Fibers in Concrete Reinforced concrete bars - Basalt.Todaybasalt.today/images/fibers.pdf · Reinforced concrete bars. ... good ductility for common rebar grades no coatings to chip,

Fibers in Concrete

P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials

Reinforced concrete bars

Fibers in Concrete


Size of bars

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Fibers in Concrete


Epoxi-coated bar

The process of applying fusion-bonded epoxy coating to steel reinforcement involves four major steps: surface preparation, heating, powder application and curing.

From crsi

Fibers in Concrete


Epoxy coated reinforcement

Fibers in Concrete


Specifications

Standard specifications for epoxy-coated reinforcing steel are available from the American Society for Testing and Materials (ASTM A775, ASTM A934 and ASTM D3963) and the American Association of State Highway and Transportation Officials (AASHTO M284). In addition, ASTM Standard Specification A884 is available for epoxy-coated welded wire fabric.

Fibers in Concrete


Stainless steel

Stainless steel is produced in an electric arc furnace using recycled stainless scrap and various chromium alloys. Nickel, molybdenum, and other alloys are added as needed. Final alloy additions are made to meet the specified chemistry for the stainless steel type being produced.

From http://www.fhwa.dot.gov/resourcecenter/tech2.htm

Fibers in Concrete


Benefits

inherently good corrosion resistance reduced life cycle costs (for reinforced concrete) good strength good weldability for common rebar grades good ductility for common rebar grades no coatings to chip,

crack, deteriorate no coatings to damage and repair no exposed ends to coat (solid stainless steel bars) can withstand shipping, handling, fabrication magnetic or non-magnetic (depends on alloy) good mechanical properties for common rebar grades at

high and low temperatures


Fibers in Concrete


Construction

Because of the corrosion resistance of stainless steel, it has a long service life compared to mild steel. Even though stainless steel has a higher initial cost, the life cycle cost is lower because the frequency and cost of future maintenance and replacement work is reduced.


Fibers in Concrete


Standards

Stainless steel reinforcing bars are covered by ASTM A955M, Standard Specification for Deformed and Plain Stainless Steel Bars for Concrete Reinforcement. The alloys covered are 304, 304L (low carbon content), 316, 316L (low carbon content), 316LN (low carbon content and nitrogen added), and 2205.

Fiber Reinforced Concrete

Fibers in Concrete


Old Concept

Exodus 5:6, And Pharaoh commanded the same day the

taskmasters of the people, and their officers, saying, Ye shall no more give the people straw to make brick,

as heretofore: let them go and gather straw for themselves

Egyptians used straw to reinforce mud bricks, but there is evidence that asbestos fiber was used to reinforce clay posts about 5000 years ago.

Fibers in Concrete


Growth Industry

Even though the market for fiber reinforced concrete is still small compared to the overall production of concrete, in North America there has been an yearly growth rate of 20% and that the worldwide yearly consumption of fibers used in concrete is 300,000 tons.

Fibers in Concrete


Classification according to volume fraction

Low volume fraction (<1%)

Moderate volume fraction (between 1 and 2%)

High volume fraction (greater than 2)

Fibers in Concrete


Low volume fraction

The fibers are used to reduce shrinkage cracking. These fibers are used in slabs and pavements that have large exposed surface leading to high shrinkage crack.

Disperse fibers offer various advantages of steel bars and wiremesh to reduce shrinkage cracks:– (a) the fibers are uniformly distributed in

three-dimensions making an efficient load distribution;

– (b) the fibers are less sensitive to corrosion than the reinforcing steel bars,

– (c) the fibers can reduce the labor cost of placing the bars and wiremesh.

Fibers in Concrete


Moderate volume fraction

The presence of fibers at this volume fraction increase the modulus of rupture, fracture toughness, and impact resistance. These composites are used in construction methods such as shotcrete and in structures that require energy absorption capability, improved capacity against delamination, spalling, and fatigue.

Fibers in Concrete


High volume fraction

The fibers used at this level lead to strain-hardening of the composites. Because of this improved behavior, these composites are often referred as high-performance fiber-reinforced composites (HPFRC). In the last decade, even better composites were developed and are referred as ultra-high-performance fiber-reinforced concretes (UHPFRC).

Fibers in Concrete


Toughening Mechanism

Fibers in Concrete


Mechanism

The composite will carry increasing loads after the first cracking of the matrix if the pull-out resistance of the fibers at the first crack is greater than the load at first cracking;

At the cracked section, the matrix does not resist any tension and the fibers carry the entire load taken by the composite.

With an increasing load on the composite, the fibers will tend to transfer the additional stress to the matrix through bond stresses. This process of multiple cracking will continue until either fibers fail or the accumulated local debonding will lead to fiber pull-out .

Fibers in Concrete


Fibers in Concrete


Optimization Process

From a material and structural point of view, there is a delicate balance in optimizing the bond between the fiber and the matrix.

If the fibers have a weak bond with the matrix, they can slip out at low loads and do not contribute very much to bridge the cracks. In this situation, the fibers do not increase the toughness of the system.

If the bond with the matrix is too strong, many of the fibers may break before they dissipate energy by sliding out. In this case, the fibers behave as non-active inclusions leading to only marginal improvement in the mechanical properties.

Fibers in Concrete


Role of Fiber Size

To bridge the large number of microcracks in the composite under load and to avoid large strain localization it is necessary to have a large number of short fibers. The uniform distribution of short fibers can increase the strength and ductility of the composite.

Long fibers are needed to bridge discrete macrocracks at higher loads; however the volume fraction of long fibers can be much smaller than the volume fraction of short fibers. The presence of long fibers significantly reduces the workability of the mix.

Fibers in Concrete


Fiber size

Fibers in Concrete


Materials

It is well known that the addition of any type of fibers to plain concrete reduces the workability.

Since fibers impart considerable stability to a fresh concrete mass, the slump cone test is not a good index of workability. For example, introduction of 1.5 volume percent steel or glass fibers to a concrete with 200 mm of slump is likely to reduce the slum of the mixture to about 25 mm, but the placeability of the concrete and its compactability under vibration may still be satisfactory.

Therefore, the Vebe test is considered more appropriate for evaluating the workability of fiber-reinforce concrete mixtures.

Fibers in Concrete


Vebe Test

Fibers in Concrete


Elastic modulus, creep, and drying shrinkage

Inclusion of steel fibers in concrete has little effect on the modulus of elasticity, drying shrinkage, and compressive creep.

Tensile creep is reduced slightly, but flexural creep can be substantially reduced when very stiff carbon fibers are used.

However, in most studies, because of the low volume the fibers simply acted as rigid inclusions in the matrix, without producing much effect on the dimensional stability of the composite

Fibers in Concrete


Durability

When well compacted and cured, concretes containing steel fibers seem to possess excellent durability as long as fibers remain protected by the cement paste.

In most environments, especially those containing chloride, surface rusting is inevitable but the fibers in the interior usually remain uncorroded.

Long-term tests of steel-fiber concrete durability at the Battelle Laboratories in Columbus, Ohio, showed minimum corrosion of fibers and no adverse effect after 7 years of exposure to deicing salt

Fibers in Concrete


Glass Fibers

Ordinary glass fiber cannot be used in portland cement mortars or concretes because of chemical attack by the alkaline cement paste.

Zirconia and other alkali-resistant glass fibers possess better durability to alkaline environments, but even these are reported to show a gradual deterioration with time.

Similarly, most natural fibers, such as cotton and wool, and many synthetic polymers suffer from lack of durability to the alkaline environment of the portland cement paste.

Fibers in Concrete


Ultra-High-Performance Fiber-Reinforced Composites

There is a new generation of high performance fiber-reinforced composites. In many of these materials the strength, toughness, and durability are significantly improved.

Fibers in Concrete


Compact Reinforced Composites (CRC)

Researchers in Denmark created Compact Reinforced Composites using metal fibers, 6 mm long and 0.15 mm in diameter, and volume fractions in the range of 5 to 10 %.

High frequency vibration is needed to obtain adequate compaction. These short fibers increase the tensile strength and toughness of the material.

The increase of strength is greater than the increase in ductility, therefore the structural design of large beams and slabs requires that a higher amount of reinforcing bars be used to take advantage of the composite.

Fibers in Concrete


Compact Reinforced Composites (CRC)

The short fibers are an efficient mechanism of crack control around the reinforcing bars.

The final cost of the structure will be much higher than if the structure would be made by traditional methods, therefore the use of compact reinforced composites is mainly justified when the structure requires special behavior, such as high impact resistance or very high mechanical properties.

Fibers in Concrete


Reactive Powder Concrete (RPC)

Investigators in France by adding metal fibers, 13 mm long and 0.15 mm in diameter, with a maximum volume fraction of 2.5%.

This composite uses fibers that are twice as long as the compact reinforced composites therefore, because of workability limitations, cannot incorporate the same volume fraction of fibers.

The smaller volume fraction results in a smaller increase in the tensile strength of the concrete. Commercial versions of this product have further improved the strength of the matrix, chemically treated the surface of the fiber, and added microfibers.

Fibers in Concrete


Fibers in Concrete


Another view

Strength


AT EQUAL LOAD CARRYING CAPACITY

WEIGHT OF BEAMS (kg/linear m) :

140112 530 467

Ductal Steel

LAFARGE

Strength


®

LAFARGE

Strength


MONACO TRAIN STATION

Acoustic Panels

LAFARGE

Fibers in Concrete


Slurry-Infiltrated-fibered concrete (SIFCON)

The processing of this composite consists in placing the fibers in a formwork and then infiltrating a high w/c ratio mortar slurry to coat the fibers.

Compressive and tensile strengths up to 120 MPa and 40 MPa, respectively have been obtained. Modulus of rupture up 90 MPa and shear strength up to 28 MPa have been also reported.

In direct tension along the direction of the fibers, the material shows a very ductile response. This composite has been used in pavements slabs, and repair

Fibers in Concrete


SiFCON

Fibers in Concrete


SIFCON

Fibers in Concrete


Engineered Cementitious Composite (EEC)

The ultra high-ductility of this composite, 3-7%, was obtained by optimizing the interactions between fiber, matrix and its interface.

Mathematical were developed so that a small volume fraction of 2% was able to provide the large ductility.

The material has a very high stain capacity and toughness and controlled crack propagation

Fibers in Concrete



The manufacturing of ECC can be done by normal casting or by extrusion.

By using an optimum amount of superplasticizer and non-ionic polymer with steric action, it was possible to obtain self-compacting casting.

Experimental results with extruded pipes indicate that the system has a plastic yielding behavior instead of the typical brittle fracture exhibited when plain concrete is used.

Fibers in Concrete



Fibers in Concrete


Multiscale-Scale Fiber-Reinforced Concrete (MSFRC)

Researchers the Laboratoire Central des Ponts et Chaussees (France) proposed to combine short and long fibers to increase the tensile strength, the bearing capacity, and the ductility).

With this blend, good workability was achieved with fiber volume fractions up to 7%.

One typical combination of fibers is 5% straight drawn steel fibers, 5-mm long and 0.25 mm in diameter, and 2% hooked-end drawn steel fibers, 25-mm long and 0.3 mm in diameter.

Fibers in Concrete


Construction

Fibre Reinforced Polymer (FRP) Composites

From http://gnatchung.tripod.com/FRP/

Fibers in Concrete


FRP - CIVIL STRUCTURESCURRENT FIELD ACTIVITIES

Pedestrian Bridges Highway Bridges Seismic Retrofit Columns Bridge Strengthening Bridge Repairs

From FHWA

Fibers in Concrete


FRP TECHNOLOGYCHARACTERISTICS

High Strength High Resistance to Corrosion and Chemical High Resistance to Elevated Temperature High Resistance to Abrasion Toughness Fatigue Light Weight

From FHWA

Fibers in Concrete


FRP TECHNOLOGYADVANTAGES

Ease in Fabrication, Manufacturing, Handling, and Erection

Year-Round Construction Short Project Time Delivery High Performance Durability (Jury Still Out) Excellent Strength-to-Weight Ratio

From FHWA

Fibers in Concrete


FRP TECHNOLOGYDISADVANTAGES -1

High First Cost Creep and Shrinkage Potential for Environmental Degradation (Alkalis’

Attack, UV Radiation Exposure, Moisture Absorption, etc.)

Consistency of Material Properties

From FHWA

Fibers in Concrete


FRP TECHNOLOGYPUBLIC CONCERNS

Fire/Flame Resistance Smoke Toxicity Fuel Spills Vandalism/Theft Inspectibility Repairability

From FHWA

Fibers in Concrete


Applications: FRP

New bridges

Fibers in Concrete


Applications: Strengthening

Carbon fibre strips were used to strengthen balcony slabs

Westgate Bridge in Melbourne, Australia, incorporates 50 km of carbon FRP laminates and external post tensioning for 600 metres of the western approach Brick bridge piers were strengthened by installing FRP sheets

www.savcorart.com.au/graphics/ strengthening_main.JPG

Fibers in Concrete


Reinforcement

The FRP composite rebar is made from high strength glass fibers along with an extremely durable vinyl ester resin. The glass fibers impart strength to the rod while the vinyl ester resin imparts excellent corrosion resistance properties in harsh chemical and alkaline environments.

www.pulwellpultrusions.com/ products4.htm

Fibers in Concrete


FRP -TYPICAL PROPERTIES

FIBER STRENGTH (KSI)

MODULUS(MSI)

STRAIN(%)

E-Glass 350 6 2S-Glass 500 6 3CF-Pan 600 33-50 2C-Pitch GP 200 6 0.3Pitch UHM 400 70-120 0.5Aramid 500 10-20 2Ceramic 100 10-40 2Nylon 50 0.5 5-50

Source: Tonen Energy CorpFrom FHWA

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Fibers in Concrete Reinforced concrete bars - Basalt.Todaybasalt.today/images/fibers.pdf · Reinforced concrete bars. ... good ductility for common rebar grades no coatings to chip,