INNOVATIONS FORUM

ENGINEERED CEMENTITIOUS deformation is typically represented by a softening stress-crack

opening relationship. In ECC, the first cracking is followed by
COMPOSITES FOR a rising stress accompanied by increasing strain. This strain-
STRUCTURAL ApPLICATIONS hardening response gives way to the common FRC tension-
softening response only after several percent of straining has
been attained, thus achieving a stress-strain curve with shape
similar to that of a ductile metal. Closely associated with the
INTRODUCTION strain-hardening behavior is the high fracture toughness of
ECC, reaching around 30 kJ/m2 , similar to that of aluminum
In the last several decades, concrete with increasingly high
alloys (Maalej et al. 1995). In addition, the material is ex-
compressive strength has been used for structural applications.
tremely damage tolerant (Li 1997), and remains ductile even
However, most of these materials remain brittle. In some cases,
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in severe shear loading conditions (Li et al. 1994). To illustrate

the brittleness as measured by the brittleness number (Hiller-
the ductility of ECC, Fig. 2 shows the deformed shape of a
borg 1983) actually increases as the compressive strength goes
ECC plate subjected to flexural load. These behaviors appear
up. This poses potential danger and limitations of high-
to be scale invariant, confirmed by specimens with sizes rang-
strength concrete in structural applications. In certain loca-
ing from centimeters to meters (maximum 1.5 m longest di-
tions, such as where steel and concrete come into contact (e.g.,
mension) scale. The compressive strength of ECC varies from
steel anchors in concrete at column base) or in connections of
30 to 70 MPa, depending on the matrix composition. Com-
steeVconcrete hybrid structures, the high stress concentration
pressive strain capacity is approximately double that of FRCs
created can lead to fracture failure of the concrete. In seismic
(0.4-0.65%) (Li, in press, 1998).
elements, high ductility in the concrete can make a significant
A most common question asked of ECC is how it achieves
difference in the seismic response of the overall structure.
its unique ductile properties, but uses ingredients similar to
These and other examples point to the need to develop cost-
those for FRC or HPFRC, and at the same time contains such
effective high-ductility cementitious materials suitable for
a small amount (typically less than 2% by volume) of discon-
struct~ra~ applications. In .the last several years, the University
tinuous fibers. The answer lies in the composite constituent
of MIchIgan has been mvestigating a composite material
tailoring. A fiber has several attributes-length, diameter,
known as Engineered Cementitious Composites (ECC). In
strength, elastic modulus, etc. Interface has chemical and fric-
many respects, this material has characteristics similar to me-
tional bonds, as well as other characteristics such as slip-hard-
dium- to high-strength concrete. However, the tensile strain
ening behavior. And a cementitious matrix has fracture tough-
~apacity generally exceeds 1% with the most ductile composite
ness, elastic modulus, and flaw size, which can be controlled
m the.6-8% range. This article briefly reviews these emerging
within a certain range. The tailoring process selects or other-
matenals, and also reports on some ongoing developmental
wise modifies these "micromechanical" parameters so that
application studies.
their combination gives rise to the ECC composite with its
attendant properties. Tailoring is guided by micromechanical
WHAT IS ECC? analyses (Li and Leung 1992; Li 1993; Kanda and Li, in press,
In terms of material constituents, ECC utilizes similar in-
gredients as fiber reinforced concrete (FRC). It contains water,
cement, sand, fiber, and some common chemical additives.
Coarse aggregates are not used as they tend to adversely affect
the .u.nique ductile behavior of the composite. A typical com-
posItIOn employs w/c ratio and sand/cement ratio of 0.5 or
lower. Unlike some high-performance FRC, ECC does not
utili~ lar~e amounts o~ fiber. In general, 2% or less by volume
?f dIs~ontmuous fiber IS adequate, even though the composite
IS deSIgned for structural applications. Because of the rela-
~ively small amount of fibers, and its chopped nature, the mix- oL.-.....L._L---L._.L.---L._.L.--l.----J
mg process of ECC is similar to that employed in mixing o 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08
normal concrete. Also, by deliberately limiting the amount of Strain
fibers, a number of proprietary studies have concluded eco- FIG. 1. Tensile Strain-Hardening Behavior of PE-ECC
nOl~ic feasibility of ECC in specific structural applications.
Vanous fiber types can be used in ECC, but the detail com-
position must obey certain rules imposed by micromechanics
considerat!ons (Li, in press, 1998; Kanda and Li, in press,
1998). ThIS means that the fiber, cementitious matrix and the
interface (mechanical and geometric) properties must be of a
correct combination in order to attain the unique behavior of
ECCs. Thus ECC designs are guided by micromechanical prin-
ciples. Most data so far have been collected on PVA-ECC
(reinforced with PolyVinyl Alcohol fibers) and PE-ECC (re-
inforced with high modulus polyethylene fibers).
The most fundamental mechanical property difference be-
tween ECC and FRC is that ECC strain-hardens rather than
tension-softens after first cracking (Fig. 1). In FRC or fiber
reinforced high-strength concrete, the first crack continues to
open up as fibers are pulled out or ruptured and the stress-
carrying capacity decreases. This postpeak tension-softening FIG. 2. Flexural Behavior of PE-ECC

66/ JOURNAL OF MATERIALS IN CIVIL ENGINEERING / MAY 1998

J. Mater. Civ. Eng. 1998.10:66-69.

 1998), which quantitatively accounts for the mechanical inter- reveal a much higher crack density, about four times that of
actions between the fiber, matrix, and interface when the com- the RIC specimens. Almost all cracks have opening less than
posite is loaded. Unlike the even smaller amount of fibers used 0.1 mm in the R1ECC compared with millimeter-size cracks
in shrinkage control in some FRCs, fibers in ECC are used to in the RIC specimens.
create composite properties suitable for structural applications. The load-deformation envelope curves for the test speci-
mens are summarized in Fig. 4. It is concluded that by re-
APPLICATION STUDIES placing plain concrete with ECC in the shear beam, (1) Load
capacity increased by 50% and ultimate deformation by 200%
A number of investigations have been conducted on the ap- under shear tension failure mode (comparing ECC-I-O to RC-
plications of ECC in structural applications at the University 1-0); and (2) load capacity increased by 50% and ultimate
of Michigan in the United States, and at the University of deformation remains the same under shear compression failure
Tokyo, Kajima Corporation, and the Building Research Insti- mode (comparing ECC-I-I to RC-I-I).
tute, Tsukuba City, in Japan. These studies include the use of These observations and Fig. 4 suggest that R1ECC outper-
ECC in shear elements subjected to cyclic loading, in me- forms RIC in shear performance (load capacity, ductility, and
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chanical fuse elements in beam-column connections, in shear crack control). R1ECC beams behave in a ductile manner even
wall retrofitting of RIC buildings, in RIC beams as durable without transverse reinforcement (but is further enhanced by
cover for rebar corrosion control, and in general concrete combining ECC with transverse reinforcement), and remain
structural repair. Highlights of some of these studies are in- ductile even for short span shear elements which are known
cluded here to illustrate the potential practical uses of ECC. to fail in a brittle manner with normal concrete. This investi·
Other investigations on ECC and its applications are being gation establishes confidence in the application of ECCs in
planned in Denmark and Australia. structural shear elements.
To investigate the structural strength and ductility of rein- The use of ECC in the hinging zone of a beam-column
forced beams under cyclic loads, PVA-ECC (with Vf = 2%) connection was investigated by Mishra (1995). Using normal
beams with conventional steel reinforcements (RIECC) have detailing, it was found that the hysteretic loops were more full
recently been tested with four point offset loading, with the in the PE-ECC connection with many more load cycles sus-
midspan subjected to fully reversed uniform shear load (Kanda tained, resulting in a total energy absorption 2.8 times that of
et al., in press, 1998). Varied parameters in the tests include the RIC specimen (Fig. 5). The cracking behavior was similar
the span/depth ratio and amount of shear reinforcement. Con- to those described above for the shear beam specimens. Be-
trol specimens with ordinary concrete (RIC) of similar com- cause of the lower first crack strength of this ECC, the damage
pressive strength (30 MPa) as the ECC were also tested. initiates inside the hinge zone as designed. This investigation
Fig. 3 shows the double set of diagonal crack patterns in suggests the potential of ECC to serve as a mechanical fuse
the shear span of the failed specimens. The R1ECC specimens in critical structural systems which may be subjected to severe
earthquake loads.
The use of a PVA-ECC in precast shear panels for building
wall retrofits is being investigated numerically (Kabele et al.
1997) and experimentally (Kanda et al., in press, 1998). Using
1 0 ........-.....,....,-.......-,."...,..~"t"""I .........-~~...- .........,
o : Trans. rei.~f. yiel • :
8 --_.•._........ .. _.:...::_~... ..,-;-;-:-:.__.
o
~ 6
'"
i 4
j
'" 2

5 10 15 20
Rotation angle (x10· 3 rad.)

FIG. 4. Shear Stress-Rotation Envelope Curves for Various

Specimens. Each Curve Is Labeled [Material-Span/Depth
Ratio-Shear Reinforcement (0/0)]

-g 400 F- + ,........... ,........... +........... 'MIl

-eo
~ 300
>.
E' 200
~
E 100
c3
OJ 0.4 0.8 12 1.6
Displacement (in.)

FIG. 3. Damage Pattern of Cyclic Loaded Shear Beams: (a) RI FIG. 5. Energy Absorption Record In Cyclically Loaded Beam-
ECC; (b) RIC Column Connection

JOURNAL OF MATERIALS IN CIVIL ENGINEERING / MAY 1998/67

J. Mater. Civ. Eng. 1998.10:66-69.

 10.--------,
for enhancing the corrosion durability of RIC structures (Maa-
8 lej and Li 1995). The fine cracks and antispall properties of
~6 PVA-ECC
the PE-ECC demonstrate the potential of this material in
';4 achieving the durability function. In addition, PE-ECC reveals
.....
2 Plain-concrel e a novel kink-crack trapping behavior when used as a repair
o L---'---'---'_.LJ material in concrete structures (Lim and Li 1997). This be-
o 0.004 0.008
Yav(%)
havior eliminates the deterioration mechanisms of delamina-
tion and spalling in the repair material commonly observed in
FIG. 6. Computed Load-Deformation Capacity of Shear Panel repaired concrete structures.
for Building Wall Retrofit
Some additional potential applications of ECC are in high
energy absorption structures/devices, including short columns,
111-111-======
/--+ofd dampers, joints for steel elements, and connections for hybrid
-.,.,---&--In.....11r--__ steellRC structures. Structures subjected to impact or 3D load-
Connection ;. High Tension
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Plale " . Bolt

ing may also take advantage of the isotropic energy absorption
/ behavior of ECC, such as highway pavements, bridge decks,
and blast-resistant building core elements. In addition, struc-

·· ..::
a::x:; • ,j: tures subjected to large deformations, such as underground
Panel

•• structures that need to conform to soil deformation and require

leak prevention, are also potential targets for ECC applica-
tions. Other applications of ECC being considered are in per-
manent form work, extruded elements with structural proper-
ties, FRP reinforced concrete structures, and as a binder for
radioactive waste treatment (Wu et al. 1996) for leaching con-
FIG. 7. Dry Joint Configuration trol.

CONCLUSIONS
120
100
The theoretical background and design methodology of
ECC have been established. Application studies of this mate-
~ 80 rial are emerging at the present time. Development work is
~ 60 international and interdisciplinary (involving materials and
40 1...---..1..-.....-·_···.. ········ ..·....·-·······....·_.._· structural engineers), and involves intersector cooperation be-
x Mortar
20 o PVA-ECC

o......~~+~~~10~~~-;':15,.......~~20'
Displacement (mm)

FIG. 8. Load-Deformation Capacities of Indent Tests

a FEM simulation of rigidly jointed shear panels and a ma-

terial constitutive model which captures the strain-hardening
behavior of ECC, it is found that the PVA-ECC panel sus-
tained much higher seismic load and deformation capacity in
comparison with similar panels made with plain concrete (Fig.
6). The ability of the ECC to relax the stress and redistribute
the damage at the joints to the interior of the shear panel is
responsible for the improved structural strength and ductility
observed in the ECC panels. The prevention of localized frac-
ture at the joint was also demonstrated in a shear test of a dry
joint using steel bolt (Fig. 7) (Kanda et aI., in press, 1998).
The damage tolerant property of ECC prompted its appli-
cation in the above mentioned dry joint. A critical test of this
concept was conducted with indentation tests of steel plates
on PVA-ECC slabs. The test was conducted for the assessment
of maximum allowable bolt force used in the joint between
panels for rapid on-site retrofit installations. Fig. 8 shows the
test results. The maximum bolt force for the ECC slab was
about double that of the control mortar slab, while the defor-
mation capacity was almost one order of magnitude higher.
The mortar failed by a brittle fracture mode (Fig. 9) while a
"plastic" indent was observed for the ECC specimen. The
superior damage tolerance of ECC further increases allowable
bolt force due to high material reliability compared with mor-
tar, thus enabling one to achieve high performance panel joint
with simple details.
OTHER POTENTIAL APPLICATIONS
Apart from structural application studies briefly described FIG. 9. Failure Modes of (a) Mortar Slab; (b) PVA-ECC Slab;
above, ECC has also been investigated as a protective layer and (c) Close-up View near Indent

68/ JOURNAL OF MATERIALS IN CIVIL ENGINEERING / MAY 1998

J. Mater. Civ. Eng. 1998.10:66-69.

 tween governments, industry, and academia. The relatively Sydney, Australia. B. L. Karihaloo, Y. W. Mai, M. I. Ripley, and R. O.
small amount of fibers (less than or equal to 2%) utilized en- Ritchie, eds., Pergamon, Oxford, U.K., 619-630.
Li, V. C., and Leung, C. K. Y. (1992). "Steady state and multiple cracking
sures economic feasibility in practical applications, whether in of short random fiber composites." J. Engrg. Mech., ASCE, 118(11),
precast elements or on-site constructions. The results of some 2246-2264.
application studies highlighted in this Forum article provides Li. V. C., et al. (1994). "On the shear behavior of engineered cementitious
confidence in the widening use of ECC in a broad range of composites." J. Advanced Cement Based Mat., 1(3), 142-149.
new and retrofitted concrete structures. Lim, Y. M., and Li. V. C. (1997). "Durable repair of aged infrastructures
using trapping mechanism of engineered cementitious composites." J.
Cement and Concrete Composites. 19(4), 373-385.
ACKNOWLEDGMENTS Maalej, M.• Hashida, T., and Li. V. C. (1995). "Effect of fiber volume
fraction on the off-crack-plane fracture energy in strain-hardening en-
Many people have been involved in the development of ECCs and gineered cementitious composites." J. Am. Ceramics Soc., 78(12).
their applications, both in and outside of the ACE-MRL at the University 3369-3375.
of Michigan. The writers would like to thank each and every one of them Maalej. M., and Li, V. C. (1995). "Introduction of strain hardening en-
for their significant contributions over the years. The research associated gineered cementitious composites in the design of reinforced concrete
Downloaded from ascelibrary.org by Technische Universitat Munchen on 07/08/15. Copyright ASCE. For personal use only; all rights reserved.

with ECC and its applications have been supported by a number of gov- flexural members for improved durability." ACI Struct. J., 92(2),
ernment agencies and industrial concerns. The continued support of the 167-176.
National Science Foundation deserves special mention. The writers also Mishra, D. (1995). "Design of pseudo strain-hardening cementitious
wish to express our appreciation to two anonymous reviewers who pro- composites for a ductile plastic hinge," PhD thesis, University of
vided helpful comments. Michigan, Ann Arbor, Mich.
Wu, H. C., Li, V. C., Lim, Y. M., Hayes, K. F., and Chen, C. C. (1996).
APPENDIX. REFERENCES "Control of Cs leachability in cementitious binders." J. Mat. Sci. Lett.•
15(19), 1736-1739.
Hillerborg, A. (1983). "Analysis of one single crack." Fracture mechan-
ics of concrete, F. H. Wittmann, ed., Elsevier Science Publishers BV, Victor C, Li
Amsterdam, The Netherlands, 223-249. ACE-MRL
Kabele, P., Li, V. C., Horii, H., Kanda, T., and Takeuchi, S. (1997). "Use Department of Civil and Environmental Engineering
of BMC for ductile structural members." Proc.• 5th Int. Symp. on Brit- University of Michigan
tle Matrix Composites (BMC-5J. Woodhead Publishing Lim., Warsaw,
Poland, 579-588. Ann Arbor, MI48109-2125
Li. V. C. (1993). "From micromechanics to structural engineering-the
design of cementitious composites for civil engineering applications." Tetsushi Kanda
J. Struct. Mech. and Earthquake Engrg., 10(2),37-48. Kajima Technical Research Institute
Li, V. C. (1997). "Damage tolerance of engineered cementitious com- Kajima Corporation
posites." Adv. in Fracture Res., Proc., 9th ICF Conf. on Fracture. Tokyo, Japan

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