Transcript Slide 1

• Gajanan Choudhary
• Prerit Varun
• Sayan Dey
• Sourabh Jain
• Sittula Venkatesh
• Anshuman Pandey
• Invented by Victor C. Li and Huan Joon Kong in 1992
• Belongs to the class of ultra ductile fiber reinforced
cementitious composties.
• Mortar based composite reinforced with specially
selected short, random fibers.
• Ingredients are cement, sand, water, commercial
admixtures and the most important ne being the fiber
Polyvinyl Alcohol (PVA).
• Lack of durability of OPC or RCC.
• Brittle nature of traditional normal concrete.
• Development of wide cracks allowing penetration of
water, chlorides and other corrosive chemicals further
accelerating cracking finally leading to failure.
• Need for material which withstands cracking and thus
corrosion.
• Need for material to be elastic and withstand high
amount of strain or deformation.
• Solution to the problem: ECC
• Unlike common Fiber reinforced concrete, ECC is a
micromechanically designed material.
• Means that the mechanical interactions between the
fiber and the matrix are quantified and described by a
micromehchanical model which takes into account the
material properties.
• Looks like OPC except that it does not contain coarse
aggregates.
• Can withstand high amount of deformation or strain.
•Strain Capacity of OPC is .1% while that of ECC is 3% to
7%, i.e. 300 to 700 times that of OPC
• OPC costs $100/m3, RCC costs $200/m3, and ECC costs
$350/m3.
• But maintenance cost of ECC throughout the life cycle is
low as compared to either OPC or RCC. For example, the
total life cycle cost of a conventional expansion joint
bridge in the US is $35.7million while that of an ECC link
slab bridge is $22.5million.
• Only initial set up cost of ECC is higher, but
accompanying increase in the service life and decrease in
maintenance costs adequately make up for the initial
higher costs.
• 40% lighter and 500 times more resistant to cracking.
• More important are the environmental and social costs
of ECC Bridge systems.
• Less overall material is used.
• 37% reduction in traffic congestion.
• 40% reduction in primary energy consumed.
• 43% reduction in Carbon monoxide emissions.
• 39% reduction in Carbon dioxide emissions.
• 45% reduction in Sulphur dioxide emissions.
MICROCRACKING
 Microcracking means that a large number of small
microcracks are formed starting from pre-existing
flaws.
 Crack width is not controlled for conventional
concrete and ranges from few hundred microns to few
mm.
 In ECC, the crack length is limited to 200 micron.
 Cracks having width upto 50 microns show complete
recovery .
microcracking in concrete
SELF HEALING PROPERTY
 Self-healing materials are a class of smart
materials that have the structurally incorporated
ability to repair damage caused by mechanical
usage over time
 In the presence of water (during a rainstorm, for
instance) unreacted cement particles recently
exposed due to cracking hydrate and form a
number of products ( Calcium Carbonate , etc.)
that expand and fill in the crack.
For self healing the following steps
have to take place:
 Further hydration of unreacted cement
 Expansion of the concrete in the crack flank
 Crystallization
 Closing of the cracks by solid matter in the water
 Closing of the crack by spalling of loose cement
particles resulting from cracking.
The process of carbonation reaction is the
following:
Piezoresistive Property
 The piezoresistive effect describes the
changing resistivity of a subastance due to
applied mechanical stress.
 It is used in Strain and Cracking Surveillance
 The piezoresistive property of ECC structural
specimens are exploited to directly measure levels of
cracking pattern and tensile strain. The change in
piezoresistivity correlates the cracking and strain in
the ECC matrix and results in a nonlinear change in
the material conductivity.
 When combined with a more conductive material
(metal wires, carbon nanotubes, etc.) all cement
materials can increase and be used for damagesensing.
 This is based on the fact that conductivity will change
as damage occurs
 conductive ECC for damage-sensing applications are
being developed by a number of research groups.
Corrosion Resistance
 The microcracking behavior leads to
superior corrosion resistance
 The cracks are so small and numerous that it is
difficult for aggressive media to penetrate and attack
the reinforcing steel
STRESS - STRAIN
 Due to microcracking, lots of steady-state “flat-cracks”
develop throughout the material.
 Delocalises the effect of stess at any 1 point.
 Cracks develop upto an avg width of 60 micron.
 More stress leads to more cracks till the material is
saturated with cracks.
 Finally a single crack localizes and the material
continues to tension-soften throughout failure.
SOME OTHER PROPERTIES
 Ductility – The microcracks lead to strain bearing capacity
of 3-5%. This is called pseudo-strain and gives a strain
carrying capacity of 300 times of portland cement to ECC.
 Durability – Due to strain-hardening and self-healing
properties, ECC can survive in harsh environmental
exposure, freeze, thaw, abrasive wear and fatigue.
 Shear bearing capacity - Under shear, ECC develops
multiple cracking with cracks aligned normal to the
principal tensile direction. Because the tensile behavior of
ECC is ductile, the shear response is correspondingly
ductile. As a result, ECC elements may need less or no
conventional steel shear reinforcements.
 Compatible deformation between ECC and
reinforcement: There is no shear lag between the
steel and the ECC, resulting in a very low level of shear
stress at their interface. This phenomenon is unique in
R/ECC.
 Tight crack width control: The steady-state width
of microcracks can be modified by changing the type
of fibre and interface properties. The tight crack width
in ECC has advantageous implications on structural
durability and on the minimization of repair needs
subsequent to severe loading of an ECC member.
Failure in R/C and development of microcracks in
R/ECC
Composition of ECC
 ECC is an easily molded mortar-based composite,
reinforced with specially selected short random fibers.
 Moderately low fiber volume fraction less than 2-3%.
 Unlike the fiber-reinforced composite which have high
fiber content
 The Fibers generally used can be
UHMWPE (ultrahigh molecular weight
polyethene)
2. PVA (polyvinyl alcohol)
 Coarse sand particles and aggregates are not used
 Very fine sand particles are used
 Fly ash is also used
1.
UHMWPE
(ultrahigh molecular weight polyethene)
 UHMWPE has extremely long
chains, with molecular
weight numbering in the millions
 The longer chain serves to
transfer load more effectively by
strengthening intermolecular
interactions
Hemp stem showing fibers.
PVA
(Polyvinyl Alcohol)
 Polyvinyl alcohol has
excellent film forming,
emulsifying, and
adhesive properties
 It has high tensile
strength and flexibility
There are 4 different types of ECC.
1.Sprayable ECC
2.Extrudable ECC
3.Lt. wt. ECC
4.Self Compacting ECC
Sprayable ECC
 Sprayable concrete is also known as shotcrete
 A special version of ECC was developed recently for
spray repair operation.
 It undergoes placement and compaction at the same
time due to the force with which it is projected from
the nozzle
 The fresh mix must be deformable during the mixing
and pumping process.
 But it must stiffen up rapidly after the sprayed ECC
reaches the concrete substrate.
 This was attained through optimal combinations of
1.
2.
3.
Superplasticizer
Viscosity agent
Calcium aluminate cement particles
Spraying of ECC in action
 Superplasticizers are additives that increase the fluidity of
the material to which they are added
 Unless the mix is "starved" of water, the strength of
concrete is inversely proportional to the amount of water
added
 But workability depends on fludity.
 So superplasticizers are used to maintain the workability as
well as the strength
 Calcium aluminate cement particles have faster hardening
properties
The Strength
 The strain capacity and tensile strength of the sprayed
ECC is comparable with that of ECC specimens cast
with external consolidation
 The ultimate tensile strain of the sprayed ECC ranges
from 1.5 to 2.0%
Extrudable ECC
 Extrusion is a process used to create objects of a fixed
cross-sectional profile.
 A material is pushed or drawn through a die of the
desired cross-section
 Very complex cross-sections can be made by extrusion
 An extrudable ECC for use in the extrusion of pipes
was first developed in 1998.
 Extruded ECC pipes have both higher load capacity
and higher deformability than any other extruded
fiber-reinforced composite (FRC) `pipes.
The extrusion of a 100 mm ECCpipe
Lt. Wt./low density ECC
 'Lightweight'(i.e. low density) ECC have been
developed through the addition of air voids, glass
bubbles, polymer spheres,and/or lightweight
aggregate.
 Experiments have been conducted to test the
properties of ECC’s developed through different
methods.
 The experimental results show that multiple cracking
and strain hardening can be achieved by all these
approaches.
 however, tensile and compressive strengths and
robustness of strain capacity significantly vary with
content and type of lightweight "filler" used.
 Finally they have found out that “Mixes by adding glass
micro-bubbles with controlled size distribution”
exhibit more superior mechanical performances than
other approaches.
 Compared to other lightweight cements, lightweight
ECC has superior compressive and tensile strength,
crack-width control, and damage tolerance.
 Applications include floating homes, barges, and
canoes.
SELF COMPACTING CONCRETE
 refers to a concrete that can flow under its own weight.
 For instance, a self-compacting material would be able
to fill a mold containing
 elaborate pre-positioned steel reinforcement without
the need of vibration or shaking to ensure even
distribution.
 Self-compacting ECC was developed through the use
of chemical admixturesto decrease viscosity and
through controlling particle interactions with mix
proportioning.
 conventional concrete or cement materials tend to be
brittle and are very susceptible to failing wen subjected
to tensile loading.to
 overcome this short coming ECC have been developed.
 ECC's have high ductility and high toughness.
 this property of them allows them to be used in
demanding structure where severe loading or high
deformation is imposed.
Properties
Design
Methodology
Fiber
Matrix
Interface
Mechanical
Properties
Tensile strain
Crack width
FRC
N.A.
Common HPFRCC
ECC
Use high Vf
Micromechanics
based, minimize Vf for
cost and processibility
Tailored, polymer
Any type, Vf usually Mostly steel, Vf usually
fibers, Vf usually less
less than 2%; df for
> 5%; df ~ 150
than 2%; df < 50
steel ~ 500 micrometre
micrometre
micrometre
Controlled for matrix
Coarse aggregates
Fine aggregates
toughness, flaw size;
fine sand
Chemical and
frictional bonds
Not controlled
Not controlled
controlled for bridging
properties
Strain-softening:
Strain-hardening:
Strain-hardening:
0.1%
<1.5%
>3% (typical); 8% max
Unlimited
Typically several
Typically < 100
hundred micrometres,
micrometres during
unlimited beyond 1.5%
strain-hardening[1
strain
]
1) The Mitaka Dam
near Hiroshima was repaired using
ECC in 2003[5]. The surface of the
then 60-year old dam was severely
damaged, showing evidence of
cracks, spalling, and some water
leakage. A 20 mm-thick layer of
ECC was applied by spraying over
the 600 m2 surface.
2) Also in 2003, an earth retaining wall in
Gifu, Japan, was repaired using ECC[6].
Ordinary portland cement could not be
used due to the severity of the cracking
in the original structure, which would
have caused reflective cracking. ECC was
intended to minimize this danger; after
one year only microcracks of tolerable
width were observed.
3)The 95 m (312 ft.) Glorio Roppongi high-rise
apartment building in Tokyo contains a total of
54 ECC coupling beams (2 per story) intended
to mitigate earthquake damage [7]. The
properties of ECC (high damage tolerance, high
energy absorption, and ability to deform under
shear) give it superior properties in seismic
resistance applications when compared to
ordinary portland cement. Similar structures
include the 41-story Nabeaure Yokohama
Tower (4 coupling beams per floor.)
4) The 1-km (0.6 mile) long Mihara Bridge
in Hokkaido, Japan was opened to traffic in
2005 [8]. The steel-reinforced road bed contains
nearly 800 m3 of ECC material. The tensile
ductility and tight crack control behavior of
ECC led to a 40 % reduction in material used
during construction.
5) Similarly, a 225-mm thick ECC bridge deck on interstate 94 in Michigan was
completed in 2005[9] . 30 m3 of material was used, delivered on-site in standard
mixing trucks. Due to the unique mechanical properties of ECC, this deck also
used less material than a proposed deck made of ordinary portland cement.
Both the University of Michigan and the Michigan Department of
Transportation are monitoring the bridge in an attempt to verify the theoretical
superior durability of ECC; after 4 years of monitoring, performance remained
undiminished.