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Reinforced concrete

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Reinforced concrete is concrete in which the material's undesirably lowtensile strength and elasticity are counteracted by the inclusion of reinforcingstructures that have high tensile strength. The structures usually, though notnecessarily, are reinforcing bars of steel (rebar) and also usually, though alsonot necessarily, are embedded passively in the concrete before it sets. Suchreinforcing structures are designed primarily to take up working stresses thatotherwise would have placed regions within the concrete mass underunacceptable tension. Modern concrete reinforcing structures however, mayinstead or in addition contain non-steel materials with high tensile strength.

They also may be permanently stressed before or after the mass sets, so as toimprove the behaviour of the final structure under working loads. These twoexpedients are known as (pre-stressing) and (post-stressing) respectively.

For a strong, ductile and durable construction the reinforcement needs to havethe following properties at least:

High strengthHigh toleration oftensile strainGood bond to the concrete, irrespective of pH, moisture, and similarfactors

Thermal compatibility, not causing unacceptable stresses in response tochanging temperatures.Durability in the concrete environment, irrespective of corrosion orsustained stress for example.

Contents

1 Use in construction2 Behavior of reinforced concrete

2.1 Materials2.2 Key characteristics2.3 Mechanism of composite action of reinforcement and concrete2.4 Anchorage (bond) in concrete: Codes of specifications2.5 Anti-corrosion measures

3 Reinforcement and terminology of Beams4 Prestressed concrete

Reinforced concrete - Wikipedia, the free encyclo... http://en.wikipedia.org/wiki/Reinforced_conc

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5 Common failure modes of steel reinforced concrete5.1 Mechanical failure5.2 Carbonation5.3 Chlorides5.4 Alkali silica reaction5.5 Conversion of high alumina cement

5.6 Sulphates6 Steel plate construction7 Fiber-reinforced concrete8 Non-steel reinforcement9 See also10 References11 Further reading12 External links

[edit] Use in construction

Rebars ofSagrada Famlia's roof in construction(2009)

Concrete is reinforced to give it extra tensile strength; without reinforcement,many concrete buildings would not have been possible.

Reinforced concrete can encompass many types of structures and components,including slabs, walls, beams, columns, foundations, frames and more.

Reinforced concrete can be classified as precast or cast in-situ concrete.

Designing and implementing the most efficient floor system is key to creatingoptimal building structures. Small changes in the design of a floor system canhave significant impact on material costs, construction schedule, ultimatestrength, operating costs, occupancy levels and end use of a building.

[edit] Behavior of reinforced concrete[edit] Materials

Concrete is a mixture of coarse (stone or brick chips) and fine (generally sandor crushed stone) aggregates with a binder material (usually Portland cement).When mixed with a small amount of water, the cement hydrates to form


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microscopic opaque crystal lattices encapsulating and locking the aggregateinto a rigid structure. Typical concrete mixes have high resistance tocompressivestresses (about 4,000 psi (28 MPa)); however, any appreciabletension (e.g., due to bending) will break the microscopic rigid lattice, resultingin cracking and separation of the concrete. For this reason, typicalnon-reinforced concrete must be well supported to prevent the development of

tension.

If a material with high strength in tension, such as steel, is placed in concrete,then the composite material, reinforced concrete, resists not onlycompression but also bending and other direct tensile actions. A reinforcedconcrete section where the concrete resists the compression and steel resiststhe tension can be made into almost any shape and size for the constructionindustry.

[edit] Key characteristics

Three physical characteristics give reinforced concrete its special properties:

the coefficient of thermal expansion of concrete is similar to that of steel,eliminating large internal stresses due to differences in thermal expansionor contraction.

1.

when the cement paste within the concrete hardens, this conforms to thesurface details of the steel, permitting any stress to be transmittedefficiently between the different materials. Usually steel bars areroughened or corrugated to further improve the bond or cohesionbetween the concrete and steel.

2.

the alkaline chemical environment provided by the alkali reserve (KOH,NaOH) and the portlandite (calcium hydroxide) contained in thehardened cement paste causes a passivating film to form on the surface ofthe steel, making it much more resistant to corrosion than it would be inneutral or acidic conditions. When the cement paste exposed to the airand meteoric water reacts with the atmospheric CO2, portlandite and theCalcium Silicate Hydrate (CSH) of the hardened cement paste becomeprogressively carbonated and the high pH gradually decreases from 13.5 12.5 to 8.5, the pH of water in equilibrium with calcite (calciumcarbonate) and the steel is no longer passivated.

3.

As a rule of thumb, only to give an idea on orders of magnitude, steel isprotected at pH above ~11 but starts to corrode below ~10 depending on steelcharacteristics and local physico-chemical conditions when concrete becomescarbonated. Carbonation of concrete along with chloride ingress are amongst

the chief reasons for the failure ofreinforcement bars in concrete.[1]


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The relative cross-sectional area of steel required for typical reinforcedconcrete is usually quite small and varies from 1% for most beams and slabs to6% for some columns. Reinforcing bars are normally round in cross-section andvary in diameter. Reinforced concrete structures sometimes have provisionssuch as ventilated hollow cores to control their moisture & humidity.

Distribution of concrete (in spite of reinforcement) strength characteristicsalong the cross-section of vertical reinforced concrete elements is

inhomogeneous.[2]

[edit] Mechanism of composite action of reinforcement and

concrete

The reinforcement in a RC structure, such as a steel bar, has to undergo thesame strain or deformation as the surrounding concrete in order to preventdiscontinuity, slip or separation of the two materials under load. Maintaining

composite action requires transfer of load between the concrete and steel. Thedirect stress is transferred from the concrete to the bar interface so as tochange the tensile stress in the reinforcing bar along its length. This loadtransfer is achieved by means of bond (anchorage) and is idealized as acontinuous stress field that develops in the vicinity of the steel-concreteinterface.

[edit] Anchorage (bond) in concrete: Codes of specifications

Because the actual bond stress varies along the length of a bar anchored in a

zone of tension, current international codes of specifications use the concept ofdevelopment length rather than bond stress. The main requirement for safetyagainst bond failure is to provide a sufficient extension of the length of the barbeyond the point where the steel is required to develop its yield stress and thislength must be at least equal to its development length. However, if the actualavailable length is inadequate for full development, special anchorages mustbe provided, such as cogs or hooks or mechanical end plates. The sameconcept applies to lap splice length mentioned in the codes where splices(overlapping) provided between two adjacent bars in order to maintain therequired continuity of stress in the splice zone.

[edit] Anti-corrosion measures

In wet and cold climates, reinforced concrete for roads, bridges, parkingstructures and other structures that may be exposed to deicing salt maybenefit from use of epoxy-coated, hot dip galvanised or stainless steel rebar,although good design and a well-chosen cement mix may provide sufficient


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protection for many applications. Epoxy coated rebar can easily be identifiedby the light green colour of its epoxy coating. Hot dip galvanized rebar may bebright or dull grey depending on length of exposure, and stainless rebarexhibits a typical white metallic sheen that is readily distinguishable fromcarbon steel reinforcing bar. Reference ASTM standard specificationsA767Standard Specification for Hot Dip Galvanised Reinforcing Bars,A775

Standard Specification for Epoxy Coated Steel Reinforcing Bars andA955Standard Specification for Deformed and Plain Stainless Bars for ConcreteReinforcement.

Another, cheaper way of protecting rebars is coating them with zinc

phosphate.[3] Zinc phosphate slowly reacts with calcium cations and thehydroxyl anions present in the cement pore water and forms a stablehydroxyapatite layer.

Penetrating sealants typically must be applied some time after curing. Sealants

include paint, plastic foams, films and aluminum foil, felts or fabric mats sealedwith tar, and layers ofbentonite clay, sometimes used to seal roadbeds.

Corrosion inhibitors, such as calciumnitrite [Ca(NO2)2], can also be added tothe water mix before pouring concrete. Generally, 12 wt. % of [Ca(NO2)2] withrespect to cement weight is needed to prevent corrosion of the rebars. Thenitrite anion is a mild oxidizer that oxidizes the soluble and mobile ferrous ions

(Fe2+) present at the surface of the corroding steel and causes it to precipitateas an insoluble ferric hydroxide (Fe(OH)3). This causes the passivation of steelat the anodic oxidation sites. Nitrite is a much more active corrosion inhibitor

than nitrate, a less powerful oxidizer of the divalent iron.

[edit] Reinforcement and terminology of Beams

A beam bends under bending moment, resulting in a small curvature. At theouter face (tensile face) of the curvature the concrete experiences tensilestress, while at the inner face (compressive face) it experiences compressivestress.

Asingly reinforced beam is one in which the concrete element is only

reinforced near the tensile face and the reinforcement, called tension steel, isdesigned to resist the tension.

Adoubly reinforced beam is one in which besides the tensile reinforcementthe concrete element is also reinforced near the compressive face to help theconcrete resist compression. The latter reinforcement is called compressionsteel. When the compression zone of a concrete is inadequate to resist the


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compressive Moment(positive moment), extra reinforcement has to be providedif the architect limits the dimensions of the section.

An under-reinforced beam is one in which the tension capacity of the tensilereinforcement is smallerthan the combined compression capacity of theconcrete and the compression steel (under-reinforced at tensile face). When

the reinforced concrete element is subject to increasing bending moment, thetension steel yields while the concrete does not reach its ultimate failurecondition. As the tension steel yields and stretches, an "under-reinforced"concrete also yields in a ductile manner, exhibiting a large deformation andwarning before its ultimate failure. In this case the yield stress of the steelgoverns the design.

An over-reinforced beam is one in which the tension capacity of the tensionsteel is greaterthan the combined compression capacity of the concrete andthe compression steel (over-reinforced at tensile face). So the "over-reinforcedconcrete" beam fails by crushing of the compressive-zone concrete and beforethe tension zone steel yields, which does not provide any warning beforefailure as the failure is instantaneous.

Abalanced-reinforced beam is one in which both the compressive and tensilezones reach yielding at the same imposed load on the beam, and the concretewill crush and the tensile steel will yield at the same time. This designcriterion is however as risky as over-reinforced concrete, because failure issudden as the concrete crushes at the same time of the tensile steel yields,

which gives a very little warning of distress in tension failure.[4]

Steel-reinforced concrete moment-carrying elements should normally bedesigned to be under-reinforced so that users of the structure will receivewarning of impending collapse.

The characteristic strength is the strength of a material where less than 5%of the specimen shows lower strength.

The design strength or nominal strength is the strength of a material,including a material-safety factor. The value of the safety factor generallyranges from 0.75 to 0.85 inAllowable Stress Design.

The ultimate limit state is the theoretical failure point with a certainprobability. It is stated under factored loads and factored resistances.

[edit] Prestressed concrete

Main article: Prestressed concrete


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Prestressed concrete is a technique that greatly increases loadbearingstrength of concrete beams. The reinforcing steel in the bottom part of thebeam, which will be subjected to tensile forces when in service, is placed intension prior to the concrete being poured around it. Once the concrete hashardened, the tension on the reinforcing steel is released, placing a built-incompressive force on the concrete. When loads are applied, the reinforcing

steel takes on more stress and the compressive force in the concrete isreduced, but does not become a tensile force. Since the concrete is always

under compression, it is less subject to cracking and failure.[5]

[edit] Common failure modes of steel reinforcedconcrete

Reinforced concrete can fail due to inadequate strength, leading to mechanicalfailure, or due to a reduction in its durability. Corrosion and freeze/thaw cycles

may damage poorly designed or constructed reinforced concrete. When rebarcorrodes, the oxidation products (rust) expand and tends to flake, cracking theconcrete and unbonding the rebar from the concrete. Typical mechanismsleading to durability problems are discussed below.

[edit] Mechanical failure

Cracking of the concrete section can not be prevented; however, the size andlocation of the cracks can be limited and controlled by reinforcement,placement of control joints, the curing methodology and the mix design of the

concrete. Cracking defects can allow moisture to penetrate and corrode thereinforcement. This is a serviceability failure in limit state design. Cracking isnormally the result of an inadequate quantity of rebar, or rebar spaced at toogreat a distance. The concrete then cracks either under excess loading, or dueto internal effects such as early thermal shrinkage when it cures.

Ultimate failure leading to collapse can be caused by crushing of the concrete,when compressive stresses exceed its strength; byyielding or failure of therebar, when bending or shear stresses exceed the strength of thereinforcement; or by bond failure between the concrete and the rebar.

[edit] Carbonation

Concrete wall cracking assteel reinforcing corrodes


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and swells. Rust has alower density than metal,so it expands as it forms,cracking the decorativecladding off the wall, aswell as damaging the

structural concrete. Thebreakage of material fromthe surface is calledspalling.

Detailed view of spalling.The apparently thin layerof concrete between thesteel and the surface

suggests, or similarproblems of corrosion fromexternal exposureMain article: carbonatation

Carbonation, or neutralisation, is a chemical reaction between carbon dioxidein the air with calcium hydroxide and hydrated calcium silicate in theconcrete.

When designing a concrete structure, it is normal to state the concrete coverfor the rebar (the depth within the object that the rebar will be). The minimum

concrete cover is normally regulated by design or building codes. If thereinforcement is too close to the surface, early failure due to corrosion mayoccur. The concrete cover depth can be measured with a cover meter.However, carbonated concrete only becomes a durability problem when thereis also sufficient moisture and oxygen to cause electro-potential corrosion ofthe reinforcing steel.

One method of testing a structure for carbonation is to drill a fresh hole in thesurface and then treat the cut surface with phenolphthalein indicator solution.This solution will turn [pink] when in contact with alkaline concrete, making it

possible to see the depth of carbonation. An existing hole is no good becausethe exposed surface will already be carbonated.

[edit] Chlorides

Chlorides, including sodium chloride, can promote the corrosion of embeddedsteelrebar if present in sufficienty high concentration. Chloride anions induce


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both localized corrosion (pitting corrosion) and generalized corrosion of steelreinforcements. For this reason, one should only use fresh raw water or potablewater for mixing concrete, ensure that the coarse and fine aggregates do notcontain chlorides, and not use admixtures that contain chlorides.

Rebar for foundations andwalls of sewage pumpstation.

The Paulins Kill Viaduct,Hainesburg, New Jersey,is 115 feet (35 m) tall and1,100 feet (335 m) long,

and was heralded as thelargest reinforcedconcrete structure in theworld when it wascompleted in 1910 as partof the Lackawanna Cut-Offrail line project. TheLackawanna Railroad wasa pioneer in the use ofreinforced concrete.

It was once common for calcium chloride to be used as an admixture topromote rapid set-up of the concrete. It was also mistakenly believed that itwould prevent freezing. However, this practice has fallen into disfavor once thedeleterious effects of chlorides became known. It should be avoided when everpossible.

The use of de-icing salts on roadways, used to reduce the freezing point ofwater, is probably one of the primary causes of premature failure of reinforcedor prestressed concrete bridge decks, roadways, and parking garages. The useofepoxy-coated reinforcing bars and the application ofcathodic protection has

mitigated this problem to some extent. Also FRP rebars are known to be lesssusceptible to chlorides. Properly designed concrete mixtures that have beenallowed to cure properly are effectively impervious to the effects of deicers.

Another important source of chloride ions is from sea water. Sea watercontains by weight approximately 3.5 wt.% salts. These salts include sodiumchloride, magnesium sulfate, calcium sulfate, and bicarbonates. In water these


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salts dissociate in free ions (Na+, Mg2+, Cl-, SO42-, HCO3

-) and migrate withthe water into the capillaries of the concrete. Chloride ions are particularlyaggressive for the corrosion of the carbon steel reinforcement bars and makeup about 50% of these ions.

In the 1960s and 1970s it was also relatively common for Magnesite, a chloride

rich carbonate mineral, to be used as a floor-topping material. This was doneprincipally as a levelling and sound attenuating layer. However it is nowknown that when these materials came into contact with moisture it produceda weak solution ofhydrochloric acid due to the presence ofchlorides in themagnesite. Over a period of time (typically decades) the solution causedcorrosion of the embedded steelrebars. This was most commonly found in wetareas or areas repeatedly exposed to moisture.

[edit] Alkali silica reaction

Main article:Alkali Silica Reaction

This a reaction ofamorphoussilica (chalcedony, chert, siliceouslimestone)

sometimes present in the aggregates with the hydroxyl ions (OH-) from thecement pore solution. Poorly crystallized silica (SiO2) dissolves and dissociatesat high pH (12.5 - 13.5) in alkaline water. The soluble dissociated silicic acidreacts in the porewater with the calcium hydroxide (portlandite) present in thecement paste to form an expansive calcium silicate hydrate (CSH). The alkalisilica reaction (ASR), causes localised swelling responsible oftensile stress andcracking. The conditions required for alkali silica reaction are threefold: (1)

aggregate containing an alkali-reactive constituent (amorphous silica), (2)sufficient availability of hydroxyl ions (OH-), and (3) sufficient moisture, above

75 % relative humidity (RH) within the concrete.[6][7] This phenomenon issometimes popularly referred to as "concrete cancer". This reaction occursindependently of the presence of rebars: massive concrete structures such asdams can be affected.

[edit] Conversion of high alumina cement

Resistant to weak acids and especially sulfates, this cement cures quickly andreaches very high durability and strength. It was greatly used after World WarII for making precast concrete objects. However, it can lose strength with heator time (conversion), especially when not properly cured. With the collapse ofthree roofs made of prestressed concrete beams using high alumina cement,this cement was banned in the UKin 1976. Subsequent inquiries into thematter showed that the beams were improperly manufactured, but the ban


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remained.[8]

[edit] Sulphates

Sulfates (SO4) in the soil or in groundwater, in sufficient concentration, canreact with the Portland cement in concrete causing the formation of expansiveproducts, e.g. ettringite or thaumasite, which can lead to early failure of thestructure. The most typical attack of this type is on concrete slabs andfoundation walls at grade where the sulfate ion, via alternate wetting anddrying, can increase in concentration. As the concentration increases, theattack on the Portland cement can begin. For buried structures such as pipe,this type of attack is much rarer especially in the Eastern half of the UnitedStates. The sulfate ion concentration increases much slower in the soil massand is especially dependent upon the initial amount of sulfates in the nativesoil. The chemical analysis of soil borings should be done during the designphase of any project involving concrete in contact with the native soil to check

for the presence of sulfates. If the concentrations are found to be aggressive,various protective coatings can be used. Also, in the US ASTM C150 Type 5Portland cement can be used in the mix. This type of cement is designed to beparticularly resistant to a sulfate attack.

[edit] Steel plate construction

Main article: Steel plate construction

In steel plate construction, stringers join parallel steel plates. The plate

assemblies are fabricated off site, and welded together on-site to form steelwalls connected by stringers. The walls become the form into which concrete ispoured. Steel plate construction speeds reinforced concrete construction bycutting out the time consuming on-site manual steps of tying rebar andbuilding forms. The method has excellent strength because the steel is on theoutside, where tensile forces are often greatest.

[edit] Fiber-reinforced concrete

Main article: Fiber reinforced concreteFiber reinforcement is mainly used in shotcrete, but can also be used in normalconcrete. Fiber-reinforced normal concrete is mostly used for on-ground floorsand pavements, but can be considered for a wide range of construction parts(beams, pillars, foundations, etc.), either alone or with hand-tied rebars.

Concrete reinforced with fibers (which are usually steel, glass, or plastic


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fibers) is less expensive than hand-tied rebar, while still increasing the tensilestrength many times. Shape, dimension, and length of fiber are important. Athin and short fiber, for example short, hair-shaped glass fiber, will only beeffective the first hours after pouring the concrete (reduces cracking while theconcrete is stiffening) but will not increase the concrete tensile strength. Anormal-size fiber for European shotcrete (1 mm diameter, 45 mm lengthsteel

or plastic) will increase the concrete's tensile strength.

Steel is the strongest commonly-available fiber, and comes in different lengths(30 to 80 mm in Europe) and shapes (end-hooks). Steel fibers can only be usedon surfaces that can tolerate or avoid corrosion and rust stains. In some cases,a steel-fiber surface is faced with other materials.

Glass fiber is inexpensive and corrosion-proof, but not as ductile as steel.Recently, spun basalt fiber, long available in Eastern Europe, has becomeavailable in the U.S. and Western Europe. Basalt fibre is stronger and lessexpensive than glass, but historically has not resisted the alkaline environmentofportland cement well enough to be used as direct reinforcement. Newmaterials use plastic binders to isolate the basalt fiber from the cement.

The premium fibers are graphite-reinforced plastic fibers, which are nearly asstrong as steel, lighter-weight, and corrosion-proof. Some experiments havehad promising early results with carbon nanotubes, but the material is still fartoo expensive for any building.

[edit] Non-steel reinforcement

There is considerable overlap between the subjects of non-steel reinforcementand fiber-reinforcment of concrete. The introduction of non-steel reinforcementof concrete is relatively recent; it takes two major forms: non-metallic rebarrods, and non-steel (usually also non-metallic) fibres incorporated into thecement matrix. For example there is increasing interest in glass fiberreinforced concrete (GFRC) and in various applications of polymer fibresincorporated into concrete. Although currently there is not much suggestionthat such materials will in general replace metal rebar, some of them havemajor advantages in specific applications, and there also are new applicationsin which metal rebar simply is not an option. However, the design and

application of non-steel reinforcing is fraught with challenges; for one thing,concrete is a highly alkaline environment, in which many materials, includingmost kinds of glass, have a poor service life. Also, the behaviour of suchreinforcing materials differ from the behaviour of metals, for instance in terms

of shear strength, creep and elasticity.[9][10]

Fibre-Reinforced Polymer (FRP) (Fibre-reinforced plastic or FRP) and Glass-


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reinforced plastic (GRP) consist of fibres ofpolymer, glass, carbon, aramid orother polymers or high-strength fibres set in a resin matrix to form a rebar rodor grid or fibres. These rebars are installed in much the same manner as steel.The cost is higher but, suitably applied, the structures have advantages, inparticular a dramatic reduction in problems related to corrosion, either byintrinsic concrete alkalinity or by external corrosive fluids that might

penetrate the concrete. These structures can be significantly lighter andusually have a longer service life. The cost of these materials has droppeddramatically since their widespread adoption in the aerospace industry and bythe military.

In particular FRP rods are useful for structures where the presence of steelwould not be acceptable. For example, MRI machines have huge magnets, andaccordingly require non-magnetic buildings. Again, toll booths that read radiotags need reinforced concrete that is transparent to radio waves. Also, wherethe design life of the concrete structure is more important than its initial costs,

non-steel reinforcing often has its advantages where corrosion of reinforcingsteel is a major cause of failure. In such situations corrosion-proof reinforcingcan extend a structure's life substantially, for example in the intertidal zone.FRP rods may also be useful in situations where it is likely that the concretestructure may be compromised in future years, for example the edges ofbalconies when balustrades are replaced and bathroom floors in multi-storyconstruction where the service life of the floor structure is likely to be manytimes the service life of the waterproofing building membrane.

Plastic reinforcement often is stronger, or at least has a better strength toweight ratio than reinforcing steels. Also, because it resists corrosion, it does

not need a protective concrete cover as thick as steel reinforcement does(typically 30 to 50 mm or more). FRP-reinforced structures therefore can belighter and last longer. Accordingly, for some applications the whole-life costwill be price-competitive with steel-reinforced concrete.

The material properties of FRP or GRP bars differ markedly from steel, so thereare differences in the design considerations. FRP or GRP bars have relativelyhigher tensile strength but lower stiffness, so that Deflections are likely to behigher than for equivalent steel-reinforced units. Structures with internal FRPreinforcement typically have an elastic deformability comparable to the plastic

deformability (ductility) of steel reinforced structures. Failure in either case ismore likely to occur by compression of the concrete than by rupture of thereinforcement. Deflection is always a major design consideration for reinforcedconcrete. Deflection limits are set to ensure that crack widths in steel-reinforced concrete are controlled to prevent water, air or other aggressivesubstances reaching the steel and causing corrosion. For FRP-reinforcedconcrete, aesthetics and possibly water-tightness will be the limiting criteria


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for crack width control. FRP rods also have relatively lower compressivestrengths than steel rebar, and accordingly require different designapproaches for reinforced concrete columns.

One drawback to the use of FRP reinforcement is the limited fire resistance.Where fire safety is a consideration, structures employing FRP have to

maintain their strength and the anchoring of the forces at temperatures to beexpected in the event of fire. For purposes offireproofing an adequatethickness of cement concrete cover or protective cladding is necessary. The

disadvantages are not on the side of the FRP however, addition of 1 kg/m3 ofpolypropylene fibers to concrete has been shown to reduce spalling during a

simulated fire.[11] (The improvement is thought to be due to the formation ofpathways out of the bulk of the concrete, allowing steam pressure to

dissipate.[11])

Another problem is the effectiveness of shear reinforcement. FRP rebar

stirrups formed by bending before hardening generally perform relativelypoorly in comparison to steel stirrups or to structures with straight fibres.When strained, the zone between the straight and curved regions are subjectto strong bending, shear, and longitudinal stresses. Special design techniquesare necessary to deal with such problems.

There is growing interest in application of external reinforcement of existingstructures with advanced materials such as carbon fibre, that can impartexceptional strength.

[edit] See also

FerrocementCover MeterConcrete coverFalseworkFormworkFranois CoignetTypes of concrete

[edit] References

^Emerging Corrosion Control Technologies for Repair and Rehabilitationof Concrete Structures

1.

^article "Concrete Inhomogeneity of Vertical Cast-In-Situ Elements InFrame-Type Buildings".

2.


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^ "Effect of zinc phosphate chemical conversion coating on corrosionbehaviour of mild steel in alkaline medium: protection of rebars inreinforced concrete" Sci. Technol. Adv. Mater. 9 (2008) 045009 (freedownload)

3.

^ Nilson, Darwin , Dolan.Design of Concrete Structures. theMacGraw-Hill Education, 2003. p. 80-90.

4.

^http://www.ferrericon.com/Whatis.html5.^"h2g2 - Concrete Cancer". BBC. http://www.bbc.co.uk/dna/h2g2/A4014172. Retrieved 2009-10-14.

6.

^[1]7.^"HAC". Web.archive.org. Archived from the original on 2005-09-11.http://web.archive.org/web/20050911210803/http://www.quest-tech.co.uk/hac.htm. Retrieved 2009-10-14.

8.

^ BS EN 1169:1999 Precast concrete products. General rules for factoryproduction control of glass-fibre reinforced cement. British StandardsInstitute: http://shop.bsigroup.com/ISBN 0-580-32052-9

9.

^ BS EN 1170-5:1998 Precast concrete products. Test method forglass-fibre reinforced cement. http://shop.bsigroup.com/ISBN0-580-29202-9

10.

^ ab Arthur W. Darby (2003), 57. The Airside Road Tunnel, HeathrowAirport, England, "Unknown title", www.tunnels.mottmac.com: p. 645,http://www.tunnels.mottmac.com/files/project/3372/Airside_Road_Tunnel.pdf

11.

[edit] Further reading

Threlfall A., et al.Reynolds's Reinforced Concrete Designer's Handbook 11th ed.ISBN 978-0-419-25830-8.Newby F.,Early Reinforced Concrete, Ashgate Variorum, 2001, ISBN978-0-86078-760-0.Kim, S., Surek,J and J. Baker-Jarvis. "Electromagnetic Metrology onConcrete and Corrosion."Journal of Research of the National Institute ofStandards and Technology ), Vol. 116, No. 3 (May-June 2011): 655-669.

[edit] External links

Short film on the early reinforced concrete buildings that Tecton designedwith Ove Arup for Dudley Zoo in the 1930sConcrete Research: http://www.concreteresearch.orgReinforced Concrete Spructures Video Lectures By Prof. N.Dhang,Department of Civil Engineering, IIT KharagpurTimeline of concrete


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