Last edited 04 Apr 2018

Types of concrete

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Contents

[edit] Introduction

Concrete is the most commonly used man-made material on earth. It is an important construction material used extensively in buildings, bridges, roads and dams. Its uses range from structural applications, to paviours, kerbs, pipes and drains.

Concrete is a composite material, consisting mainly of Portland cement, water and aggregate (gravel, sand or rock). When these materials are mixed together, they form a workable paste which then gradually hardens over time.

There are several different types of concrete, including:

[edit] Plain/ordinary concrete

This type of concrete is one of the most commonly-used, often for the construction of pavements and where buildings don’t require very high tensile strength. The constituents are cement, sand and aggregate, mixed with water, typically in the ratio 1:2:4.

As it is unreinforced, this type of concrete is unsuitable for many structures as it is relatively poor at withstanding stresses induced by vibrations, wind loading, and so on.

[edit] Lightweight concrete

Also known as cellular concrete, this is a very 'flowable' material and so can be easily poured by using gravity and is self-levelling. It is typically used to construct floor slabs, window panels and roofs.

The types of aggregates that are used for lightweight concrete include pumice, scoria, expanded shales and clays. It has very low thermal conductivity, usually with a k value of around 0.3 W/mK, whereas plain concrete can be as high as 10-12 W/mK.

[edit] High density concrete

This type of heavyweight concrete has a greater density than other types and is manufactured using crushed rocks as coarse aggregate. As it provides good protection from x-rays and radiation, it is often used in nuclear power plants and other such buildings.

[edit] Reinforced concrete

Reinforced concrete (RC) is a versatile composite and one of the most widely used materials in modern construction.

To increase its overall strength, steel rods, wires, mesh or cables can be embedded in concrete before it sets (or laid before the concrete is poured). This reinforcement, often known as rebar, resists tensile forces, whilst concrete resists compressive forces (and is inherently weak at resisting tensile forces). By forming a strong bond together, the two materials combine to resist a variety of applied forces, effectively acting as a single structural element.

For more information, see Reinforced concrete.

[edit] Precast concrete

This is a form of concrete that is prepared, cast and cured off-site, usually in a controlled factory environment, using reusable moulds. Precast concrete elements can be joined to other elements to form a complete structure. They are typically used for structural components such as; wall panels, beams, columns, floors, staircases, pipes, tunnels, and so on.

For more information, see Precast concrete.

[edit] Prestressed concrete

Prestressed concrete is a structural material that allows for predetermined, engineering stresses to be placed in members to counteract the stresses that will occur when they are subject to loading. It combines the high strength compressive properties of concrete with the high tensile strength of steel.

In reinforced concrete, stresses are carried by the steel reinforcement, whereas prestressed concrete supports the load by induced stresses throughout the entire structural element.

It is now commonly used for floor beams, piles and railways sleepers, as well as structures such as bridges, water tanks, roofs and runways.

For more information, see Prestressed concrete.

[edit] Glass reinforced concrete

Glass reinforced concrete (GRC), or glass-fibre reinforced concrete (GFRC), is a construction material that is commonly used to form exterior cladding panels.

GRC is composed from high-strength, alkali-resistant glass fibres embedded in a concrete matrix. The fibres act as the principal load-carrying component, while the surrounding matrix keeps them in position, and transfers load between the fibres. Both fibres and matrix are capable of retaining their physical and chemical identities, while combining their properties to create a high-performance composite.

For more information, see Glass reinforced concrete.

[edit] Air-entrained concrete

This is a form of plain concrete that contains microscopic air bubbles that range in size from a few thousandths of an inch in diameter to a few hundredths, and typically constitute between 4 and 7% of the total volume of the concrete.

The air bubbles create chambers for water to expand into when it freezes, thereby relieving internal pressure on the concrete. It is manufactured by introducing air-entraining agents as the concrete is mixed, or by using air-entraining Portland cement.

For more information, see Admixtures in concrete.

[edit] Self-compacting concrete

The introduction of self-compacting concrete (SCC) is regarded by some as one of the most important recent advancements in the concrete technology. It is a non-segregating concrete that can flow under its own weight, spread, fill formwork, and encapsulate reinforcements without the need for mechanical consolidation. Because of its exceptional flowing properties, SCC is used predominately in the construction of complex concrete frames.

For more information, see Self-compacting concrete.

[edit] Smart concrete

Smart concrete technology offers an alternative method for monitoring the health of reinforced concrete structures. It works by adding a small quantity of short carbon fiber to concrete with a conventional concrete mixer which modifies the electrical resistance of the concrete in response to strain or stress. This can be used to monitor stress or strain in concrete structures, identifying potential problems before the concrete fails.

Smart concrete is capable of sensing very small structural flaws and hence finds application in checking the internal condition of structures, particularly after an earthquake.

Smart concrete technology has undergone extensive laboratory testing, but is yet to hit the market.

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