Concrete

Concrete is the most versatile and most widely used construction material worldwide and it is the most commonly used man-made material on earth. A composite material that consists essentially of a binding medium, such as a mixture of portland cement and water, within which are embedded particles or fragments of aggregate, usually a combination of fine and coarse aggregate. It is an important construction material and is used extensively in buildings, bridges, roads, dams etc. It can be engineered to satisfy a wide range of performance specifications, unlike other building materials, such as natural stone or steel, which generally have to be used as they are. Because the tensile strength of concrete is much lower than its compressive strength, it is typically reinforced with steel bars, in which case it is known as Reinforced Cement Concrete (RCC).

Fresh concrete or plastic concrete is a freshly mixed material which can be moulded into any shape. The relative quantities of cement, aggregates and water mixed together, control the properties of concrete in the wet state as well as in the hardened state.

History of Concrete

Roman Concrete

As in modern construction, the Romans used wooden formworks and cast the concrete into them. Often, forms were built up using stone or brick. In tall structures, dense stone was used as aggregate at the bottom and light stone was used higher up.

Advantages

• It was strong and easier to use than stone for making smooth shapes (such as domes)
• It could set under water, so it could be used for piers and pediments of bridges and aqueducts

Disadvantages

• It takes a long time (up to a year) to reach high strength (so structures can sag before hardening)
• The raw materials (viz., volcanic ash) are not widely available

After the fall of Rome, concrete technology was lost in Western Europe until the 19th century. In 1756, John Smeaton was commissioned to build the Eddystone Lighthouse off the Cornwall coast (England). Contemporary mortars would not set under water, so he experimented with various local limestones. When limestone containing clay was fired, the resulting lime gained strength under water. In 1824, Joseph Aspdin patented Portland cement (so named because it was said to resemble Portland stone - a high quality limestone quarried near Portland). It is made byfiring clay and limestone (but at too low a temperature). In 1845, Isaac Johnson made the type of cement now known as Portland cement.

Uses of concrete

Many structural elements like footings, columns, beams, chejjas, lintels, roofs are made with RCC and it is used for making storage structures like water tanks, bins, silos, bunkers, bridges, dams, retaining walls etc.

Benefits of concrete

• It is a relatively cheap material and has a relatively long life with few maintenance requirements. It is strong in compression
• Before it hardens it is a very pliable substance that can easily be shaped
• It is non-combustible

Limitations of concrete

The limitations of concrete include:

• Relatively low tensile strength when compared to other building materials
• Low ductility
• Low strength-to-weight ratio
• It is susceptible to cracking

Ingredients of Concrete

• Cement
• Water
• Fine Aggregate
• Coarse Aggregate
• Admixtures