SEMINAR REPORT ON BENDABLE CONCRETEPRESENTED BY

CHITARI NAGESH BABASAHEBI ST SEM M.TECH. IN STRUCTURAL ENGINEERING BASAVESHWAR ENGINEERING COLLEGE BAGALKOT

ABSTRACT

Engineered Cementitious Composites (ECC) is an ultra-ductile fiber reinforced ultracementitious material that embodies a micromechanics based design concept. concept. The tensile ductility and self-controlled selftight crack width characteristics are conducive to enhancing structural safety under severe loading, and durability under normal service loading. loading.

The cost of ECC is currently about three times that of normal concrete per cubic yard. yard. However, a number of commercial projects in Japan and Australia have already demonstrated that initial construction cost saving can be achieved when ECC is used, through smaller structural member size, reduced or eliminated steel reinforcement, elimination of other structural protective systems, and faster construction offered by the unique fresh and hardened properties of ECC .

The advantages offered by ECC over conventional concrete become even more compelling. ECC is a field-ready compelling. fieldductile concrete that has the potential to significantly contribute to enhancing infrastructure safety, durability and sustainability. sustainability. These properties of ECC and its applications are reviewed in the seminar work. work.

INTRODUCTION

Demands on Future Concrete: Concrete:Concrete is ubiquitous. ubiquitous. Annually, more than one ton per capita of concrete is cast for infrastructure construction worldwide. By many worldwide. measures, concrete is an excellent construction material. material. However, the mechanical properties and functional characteristics 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 1) Brittle failure under severe loading:loading: Infrastructures are subjected to severe natural loadings such as earthquakes, which see no national boundaries. In boundaries. some cases, serious damages have occurred to infrastructures including buildings, roadways and bridges. bridges.

Infrastructure failure can often be traced to brittle fracture of concrete, e.g. bond splitting, cover spalling, and core crushing resulting in subsequent collapse of bridge piers or columns in soft first stories in buildings. buildings. Deterioration is not as dramatic as collapse of infrastructure, the magnitude of this problem in terms of dollar cost dwarfs those associated with failure due to severe loading. loading.

2)Deterioration under normal service loading:loading:

A major cause of lack of durability of reinforced concrete structure may be traced to cracking of concrete which may lead to steel reinforcement corrosion and other problems. problems. 3) Lack of sustainability of RC structures:structures: The sustainability of RC infrastructure has come into question in recent years. years. Globally, the huge flow of material driven by concrete production causes significant societal and environmental impacts. impacts.

1)

Highly ductile: - With ability to yield ductile:

like a metal when overloaded, even under severe impact load or large imposed deformation, thus providing infrastructure safety. safety.2)

ability to withstand mechanical and environmental loads under normal service conditions, thus providing service life significantly higher than current infrastructure. infrastructure.

Highly durable: - with durable:

3) Highly sustainable: - minimize natural sustainable:

resource use and pollution emission, during the full life cycle (material production, construction and use, end of life demolition) of an infrastructure, thus ensuring harmonious interaction between the built and the natural environment. environment. If 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 micromechanics-based micromechanicsmaterial design, maximum ductility in excess of 3% under uniaxial tensile loading can be attained with 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 stressstress-strain curve of a ECC containing 2% Poly Vinyl Alcohol (PVA) fiber. The properties of PVA fibers are given in the table below.

Properties of PVA fibersLength (mm) Diameter ( m) Volume fraction (%) Elastic modulus (GPa) Fiber strength (MPa) Interfacial bond strength (MPa) 12 40 2 40 1600 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

Earthquake resistant structures:structures: The no of experiments confirm significant improvements in damage tolerance, suppressing many of the commonly observed failure modes in RC such as cover spalling. Additionally, the amount spalling. of steel shear reinforcement can be drastically reduced since ECC remains highly ductile in shear. shear.

Durable and sustainable infrastructure Structures have enhanced durability when applying ECC. Freeze-thaw exposure, Freezeaccelerated 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

Hand finishing of ECC link slab on Grove Street Bridge Project

Patch repair on a bridge deck.

Comparison between ECC, FRC, and HPFRCCProperties FRC Common HPFRCC ECC

Mechanical Properties

Strain-softening:

Strain-hardening:

Strain-hardening:

Tensile strain

0.1%

3% (typical); 8% max

Typically several Crack width Unlimited hundred micrometers, unlimited beyond 1.5% strain

Typically < 100 micrometers during strain-hardening

Coarse aggregates, Fine Fine aggregates and Matrix aggregates and Cement Cement

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 Mostly steel, Vf usually Tailored, polymer fibers , Vf usually less than 2%; df < 50 micrometer

less than 2%; df for steel > 5%; df ~ 150 ~ 500 micrometer micrometer

FRC:- FIBER REINFORCED CONCRETE HPFRCC:- High Performance Fiber Reinforced Cement Concrete

MODERN TECHNIQUES

Spray able ECC Technology :-In the development concept of spray able ECC, micromechanics is adapted to properly select the matrix, fiber, and interface properties to exhibit strain-hardening and strainmultiple cracking behaviors in the composites. composites. Within the pre-determined premicromechanical constraints, the fluid properties are controlled by the rheological process design to develop flocculations between cementitious particles at a proper rate. rate.

Lightweight ECC Technology