Reinforced concrete at Sainte Jeanne d'Arc Church (Nice, France): architect Jacques Dror, 1926–1933

Reinforced concrete is concrete in which reinforcement bars ("rebars") or fibers have been incorporated to strengthen a material that would otherwise be brittle. Sainte Jeanne d'Arc is a Catholic church located in Nice, France noticeable for its original architecture Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag A rebar, or reinforcing bar, is a common Steel bar and is commonly used in Reinforced concrete and reinforced Masonry structures In industrialised countries, nearly all concrete used in construction is reinforced concrete.

History

The use of reinforced concrete is a relatively recent invention, usually attributed to Joseph-Louis Lambot in 1848. Joseph-Louis Lambot (born May 22 1814 in Montfort sur Argens died August 2 1887 in Brignoles is the inventor of ferro-cement, which led to the development of what is now The year 1848 in architecture involved some significant events Joseph Monier, a French gardener, patented a design for reinforced garden tubs in 1867, and later patented reinforced concrete beams and posts for railway and road guardrails. Joseph Monier ( November 8, 1823, Saint-Quentin-la-Poterie, France &mdash March 13, 1906, Paris) was a French The year 1867 in architecture involved some significant events The first application of reinforced concrete as a material for the construction of buildings took place in 1864 when William Boutland Wilkinson built a house in Newcastle-Upon-Tyne, UK. ^[1] The patent for this building material was obtained as early as 1854. ^[2]

Early reinforced concrete remained a patented rather than generic product, with different firms developing competing systems. The German company Wayss & Freitag was formed in 1875, with A. The year 1875 in architecture involved some significant events G. Wayss publishing a book on reinforced concrete in 1887. The year 1887 in architecture involved some significant events Their major competitor in Europe was the firm of Francois Hennebique, set up in 1892. François Hennebique ( April 26, 1842 &ndash 7 March, 1921) was a French Engineer and self-educated builder who patented The year 1892 in architecture involved some significant events Hennebique completed over 7,000 structures in reinforced concrete within his firm's first ten years. ^[3]

A reinforced concrete system was patented in the United States by Thaddeus Hyatt in 1878. The year 1878 in architecture involved some significant events The first reinforced concrete building constructed in the United States was the Pacific Coast Borax Company's refinery in Alameda, California, built in 1893. The Pacific Coast Borax Company (PCB was a United States Mining company founded in 1890 by the American Borax magnate Francis Marion Smith Alameda is a city in Alameda County, California, United States. The year 1893 in architecture involved some significant events

The major developments of reinforced concrete have taken place since the year 1900; and from the late 20th century, engineers have developed sufficient confidence in a new method of reinforcing concrete, called prestressed concrete, to make routine use of it. Prestressed concrete is a method for overcoming the Concrete 's natural weakness in tension.

Use in construction

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. A wall is a usually solid structure that defines and sometimes protects an area A column in Structural engineering is a vertical structural element that transmits through compression, the weight of the structure above to other structural A foundation is a Structure that transfers loads to the earth Framing, in construction known as light frame construction, is a building technique based around structural members usually called studs, which provide a stable

Reinforced concrete can be classified as precast concrete and cast in-situ concrete. Precast concrete is a form of construction where concrete is cast in a reusable mold or "form" which is then cured in a controlled environment transported to the construction Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag

Much of the focus on reinforcing concrete is placed on floor systems. A floor is the walking surface of a room or vehicle Floors vary from simple dirt in a cave to many-layered surfaces using modern technology Designing and implementing the most efficient floor system is key to creating optimal building structures. Small changes in the design of a floor system can have significant impact on material costs, construction schedule, ultimate strength, operating costs, occupancy levels and end use of a building.

Behaviour of reinforced concrete

Materials

Tied rebar

Reinforced concrete street light pole. A rebar, or reinforcing bar, is a common Steel bar and is commonly used in Reinforced concrete and reinforced Masonry structures Concrete poles are less expensive than traditional steel or aluminium poles and may outlast them.

Concrete is a mixture of cement (usually Portland cement) and stone aggregate. Portland cement is the most common type of Cement in general usage in many parts of the world as it is a basic ingredient of Concrete, mortar, Stucco Construction aggregate, or simply " aggregate " is a broad category of coarse particulate Material used in Construction, including When mixed with a small amount of water, the cement hydrates to form a microscopic opaque crystal lattice structure encapsulating and locking the aggregate into its rigid structure. Hydrate is a term used in Inorganic chemistry and Organic chemistry to indicate that a substance contains Water. Typical concrete mixes have high resistance to compressive stresses (about 4,000 psi (27. Physical compression is the result of the subjection of a material to Compressive stress, resulting in reduction of Volume. Stress is a measure of the average amount of Force exerted per unit Area. 5 MPa)); however, any appreciable tension (e. In Physics String Tension is the magnitude of the pulling force exerted by a string cable chain or similar object on another object g. due to bending) will break the microscopic rigid lattice resulting in cracking and separation of the concrete. This article is about structural behavior For other meanings see Bending (disambiguation. For this reason, typical non-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 compression but also bending, and other direct tensile actions. Steel is an Alloy consisting mostly of Iron, with a Carbon content between 0 A reinforced concrete section where the concrete resists the compression and steel resists the tension can be made into almost any shape and size for the construction industry.

Depending on the type of concrete mix and steel employed, reinforced concrete structures can support 300 to 500 times their combined weight and behave, according to general mechanics, as a single structural entity. Although concrete and steel would appear to have a weight disadvantage, this support ratio is competitive with student balsa-wood bridges.

Key characteristics

Three physical characteristics give reinforced concrete its special properties. First, the coefficient of thermal expansion of concrete is similar to that of steel, eliminating internal stresses due to differences in thermal expansion or contraction. When the Temperature of a substance changes the energy that is stored in the Intermolecular bonds between atoms changes In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature Second, when the cement paste within the concrete hardens this conforms to the surface details of the steel, permitting any stress to be transmitted efficiently between the different materials. Usually steel bars are roughened or corrugated to further improve the bond or cohesion between the concrete and steel. A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic Third, the alkaline chemical environment provided by calcium carbonate (lime) causes a passivating film to form on the surface of the steel, making it much more resistant to corrosion than it would be in neutral or acidic conditions. pH is the measure of the acidity or alkalinity of a Solution. Calcium carbonate is a Chemical compound with the Chemical formula Ca[[Carbon C]] O 3 Limestone is a Sedimentary rock composed largely of the Mineral Calcite ( Calcium carbonate: CaCO3 Passivation is the process of making a material "passive" in relation to another material prior to using the materials together Corrosion means the breaking down of essential properties in a material due to Chemical reactions with its surroundings

The reinforcing bars are generally sufficiently well-bonded to the concrete to resist most tension forces. However, where this is not the case, anchorage of the steel can be increased by bending the steel, for example into a 90 degree bend or 180 degree hook.

In some structural members where a small cross-section is desired, steel may be used to carry some of the compressive load as well as tensile load. This occurs, for example, in columns. In general, beams and slabs have reinforcing steel on all faces, whether or not they are in tension, as this helps to tie the concrete together and prevents cracking from other causes, such as the early thermal shrinkage which occurs as the concrete cures. In the case of continuous beams where the tensile stress alternates between top and bottom of the member, multiple runs (layers) of steel may be used or the steel may be bent into a zig-zag shape within the beam.

The relative cross-sectional area of steel required for typical reinforced concrete is usually quite small and varies from 1% for most beams and slabs to 6% for some columns. Area is a Quantity expressing the two- Dimensional size of a defined part of a Surface, typically a region bounded by a closed Curve. Reinforcing bars are normally round in cross-section and vary in diameter (see rebar for more information). In the United States, rebar comes in two grades of carbon content, Grade 60 and Grade 40, which typically sell for the same price. Grade 60 has a higher carbon content and, therefore, a higher tensile strength, but its stiffness can make it difficult to bend and cut. Galvanised, epoxy-coated, and stainless steel rebar are also available for use in corrosive environments. In Chemistry, epoxy or polyepoxide is a Thermosetting Epoxide Polymer that cures (polymerizes and crosslinks when mixed with a In Metallurgy, stainless steel is defined as a Steel Alloy with a minimum of 11

Reinforced concrete structures sometimes have provisions such as ventilated hollow cores to control their moisture & humidity.

Anti-corrosion measures

In wet and cold climates, reinforced concrete for roads, bridges, parking structures and other structures that may be exposed to deicing salt may benefit from use of epoxy-coated, hot dip galvanised or stainless steel rebar, although good design and a well-chosen cement mix may provide sufficient protection for many applications. De-icing is the process of removing Ice from a Surface. Anti-icing is the process of Preventing ice from forming on a surface Epoxy coated rebar can easily be identified by the light green colour of its epoxy coating. Hot dip galvanized rebar may be bright or dull grey depending on length of exposure, and stainless rebar exhibits a typical white metallic sheen that is readily distinguishable from carbon steel reinforcing bar. Reference ASTM standard specifications A767 Standard Specification for Hot Dip Galvanised Reinforcing Bars, A775 Standard Specification for Epoxy Coated Steel Reinforcing Bars and A955 Standard Specification for Deformed and Plain Stainless Bars for Concrete Reinforcment

Penetrating sealants typically must be applied some time after curing. Sealants include paint, plastic foams, films and aluminum foil, felts or fabric mats sealed with tar, and layers of bentonite clay, sometimes used to seal roadbeds. WikipediaManual of Style#National varieties of English --> Aluminium foil (known Bentonite is an absorbent Aluminium phyllosilicate generally impure Clay consisting mostly of Montmorillonite.

Common failure modes of steel reinforced concrete

Reinforced concrete can fail due to inadequate strength, leading to mechanical failure, or due to a reduction in its durability. Corrosion and freeze/thaw cycles may damage poorly designed or constructed reinforced concrete. When rebar corrodes, the oxidation products (rust) expand and tends to flake, cracking the concrete and unbonding the rebar from the concrete. Rust is a general term for a series of Iron oxides, usually red oxides formed by the reaction of Iron with Oxygen in the presence of water or air Typical mechanisms leading to durability problems are discussed below.

Mechanical failure

Reinforced concrete can be considered to fail when significant cracks occur. Cracking of the concrete section can not be prevented however the size of the cracks can be limited and controlled by reinforcemnet. Cracking defects can allow moisture to penetrate and corrode the reinforcement. This is a serviceability failure in limit state design. Limit state design (LSD refers to a design methodology used in Structural engineering. Limit state design (LSD refers to a design methodology used in Structural engineering. Cracking is normally the result of an inadequate quantity of rebar, or rebar spaced at too great a distance. The concrete then cracks either under excess loading, or due to internal effects such as early thermal shrinkage when it cures.

Ultimate failure leading to collapse can be caused by crushing of the concrete matrix, when stresses exceed its strength; by yielding of the rebar; or by bond failure between the concrete and the rebar. The yield strength or yield point of a Material is defined in Engineering and Materials science as the stress at which a material

Carbonatation / Carbonation

Rebar for foundations and walls of sewage pump station.

The water in the pores of the cement is normally alkaline. In Chemistry, an alkali (from Arabic: Al-Qaly القلي القالي) is a basic, ionic salt of an Alkali metal This alkaline environment is one in which the steel is passive and does not corrode. According to the pourbaix diagram for iron, the metal is passive when pH is above 9. In Chemistry, a Pourbaix diagram, also known as a potential/pH diagram, maps out possible stable ( equilibrium) phases of an aqueous electrochemical system 5. ^[4] The carbon dioxide from the air reacts with the alkali in the cement and makes the pore water more acidic, thus lowering the pH. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five In Chemistry, an alkali (from Arabic: Al-Qaly القلي القالي) is a basic, ionic salt of an Alkali metal Carbon dioxide will start to carbonate the cement in the concrete from the moment the object is made. This carbonatation process (in Britain, called carbonation) will start at the surface, then slowly move deeper and deeper into the concrete. Carbonatation is a chemical reaction where Calcium hydroxide reacts with Carbon dioxide and forms insoluble Calcium carbonate: Ca(OH2 If the object is cracked, the carbon dioxide of the air will be better able to penetrate into the concrete. When designing a concrete structure, it is normal to state the concrete cover for the rebar (the depth within the object that the rebar will be). Concrete cover is the region between the exposed Concrete surface and the nearest surface of the reinforcing bar, in Reinforced concrete members The minimum concrete cover is normally regulated by design or building codes. A building code, or building control, is a set of rules that specify the minimum acceptable level of safety for constructed objects such as Buildings and Nonbuilding If the reinforcement is too close to the surface, early failure due to corrosion may occur.

One method of testing a structure for carbonatation is to drill a fresh hole in the surface and then treat the surface with phenolphthalein. A drill (from Dutch Drillen) is Phenolphthalein is a Chemical compound with the formula C 20 H 14 O 4 (often written as " HIn This will turn pink when in contact with alkaline cement, making it possible to see the depth of carbonatation. Pink is a pale Red Color that was first recorded in the 17th century to describe the pale red Flowers of pinks, Flowering plants An existing hole is no good because the exposed surface will already be carbonated.

Chlorides

The Paulins Kill Viaduct, Hainesburg, New Jersey, is 115 feet (35 m) tall and 1,100 feet (335 m) long, and was heralded as the largest reinforced concrete structure in the world when it was completed in 1910 as part of the Lackawanna Cut-Off rail line project. The Paulinskill Viaduct, also known as the Hainesburg Viaduct, is a railroad bridge which crosses the Paulins Kill in Knowlton Township, New Jersey The Lackawanna Cut-Off was a high-speed double-track railway line in the USA which was constructed by the Delaware Lackawanna and Western Railroad between The Lackawanna Railroad was a pioneer in the use of reinforced concrete

Chlorides, including sodium chloride, promote the corrosion of steel rebar. The Delaware Lackawanna and Western Railroad Company ( DL&W or Lackawanna) was a Railroad connecting Pennsylvania 's Lackawanna Valley The chloride Ion is formed when the element Chlorine picks up one Electron to form an Anion (negatively-charged ion Cl&minus For sodium chloride in the diet see Salt. Sodium chloride, also known as common salt, table salt, or Halite, is a For this reason, in mixing concrete only water, cement and aggregates with a low chloride content may be used, and the use of salt for deicing concrete pavements is avoided where possible.

Alkali silica reaction

For Full Article, See: Alkali Silica Reaction

This is found when the cement is too alkaline, due to a reaction of the silica in the aggregates with the alkali. Alkali-Silica Reaction (ASR is a reaction between reactive Silica (in the Concrete aggregates and an Alkali (usually present in the Cement) The Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide The silica (SiO₂) reacts with the alkali to form a silicate in the Alkali silica reaction (ASR), this causes localised swelling which causes cracking. For the Artificial intelligence Androids of the 1990s Science fiction series Space Above and Beyond, see Silicate (AI The conditions for alkali silica reaction are: (1) aggregate containing an alkali reactive constituent, (2) sufficiently high alkalinity, and (3) sufficient moisture, above 75%RH within the concrete. ^[5][6] This phenomenon has been popularly referred to as "concrete cancer". A euphemistic name for a failure mode of Concrete. If the cement component is too alkaline it reacts with atmospheric Carbon dioxide, and the structure will begin to deteriorate

Conversion of high alumina cement

Resistant to weak acids and especially sulfates, this cement cures quickly and reaches very high durability and strength. It was greatly used after World War II for making precast concrete objects. World War II, or the Second World War, (often abbreviated WWII) was a global military conflict which involved a majority of the world's nations, including However, it can lose strength with heat or time (conversion), especially when not properly cured. With the collapse of three roofs made of prestressed concrete beams using high alumina cement, this cement was banned in the UK in 1976. A ban (derived from Banishment) is generally any Decree that prohibits something The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located Subsequent inquiries into the matter showed that the beams were improperly manufactured, but the ban remained. ^[7]

Sulfates

Sulfates in soil or groundwater can react with Portland cement causing expansive products, e. g ettringite or thaumasite, which can lead to early failure. Ettringite is a hexacalcium aluminate trisulfate Hydrate, (CaO6(Al2O3(SO33 · 32 H2O Thaumasite is a silicate mineral with an unusual composition Ca 3 Si ( C[[oxygen O]]3( SO sub>4(O H

Fiber-reinforced concrete

Main article: Fiber reinforced concrete

Fiber-reinforcement is mainly used in shotcrete, but can also be used in normal concrete. Fiber reinforced concrete (FRC is Concrete containing fibrous material which increases its structural integrity Shotcrete and gunite are two commonly used terms for substances applied via Pressure hoses Shotcrete is mortar or (usually Concrete conveyed Fiber-reinforced normal concrete are mostly used for on-ground floors and pavements, but can be considered for a wide range of construction parts (beams, pilars, foundations etc) either alone or with hand-tied rebars.

Concrete reinforced with fibers (which are usually steel, glass or "plastic" fibers) is less expensive than hand-tied rebar, while still increasing the tensile strength many times. Glass in the common sense refers to a Hard, Brittle, transparent Solid, such as that used for Windows many A fibre-reinforced plastic ( FRP) (also fibre-reinforced polymer) is a Composite material comprising a Polymer matrix reinforced with fibres Shape, dimension and length of fiber is important. A thin and short fiber, for example short hair-shaped glass fiber, will only be effective the first hours after pouring the concrete (reduces cracking while the concrete is stiffening) but will not increase the concrete tensile strength. A normal size fibre for European shotcrete (1 mm diameter, 45 mm length—steel or "plastic") will increase the concrete tensile strength.

Steel is the strongest commonly-available fiber, and come in different lengths (30 to 80 mm in Europe) and shapes (end-hooks). Steel fibres can only be used on 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 become available in the U. Basalt fiber or fibre is a Material made from extremely fine Fibers of Basalt, which is composed of the Minerals Plagioclase Eastern Europe is a general term that refers to the Geopolitical region encompassing the easternmost part of the European continent. S. and Western Europe. Basalt fibre is stronger and less expensive than glass, but historically, has not resisted the alkaline environment of portland cement well enough to be used as direct reinforcement. Portland cement is the most common type of Cement in general usage in many parts of the world as it is a basic ingredient of Concrete, mortar, Stucco New materials use plastic binders to isolate the basalt fiber from the cement.

The premium fibers are graphite reinforced plastic fibers, which are nearly as strong as steel, lighter-weight and corrosion-proof. The Mineral graphite, as with Diamond and Fullerene, is one of the Allotropes of carbon. Some experimeters have had promising early results with carbon nanotubes, but the material is still far too expensive for any building. See also Graphene, Buckypaper Carbon nanotubes (CNTs are Allotropes of carbon with a nanostructure that can have a length-to-diameter

Non-steel reinforcement

Some construction cannot tolerate the use of steel. For example, MRI machines have huge magnets, and require nonmagnetic buildings. Another example are toll-booths that read radio tags, and need reinforced concrete that is transparent to radio. Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light.

In some instances, the lifetime of the concrete structure is more important than its strength. Since corrosion is the main cause of failure of reinforced concrete, a corrosion-proof reinforcement can extend a structure's life substantially.

For these purposes some structures have been constructed using fiber-reinforced plastic rebar, grids or fibers. A fibre-reinforced plastic ( FRP) (also fibre-reinforced polymer) is a Composite material comprising a Polymer matrix reinforced with fibres The "plastic" reinforcement can be as strong as steel. Because it resists corrosion, it does not need a protective concrete cover of 30 to 50 mm or more as steel reinforcement does. This means that FRP-reinforced structures can be lighter, have longer lifetime and for some applications be price-competitive to steel-reinforced concrete.

The main barrier to use of FRP reinforcement is the fact that it is neither ductile nor fire resistant. Structures employing FRP rebars may therefore exhibit a less ductile structural response, and decreased fire resistance.

However, the addition of short monofilament polypropylene fibres to the concrete during mixing may have the beneficial effect of reducing spalling during a fire. Spall are flakes of a material that are broken off a larger solid body and can be produced by a variety of mechanisms including as a result of Projectile impact Corrosion In a severe fire, such as the Channel Tunnel fire, conventionally reinforced concrete can suffer severe spalling leading to failure. This is in part due to the pore water remaining within the concrete boiling explosively; the steam pressure then causes the spalling. The action of fibres within the concrete is due to their ability to melt, forming pathways out through the concrete, allowing the steam pressure to dissipate.

References

1. ^ http://www.newcastle.gov.uk/wwwfileroot/localstudies/factsheets/Factsheet2People.pdf
2. ^ Wilkinson 2
3. ^ Billington, David P. : "The Tower and the Bridge", Princeton University Press, 1983
4. ^ Pourbaix diagram of iron
5. ^ BBC - h2g2 - Concrete Cancer
6. ^ http://www.cementindustry.co.uk/main.asp?page=272
7. ^ http://www.quest-tech.co.uk/hac.htm

See also

• Building construction
• Bridge Disasters
• Construction engineering
• Fiber reinforced concrete
• Formwork
• Precast concrete
• Prestressed concrete
• Structural engineering
• Structural failure
• Tie rod
• Steel fixer
• Composite material