CONCRETE & CEMENTS

Dr. Ir. Sotya Astutiningsih, M.Eng Departemen Teknik Metalurgi & Material Fakultas Teknik Universitas Indonesia

Concrete

is a construction material composed of cement (commonly Portland cement) as well as other cementitious materials such as fly ash and slag cement, aggregate (generally a coarse aggregate such as gravel, limestone, or granite, plus a fine aggregate such as sand), water, and chemical admixtures.

The word concrete comes from the Latin word "concretus", which means "hardened" or "hard".

Hardening of concrete/cements Concrete solidifies and hardens after mixing with

water and placement due to a chemical process known as hydration.

The water reacts with the cement, which bonds the other components together, eventually creating a stone-like material.

Concrete is used to make pavements, architectural structures, foundations, motorways/roads, bridges/overpasses, parking structures, brick/block walls and footings for gates, fences and poles.

Utilization

Concrete is used more than any other man-made material in the world.[1] As of 2006, about 7.5 cubic kilometres of concrete are made each year—more than one cubic metre for every person on Earth.[2] Concrete powers a US $35-billion industry which employs more than two million workers in the United States alone.[citation

needed] More than 55,000 miles (89,000 km) of highways in America are paved with this material. The People's Republic of China currently consumes 40% of the world's cement/concrete production.

The Baths of Caracalla, in 2003

Aqueduct of Segovia

The secret of concrete was lost for 13 centuries until 1756, when the British engineer John Smeaton pioneered the use of hydraulic lime in concrete, using pebbles and powdered brick as aggregate. Portland cement was first used in concrete in the early 1840s. This version of history has been challenged however, as the Canal du Midi was constructed using concrete in 1670.[3]

Environmental issues

Recently, the use of recycled materials as concrete ingredients is gaining popularity because of increasingly stringent environmental legislation. The most conspicuous of these is fly ash, a by-product of coal-fired power plants. This has a significant impact by reducing the amount of quarrying and landfill space required, and, as it acts as a cement replacement, reduces the amount of cement required to produce a solid concrete. As cement production creates massive quantities of carbon dioxide, cement-replacement technology such as this will play an important role in future attempts to cut carbon dioxide emissions.

Concrete additives have been used since Roman and Egyptian times, when it was discovered that adding volcanic ash to the mix allowed it to set under water. Similarly, the Romans knew that adding horse hair made concrete less liable to crack while it hardened, and adding blood made it more frost-resistant[4].

In modern times, researchers have experimented with the addition of other materials to create concrete with improved properties, such as higher strength or electrical conductivity.

Composition There are many types of concrete available, created by varying the proportions of the main ingredients below.

The mix design depends on the type of structure being built, how the concrete will be mixed and delivered, and how it will be placed to form this structure

Cement

Portland cement is the most common type of cement in general usage. It is a basic ingredient of concrete, mortar, and plaster. English engineer Joseph Aspdin patented Portland cement in 1824; it was named because of its similarity in colour to Portland limestone, quarried from the English Isle of Portland and used extensively in London architecture. It consists of a mixture of oxides of calcium, silicon and aluminium. Portland cement and similar materials are made by heating limestone (a source of calcium) with clay, and grinding this product (called clinker) with a source of sulfate (most commonly gypsum). The manufacturing of Portland cement creates about 5 percent of human CO2 emissions.[5]

Water Combining water with a cementitious material

forms a cement paste by the process of hydration. The cement paste glues the aggregate together, fills voids within it, and allows it to flow more easily.

Less water in the cement paste will yield a stronger, more durable concrete; more water will give an easier-flowing concrete with a higher slump.[6]

Impure water used to make concrete can cause problems, when setting, or in causing premature failure of the structure.

Reaction: Cement chemist notation:

C3S + H2O → CSH(gel) + CaOH

Standard notation:

Ca3SiO5 + H2O → (CaO)•(SiO2)•(H2O)(gel) + Ca(OH)2

Balanced:

2Ca3SiO5 + 7H2O → 3(CaO)•2(SiO2)•4(H2O)(gel) + 3Ca(OH)2

Aggregates Fine and coarse aggregates make up the bulk of a concrete

mixture. Sand, natural gravel and crushed stone are mainly used for this purpose. Recycled aggregates (from construction, demolition and excavation waste) are increasingly used as partial replacements of natural aggregates, while a number of manufactured aggregates, including air-cooled blast furnace slag and bottom ash are also permitted.

Decorative stones such as quartzite, small river stones or crushed glass are sometimes added to the surface of concrete for a decorative "exposed aggregate" finish, popular among landscape designers.

Reinforcement

Concrete is strong in compression, as the aggregate efficiently carries the compression load. However, it is weak in tension as the cement holding the aggregate in place can crack, allowing the structure to fail. Reinforced concrete solves these problems by adding either metal reinforcing bars, glass fiber, or plastic fiber to carry tensile loads.

Chemical admixtures Chemical admixtures are materials in the form

of powder or fluids that are added to the concrete to give it certain characteristics not obtainable with plain concrete mixes. In normal use, admixture dosages are less than 5% by mass of cement, and are added to the concrete at the time of batching/mixing.[7] The most common types of admixtures [8] are:

Accelerators

Retarders

Air entrainments

Plasticizers

Pigments

Corrosion inhibitors

The most common types of admixtures [8] are:

Accelerators

Ordinary PC will achieves its optimum strength in 28 days

Certain application, especially in repair, requires rapid hardening

speed up the hydration (hardening) of the concrete. Typical materials used are CaCl2 and NaCl.

Disadvantages: induce corrosion to metal reinforcement

Retarders

slow the hydration of concrete, and are used in large or difficult pours where partial setting before the pour is complete is undesirable. A typical retarder is sugar (C6H12O6).

Air entrainments

add and distribute tiny air bubbles in the concrete, which will reduce damage during freeze-thaw cycles thereby increasing the concrete's durability. However, entrained air is a trade-off with strength, as each 1% of air may result in 5% decrease in compressive strength.

Plasticizers

Plasticizers (water-reducing admixtures) increase the workability of plastic or "fresh" concrete, allowing it be placed more easily, with less consolidating effort. Superplasticizers (high-range water-reducing admixtures) are a class of plasticizers which have fewer deleterious effects when used to significantly increase workability. Alternatively, plasticizers can be used to reduce the water content of a concrete (and have been called water reducers due to this application) while maintaining workability. This improves its strength and durability characteristics.

others

Pigments can be used to change the color of concrete, for aesthetics.

Corrosion inhibitors are used to minimize the corrosion of steel and steel bars in concrete. Bonding agents are used to create a bond between old and new concrete. Pumping aids improve pumpability, thicken the paste, and reduce dewatering – the tendency for the water to separate out of the paste

Mineral admixtures and blended cements There are inorganic materials that also have

pozzolanic or latent hydraulic properties. These very fine-grained materials are added to the concrete mix to improve the properties of concrete (mineral admixtures),[7] or as a replacement for Portland cement (blended cements).[9]

Fly ash

: A by product of coal fired electric generating plants, it is used to partially replace Portland cement (by up to 60% by mass). The properties of fly ash depend on the type of coal burnt. In general, silicious fly ash is pozzolanic, while calcareous fly ash has latent hydraulic properties.[10]

Ground granulated blast furnace slag (GGBFS or GGBS): A by product of steel

production, is used to partially replace Portland cement (by up to 80% by mass). It has latent hydraulic properties.[11]

Silica fume

A by-product of the production of silicon and ferrosilicon alloys. Silica fume is similar to fly ash, but has a particle size 100 times smaller. This results in a higher surface to volume ratio and a much faster pozzolanic reaction. Silica fume is used to increase strength and durability of concrete, but generally requires the use of superplasticizers for workability.[12]

High Reactivity Metakaolin (HRM): Metakaolin produces concrete with strength

and durability similar to concrete made with silica fume. While silica fume is usually dark gray or black in color, high reactivity metakaolin is usually bright white in color, making it the preferred choice for architectural concrete where appearance is important.

CEMENTITIOUS MATERIALS FOR CONCRETE

American Concrete Institute (ACI) Committee E-701 Materials for Concrete Construction

Introduction

Cement – hydraulic cement

Portland cement: The most common hydraulic cement used in construction

Hydraulic cement, definition

A cement that sets and hardens by chemical reaction with water and is capable of doing so underwater.

Manufacture of Portland cement Bricklayer Joseph Aspdin of Leeds, England first

made portland cement early in the 19th century by burning powdered limestone and clay in his kitchen stove. By this crude method he laid the foundation for an industry which annually processes literally mountains of limestone, clay, cement rock, and other materials into a powder so fine it will pass through a sieve capable of holding water. Cement is so fine that one pound of cement contains 150 billion grains.

Portland cement, the basic ingredient of concrete, is a closely controlled chemical combination of calcium, silicon, aluminum, iron and small amounts of other ingredients to which gypsum is added in the final grinding process to regulate the setting time of the concrete. Lime and silica make up about 85% of the mass. Common among the materials used in its manufacture are limestone, shells, and chalk or marl combined with shale, clay, slate or blast furnace slag, silica sand, and iron ore.

P

Manufacture of Portland cement Raw materials:

CaCO3 (calcareous materials) from chalk or limestone

Aluminosilicates (argillaceous materials) from clays, some volcanic rocks or ash

Crushing & mixing in ball mils

Heating to ~1500C in rotary kiln

Two Manufacturing Processes

Wet process; the raw mat are ground and mixed with water and the resultant slurry is fed into the kiln

Dry process;The raw mat are fed into the kiln in dry powder form

Virtual cement plant tour: http://www.cement.org/basic/images/flashtour.html

crushing

When rock is the principal raw material, the first step after quarrying in both processes is the primary crushing. Mountains of rock are fed through crushers capable of handling pieces as large as an oil drum. The first crushing reduces the rock to a maximum size of about 6 inches. The rock then goes to secondary crushers or hammer mills for reduction to about 3 inches or smaller.

crushing

When rock is the principal raw material, the first step after quarrying in both processes is the primary crushing. Mountains of rock are fed through crushers capable of handling pieces as large as an oil drum. The first crushing reduces the rock to a maximum size of about 6 inches. The rock then goes to secondary crushers or hammer mills for reduction to about 3 inches or smaller.

Wet process

In the wet process, the raw materials, properly proportioned, are then ground with water, thoroughly mixed and fed into the kiln in the form of a "slurry" (containing enough water to make it fluid). In the dry process, raw materials are ground, mixed, and fed to the kiln in a dry state. In other aspects, the two processes are essentially alike.

rotary kilns

The raw material is heated to about 2,700 degrees F in huge cylindrical steel lined with special firebrick. Kilns are frequently as much as 12 feet in diameter ­ large enough to accommodate an automobile and longer in many instances than the height of a 40-story building. Kilns are mounted with the axis inclined slightly from the horizontal. The finely ground raw material or the slurry is fed into the higher end. At the lower end is a roaring blast of flame, produced by precisely controlled burning of powdered coal, oil or gas under forced draft.

clinker

As the material moves through the kiln, certain elements are driven off in the form of gases. The remaining elements unite to form a new substance with new physical and chemical characteristics. The new substance, called clinker, is formed in pieces about the size of marbles.

Clinker is discharged red-hot from the lower end of the kiln and generally is brought down to handling temperature in various types of coolers. The heated air from the coolers is returned to the kilns, a process that saves fuel and increases burning efficiency.

Phases in Portland cement clinker Tricalcium silicate C3S

Dicalcium silicate C2S

Tricalcium aluminate C3A

Calcium alumino ferrite C4AF

Hydration of cement clinker

Hydration involves many different reactions, often occurring at the same time. As the reactions proceed, the products of the cement hydration process gradually bond together the individual sand and gravel particles, and other components of the concrete, to form a solid mass.

Reaction: Cement chemist notation: C3S + H2O → CSH(gel) + CaOH

Standard notation: Ca3SiO5 + H2O → (CaO)•(SiO2)•(H2O)(gel) + Ca(OH)2

Balanced: 2Ca3SiO5 + 7H2O → 3(CaO)•2(SiO2)•4(H2O)(gel) + 3Ca(OH)2

Types of Portland Cement ASTM C 150

PC consists of mainly C3S + C2S ~75% -- Calcium-silicate based cements

Type I

Type II

Type III

Type IV

Type V

Type I

General purpose, used for most types of constructions; pavements, bridges, reinforced concretes, masonry, water pipes

Type II

Moderate sulfate resistance

For drainage and environmental structures

Moderate heat of hydration; mass concrete, dams, large pies

Type III

High early strength; precast concrete

Faster rate of heat of hydration ; for cold weather; faster strength development

Type IV

Minimum heat of hydration; for massive structures (to minimize thermal crack)

Slow rate of strength development

Other method of controlling temp: Type II + pozzolans or slag, and remove heat with coolants

Type V

High sulfate resistance

Strength development slower compared to Type I

Blended cements ASTM C 595 and C 1157 Portland blast – furnace slag cement (Type IS)

Portland – pozzolan cement (Type II and Type P)

Pozzolan-modified portland cement (Type I (PM)

Slag cement (Type S)

Slag-modified portland (Type I (SM))

CONCRETE PRODUCTION

The processes used vary dramatically, from hand tools to heavy industry, but result in the concrete being placed where it cures into a final form.

Mixing concrete Thorough mixing is essential for the production of uniform, high quality

concrete. Therefore, equipment and methods should be capable of effectively mixing concrete materials containing the largest specified aggregate to produce uniform mixtures of the lowest slump practical for the work. Separate paste mixing has shown that the mixing of cement and water into a paste before combining these materials with aggregates can increase the compressive strength of the resulting concrete.[13] The paste is generally mixed in a high-speed, shear-type mixer at a w/cm (water to cement ratio) of 0.30 to 0.45 by mass. The cement paste premix may include admixtures, e.g. accelerators or retarders, plasticizers, pigments, or fumed silica. The latter is added to fill the gaps between the cement particles. This reduces the particle distance and leads to a higher final compressive strength and a higher water impermeability.[14] The premixed paste is then blended with aggregates and any remaining batch water, and final mixing is completed in conventional concrete mixing equipment.[15]

Mixing concrete

Workability Workability is the ability of a fresh (plastic) concrete mix to

fill the form/mold properly with the desired work (vibration) and without reducing the concrete's quality. Workability depends on water content, aggregate (shape and size distribution), cementitious content and age (level of hydration), and can be modified by adding chemical admixtures. Raising the water content or adding chemical admixtures will increase concrete workability. Excessive water will lead to increased bleeding (surface water) and/or segregation of aggregates (when the cement and aggregates start to separate), with the resulting concrete having reduced quality. The use of an aggregate with an undesirable gradation can result in a very harsh mix design with a very low slump, which cannot be readily made more workable by addition of reasonable amounts of water.

Pouring a concrete floor for a commercial building, (slab-on-grade)

Curing In all but the least critical applications, care

needs to be taken to properly cure concrete, and achieve best strength and hardness. This happens after the concrete has been placed. Cement requires a moist, controlled environment to gain strength and harden fully. The cement paste hardens over time, initially setting and becoming rigid though very weak, and gaining in strength in the days and weeks following. In around 3 weeks, over 90% of the final strength is typically reached though it may continue to strengthen for decades.[17]

Hydration and hardening of concrete during the first three days is critical. Abnormally fast drying and shrinkage due to factors such as evaporation from wind during placement may lead to increased tensile stresses at a time when it has not yet gained significant strength, resulting in greater shrinkage cracking. The early strength of the concrete can be increased by keeping it damp for a longer period during the curing process. Minimizing stress prior to curing minimizes cracking. High early-strength concrete is designed to hydrate faster, often by increased use of cement which increases shrinkage and cracking

During this period concrete needs to be in conditions with a controlled temperature and humid atmosphere. In practice, this is achieved by spraying or ponding the concrete surface with water, thereby protecting concrete mass from ill effects of ambient conditions. The pictures to the right show two of many ways to achieve this, ponding – submerging setting concrete in water, and wrapping in plastic to contain the water in the mix.

Properly curing concrete leads to increased strength and lower permeability, and avoids cracking where the surface dries out prematurely. Care must also be taken to avoid freezing, or overheating due to the exothermic setting of cement (the Hoover Dam used pipes carrying coolant during setting to avoid damaging overheating). Improper curing can cause scaling, reduced strength, poor abrasion resistance and cracking.

Properties Strength Concrete has relatively high compressive strength,

but significantly lower tensile strength. It is fair to assume that a concrete samples tensile strength is about 10%-15% of its compressive strength.[18] As a result, without compensating, concrete would almost always fail from tensile stresses – even when loaded in compression. The practical implication of this is that concrete elements subjected to tensile stresses must be reinforced with materials that are strong in tension.

Reinforced concrete is the most common form of concrete. The reinforcement is often steel, rebar (mesh, spiral, bars and other forms). Structural fibers of various materials are available.

Concrete can also be prestressed (reducing tensile stress) using internal steel cables (tendons), allowing for beams or slabs with a longer span than is practical with reinforced concrete alone. Inspection of concrete structures can be non-destructive if carried out with equipment such as a Schmidt hammer, which is used to estimate concrete strength.

Elasticity The modulus of elasticity of concrete is a

function of the modulus of elasticity of the aggregates and the cement matrix and their relative proportions. The modulus of elasticity of concrete is relatively constant at low stress levels but starts decreasing at higher stress levels as matrix cracking develops. The elastic modulus of the hardened paste may be in the order of 10-30 GPa and aggregates about 45 to 85 GPa. The concrete composite is then in the range of 30 to 50 GPa.

Expansion and shrinkage Concrete has a very low coefficient of thermal expansion.

However, if no provision is made for expansion, very large forces can be created, causing cracks in parts of the structure not capable of withstanding the force or the repeated cycles of expansion and contraction.

As concrete matures it continues to shrink, due to the ongoing reaction taking place in the material, although the rate of shrinkage falls relatively quickly and keeps reducing over time (for all practical purposes concrete is usually considered to not shrink due to hydration any further after 30 years). The relative shrinkage and expansion of concrete and brickwork require careful accommodation when the two forms of construction interface.

Because concrete is continuously shrinking for years after it is initially placed, it is generally accepted that under thermal loading it will never expand to its originally placed volume.

Cracking Concrete cracks due to tensile stress induced by

shrinkage or stresses occurring during setting or use. Various means are used to overcome this. Fiber reinforced concrete uses fine fibers distributed throughout the mix or larger metal or other reinforcement elements to limit the size and extent of cracks. In many large structures joints or concealed saw-cuts are placed in the concrete as it sets to make the inevitable cracks occur where they can be managed and out of sight. Water tanks and highways are examples of structures requiring crack control.

Shrinkage cracking Shrinkage cracks occur when concrete members undergo

restrained volumetric changes (shrinkage) as a result of either drying, autogenous shrinkage or thermal effects. Restraint is provided either externally (i.e. supports, walls, and other boundary conditions) or internally (differential drying shrinkage, reinforcement). Once the tensile strength of the concrete is exceeded, a crack will develop. The number and width of shrinkage cracks that develop are influenced by the amount of shrinkage that occurs, the amount of restraint present and the amount and spacing of reinforcement provided.

Plastic-shrinkage cracks are immediately apparent, visible within 0 to 2 days of placement, while drying-shrinkage cracks develop over time. Autogenous shrinkage also occurs when the concrete is quite young and results from the volume reduction resulting from the chemical reaction of the portland cement.

Tension cracking Concrete members may be put into tension by applied

loads. This is most common in concrete beams where a transversely applied load will put one surface into compression and the opposite surface into tension due to induced bending. The portion of the beam that is in tension may crack. The size and length of cracks is dependent on the magnitude of the bending moment and the design of the reinforcing in the beam at the point under consideration. Reinforced concrete beams are designed to crack in tension rather than in compression. This is achieved by providing reinforcing steel which yields before failure of the concrete in compression occurs and allowing remediation, repair, or if necessary, evacuation of an unsafe area.

Creep Creep is the term used to describe the

permanent movement or deformation of a material in order to relieve stresses within the material. Concrete which is subjected to long-duration forces is prone to creep. Short-duration forces (such as wind or earthquakes) do not cause creep. Creep can sometimes reduce the amount of cracking that occurs in a concrete structure or element, but it also must be controlled. The amount of primary and secondary reinforcing in concrete structures contributes to a reduction in the amount of shrinkage, creep and cracking.

Damage modes Fire

Aggregate expansion

Sea water effects

Bacterial corrosion

Chemical damage

Fire Due to its low thermal conductivity, a layer of concrete is frequently used for fireproofing of steel

structures. However, concrete itself may be damaged by fire.

Up to about 300 °C, the concrete undergoes normal thermal expansion. Above that temperature, shrinkage occurs due to water loss; however, the aggregate continues expanding, which causes internal stresses. Up to about 500 °C, the major structural changes are carbonation and coarsening of pores. At 573 °C, quartz undergoes rapid expansion due to Phase transition, and at 900 °C calcite starts shrinking due to decomposition. At 450-550 °C the cement hydrate decomposes, yielding calcium oxide. Calcium carbonate decomposes at about 600 °C. Rehydration of the calcium oxide on cooling of the structure causes expansion, which can cause damage to material which withstood fire without falling apart. Concrete in buildings that experienced a fire and were left standing for several years shows extensive degree of carbonation.

Concrete exposed to up to 100 °C is normally considered as healthy. The parts of a concrete structure that is exposed to temperatures above approximately 300 °C (dependent of water/cement ratio) will most likely get a pink color. Over approximately 600 °C the concrete will turn light grey, and over approximately 1000 °C it turns yellow-brown.[22] One rule of thumb is to consider all pink colored concrete as damaged that should be removed.

Fire will expose the concrete to gases and liquids that can be harmful to the concrete, among other salts and acids that occur when gasses produced by fire come into contact with water.

Aggregate expansion Various types of aggregate undergo chemical reactions in concrete,

leading to damaging expansive phenomena. The most common are those containing reactive silica, that can react (in the presence of water) with the alkalis in concrete (K2O and Na2O, coming principally from cement). Among the more reactive mineral components of some aggregates are opal, chalcedony, flint and strained quartz. Following the reaction (Alkali Silica Reaction or ASR), an expansive gel forms, that creates extensive cracks and damage on structural members. On the surface of concrete pavements the ASR can cause pop-outs, i.e. the expulsion of small cones (up to 3 cm about in diameter) in correspondence of aggregate particles. When some aggregates containing dolomite are used, a dedolomitization reaction occurs where the magnesium carbonate compound reacts with hydroxyl ions and yields magnesium hydroxide and a carbonate ion. The resulting expansion may cause destruction of the material. Far less common are pop-outs caused by the presence of pyrite, an iron sulfide that generates expansion by forming iron oxide and ettringite. Other reactions and recrystallizations, e.g. hydration of clay minerals in some aggregates, may lead to destructive expansion as well.

Sea water effects Concrete exposed to sea water is susceptible to its corrosive

effects. The effects are more pronounced above the tidal zone than where the concrete is permanently submerged. In the submerged zone, magnesium and hydrogen carbonate ions precipitate a layer of brucite, about 30 micrometers thick, on which a slower deposition of calcium carbonate as aragonite occurs. These layers somewhat protect the concrete from other processes, which include attack by magnesium, chloride and sulfate ions and carbonation. Above the water surface, mechanical damage may occur by erosion by waves themselves or sand and gravel they carry, and by crystallization of salts from water soaking into the concrete pores and then drying up. Pozzolanic cements and cements using more than 60% of slag as aggregate are more resistant to sea water than pure Portland cement.

Bacterial corrosion Bacteria themselves do not have noticeable effect

on concrete. However, anaerobic bacteria (Thiobacillus) in untreated sewage tend to produce hydrogen sulfide, which is then oxidized by aerobic bacteria present in biofilm on the concrete surface above the water level to sulfuric acid which dissolves the carbonates in the cured cement and causes strength loss. Concrete floors lying on ground that contains pyrite are also at risk. Using limestone as the aggregate makes the concrete more resistant to acids, and the sewage may be pretreated by ways increasing pH or oxidizing or precipitating the sulfides in order to inhibit the activity of sulfide utilizing bacteria.

Chemical damage Carbonation

Chlorides

Sulphates

Distillate Water

Carbonation Carbon dioxide from air can react with the calcium hydroxide in

concrete to form calcium carbonate. This process is called carbonation, which is essentially the reversal of the chemical process of calcination of lime taking place in a cement kiln. Carbonation of concrete is a slow and continuous process progressing from the outer surface inward, but slows down with increasing diffusion depth. Carbonation has two effects: it increases mechanical strength of concrete, but it also decreases alkalinity, which is essential for corrosion prevention of the reinforcement steel. Below a pH of 10, the steel's thin layer of surface passivation dissolves and corrosion is promoted. For the latter reason, carbonation is an unwanted process in concrete chemistry. Carbonation can be tested by applying Phenolphthalein solution, a pH indicator, over a fresh fracture surface, which indicates non-carbonated and thus alkaline areas with a violet color.

Chlorides Chlorides, particularly calcium chloride, have

been used to shorten the setting time of concrete.[23] However, calcium chloride and (to a lesser extent) sodium chloride have been shown to leach calcium hydroxide and cause chemical changes in Portland cement, leading to loss of strength,[24] as well as attacking the steel reinforcement present in most concrete.

Sulphates & Distillate Water Sulphates in solution in contact with concrete

can cause chemical changes to the cement, which can cause significant microstructural effects leading to the weakening of the cement binder.

Distillate water can wash out calcium content in concrete, leaving the concrete in brittle condition. Source of distillate water such as steam or hot water.

Types of concrete Regular concrete High-strength concrete

Stamped concrete High-performance

concrete Self-consolidating

concretes

Vacuum concretes

Shotcrete Pervious concrete

Cellular concrete

Cork-cement composites

Roller-compacted concrete

Glass concrete

Asphalt concrete Rapid strength concrete Rubberized concrete

Polymer concrete Geopolymer or green

concrete Limecrete

Refractory Cement

Innovative mixtures

references

^ The Skeptical Environmentalist: Measuring the Real State of the World, by Bjorn Lomborg, p 138. ^ "Minerals commodity summary - cement - 2007". 2007-06-01. http://minerals.usgs.gov/minerals/pubs/commodity/cement/index.html. Retrieved on 2008-01-16. ^ http://www.allacademic.com/meta/p_mla_apa_research_citation/0/2/0/1/2/p20122_index.html ^ http://www.djc.com/special/concrete/10003364.htm ^ Fountain, Henry (March 30, 2009). "Concrete Is Remixed With Environment in Mind". The New York Times. http://www.nytimes.com/2009/03/31/science/earth/31conc.html. Retrieved on 2009-03-30. ^ Missing File ^ a b U.S. Federal Highway Administration. "Admixtures". http://www.fhwa.dot.gov/infrastructure/materialsgrp/admixture.html. Retrieved on 2007-01-25. ^ Cement Admixture Association. "CAA". www.admixtures.org.uk. http://www.admixtures.org.uk/publications.asp. Retrieved on 2008-04-02. ^ Kosmatka, S.H.; Panarese, W.C. (1988). Design and Control of Concrete Mixtures. Skokie, IL, USA: Portland Cement Association. pp. 17, 42, 70, 184. ISBN 0-89312-087-1. ^ U.S. Federal Highway Administration. "Fly Ash". http://www.fhwa.dot.gov/infrastructure/materialsgrp/flyash.htm. Retrieved on 2007-01-24. ^ U.S. Federal Highway Administration. "Ground Granulated Blast-Furnace Slag". http://www.fhwa.dot.gov/infrastructure/materialsgrp/ggbfs.htm. Retrieved on 2007-01-24. ^ U.S. Federal Highway Administration. "Silica Fume". http://www.fhwa.dot.gov/infrastructure/materialsgrp/silica.htm. Retrieved on 2007-01-24. ^ Premixed Cement Paste ̂The use of micro- and nanosilica in concrete ^ Measuring, Mixing, Transporting, and Placing Concrete ̂U.S. patent 5,443,313 - Method for producing construction mixture for concrete ^ "Concrete Testing". http://technology.calumet.purdue.edu/cnt/rbennet/concrete%20lab.htm. Retrieved on 2008-11-10. ̂a b ACI Committee 318 (2008). ACI 318-08: Building Code Requirements for Structural Concrete and Commentary. American Concrete Institute. ISBN 0870312642. ^ David Hambling (April 13, 2007). "Iran's Invulnerable Bunkers?". Wired. http://blog.wired.com/defense/2007/04/irans_superconc.html. Retrieved on 2008-01-29. ^ "Thermal Coefficient of Portland Cement Concrete". Portland Cement Concrete Pavements Research. Federal Highway Administration. http://www.fhwa.dot.gov/pavement/pccp/thermal.cfm. Retrieved on 2008-01-29. ^ Jones, Katrina (1999). "Density of Concrete". The Physics Factbook. http://hypertextbook.com/facts/1999/KatrinaJones.shtml. ^ Norwegian Building Research Institute, publication 24. Fire-damage to buildings. ^ "Accelerating Concrete Set Time". 1999-06-01. http://www.fhwa.dot.gov/infrastructure/materialsgrp/acclerat.htm. Retrieved on 2007-01-16. ^ ;Kejin Wanga, Daniel E. Nelsena and Wilfrid A. Nixon, "Damaging effects of deicing chemicals on concrete materials", Cement and Concrete Composites Vol. 28(2), pp 173-188. doi:10.1016/j.cemconcomp.2005.07.006 ^ Time:Cementing the future ^ American Shotcrete Association Homepage ^ http://www.litebuilt.com/ ̂http://www.ecosmarte.com.au/construction/lightconcrete.htm ^ http://www.litebuilt.com/table1.html ^ http://www.litebuilt.com/table2.html ^ http://www.litebuilt.com/table3.html ^ Gibson, L.J. & Ashby, M.F. 1999. Cellular Solids: Structure and Properties; 2nd Edition (Paperback), Cambridge Uni. Press. pp.453-467. ^ Karade S.R., Irle M.A., Maher K. 2006. Influence of granule properties and concentration on cork-cement compatibility. Holz als Roh- und Werkstoff. 64: 281–286 (DOI 10.1007/s00107-006-0103-2). ^ Roller-Compacted Concrete (RCC) Pavements | Portland Cement Association (PCA) ^ K.H. Poutos, A.M. Alani, P.J. Walden, C.M. Sangha. (2008). Relative temperature changes within concrete made with recycled glass aggregate. Construction and Building Materials, Volume 22, Issue 4, Pages 557-565. ^ Crumb Rubber Concrete - Precast Solutions Magazine Fall 2004 ^ Emerging Construction Technologies ^ ASU researcher puts recalled Firestone tires to good use ̂Experimental Study on Strength, Modulus of Elasticity, and Damping Ratio of Rubberized Concrete ^ Zeobond is one such manufacturer that has built and operates the world’s first geopolymer concrete plant for the local Australian market with several additional plants coming online in Asia and North America in 2008 . According to this manufacturer its E-Crete branded concrete can be used in all applications where concrete is used today. ^ Green Cement ABC Catalyst program first broadcast 22 May 2008. ^ An Investigation Into The Feasibility Of Timber And Limecrete Composite Flooring ^ Self-healing concrete for safer, more durable infrastructure Physorg.com April 22nd, 2009 ^ Revealed: The cement that eats carbon dioxide Alok Jha, The Guardian, 31 December 2008 ^ Eco-Cement TecEco Pty ^ a b c "Cool Pavement Report" (PDF). Environmental Protection Agency. June 2005. http://www.epa.gov/heatisland/resources/pdf/CoolPavementReport_Former%20Guide_complete.pdf . Retrieved on 2009-02-06. ^ a b Gore, A; Steffen, A (2008). World Changing: A User's Giode for the 21st Century. New York: Abrams. pp. 258. ^ "Concrete facts". Pacific Southwest Concrete Alliance. http://www.concreteresources.net/categories/4F26A962-D021-233F-FCC5EF707CBD860A/fun_facts.html. Retrieved on 2009-02-06.