Dictionary
a strong hard building material composed of sand and gravel and cement and water cover with cement "concrete the walls" form into a solid mass coalesce capable of being perceived by the senses not abstract or imaginary "concrete objects such as trees" formed by the coalescence of particles
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Wikipedia
Otheruses In construction, concrete is a composite material composite building material made from the combination of aggregate (composite)aggregate and cement Matrixbinder. The most common form of concrete is Portland cement concrete, which consists of mineral aggregate (generally gravel and sand), Portland cement and water (molecule)water. It is commonly believed that concrete dries after mixing and placement. Actually, concrete does not solidify because water evaporationevaporates, but rather cement hydrationhydrates, gluing the other components together and eventually creating a stone-like material. When used in the generic sense, this is the material referred to by the term concrete. Concrete is used to make pavements, building structures, foundations, motorways/roads, overpasses, parking structures, bases for gates/fences/poles, and cement in brick or block walls. An old name for concrete is liquid stone.
History - The Assyrian peopleAssyrians and Babylonians used clay as cement in their concretes. The Ancient EgyptianEgyptians used lime and gypsum cement. In the Roman Empire, cements made from pozzolanic ash/pozzolana and an aggregate made from pumice were used to make a concrete very similar to modern portland cement concrete. In 1756, United KingdomBritish engineer John Smeaton pioneered the use of portland cement in concrete, using pebbles and powdered brick as aggregate. In the modern day, the use of recycled/reused materials as concrete ingredients is gaining popularity due to increasingly stringent environmental legislation. The most conspicuous of these is pulverized fuel ash, recycled from the ash by-products of coal power plants. This has a significant impact in reducing the amount of quarrying and the ever-attenuating landfill space.
Characteristics - During hydration and hardening, concrete needs to develop certain physical and chemical properties, among others, mechanical strength, low permeability to ingress of moisture, and chemical and volume stability. Concrete has relatively high compressive strength, but significantly lower tensile strength (about 10% of the compressive strength). As a result, concrete always fails from tensile stresses - even when loaded in compression. The practical implication of these facts is that concrete elements that are subjected to tensile stresses must be reinforced. Concrete is most often constructed with the addition of steel bar or fiber reinforcement. The reinforcement can be by bars (rebars), mesh, or fibres to produce reinforced concrete. Concrete can also be prestressed concrete prestressed (reducing tensile stress) using steel cables, allowing for beam (structure)beams or slabs with a longer span than is practical with reinforced concrete.The ultimate strength of concrete is related to water/cement ratio and the size, shape, and strength of the aggregate used. Concrete with lower water/cement ratio (down to 0.35) makes a stronger concrete than a higher ratio. Concrete made with small (1/2" or 12mm) smooth pebbles is much weaker than that made with larger (1" or 25mm) rough-surfaced broken rock pieces for example.Certain shapes are very strong in compression, such as arches and vaults, and are therefore preferred for concrete construction.Concrete is placed in a wet or plastic state, and therefore can be manipulated and molded as needed. Hydration and hardening of concrete may lead to tensile stresses at a time when it has not yet gained significant strength, resulting in shrinkage cracks. However, when concrete mix is placed in accordance with the best recommended practice, cracking may be minimal.
Additives - Additives are organic or non-organic materials in form of solids or fluids that are added to the concrete to give it certain characteristics. In normal use the additives make up less than 5% of the cement weight.The most used types of additives are: Accelerator (chemistry)Accelerators: Speed up the hydration (strengthening) of the concete. Retarders: Slow the hydration of concrete. Air-entrainers: Add and distribute air to the concrete. Plasticizers: Increase the workability of concrete.
Workability - Workability is the ability of a fresh (plastic) concrete mix to fill the form/mould properly with the desired work (vibration) and without reducing the concrete's quality. Workability depends on water content, additives, aggregate (shape and size distribution) and age (level of hydration). Raising the water content or adding plasticizer will increase the workability. Too much water will lead to bleeding (loss of water) and/or segregation (concrete start to get inhomogeneous) and the resulting concrete will have reduced quality.Workability is normally tested by slump measurement. High flow concrete, like self compacting concrete, are normaly tested by one of several flow measuring methods.Concrete slump is a simplistic measure of fresh (plastic) concrete's workability. Slump is normally determined by the ASTM C 143 or EN 12350-2 slump test standards, using the Abrams cone, into which concrete is placed for testing. When the cone is carefully lifted off the enclosed material, it will slump a certain amount due to its water content. A relatively dry sample will slump very little, and be given a slump of one or two inches (25 or 50 mm), while a relatively wet concrete sample may slump as much as six or seven inches (150 to 175 mm).To increase the slump, the rule of thumb is: US units:Add 1 US gallon of water per cubic yard of concrete in the mixer truck to increase slump by 1 inch. Adding 27 US gallons to 9 cubic yards of batched concrete will therefore increase the slump by about 3 inches. Metric units (converted from US rule of thumb) :Add 2 litres of water per cubic metre of concrete in the mixer truck to increase slump by 1 cm. Adding 54 litres to 9 cubic metres of batched concrete will therefore increase the slump by about 3 cm.Slump can also be increased by adding a plasticizer, without changing the water/cement factor.
Self compacting concretes - During the 1990s a number of countries including Japan, Sweden and France developed a range of concretes that were self-compacting. These 'SCC's are characterised by their extreme fluidity (using plasticizers), behaving more like water than the traditional viscous concrete. SCCs are characterized by extreme fluidity measured by ''flow'' or ''slump'', typically measured between 700-750 mm. no need for vibrators to compact the concrete, which can be noisy no or little need for expensive concrete pumping equipment no bleed water (excess water draining out of the concrete)SCC can offer benefits of up to 50% in labour costs, due to it being poured up to 80% faster and having reduced wear and tear on formwork.As of 2005, self compacting concretes account for 10-15% of concrete sales in some European countries.
Shotcrete / sprayed concrete - ''Main article !ShotcreteShotcreteShotcrete uses compressed air to shoot (cast) concrete to a frame or structure. Shotcrete is mostly used for rock support, especially in tunnelling. Today there are two application methods for shotcrete: the dry-mix and the wet-mix procedure. In Dry-mix the dry mixture of cement and aggregates is filled into the machine and conveyed with compressed air through the hoses. The water needed for the hydration is added at the nozzle. In 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 plasticizers and accelerator (chemistry)accelerators may be used. Shotcrete is normally reinforced by fibers.
See also - Building constructionConcrete mixerConcrete resurfacingReinforced concreteSlab-on-grade foundationsShotcreteFormwork
External link - inventors.about.com - History of !ConcreteCategory:ConcreteCateg ory:Civil? !engineeringCategory:MaterialsC ategory:ConstructionCategory:P avementsCategory:Heterogeneous ? !mixturesbg:Бетонcs:Betond a:Betonde:Betonet:Betoones:Hor migóneo:Betonofr:Bétonid:Bet onhe:בטוןms:Konkritnl:Beto nja:コンクリートno:Beton gpl:Betonpt:Concreto? !(material)ru:Бетонsimple: Concretesl:Betonsv:Betongzh: 凝土
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Websites
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precast concrete building systems
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brent
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Concrete Promotion Council of Northern California
A trade association concerned with creating awareness amongst the construction design communities of Northern California through education on the wide variety of ready mixed concrete applications available from the region's concrete producers. This educational interaction is provided in the form of general and technical presentations on the applications and their uses for all types of construction.
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Moosemilk & Sand
A concrete/cement counter tops and other cement design innovations
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ESV Teleproductions
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NAFTA GROUP
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ICF Contracting Pty Ltd
Reusable Plastic Formwork System for Commercial and Domestic Projects.
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concrete product
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NEOTEK OE P. XYSTRIS & Co.
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Tarmac Precast Concrete
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Amchem Products Pvt. Ltd
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R2TechScreed Laser Guided Screed
The R2Tech Screed uses laser guidance to improve the floor levelness on small to midsize jobs, without increasing the labor required. Call for a demonstration on your next job. 800-848-8386
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SiteCast Construction
SiteCast Construction is a Canadaian construction company based in Ottawa, Ontario. They specialize in rapid construction, high-efficiency concrete tilt up construction.
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SKATEPARKGUIDE
The only comprehensive resource for accurate, up-to-date information from industry specialists.
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Insulated Concrete Homes
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The American Concrete Institute (ACI)
ACI International is dedicated to improving the design, construction, manufacture and maintenance of concrete structures.
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Concrete.com LLC.
Concrete information source.
http://www.concrete.com/
Precast/Prestressed Concrete Institute
Organizational site includes trade, technical and public affairs information for precast/prestressed concrete producers and their clients.
http://www.pci.org/
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