Reinforced concrete

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File:Fideo o’r trawst concrit olaf yn cael ei osod – Tach 2016 Last concrete beam installation – 2016.webm Reinforced concrete is a composite material in which concrete's relatively low tensile strength and ductility are counteracted by the inclusion of reinforcement having higher tensile strength or ductility. The reinforcement is usually, though not necessarily, steel reinforcing bars (rebar) and is usually embedded passively in the concrete before the concrete sets. Reinforcing schemes are generally designed to resist tensile stresses in particular regions of the concrete that might cause unacceptable cracking and/or structural failure. Modern reinforced concrete can contain varied reinforcing materials made of steel, polymers or alternate composite material in conjunction with rebar or not. Reinforced concrete may also be permanently stressed (in tension), so as to improve the behaviour of the final structure under working loads. In the United States, the most common methods of doing this are known as pre-tensioning and post-tensioning.

History

The history of reinforced concrete dates back to the 19th Century, with the first practical applications being developed by French gardener Joseph Monier, who received a patent in 1867 for reinforced garden tubs. Following this, the technology quickly spread, with the first reinforced concrete bridge constructed by Joseph Monier in 1875. The use of reinforced concrete became more widespread in the early 20th century, as its advantages over plain concrete in terms of strength and durability became evident.

Advantages

Reinforced concrete has several advantages over other building materials like steel or wood. It has a high compressive strength compared to its weight, provides excellent fire resistance, and its materials are widely available. Additionally, reinforced concrete can be molded into a wide variety of shapes and sizes, allowing for great flexibility in architecture and civil engineering. It also benefits from the composite action between steel and concrete, which allows for efficient distribution of stress over a larger area.

Components

The primary components of reinforced concrete are:

• Concrete: A mixture of cement, water, aggregates (sand, gravel, or crushed stone), and often other additives.
• Reinforcement: Usually steel bars (rebar), but can also be fibers made of steel, glass, or plastic.

Design

The design of reinforced concrete structures is a complex task, often involving the calculation of loads, stress, and strain distribution using methods outlined in building codes such as the American Concrete Institute (ACI) Code, Eurocode 2 for the design of concrete structures, or other national standards. The design process ensures that the structure will be able to support the expected loads over its anticipated service life without excessive cracking or failure.

Construction

The construction of reinforced concrete structures involves several steps: 1. Design of the structure. 2. Preparation of the formwork into which concrete is poured. 3. Assembly of the reinforcement, which is placed within the formwork according to the design specifications. 4. Mixing, pouring, and curing of the concrete around the reinforcement. 5. Removal of formwork after the concrete has gained sufficient strength.

Maintenance

Reinforced concrete structures require maintenance to prevent damage from environmental factors such as freeze-thaw cycles, chemical attack (e.g., from chlorides leading to corrosion of the reinforcement), and physical wear and tear. Regular inspection and maintenance are crucial for extending the life of a reinforced concrete structure and ensuring its safety and structural integrity.

Environmental Considerations

While reinforced concrete is a durable and versatile material, its production, particularly the production of cement, is associated with significant carbon dioxide emissions. Efforts to reduce the environmental impact of reinforced concrete include the use of supplementary cementitious materials (SCMs) like fly ash or slag in the concrete mix, recycling concrete, and developing alternative reinforcing materials with lower environmental footprints.

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