SEMINAR REPORT ON
³BENDABLE CONCRETE´ PRESENTED BY CHITARI NAGESH BABASAHEB I ST ± SEM M.TECH. M.TECH. IN IN STRUCTURAL STRUCTURAL ENGINEERI ENGINEERING NG
BASAVESHWAR ENGINEERING COLLEGE BAGALKOT
ABSTRACT
Engi En Engineered gine nee ere red d Cem eme ent ntit itio ious us Comp Co Composites mpos osit ites es (ECC) is an ultra ultra--ductile -ductile fiber reinforced reinforced ceme ce cementitious menti ntiti tious ous mat mater mate ma teri erial rial ial al th that at em embo embodi bodies die es es a micro mi micromechanics crome mecha chanic nics s ba bas based se ed d de des sig ign n concept. conc co nce ept. The te The tens nsil ile e duc ducti duct du ctil tili ilit lity ity ty y an and and selfself -controlled -controlled tight crack wi tight widt width dth ch char arac acte teri rist stic ics s are are conducive to enhancing enhancing structural safety under severe load under adi ading ng, ng, an and and durability d u r a b il it y under normal service loading. loading.
The cost of of ECC is currently about three times that of of normal concrete per cubic yard.. However, a number of yard of commercial proj pr projects ojec ects ts in in Jap apa apan an and and Au Aust stra rali lia a have have a lr e a d y already demonstrated th a t iinitial n it ia l construction cost saving can be achieve construction achieved d when ECC is used when d,, th thro thr hrou roug ough ugh gh h smaller smal sm alle lerr stru st structural ruct ctur ural al me embe em mb ber er size, re redu reduc duced or or eliminated eliminated steel rreinforcement, einforcement, elimination of of other structural protective systems, and faster construction offered b y t h e u n iq by que qu ue fresh and hardened harde den ned properties of of ECC .
The advantages offered by ECC over conventional concrete become even more compelling. compelling. ECC is a fieldfield-ready ductile concrete that has the potential to significantly contribute to enhancing infrastructure safety, durability and sustainability.. These properties of sustainability of ECC and its applications applications are reviewed in the seminar work. work.
INTRODUCTION
Demands on Future oncrete:Concrete: ubiquitous. Concrete is ubiquitous. Annually, more than one ton per capita of concrete is cast for infrastructure construction worldwide worldwide.. By many measures, concrete is an excellent construction material material.. However, the mechanical properties and functional characteristics of of concrete will have to be improved, in some ways drastically, and these improvements are already emerging in limited forms forms..
These advancements are needed to address deficiencies in concrete infrastructure, currently facing three major challenges loading::1) Brittle failure under severe loading nfrastructures are subjected to severe Infrastructures natural loadings such as earthquakes, which see no national boundaries. boundaries. In some cases, serious damages have occurred to infrastructures including buildings, roadways and bridges bridges..
Infrastructure
failure can often be traced to brittle fracture of of concrete, e.g. bond splitting, cover spalling, and core crushing resulting in subsequent collapse of bridge piers or columns in soft first of stories in buildings buildings..
2)Deterioration under normal service loading loading::-
Deterioration is not as dramatic as collapse of of infrastructure, the magnitude of this problem in terms of terms of of dollar cost dwarfs those associated with failure due to severe loading. loading.
A major cause of of lack of of durability of reinforced concrete structure may be traced to cracking of of concrete which may lead to steel reinforcement corrosion and other problems. problems. 3) Lack of of sustainability of RC structures structures::The sustainability of of RC infrastructure has come into question in recent years years.. Globally, the huge flow of of material driven by concrete production causes significant societal and environmental impacts.. impacts
Highly ductile ductile:: - With ability to ³yield´ ³yield´
1)
like a metal when overloaded, even under severe impact load or large imposed deformation, thus providing infrastructure safety. safety. ability to withstand mechanical and environmental loads under normal service conditions, thus providing service life significantly higher than current infrastructure. infrastructure.
2)
Highly durable durable::
- with
3)
Highly sustainable sustainable:: - minimize natural
resource use and pollution emission, during the full life cycle (material production, construction and use, end of life demolition) of demolition) of of an infrastructure, thus ensuring harmonious interaction between the built and the natural environment.. environment Iff concrete behaves like steel in tension (highly ductile), while retaining all other advantages, concrete structures with enhanced serviceability and safety can be readily realized. realized.
ENGINEERED CEMENTITIOUS COMPOSITE
Concrete also known as Engineered Cementitious Composites (ECC) is a fiber reinforced cement based composite material systematically engineered to achieve high ductility under tensile and shear loading. loading. Which have 500 times more resistant to cracking and 40 percent lighter in weight.. weight
By employing micromechanicsmicromechanics-based material design, maximum ductility in excess of of 3% under uniaxial tensile loading can be attained attained with only only 2% fiber content by volume. volume. Recent research indicates that ECC holds promise in enhancing the safety, durability, and sustainability of infrastructure.. infrastructure
Figure
1 shows a typical uniaxial tensile stress--strain curve of a ECC containing stress 2% Poly Vinyl Alcohol (PVA) fiber. The properties of PVA fibers are given in the table below.
Properties
of PVA fibers
Length (mm)
12
Diameter (m)
40
Volume fraction (%)
2
Elastic modulus (GPa)
40
Fiber
1600
strength (MPa)
Interfacial
bond strength (MPa)
2.01
Typical tensile stress-strain curve and crack width development of ECC.
Making of ECC
ECC is made with ingredients typically found in concrete, including cement, sand, fly ash, and super plasticizer. However, no coarse aggregate are employed, and no air entrainment is necessary. Instead, micro-fibers are added
the resulting composite maintains self-consolidating characteristics during casting and ductile behavior after hardening.
The components in an ECC mix design is based on micromechanics on how the fiber, mortar matrix and the interface between them interact under mechanical loading. As a result, brittle fracture failure is eliminated. Instead, multiple micro racks form when the composite material is overloaded beyond the elastic state (pseudo-yielding), and the propagating micro cracks maintain very tight cracks width in accordance with the tailored nature of the bridging fibers
FLOW CHART OF IMPORTANT ELEMENT OF ECC
PROPERTIES OF ECC
Safety:- A major driver of next generation
infrastructure resistant to seismic loading is performance-based earthquake engineering. Its implementation eases the adoption of new high performance material such as ECC. In addition to collapse resistance, Billington in reviewing this subject suggested that the use of ECC could lead to highly damage tolerant structures with limited residual crack widths such that postearthquake repair costs could be minimized.
Durability
The cause of infrastructure deterioration, under combined environmental and mechanical loads, is complex. In bridges and roadways, deterioration often begins with cracking due to thermal movements or restrained drying or autogenously shrinkage cracking. These cracks are exacerbated by fatigue loading due to moving traffic.
Damage behavior
Crack width evaluation of link slab specimen during fatigue test
Coefficient of permeability versus crack width for ECC & reinforced mortar series prestrained to 1.5 in unaxial tension.Grey no indicate data normalized by number of cracks.
Micro cell & Micro cell corrosion rate measured for 1) rc 2)RECC along the reinforcement bar length
Failure
mode of a) concrete b) ECC
APPLICATIONS
structures::Earthquake resistant structures The no of of experiments confirm significant improvements in damage tolerance, suppressing many of of the commonly observed failure modes in RC such as cover spalling spalling.. Additionally, the amount of steel shear reinforcement can be of drastically reduced since ECC remains highly ductile in shear. shear.
Durable and sustainable infrastructure Structures have enhanced durability when applying ECC. Freezereeze-thaw exposure, accelerated weather exposure, fatigue, and wheel load abrasion and wear tests, all indicate high ECC material durability self± self ± controlled tight crack widths reduce transport of water and corrosives through the cover , and significantly delay corrosion of reinforcing steel. Furthermore, the ductility of ECC minimizes the potential for cover spalling spalling..
Uses of ECC in Field
MIHARA BRIDGE JAPAN
Patch
Hand finishing of ECC link slab on Grove Street Bridge Project
repair on a bridge deck.
Compar ison between ECC, FRC, and HPFRCC Properties
Mechanical Properties
Tensile strain
FRC
Common HPFRCC
Strain-softening:
Strain-hardening:
Strain-hardening:
0.1%
<1.5%
>3% (typical); 8% max
Typically several Crack width
Unlimited
hundred micrometers, unlimited beyond 1.5% strain
Matrix
ECC
Coarse aggregates, Fine Fine aggregates and aggregates and Cement
Cement
Typically < 100 micrometers during strain-hardening
Controlled for matrix toughness, fine sand, Cement, Fly ash.
Properties
FRC
Common HPFRCC
ECC
Chemical and frictional Interface
Not controlled
Not controlled
bonds controlled for bridging properties Micromechanics based,
Design Methodology
N.A.
Use high Vf
minimize Vf for cost and process ability
Any type, Vf usually Fiber
FRC:- FIBER
Mostly steel, Vf usually Tailored, polymer fibers
less than 2%; df for steel > 5%; df ~ 150
, Vf usually less than
~ 500 micrometer
2%; df < 50 micrometer
micrometer
REINFORCED CONCRETE HPFRCC:- High Performance Fiber Reinforced Cement Concrete
MODERN TECHNIQUES
Spray able ECC Technology :-In the development concept of of spray able ECC, micromechanics is adapted to properly select the matrix, fiber, and interface properties to exhibit strainstrain-hardening and multiple cracking behaviors in the composites.. Within the precomposites pre-determined micromechanical constraints, the fluid properties are controlled by the rheological process design to develop flocculations between cementitious particles at a proper rate.. rate
