what is concrete? could you give me 5 examples?

Answer 1

mortar, pavement, cement, cinder block, george bush's thought processes

Answer 2

Hmmm concrete evidence
concrete sidewalk
concrete galoshes
concrete objects such as trees
A group of things as opposed to an abstraction.

Answer 3

n construction, concrete is a composite building material made from the combination of aggregate and a cement binder.

Types of concrete

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

Regular concrete is the lay term describing concrete that is produced by following the mixing instuctions 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 to about 40 Mpa, depending on the purpose, ranging from blinding to structural concrete respectively. Also, many types of pre-mixed concrete are available which include powedered cement mixed with an aggregate, needing only water.
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High Strength Concrete

High Strength Concrete is concrete with a compressive strength generally greater than 6,000 pounds/square inch (40 MPa). High-strength concrete is made by lowering the water-cement 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 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 rather than the ultimate compressive strength.
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Self-compacting concretes

During the 1980s a number of countries including Japan, Sweden and France developed a range of concretes that were self-compacting. These self-compacting concretes (SCCs) are characterised by their extreme fluidity, behaving more like a thick fluid that is self-leveling, as opposed to the traditional concrete that needs consolidating, normally by vibration or packing.

SCCs are characterized by

* extreme fluidity as measured by flow, typically between 700-750 mm, rather than slump
* no need for vibrators to compact the concrete, which can be noisy
* placing becomes simpler
* no bleed water, or aggregate segregation
* no need for a viscosity modifying agent (VMA)

SCC can offer benefits of up to 50% in labor 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. In the American precast concrete industry, SCC represents over 75% of concrete production. 38 departments of transportation in the US accept the use of SCC for road and bridge projects.

This emerging technology is made possible by the use of polycarboxylates instead of older "high-range water reducers".
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Shotcrete

Main article: Shotcrete

Shotcrete uses compressed air to shoot (cast) concrete onto (or into) a frame or structure. Shotcrete is frequently used against vertical soil or rock surfaces, as it eliminates the need for formwork. It is sometimes 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 accelerators and fiber reinforcement may be used. [3]

The term Gunite is occasionally used for shotcrete, but properly refers only to dry-mix shotcrete, and used to be a proprietary name.
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Pervious Concrete

In pervious or "no fines" concrete, carefully controlled amounts of water and cementitious materials are used to create a paste that forms a thick coating around aggregate particles. A pervious concrete mixture contains little or no sand (fines), creating a substantial void content. Using sufficient paste to coat and bind the aggregate particles together creates a system of highly permeable, interconnected voids that drains quickly. Typically, between 15% and 25% voids are achieved in the hardened concrete, and flow rates for water through pervious concrete are typically around 480 in./hr (0.34 cm/s, which is 5 gal/ft²/ min or 200 L/m²/min), although they can be much higher. Both the low mortar content and high porosity also reduce strength compared to conventional concrete mixtures, but sufficient strength for many applications is readily achieved.

Pervious concrete pavement is a unique and effective means to address important environmental issues and support sustainable growth. By capturing rainwater and allowing it to seep into the ground, porous concrete is instrumental in recharging groundwater, reducing stormwater runoff, and meeting U.S. Environmental Protection Agency (EPA) stormwater regulations. The use of pervious concrete is among the Best Management Practices (BMPs) recommended by the EPA-- and by other agencies and geotechnical engineers across the country-- for the management of stormwater runoff on a regional and local basis. This pavement technology creates more efficient land use by eliminating the need for retention ponds, swales, and other stormwater management devices. In doing so, pervious concrete has the ability to lower overall project costs on a first-cost basis.
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Cellular concrete

Aerated concrete produced by the addition of an air-entraining agent to the concrete (or a lightweight aggregate like vermiculite ) is sometimes called Cellular concrete. See also aerated autoclaved concrete.
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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. [4] 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 normally-placed massive concrete pours.
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Asphalt concrete

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