ASTM C-1 ')') type
l. was used for .~pecimen prepnration. In this
study. clean river sand. river gravel and a
styrene-bntadiene polymeric emnlsion were
used. This latex type contains a polymer
eontenL abuuL Ll7- Ll Y"!o of total emnlsion..fhe
approximate weighl is l018.53 kg/m'.
Table 1. Mix proportions of latex modi
fied concrete used by Oregon
Dep~rlment or Transportation
(22)
~ Maler;a~unt (kg/m') 1 cement 391.5 l sand 963.5 I
gravel B2A.6! II latex 122.' I L_water 63.8~
Note; w/c ~ 0.32
The three point bending. test used
to investigate fracture energy was conducted
with a data acguisition system (12),
A beam size ofl 0.2 by 10.2 by 4 3.2
em. was chosen instead of the standMd
size in ASTM:C3l-91 (13). This size was
selected to reduce the dead weight, to allow
molds to be 'used for both flexure imd
fracture energy leSIS and to compare the
results wilh other published paper (ll).
The ,specimens were cast into
two lifts as suggested in ASTM C3' -91 ,
For the test purposes, the tension side was
designateda'i the top side. After finishing,
the specimens were covered with a plastic
sneet and wet burlap for 2L1 hr. before
demolding. The demolded specimens were
left for an additional 2L1 hr. before being
uncovered and placed in and ambient
environment until tested, similar to the
conventional curing method for LMC.
This procedure was chosen to simulate
field curing.
For early age testing, young con
crete is too fragile to demold or handle
witham disturbing the material. Therefore,
flexure and fracture energy testing at tnis
stage were conducted in a special plexiglass
mold (fig.l ). The oversize holes allow 100
gitudinal sliding in the laminated sides to
insure flexibility of the mold thus minimiz
ing it's influence on testing. The empty
molds were tested for flexure before and
after each specimen was tested, to allow the
influence of the mold to be factored out.
Mi.lterial properties
Fig, Special flexible mold for early age testing
Table 2. Mechanical properties of coarse and fine aggregates
sample 1
sieve mass percentage I retained retained
(gm.) (%)
Sand
"' ~.3 0.69
#8 109.<1 17.72
#;6 86.1 13.95
#30 79.4 ',2.86
#50 221.0 35.80
#100 95.4 15.J5
pan 2l.B 3.53
lolal 61 7..1
fineness
modulus
moisture
content
Gravel
"" 0.0
3/4·' 0.0 -
1/2" 515.0 1l6.31
3/6" 326.0 19,32
pan 271.0
lot.ll 1111.0 I
moisture Jcomem
I
!
sample 2
cum. mass percentage cum.
percentag-e retained retained percentage
retaiued (gm.) I (%) retainedI I
!,
0.69 3.5 0.62 0.62
1 B.cl1 93.6 It.,50 1 7.1 2
32.36 81.2 1 <1.32 3l.<14
45.22 69.4 12.24 J3.68
81.02 192.3 33.90 77 .58
96.J7 1Oil. 7 18.46 96.0<1
- -
27 J.17
12.5 3.97
567.2 266.J8
2.7 J 2,66
.1.02% J.J4%
- - -0.0
- -0.0 -JO.60J6.31 575.0 JO.69
d67.075.63 33.05 n.7 J ,
:'71.0
lfl1J.0
2.74% 2,76%
IIII
Compressive strC'ngth
Standanl cylinders, 15.~ by 30.5
em.. were tested for compressive strengrh
al age$ 0.5, " 2. 3. 7 and 2B days. The
loading rale recommended by ASTM C39
19y1 ('.3) was used as a gUIdeline. For very
young ages, the loading rate was useu as a
guideline. ror very young ages, the loading
rale was adjusted slightly 10 prevenr sudden
failure and extended the test duration.
Trnsile strength
Although when properly conduc[ed,
the uniaxial tensile lest provides results
that can be characterized as true tensile
strengths for concrete (10), the eharaetcris-·
ties of conerete in early age limits the use
of this test Glethod. The low tensile strength
of the material beeomes a problem because
the speeimen must carry its own weight
for the vertical test, unless sOnle special
arrangements are made- or a horizontal
uniaxial tensile teq is used as an alternative.
The-refore, a :'iimple [est, the split
ting Tes! was chosen for this study. The
15.2 by 30.:; em. cylindrical specimens were
tested according to ASTM C-c196-91 (13)
at [he same age- as the flexure test. As with
the compression test, the sugges!e-d ASTM
loading rate was used as a guideline and the
range was adjusted slightly for very young
concreted.
M~dulus of Elasticity
The bending tests were conducted
on un notched beams at ages 0.5, 1, 3, 7 and
28 days [0 detennine a modulus of eillscicity
and comp:J.rative fracture energy. A constant
deflection rate was used to control the tesr.
To prevent sudden failurc and to achieve ,\
stable f~lure mechanism for the cor:lplete
load detle-dion curvc, load and dispLlc,_'ment
rates were reduced to zero afrer the peak
load was reached. Thcn. loading ...."as
reapplied. In this study, 10- 2C~ leading
cycles were performed during e<lch test. Thc
1F11f]'i''i'''-I'iWi "-If]. 123
peak load and mid span deflection were
used to calculate the modulus of elasticity.
Fracture energ}'
Although a direct tension test has
be-en recommended by many researchers to
detennine an unambiguow; value of fraeture
energy, the three point bending nOlehed
beam, recommended by RILEM (lJ) was
chosen for this investigation. This decision
wa~ based on procedural simplicity and
equipment availability. Moreover, the young
age of the concrete made iL difficult to
perform the test in a ve-Tlical direetion.
Load was upwi.lrdly applied to 10.2
by 10.2 by .:l3.2 cm. beams (fig.2). a casting
notch on the top side, the tension side,
allowed the measurement of the creack
mouth opening displacement lcomed) and
deflection.
T(l prepare the notch, an aluminum
plate 2 mm. thick was temporarily fixed at
the top of the mold. this plll[e was removed
as soon as possible to avoid cracking. The
notch depth/bcam depth ratios in this study
were 0.2 and I).A.
Specimen Loading
In the nudy of fracture behavior
for concrete-like materia!, postpeak behavior
of particular conl:ern as well as the influence
of loading rate. In this srudy, cmod control
or stram control was: chosen to achieve a
stable test. ThlS chOICe avoided the potenJiai
effect from locatized crushing a[ the loading
point as well as the potential for change in
,oJ .,. iIL~lJ'" 28 LJ'i':;"n 2539
Fig. 2 Test set up for fracture test
internal mierostructure from crack intensity
rtear the cmck tip. This loading control
allowed Ihe study of strain softening which
requires homogenization of the non-uni
fann deformation process. The closed-loop
servo controHed hydraulic testing machine
enabled cmod to be used to control the test.
A clip gauge measured the crack opening
displacement and sent feedbaek signals to
control machine operations. The machine
was programmed 10 continue applying load
at two selected cmod rates of 0.00003175
and 0.000127 cm.!sec respectively.
It has been shown thai the loading
rates have some int1uence on fracture
energy; the higer the rale, the larger the
fracture energy (15, '23). Kormeling's study
showed that even though the loading
rate increased by a factor of 2000, the
conesponding fracture energy inereased
by only d8 to 82 percent (16), For this
study, therefore, loading ratcs were chosen
approximately equal to those used in
Konneling's study. In addition, the selected
loading rate should provide the complete
pre and post peak load-displacement rela
tionship in a short time compared to the test
age of the speeimen. The chosen loading
rates, based on these criteria, provide the
maximum load 10 be reached in about 50
120 seconds, compared to 90 seconds for
conventional concretc in Brameshuber and
Hilsdorf's study (ll).
The effect of two different loading
rates i1) also of interest although no reports
have becn found in the literafure. To
invesllgate this effect, three point bending
tests were conducted on specimens of
similar age and from the same batch. The
resuhs indicated that only a small difference
occurred in fracture energy, G f (6.2'1'0). As
a result, the testing program was conducted
Ilsing the selected rates.
In addition to cmod, mid span The ftrst experiment deals with the general
defleetion was also recorded through a strength properties of LMC. The second
LVDT (Linear Vertieal Differential Trans deals with fracture properties from bending
ducer). The measurement is based on the beams.
referenee neutral axis to avoid any error General strength properties geueraled by, localized crushing at the
The development of compre.'isive support. This potential error. reported in strength. modulus ofela."ticity, tensile strength some studies (17), may result in a difference and tlexural strength are shown in tigures 3 up to rio in the area of the load-deflection and 11. Between the ages of 5 and 9 hours, curve. It rna)' also came a ')ignifiulOt the ratio of t~ to ft decreases from about shifting. from 25- JDO~k" in reported mid B.O to 5.2 and then increases again after span deflection (ll). Before testing, beam about 9 hours. ll1is trend (fig.s) showed that dimensions ,and span were carefully the minimum ratio was reached at about lO measured. hours. This time period i~ greater than the
initial setting time but close to the final Test Results scuing time as reported by Ohama (1). A
The results of t\VO different similar Irend is reported for conventional
experiments are reported in this seellon. concrete (ll).
STRENGTH DEVELOPMENT VS TIME COMPRESSIVE STRENGTH
~, 4:00 1-'--'--~---'---~--~--'--T20.00 iL , I " IL.
0
~ 3.50 I' __ ---l---- -----Jl. ~ 1800
:r: [ .-- --+-------! _,----. ' 16.00 " ~
~ 3,00 .----.- r------=···-i···o .. 14,00 ~ )Ii'" -."---- -,----;
~
" "if. <i c ~ 0 ~ ::: ,~' -AT"· /:_-·__-+'~~~_~_·L~~~.~: "
-.:
w 0 0 " ~~' i ' ...£' r 0
(J) 1.50 H-I~t- 8.00 ~
V>~ I II (Z i [d}O -,co~ 1.00 ~f----t-~t-----t--t-----,---+----1 ~
o 4.00 0
t---+--{2.00~ '0,.5 0 ""---f-~~~-~--+-j .... ····~_+-I " 0
w0 0 : -----+---~-- 0.00 o 100 ZOO 300 400 500 500 70G
TJME. HR.
__.. .----.J
Fig. 3 Development of compressive strength and modulus of elasticity with time
I
, '" ~fUJV1 26 lh';:;1t1 2539
,--------T~N-S-,L~~-TR-E-NG-T-H-V-E-RS-U-S-T,~-E-~'-----I SPLITTING AND FLEXURAL STRENGTH
8000.00 -,---._- - I ._.~- ~--T4GOO
D ~ I I *1
§ 0000,00, ~ 7:f~/ '/ ,1---- --- -.---f 2500 ~ t;; 4000.00 L "": •. ----- ~- ==en ,! -.- ' --~2000:; .---l ," -' i I I C'r2 3000.00 -A--- ; -- --,--- - --- ---- 1500 ~
c::J ~
...: 1000.00t- -- -- - -- ~-- '- I '~,oo : "- 0.00 -- - 1 :.- , 0 -J- -------l---
o 200 400 600 800 1000 1200 TIME, HR.
L Fig. 4 Dcn'/opmeul of tensile strelJth with lime
----------, 'Ie oc!ual - lilic,i ... aet~al - f11leeJ I
J
~ o
1000 I
____J
Hi'·"··4]11I I'
" i
TIME, HR.
COMPRESSIVE - TEN~.U STRENGTH VS TIME MAIN TEST PROGRAM
,-' I
- iT I'TI,
rr'Ti ,, - _._. ! ,
of, 1
I
,) I
,- .. , I , ,
'~ ," ,
t+ 1'1 I I I , I
I I, ~-,,
r+ , ,
IiJJ, I ' I,
I, , ,
I , , , ' ,L.J
I !1 I i+ , , -- ."-. - -._4,00
1
5,00
9.00
5,00
800
10.00
7.00
, ii' iii
I,
Fig. 5 De~'eJopmenl of $lrenglh ratio with lime
---- ----
L1J:tt1fJl.l - n'mD1P1lJ 1f'11n'M'lJ""11 lJn. 127
The calculated flexural stresses and then increased agam with time. The
versus time based on the uncracked section change in deformabitity performance
and the peak load for both notched and continued up to age 28 days whereas, the
unnotched beam are ploUed in tigure. 6. defonnability in normal concrete afrer l2
It is recogniz.e,d that Ihe computed stress hours. appeared unaffected by age (ll).
at (he critical section of the notched beam Because of the characteristics of early age connot be accurarely evaluated by eonven LMC, eonsiderable attention should be paid tional methods due to the effeet of induced to each procedure step, casting, handling, flexural stress, shear stress and the notch and test setting. Variation in test results for effect itself. However, these curves show early age specimens may be due to these the same trend of increasing strength with effects as well as the limited number of test time.
specimens uscd in this study. The plo! of mid span dcfle(:tion
Fracture properties.at peak load over time (fig.?) indicates Ihe
changing deformability with the age of A typical load-cmod and load
LMC. Thispattem differs slightly from mid span deflection is shown in Figure 8.
nonnal concrete (11). For early age LMC, ln this case. stable crack growth is obtained.
the deform.ability decreased and reached Three types of behavior were observed
minimum at about 24 hours (aid = 0.2) from the load-deflection curve. The curve
FLEXURAL ~,TRENGTH- TiME NOTCHED AND UNNClTCHED BEAM Cm~PARISON
~ooo.oo o
,'I II'I
~ I ! ,
}' •• I
II l!~ ... __L._:=;: 7000 DO
! I, , I ,2: 6900_00
u I I I~ 59 00 .0 0
~ ,/ ,~ I~ (f) 4-000,00
II III ! !i,
j ; cH'-- f . , ' I", I,:·unnccII;- , . .c
~ I I I - I , ,
-----
!~ , .. L----t ,;'1 300000 :.-',,
U. :1Ii! :;" w 'notthe-,- CJ 2000_00 . "
I -~.~.~
~ ~
, , I , " ,, ,, lIf,/0;
~. .
i<1000.00 -, -,.,
II ,I " I • ! III0_00 [ ---I
1 100 1DOCO 10 1000
AGE, HP
I )I( ocl. 0_2
L__ ~ __ ovg...D.4_
Fig. 6 Development of flexural strength with time
----
128 1f'11n'l'l1J~1'l 1Jn.
,----------_._--_.._.-
. DEFORMBIlTY-TIME MID S,::lAN DEFLECTlm~- AGE RELATIONSHIP
1
.~ ::::: ~ +~T~tJt+ITfh~*~~~::::: ~ E 6.0000-' h-1+l+\lL-'LJ-~-Iftt-' U!m.1 z1 . I 'Illill LI ; ; -I~ . 00024
2'5.0000 I ilt'IIIII-;ci" ,"/ -+- ',\ '0,0022 §0
c~
c, o z
"1 00014~ 2.0000 I It·Ill',-rrc~y:ri.:-r·· I ~ ~ 1.0000 1 - 11'1,lf ~ I:~-:;I ,,' '~;.I1000"2 ~ ,,0.0000 .--, ~I-·- W --l-i--L---i- --'+I-I,Looolo
1 100 10 1000
/lGE, HR. I
I~ '-l L _ .
Fig. 7 Del-'elopment of deformabiJit.r with time
Typl,(AL LOAD-CMOD--MID SPAN DEFLECTION NOTCHED AND UN NOTCHED BEAM l
::::r-II-=t--~I=-'1- +- 1~---::L-1 I, L ~UN8 dell elmo , 1_-1 -1-- --j
SOOO - 1-;-1 - - I--r----ri----ll ,
; 4000 A'- t-± ---+ ---1-- t= I
1080 ,1/ '--Kf' -~.-t-- .-+----L -~-. I,~ if -~.L____ I L '
1 o II "--..f==~~ . 1 . -----j
0.0000 20.0000 40.DOOO 60.0000 80.0000 1 00.0000 120.0000 140.0000 DISPLACEMENT. mm/l 00I
I_NOTE: NB.=.NOTCHED BEAM. UNB=UNNOTCH~D BEAM _
C~CD OEFLECT!DN /-lEI .~CTION~I, ----------'
Fig. 8 Typical relationship of load-crack mouth opening and load-mid
span deflection of both notched and unnotched beams
LlIlf1[JU - n'i'fll)11'11J
exhibited linearly up to poinr a. This point
is considered the "elastic limit" in thi!\
study, according to ACI 5l1L1. lR-82 (lB).
Beyond this point. nonlinear perfonnance
was observed. The increasing load produced
increasing deformation which reflecled
some strain 'hardening effect. Beyond
peak load, increasing deformalion with
decreasing load reflected POSl peak lension
:;;oftening in the same manner a:-; eonven
tional eonerete (l9).
No information has been found to
define the transition point from linear to
nonline<lr eonfiguration. In Ihis study, the
"ela:;;tie limit" was chosen in the following
manner.
A third degree polynomial reV'es
sion wa:;; u:;;ed lO fit the data up to 95 pereent
of maximnm 10ad in the post peak region.
The fitted curve provided a R =-quare value
not less than :0.99. Another regression line
was used to fit the linear part of the eurve.
Zaitzev's study (19) showed that eonven
tional concrete was linear up to 65 pereent of
maximum str~ss in stress-strain relation
ship. However. from the trial regressions in
this study, it was fonnd that linear regre.~sions
from 65 to 90 pereent of the peak load,
predominantly 85 percent of peak load. ,provided bihcR square values (R = 0.98
0.99). Therefore. the linear regression line
up to 85 percent of peak load was chosen as
a reference line. The elastic point for this
~tlldy was chosen when the difference of
load between {he two tegression lines ,H the
1P11n'5"5'1Jfl11 1Jn. 129
same deformation was equal to or slightly
greater than 5 percent of peak load. From
this criteria, the load associated with the
lenstic limit, Pe, and the ratio of Pe/Pmax
were- determined.
From the calculated Pe/Pmax.,
using 5 percent eriteria, there is no evidenee
of signifiennt change in this parameter
wilh time (p = 0.:;355) (fig. 9). There is a
statistically signifieant differenee between
me;m values of Pe/Pma:ot when considering
the notch depth ratio effect (p ""' 0.0005)
(fig. 10). However, using a criterion of 1
pereent difference in peak load as an
arbitrary transition point, no difference was
observed.
Although the load-defonnation of
LMC ha.~ a similar trend as eonventional
concrete (11, 17), the ratio of Pe/Pmax is
higher in this study, eompared to Kim's
study (17). The Pe/Pmax values are 0.693
and 0.9J6 compared to 0.3 and 0.82 for
notch depth ratios 0.2 and 0.L1 respectively.
The results agree with the general eoncept
of modified pore strueture due to the latex
film fonnation which is believed to have a
pronounced effeet especially in the interface
zone. The reduced or bridged microcrack in
this zone affeets the transition from linear to
nonlinear re:;;ponse.
From the test results, all :;;pecimens
showed a bilinear relationship berween the
mid :-.pan defleetion and cmod. This finding
is similar to nonnal concrete results reponed
in Kim's study (l7). The slope S1 in the first
13011"11n'1'1l!A111!n. l'l'il!~ 28 th::41i1 2539
Fig. 9 Relationship between Pe/Pmax. with time
_- ~ -- Pe/Pnlox v'S NOTCH DEPTH RATIO - - -
1 1.0D~-·~I-··-I-T~I--
095- --t.~-t - L---4-i , ;, I · ~ 090t----l~ r .~~
".+ II--j ·r0.80 IL.--1- I -- I J
0.) 0.1 0.2 0.3 0.4- 0.5
~ NO_TC_f RATIO ..__D_EPT~ ~.-.J
Fig. 10 Relationship between Pe/Pma.,. with notch depth
-- ---
portion of the curve reflects the non-panern constant (1 7).
variation when taking age and notch depth The load-deflection cneve of
effect into considerlltion. unnotched beams (curve c in fig. 8) is slighlly
Howe~er, the performace of the different from notched beams. Althouth the
beam after post cracking mdicate,~ a strong cyclic load was manually applied after the
relationship between mid span deflection peak load to restrain the suddenly released
and cmod as shown in the typical curve fractnre energy, all unnOlched beams showed
(figurc 11). From qatis.tital analyses, there a tendency to slightly decrease in both Joad
is no evidenc~ of a relationship between and displacement. However, this observa
the slope, S2, and time (p ~ 0.51:;5). (ion is based on a limited number of test
Furthermore. there is no significant differ samples.
ence between' mean values from different The fracture energy is determined
noteh depth ratios (p = 0.0595). This rela according to the RILEM recommendation.
tionship is shown in figure l2. Therefore, from the area under the load-mid span
this parameter; 52, is assumed co be eonstant deflection curve. The calculated Gf varies
This assumption agrees with Kim's study from 2 3 to "l33.l N1m. depending on age
on conventional concrete in which this and, to some degree on nolch dep[h ratiu.
parameter has been proposed as a material from statiSltCal analy.'ies, there is :ilrong
I TYPICAL 'AI] SP4N DEFLECTION VS CMO-D- ~_.. -- ---'1· NOTrHFn RF Af./
I 9O..ooJO~. ·-1 - T I-I~ ~ I §"aooOQt-·-·-I~·-- r-1~1 I [,".0000)··-1- -r---l·-•.~·I·~I i
I E 50.0000 l._ +-- ~L __ I "I--.-j I ! 500COo J- T -+7f"-i ~--..j ~ 'Oocoo 1-_ ~-·-k:"SfI-+- ~
.~ :~~~1?f/1 C=j ]==rq D DODD 20,ODCO 400'.)00 60.0:)00 80.0000 100.0000 120.0000
1
L. CMOD' rn~/10:J __. J
Fig. 7' l)picaJ bilinear relationship between mid ~piln deflection and cmod
-------------
, .J\32 1"'1f11'1lJ?i'11 lJn. ~i'llJ'Yl 28 L~:1'1t1 2539
-~--------
51, CPE 52 'vS TIME IMAI~j TEST PROGRAM
I
I
1
10.00 1110000
TIME, HR,
I -',,~jd=(U (J/d~~l ,LJ
L_.__..~_~~=_=...:=_____='_~ --.J
Fig. 12 Relationship between stope 82 with time
,-- - - - ---_.- - ---- _ ....
FRACT JRE ENERGY VS TIMF I U.lOO & MID S='AN DEfLECTION COMPARISONI
IOJOOOO'ilT\lI'n- T ~ITTTT-RmIJJ08 I ::~~~~ r---::r-t=l~1 t ~ Llllf+ii-t-loHI~: I 700000 +--1- j :1:1 i1litffil- . c
: :::::~-T[+I+mI-+-r=t~1 .-iJ-' ,.fttt:: ~ ;00000- +-+glfi'. 111 ' ·:tfru·_.,~o, " 20.0000 - - +-+- __ - _ _ . _ ---++ -'. IC.OOOO _TI: ,.' .'"::tt ," -+~r-Imol C'.0000 -I~---J-t-++ -.. I-------t--~ , .--+-W--W-+H-o
1.00 100.00 10.00 1000.00
TIME. HR.
I ~
Fig. J3 Del-'elopment of the calculated value.., from the area under
load-mid span deflection and load-cmod ffith time
LlJ'lf1tJU - fl':i'fll)1I'1lJ
<!videnee of a linear relationship between
fracture energy o.nd time for bOlh notch
deprh ratios, 0.2 and O.L1 ( P O.OODl in buth
cases.)
The cakulnled value of Of from
the deflectiun is very close to the value from
("mod as shown 10 fig. l3. However, dead ,
weight appears to have a significant effect
in fracture energy, especially for early age
specimens. At an early age (up to 24 hours),
the effect of de~d weigth varies twm 35
350':". This effe~t decreases with (fig. 13).
After 2.4 hours, the effeet of dead weight is
primarily in the'range of 1:,-- '10%.
The relationship of fracture energy, and time is fitted as shown in fig. 1,t:R =
.891) using lhe,c4uatiou: Of - - o.nAl oj.
0,0799 In (age-hr.) - O.0686Inage - hr, r +
0,10825 (a/d)
The intluen(~e elf notch depth ralio
on fracture energy appear,~ to h;oIYe less
effe.ct in LMC, compared to normal con
crete. The effect is not clearly demonstrated
in this study (fig. l4).
For unnotched beams the fracture
energy is clearly higher [han notched beams
regardkss of the notch depth ratio. This is
due to Ihe larger amounts of microcracks
produced nct'ore the fracture process
lOne WaS fully developed. The ratio of
G( (unnotched beam to uotched beam)
varied from 3.2 to l.2 but there was no
specific relationship, due [0 age, shown in
thi~ study (fig. 1L1). The same trend was also
observed fnr the relationship between Gf
and compressive slTeuglh (fig. 15).
~ _"!_d=_C_.z_-_~_'_../_'O_0,~_"'_~_r~a_"_h~ ~----
Fig. 14 Effect of notched depth un fracture energy with time
, .. I.fUJl1 28 1J1:;1U 2539
1--" ~RA~TLlR£ ENERCY 'IS COMPRESSI\r~E STRENGTH----'-- -- ~ 'I FOR NOTCHED AND UNNO-CHED BEAM
1400000 f-I-'---~J>-p-i08
1200000 I;'NOTJH£D B"~* /1/ t/J t: 100.C000 ;' / -I /' /o¥ I
~ 80,0000 ~"-+ :f /t ---+~ / +-=-J,CO'5 '"c z : ,/'" //f;----/. I 0.4 J)
~ ::::::IXf4~ft+-I::200000~Lj -'- I'. -+1- 'l' 0,1
0
0.0000 -I*--'--t --.,-.L---.--+--_.---+-.-----l-.-- °I 000 500 10.lJO 1~ O'J 20.00 25.00 30.00 350(J
COMPRESSIVE STRENGTHN ,"P8N8 t h d o e: =Jnno c e beam I
L_ I "'_ a/d=0,L _ 0 __aid=O:~ _' '.- .REG.o/d=U,Z-.--- REG a/_d=O.4] _
Fig. 15 Relationship between fracture energy and compressive strength
Another parameter considered in is of particular concern, may be based on
fracture mechanics of concrete WiJS charac two criteria. The first criterion involve.s [he
teri<;tic length. 1 .This arbitrary parameter, period when LMC has low tensile strength, m
defined by fraclure energy. modulus of high fel f l , the second criterion involves
elasticity and tensile strength, r,mged the period when the matcrial has low
between 160-2LlOO mm. depending on defonnability. From these criteria, a par
specimens ilge. LMC showed largcr values ticular duration of interest may range from
of len ; about 3 8 times compared to the sligthly less than 9 hours to grcater than '.ill
conventional early r1ge concrete up to l day hours.
(ll). However, this parameter dramatically 2. It is recognized that. in con
decreased with time and reached the range crete -like material, stress transferring
of conventional concrete (2DO-400 mm,) mechanisms change with increasing defor
at abom 28 oays lfig. 16). malion. At peak load, for conventional
concrete the stress transferring capacity can
Discussion and conclusions be explained by the effect of strength and
1. From the test results. the criti stiffness of aggregates, mortar matrix: and
cal time when early age cracking in LMC the bond capacity between matrix and
Fig. 16 Development of characteristic length with time
x Cc
of normal concrete in which G f decreases
as notch depth ralio inereases (17, 20).
Generally the lower the ratio. the higher the
probability of available eoarse aggregates
in Ihe critical st'l:!ion, In the' macro level
of concre'te', coarse aggregates .lei as
inclusions or crack arrestors. The increased
length of possible crack paths results in a
higher resistance for crack propagation and
a higher Gr.
However in the case of LMC, bOlh
pore structure in the matrices and interface
zones are improved by film formation.
This film fannation may provide' a more
pronouneed effect than the inclusion effecl
from aggregates as found in normal con
crete. In short, the effect from aggregates as
'-----. , -
aggre'gate (1 s). For LMC. theeontribution
of latex film in bridging mierocracks and
improving bond slrength in the interfaee
zone' are probably responsible for th..
different performance,
This beneficial contrihution can be
se'en from the increasing ratio of Pe/Pmax,
Furthermore. Ihis effect appears to provide
ductility improvement. In this study, there
was a greater ratio of mid span defleetion
al failure to mid span deflection at peak
load. 10"':33,; compared to a ratio of 5-6 for
normal c0ncrele (17).
Th~ fracture energy of unnotche'd
beams was' higher than notched beams.
In this study, the effect of notch depth ratio
on fracture energy is in contrast to studies
found in normal concrete. In short, rhe effect
of notch deprh ratio is not as clearly dem
onstrated as in conventional concrete.
3. LMC's development of Gf
v.'ith time differs slightly from conventional
concrete. LMC has the tendency to continue
developing Gf to 28 days whereas with
normal concrete, after 3 day, age seems to
have less effect on fracture energy.
.1. When considering the single
fracture parameter of LMC, characteristic , kllgth, Ie::: EG f / ( the modulus of elas
ticity should be derived from either a
rension, or flexure test. Sinee latex film
is p'articularly noticeable in (arger-deforma
tions, the modulus of elasticity in tension is
about '.( times lower than the modulUS of
elasticity in compression ("21). This is not
rhe case for normal concrete in which the
modulus of elasticity is assumed to be the
same.
In summary. latex film formation
affects LMC strength rlevelnpment,
deformability and failure mechanisms,
The improvemem. especiaUy in tensile und
flexurul strengrh should provide better per
formance WhCll non-structural failUIt: is
of particular concern. This may minimiz.e
l:arly age distresses iu bridge deck overlay
which some factors such as environmental
effects, the effect from traffic iu the adjacent
}aTJ.es or shrinkage effeci may re involved.
The fracture energy development strongly
depends on time up to 28 days, At later
,oJ .,. " Lf'llJ'YI 28 u'l:::'i'lu 2539
ages, the observed values were comparable
to normal concrete.
Reference
l. National Cooperative Highway
Research Program. Latex-Modified Con
cretes and Mortars, Synthesis of Highway
Practice 179, editor V, Ramakrishnan,
Washington D. c., August, 199"2 .
2, M. Wecharatana and S.P. Shah,
Prediction of Nonlinear Fracture Process
Zone In Concrete, Journal of Engineering
Mechanics Vol. 109 No.5, 1983,
3. Soroushian Parviz and Tlili
Atef, Latex Modification effects on Meeha-
nisms of Microcrack Propagation in
Concrete Material. Transportation Research
Record 1301. Washingtion D,C., 1 QQl.
Lt. S.L. Mamsin, Microstructure.
Pore characteristics and Chloride Ion
Penetration in Conventional Concrete and
Concrete Containing Polymer Emulsion,
ACI SP 99-8, David W. Fowler Editor,
Detroit, ',987.
5. Y. Ohama, Priuciple of Latex
Modification and Some Typical Properties
of Latex Modified and Concrete, ACI
Material Journal Title no. 8Ll-M-Ll5,
Nov.lDec. lifa?
6. Y. Ohama and K,Demura,
Pore Sixe Distribution and Oxygen
Diffusion Resistance of Polymer Modified
Mortars, Cement and Concrete Research
Vol. 21 No. 5213, March/May 1091.
l"-J'lf1EJU - n1nlJ1"""-J
7. G.i G. Hoff et. al. Chemical
Polymer and Fiber Additive for Low Main
tenance Highway. NOYES Data Corp.,
Newjersy. 1977.
8. David Whiting and W. Dziedzic,
Chloride Permeability of Rigid Concrete
Bridge Deck: Overlays. Transportation
Research Record l2:M, Transportation
Research Hoari;!, Washington D.C., 1991.
9. Dvw Chemical USA, LOllg
Lasting Bridge DeLks with Modified
Concrete, Technical Paper: Form no. 181
1129-87.1'?e]..
10. Ptopcrties of Set Concrete
CEA State of Art Report, Materiaux et
Construction voL llJ No. 84, 1981.
11. W. Brameshuber and H.K.
Hilsdorf. De'lOeiopment of Strength and
Defonnability of Very Young Concrete.
SEM/RILEM. International Conference
on Ffilcture of Concrete and Rock. Texas.
19 87.
12, Validyne Engineering Corp.
UPC 607, PC' Sensor Interface Card:
Imtruction Manual Revision 2.0 CA. 1990
B. American Society of Testing
Matcrials. 1992 Annual Books of ASTM
Standards Section 4.0: Conslruction. Vol 0,4
02: Concrete 'and Aggregate. PA, 1997.
J 4. A. Hillcrborg, Results of the
Three Compartive Test Series for Delerming
the Fracture' Energy Gf of Concrete,
Materiaux et Constructions Vol. 18 NO.1 07.
1986,
15. RILEM. Fractnre Mechanics
of Concrete- Application Part A, a third draft
of a report over the State of Art, RILEM.
Sweden. 1988.
l6. Kormcling, H. A.. Strain Rate
and Temperature Behavior of Steel Fiber
concrete in Tension, doctoral Thesis, delflh
University of Technology. 1986.
17. Suk Ki Kim, The Constant
Fracture Angle Model For Cementitious
Material, Dissert;ltion (Draft), New Jersey
Institute of Technology, 1991.
18. ACI Committee 554, Statc
of The Art Report on Fiber Reinforced
Concrete, ACI Sil4.1 R - 82, Conerete
Inlernational design :md Construction,
Nov. 1982
19. Y. Zaitsev. Cnlck Propagation
in Composite Material. Fraclure Mechanies
of Concrete. FH. Wittmann editor, Elsevier
Science Publishers. Amsterdam, 1983.
20. P. Nallalhambi. B.L. Karihaloo
and B.S. Heaton. Effect of Specimen and
Crack Sizes. Water Cement Ralio and Coarse
Aggregate Texture upon Fracture Toughness
of Concrete, Magazine of Concrete Re
search, VoL 36 No. 129 Dec .. 1984.
21. Parviz S. and A. Tlili, Effect
of L~tex Modification on rhe Failure
Mechanism and Engineering Properties.
ASTM STP 1176 Polymer Modified
Hydraulic-Cement f1,Iixture. Kuhlman/
Walters editor. PhdadclphiLl, 1993.
22. Oregon Department of Trans
portation, Bridge deck overlay field reports
between 1989-1993, Oregon, 1989- 1 993,
138 11"l1f1'i'ilJilI1'i lJf1,
23. E. Bruhweiler, FR. Wittmann
and K. Rokugo, Influence of rate of luaJing
on fracture energy and strain softening
of concrete, 2nd Summary Report on
Research. Activities compiled by F.R.
Wittmann, Laboratories des Materiaux de
Construction, Lausanne, 1988.
Acknowledgements:
The Principal author acknowledges
many fruitful discussions with Professor
=.:=':= _: = _: = -- = _:=::=.. - - -; =-
Methi Wecharatana of the New Jersey
Institute of Technology. The valuable
instrumentation assistance of Mr. Andy
Brickman of OSU is gmteful acknowledged.
Also. the fmancial support of the Depart
ments of Civil Engineering. Oregon State
University and Kasetsarl University are
appreciated. Finally, material supplied by
Dow Chemical Company are greatly appre
ciated.