Types of concrete
Encyclopedia
There are many types of concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

, variations of installation, composition, finish and performance characteristics.

Mix design

Modern concrete mix designs can be complex. The design of a concrete, or the way the weights of the components of a concrete is determined, is specified by the requirements of the project and the various local building codes and regulations.

The design begins by determining the "durability" requirements of the concrete. These requirements take into consideration the weather conditions that the concrete will be exposed to in service, and the required design strength. The compressive strength of a concrete is determined by taking standard molded, standard-cured cylinder samples.

Many factors need to be taken into account, from the cost of the various additives and aggregates, to the trade offs between, the "slump" for easy mixing and placement and ultimate performance.

A mix is then designed using cement (Portland or other cementitious material), coarse and fine aggregates, water and chemical admixtures. The method of mixing will also be specified, as well as conditions that it may be used in.

This allows a user of the concrete to be confident that the structure will perform properly.

Various types of concrete have been developed for specialist application and have become known by these names..

Concrete mixes can also be designed using software programs. Such softwares provide the user an opportunity to select their preferred method of mix design and enter the material data to arrive at proper mix designs.

Regular concrete

Regular concrete is the lay term describing concrete that is produced by following the mixing instructions that are commonly published on packets of cement, typically using sand or other common material as the aggregate, and often mixed in improvised containers. This concrete can be produced to yield a varying strength from about 10 MPa (1450 psi) to about 40 MPa (5800 psi), depending on the purpose, ranging from blinding to structural concrete respectively. Many types of pre-mixed concrete are available which include powdered cement mixed with an aggregate, needing only water.

Typically, a batch of concrete can be made by using 1 part Portland cement, 2 parts dry sand, 3 parts dry stone, 1/2 part water. The parts are in terms of weight – not volume. For example, 1 cubic foot (0.028316847 m³) of concrete would be made using 22 lb (10 kg) cement, 10 lb (4.5 kg) water, 41 lb (18.6 kg) dry sand, 70 lb (31.8 kg) dry stone (1/2" to 3/4" stone). This would make 1 cubic foot (0.028316847 m³) of concrete and would weigh about 143 lb (64.9 kg). The sand should be mortar or brick sand (washed and filtered if possible) and the stone should be washed if possible. Organic materials (leaves, twigs, etc) should be removed from the sand and stone to ensure the highest strength.

High-strength concrete

High-strength concrete has a compressive strength generally greater than 6,000 pounds per square inch (40 MPa = 5800 psi). High-strength concrete is made by lowering the water-cement (W/C) ratio to 0.35 or lower. Often silica fume is added to prevent the formation of free calcium hydroxide crystals in the cement matrix, which might reduce the strength at the cement-aggregate bond.

Low W/C ratios and the use of silica fume make concrete mixes significantly less workable, which is particularly likely to be a problem in high-strength concrete applications where dense rebar cages are likely to be used. To compensate for the reduced workability, superplasticizers are commonly added to high-strength mixtures. Aggregate must be selected carefully for high-strength mixes, as weaker aggregates may not be strong enough to resist the loads imposed on the concrete and cause failure to start in the aggregate rather than in the matrix or at a void, as normally occurs in regular concrete.

In some applications of high-strength concrete the design criterion is the elastic modulus
Elastic modulus
An elastic modulus, or modulus of elasticity, is the mathematical description of an object or substance's tendency to be deformed elastically when a force is applied to it...

 rather than the ultimate compressive strength.

Stamped concrete

Stamped concrete is an architectural concrete which has a superior surface finish. After a concrete floor has been laid, floor hardeners (can be pigmented) are impregnated on the surface and a mold which may be textured to replicate a stone / brick or even wood is stamped on to give an attractive textured surface finish. After sufficient hardening the surface is cleaned and generally sealed to give a protection. The wear resistance of stamped concrete is generally excellent and hence found in applications like parking lots, pavements, walkways etc.

High-performance concrete

High-performance concrete (HPC) is a relatively new term used to describe concrete that conforms to a set of standards above those of the most common applications, but not limited to strength. While all high-strength concrete is also high-performance, not all high-performance concrete is high-strength. Some examples of such standards currently used in relation to HPC are:

Ultra-High-performance concrete

Ultra-High-performance concrete is a new type of concrete that is being developed by agencies concerned with infrastructure protection. UHPC is characterized by being a steel fibre-reinforced cement composite material with compressive strengths in excess of 150 MPa, upto and possibly exceeding 250 MPa. UHPC is also characterized by its constituent material make-up: typically fine-grained sand, silica fume, small steel fibers, and special blends of high-strength portland cement. Note that there is no large aggregate.
The current types in production (Ductal, Taktl, etc.) differ from normal concrete in compression by their strain hardening, followed by sudden brittle failure. Ongoing research into UHPC failure via tensile and shear failure is being conducted by multiple government agencies and universities around the world.

Self-consolidating concretes

During the 1980s a number of countries including Japan, Sweden and France developed concretes that are self-compacting, known as self-consolidating concrete in the United States. This self-consolidating concrete (SCCs) is characterized by:
  • extreme fluidity as measured by flow, typically between 650–750 mm on a flow table, rather than slump(height)
  • no need for vibrators
    Vibrator (mechanical)
    A vibrator is a mechanical device to generate vibrations. The vibration is often generated by an electric motor with an unbalanced mass on its driveshaft.There are many different types of vibrator...

     to compact the concrete
  • placement being easier.
  • no bleed water, or aggregate segregation
  • Increased Liquid Head Pressure, Can be detrimental to Safety and workmanship


SCC can save up to 50% in labor costs due to 80% faster pouring and reduced wear and tear
Wear and tear
Wear and tear is damage that naturally and inevitably occurs as a result of normal wear or aging. It is used in a legal context for such areas as warranty contracts from manufacturers, which usually stipulate that damage due to wear and tear will not be covered.Wear and tear is a form of...

 on formwork
Formwork
Formwork is the term given to either temporary or permanent molds into which concrete or similar materials are poured. In the context of concrete construction, the falsework supports the shuttering moulds.-Formwork and concrete form types:...

.

As of 2005, self-consolidating concretes account for 10-15% of concrete sales in some European countries. In the US precast concrete industry, SCC represents over 75% of concrete production. 38 departments of transportation in the US
Transportation in the United States
Transportation in the United States is facilitated by road, air, rail, and water networks. The vast majority of passenger travel occurs by automobile for shorter distances, and airplane for longer distances...

 accept the use of SCC for road and bridge projects.

This emerging technology is made possible by the use of polycarboxylates plasticizer
Plasticizer
Plasticizers or dispersants are additives that increase the plasticity or fluidity of the material to which they are added; these include plastics, cement, concrete, wallboard, and clay. Although the same compounds are often used for both plastics and concretes the desired effects and results are...

 instead of older naphthalene based polymers, and viscosity modifiers to address aggregate segregation.

Vacuum concretes

The use of steam to produce a vacuum inside of concrete mixing truck to release air bubbles inside the concrete is being researched. The idea is that the steam displaces the air normally over the concrete. When the steam condenses into water it will create a low pressure over the concrete that will pull air from the concrete. This will make the concrete stronger due to there being less air in the mixture. Obviously this needs to be done in a sealed container.

Shotcrete

Shotcrete (also known by the trade name Gunite) uses compressed air to shoot concrete onto (or into) a frame or structure. The greatest advantage of the process is that shotcrete can be applied overhead or on vertical surfaces without forming. It is often used for concrete repairs or placement on bridges, dams, pools, and on other applications where forming is costly or material handling and installation is difficult. Shotcrete is frequently used against vertical soil or rock surfaces, as it eliminates the need for formwork
Formwork
Formwork is the term given to either temporary or permanent molds into which concrete or similar materials are poured. In the context of concrete construction, the falsework supports the shuttering moulds.-Formwork and concrete form types:...

. It is sometimes used for rock support, especially in tunnel
Tunnel
A tunnel is an underground passageway, completely enclosed except for openings for egress, commonly at each end.A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. Some tunnels are aqueducts to supply water for consumption or for hydroelectric stations or are sewers...

ing. Shotcrete is also used for applications where seepage is an issue to limit the amount of water entering a construction site due to a high water table or other subterranean sources. This type of concrete is often used as a quick fix for weathering for loose soil types in construction zones.

There are two application methods for shotcrete.
  • dry-mix – the dry mixture of cement and aggregates is filled into the machine and conveyed with compressed air
    Compressed air
    Compressed air is air which is kept under a certain pressure, usually greater than that of the atmosphere. In Europe, 10 percent of all electricity used by industry is used to produce compressed air, amounting to 80 terawatt hours consumption per year....

     through the hoses. The water needed for the hydration is added at the nozzle.
  • wet-mix – the mixes are prepared with all necessary water for hydration. The mixes are pumped through the hoses. At the nozzle compressed air is added for spraying.

For both methods additives such as accelerators
Accelerant
Accelerants play a major role in chemistry. Most chemical reactions can be hastened with an accelerant. Accelerants alter a chemical bond, speed up a chemical process, or bring organisms back to homeostasis. Accelerants are not necessarily catalysts as they may be consumed by the process...

 and fiber reinforcement may be used.

Pervious concrete

Pervious concrete
Permeable paving
Permeable paving is a range of materials and techniques for paving roads, cycle-paths, parking lots and sidewalks that allow the movement of water and air around the paving material. Although some porous paving materials appear nearly indistinguishable from nonporous materials, their environmental...

contains a network of holes or voids, to allow air or water to move through the concrete.

This allows water to drain naturally through it, and can both remove the normal surface-water drainage infrastructure, and allow replenishment of groundwater
Groundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...

 when conventional concrete does not.

It is formed by leaving out some or all of the fine aggregate
Construction Aggregate
Construction aggregate, or simply "aggregate", is a broad category of coarse particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates are the most mined material in the world...

 (fines). The remaining large aggregate then is bound by a relatively small amount of Portland cement
Portland cement
Portland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout...

. When set, typically between 15 % and 25 % of the concrete volume is voids, allowing water to drain at around 5 gal/ft²/ min (70 L/m²/min) through the concrete.

Installation

Pervious concrete is installed by being poured into forms, then screeded off, to level (not smooth) the surface, then packed or tamped into place. Due to the low water content and air permeability, within 5–15 minutes of tamping, the concrete must be covered with a 6-mil poly plastic, or it will dry out prematurely and not properly hydrate and cure.

Characteristics

Pervious concrete can significantly reduce noise, by allowing air to be squeezed between vehicle tires and the roadway to escape. This product cannot be used on major U.S. state highways currently due to the high psi ratings required by most states. Pervious concrete has been tested up to 4500  psi so far.

Cellular concrete

Aerated concrete produced by the addition of an air-entraining agent to the concrete (or a lightweight aggregate like expanded clay pellets or cork granules and vermiculite
Vermiculite
Vermiculite is a natural mineral that expands with the application of heat. The expansion process is called exfoliation and it is routinely accomplished in purpose-designed commercial furnaces. Vermiculite is formed by weathering or hydrothermal alteration of biotite or phlogopite...

) is sometimes called cellular concrete, lightweight aerated concrete, variable density concrete, foamed concrete and lightweight or ultra-lightweight concrete, not to be confused with aerated autoclaved concrete
Aerated autoclaved concrete
Autoclaved aerated concrete , also known as autoclaved cellular concrete or autoclaved lightweight concrete , was invented in the mid-1920s by the Swedish architect and inventor Johan Axel Eriksson. It is a lightweight, precast building material that simultaneously provides structure, insulation,...

, which is manufactured off-site using an entirely different method.

In the 1977 work on A Pattern Language
A Pattern Language
A Pattern Language: Towns, Buildings, Construction is a 1977 book on architecture, urban design, and community livability. It was authored by Christopher Alexander, Sara Ishikawa and Murray Silverstein of the Center for Environmental Structure of Berkeley, California, with writing credits also to...

: Towns, Buildings and Construction
, architect Christopher Alexander
Christopher Alexander
Christopher Wolfgang Alexander is a registered architect noted for his theories about design, and for more than 200 building projects in California, Japan, Mexico and around the world...

 wrote in pattern 209 on Good Materials:

"Regular concrete is too dense. It is heavy and hard to work. After it sets one cannot cut into it, or nail into it. And surface is ugly, cold, and hard in feeling unless covered by expensive finishes not integral to the structure.

And yet concrete, in some form, is a fascinating material. It is fluid, strong, and relatively cheap. It is available in almost every part of the world. A University of California professor of engineering sciences, P. Kumar Mehta, has even just recently found a way of converting abandoned rice husks into Portland cement.

Is there any way of combining all these good qualities of concrete and also having a material which is light in weight, easy to work, with a pleasant finish? There is. It is possible to use a whole range of ultra-lightweight concretes which have a density and compressive strength very similar to that of wood. They are easy to work with, can be nailed with ordinary nails, cut with a saw, drilled with wood-working tools, easily repaired.

We believe that ultra-lightweight concrete is one of the most fundamental bulk materials of the future."

The variable density is normally described in kg per m³, where regular concrete is 2400 kg/m³. Variable density can be as low as 300 kg/m³, although at this density it would have no structural integrity at all and would function as a filler or insulation use only. The variable density reduces strength to increase thermal and acoustical insulation by replacing the dense heavy concrete with air or a light material such as clay, cork granules and vermiculite. There are many competing products that use a foaming agent that resembles shaving cream to mix air bubbles in with the concrete. All accomplish the same outcome: to displace concrete with air.

Cork-cement composites

Waste Cork granules are obtained during production of bottle stoppers from the treated bark of Cork oak
Cork Oak
Quercus suber, commonly called the Cork Oak, is a medium-sized, evergreen oak tree in the section Quercus sect. Cerris. It is the primary source of cork for wine bottle stoppers and other uses, such as cork flooring. It is native to southwest Europe and northwest Africa.It grows to up to 20 m,...

. These granules have a density of about 300 kg/m³, lower than most lightweight aggregates used for making lightweight concrete. Cork granules do not significantly influence cement hydration, but cork dust may. Cork cement composites have several advantages over standard concrete, such as lower thermal conductivities, lower densities and good energy absorption characteristics. These composites can be made of density from 400 to 1500 kg/m³, compressive strength from 1 to 26 MPa, and flexural strength from 0.5 to 4.0 MPa.

Roller-compacted concrete

Roller-compacted concrete, sometimes called rollcrete, is a low-cement-content stiff concrete placed using techniques borrowed from earthmoving and paving work. The concrete is placed on the surface to be covered, and is compacted in place using large heavy rollers typically used in earthwork. The concrete mix achieves a high density and cures over time into a strong monolithic block. Roller-compacted concrete is typically used for concrete pavement, but has also been used to build concrete dams, as the low cement content causes less heat to be generated while curing than typical for conventionally placed massive concrete pours.

Glass concrete

The use of recycled glass as aggregate in concrete has become popular in modern times, with large scale research being carried out at Columbia University in New York. This greatly enhances the aesthetic appeal of the concrete. Recent research findings have shown that concrete made with recycled glass aggregates have shown better long term strength and better thermal insulation due to its better thermal properties of the glass aggregates.

Asphalt concrete

Strictly speaking, asphalt
Asphalt concrete
Asphalt concrete is a composite material commonly used in construction projects such as road surfaces, airports and parking lots. It consists of asphalt and mineral aggregate mixed together, then laid down in layers and compacted...

 is a form of concrete as well, with bituminous materials replacing cement as the binder.

Rapid strength concrete

This type of concrete is able to develop high resistance within few hours after being manufactured. This feature has advantages such as removing the formwork early and to move forward in the building process at record time, repair road surfaces that become fully operational in just a few hours.

Rubberized concrete

While "rubberized asphalt
Rubberized asphalt
Rubberized asphalt concrete , also known as asphalt rubber or just rubberized asphalt, is pavement material that consists of regular asphalt concrete mixed with crumb rubber–ground, used tires that might otherwise be discarded, taking up space in landfills, if they were not re-directed for use as...

 concrete" is common, rubberized Portland cement concrete ("rubberized PCC") is still undergoing experimental tests, as of 2009.

Polymer concrete

Polymer concrete
Polymer concrete
Polymer concrete is part of group of concretes that use polymers to supplement or replace cement as a binder. The types include polymer-impregnated concrete, polymer concrete, and polymer-Portland-cement concrete...

 is concrete which uses polymers to bind the aggregate. Polymer concrete can gain a lot of strength in a short amount of time. For example, a polymer mix may reach 5000 psi in only four hours. Polymer concrete is generally more expensive than conventional concretes.

Geopolymer or green concrete

Geopolymer concrete is a greener alternative to ordinary Portland cement made from inorganic aluminosilicate (Al-Si) polymer compounds that can utilise 100% recycled industrial waste (e.g. fly ash
Fly ash
Fly ash is one of the residues generated in combustion, and comprises the fine particles that rise with the flue gases. Ash which does not rise is termed bottom ash. In an industrial context, fly ash usually refers to ash produced during combustion of coal...

 and slag
Slag
Slag is a partially vitreous by-product of smelting ore to separate the metal fraction from the unwanted fraction. It can usually be considered to be a mixture of metal oxides and silicon dioxide. However, slags can contain metal sulfides and metal atoms in the elemental form...

) as the manufacturing inputs resulting in up to 80% lower carbon dioxide emissions. Greater chemical and thermal resistance, and better mechanical properties, are said to be achieved by the manufacturer at both atmospheric and extreme conditions.

Similar concretes have not only been used in Ancient Rome
Ancient Rome
Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....

 (see Roman concrete
Roman concrete
Roman concrete was a material used in construction during the late Roman Republic through the whole history of the Roman Empire. Roman concrete was based on a hydraulic-setting cement with many material qualities similar to modern Portland cement...

) as mentioned but also in the former Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

 in the 1950s and 1960s. Buildings in Ukraine
Ukraine
Ukraine is a country in Eastern Europe. It has an area of 603,628 km², making it the second largest contiguous country on the European continent, after Russia...

 are still standing after 45 years so that this kind of formulation has a sound track record.

Limecrete

Limecrete or lime concrete is concrete where cement is replaced by lime.
One successful formula was developed in the mid 1800s by Dr. John E. Park

Refractory Cement

High-temperature applications, such as masonry oven
Masonry oven
A masonry oven, colloquially known as a brick oven or stone oven, is an oven consisting of a baking chamber made of fireproof brick, concrete, stone, or clay. Though traditionally wood-fired, coal-fired ovens were common in the 19th century, modern masonry ovens are often fired with natural gas or...

s and the like, generally require the use of a refractory
Refraction (metallurgy)
In metallurgy, refraction is a property of metals that indicates their ability to withstand heat. Metals with a high degree of refraction are referred to as refractory. These metals derive their high melting points from their strong intermolecular forces...

 cement; concretes based on Portland cement can be damaged or destroyed by elevated temperatures, but refractory concretes are better able to withstand such conditions. Materials may include calcium aluminate cements
Calcium aluminate cements
Calcium aluminate cements are cements consisting predominantly of hydraulic calcium aluminates. Alternative names are "aluminous cement", "high-alumina cement" and "Ciment fondu" in French...

, fire clay
Fire clay
Fire clay is a term applied to a range of refractory clays used in the manufacture of ceramics, especially fire brick.High grade fire clays can withstand temperatures of 1775°C , but to be referred to as a "fire clay" the material must withstand a minimum temperature of 1515°C...

, ganister
Ganister
A ganister is hard, fine-grained quartzose sandstone, or orthoquartzite, used in the manufacture of silica brick typically used to line furnaces...

 and minerals high in aluminum.

Concrete cloth

A recent innovation is the concrete cloth. It consists of a three-dimensional fiber matrix, containing a specially formulated dry concrete mix. A PVC backing on one surface of the cloth ensures the material is completely waterproof, while hydrophilic fibers on the opposite surface aid hydration by drawing water into the cement. Concrete cloth can be used to rapidly create waterproof, fireproof, fiber-reinforced thin concrete forms across a wide range of applications: rapid trackway or landing surfaces, structural reinforcement, ground stabilization, ballistic protection and sterile concrete shelters.

Innovative mixtures

On-going research into alternative mixtures and constituents has identified potential mixtures that promise radically different properties and characteristics.

One university has identified a mixture with much smaller crack propagation that does not suffer the usual cracking and subsequent loss of strength at high levels of tensile . Researchers have been able to take mixtures beyond 3 percent strain, past the more typical 0.1% point at which failure occurs.

Other institutions have identified magnesium silicate (talc
Talc
Talc is a mineral composed of hydrated magnesium silicate with the chemical formula H2Mg34 or Mg3Si4O102. In loose form, it is the widely-used substance known as talcum powder. It occurs as foliated to fibrous masses, its crystals being so rare as to be almost unknown...

) as an alternative ingredient to replace Portland cement in the mix. This avoids the usual high-temperature production process that is very energy and greenhouse gas
Greenhouse gas
A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...

 intensive and actually absorbs carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 while it cures.

Gypsum concrete

Gypsum concrete is a building material
Building material
Building material is any material which is used for a construction purpose. Many naturally occurring substances, such as clay, sand, wood and rocks, even twigs and leaves have been used to construct buildings. Apart from naturally occurring materials, many man-made products are in use, some more...

 used as a floor underlayment used in wood-frame
Framing (construction)
Framing, in construction known as light-frame construction, is a building technique based around structural members, usually called studs, which provide a stable frame to which interior and exterior wall coverings are attached, and covered by a roof comprising horizontal ceiling joists and sloping...

 and concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

 construction for fire ratings, sound reduction, radiant heating
Radiant heating
Radiant heating is a technology for heating indoor and outdoor areas. Heating by radiant energy is observed everyday, the warmth of the sunshine being probably the most commonly observed example. Radiant heating as a technology is typically more narrowly defined...

, and floor leveling. It is a mixture of gypsum
Gypsum
Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...

, Portland cement
Portland cement
Portland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout...

, and sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...

.
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