Concrete as a building material
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Concrete is a building material which has been in use since the Roman times. It is a complex mixture of water, coarse granular material usually sand or gravel. Cement fills the spaces among the granular material and acts as a binder that glues them together. The Panama Canal, the Hoover Dam, and the Roman Pantheon are some of renowned structures made of concrete. (PCA)
Concrete usage dates back thousands of years ago. Concrete was used for building of many ancient structures. Heinrich Schliemann, a German archaeologist discovered concrete floors in a royal palace of Tiryns, Greece, which dates approximately 1400-1200 BC. The Romans also used concrete on large scale from 300 BC to 476 AD. Roman concrete was made from an aggregate of pumice, pozzolana and quicklime. (Jacobs 4). Modern concrete is different from the Romans concrete in two ways. First, its mixer of a homogeneous fluid, this allows it to be poured into forms instead of hand-layering together with the arrangement of gravel, in Roman practice, this comprised of debris. Second, modern cement is integrated with steel that reinforces it to great strength in tension. Roman concrete depended only on the strength of the concrete bonds to withstand tension. The idea of reinforced concrete was invented by Joseph Monier in 1849. The first reinforced concrete bridge was built that year. (Constructor) Concrete has many benefits. It is economical when ingredients are readily available. Its long life and relatively low maintenance requirements increase its economic benefits. It does not rot, corrode, or decay as other building materials. It has the ability to be molded or cast into almost any desired shape. Building of the distinctive concrete forms and casting usually occur on the construction-site which reduces cost. Concrete is a non-combustible material which makes it fire-safe and able to withstand high temperatures. It is resistant to wind, water, rodents, and insects. Hence, concrete is often used for storm shelters. (Civil Engineering Forum)
Concrete has comparatively high compressive strength but much lower tensile strength. This is the reason why it is usually reinforced with steel which is materials that is strong in tension. The elasticity of concrete is comparatively unvarying at low stress levels but start becoming less at higher stress levels as cracking develops. It has a very low coefficient of thermal expansion properties and shrinks as it grows old. All structures made of concrete crack to some degree. This is due to shrinkage and tension. It has the tendency to creep and therefore should not be subjected to forces for long-duration. [ (Taylor , 300) ]
Tests are usually performed to ensure that the properties of concrete match the specifications of its application. Different mixers of concrete ingredients produce different strengths. The strengths are measured in MPa or psi. Concrete of different strengths is used for different applications. Concrete that has low-strength ranging from 2000 psi or less is usually used when the construction is lightweight. This is lightweight concrete is produced by adding lightweight aggregates, air or foams. This mixture has the side effect of reducing the strength of the cement.
Concrete of strength ranging from 3000-psi to 4000-psi is often used for most routine construction work. 5000-psi concrete is commercially available and is more durable, in spite of the fact that it is more expensive. 5000-psi concrete is used for larger civil engineering projects. Concrete having strengths of above 5000 psi are usually used for specific building parts for example, lower floor columns of high-rise buildings usually use concrete of at least 12,000 psi. This is done keep columns small in size. To lower the number of spans required in bridges construction, long beams of 10,000 psi concrete are used. In rare cases, if a structure needs to be very rigid, very high strength concrete may be used, much stronger than is required in order to hold the service loads. For these reasons 19,000 psi concrete have been in use commercially. [ (Bye , 200) ]
There are many types of concrete which vary in their performance characteristics due to the proportions of their ingredients to suit their purpose. Self-compacting concretes uses super plasticizers to achieve its sticky like self-leveling fluid. Pump concrete more sand than normal concrete. Its smoothness allows it to be easily pumped. It requires a lot of water and more cement to maintain its wetness and appropriate strength. Sprayed uses compressed air to cast it to a construction site. It can be a dry-mix which comprises of a dry mixture of cement and aggregates. Water needed for hydration is added at the nozzle. It can also be a wet-mix concrete that is already hydrated.
Normal concrete is the most common concreting applications. Tremmie concrete is used for casting columns and loads where concrete needs to flow into position. Chipping concrete is prepared by passing the mixture between small size stones or very small spaces. Mortar concrete is porous mass that has no sand in the mixture. Reinforced concrete is wrapped in a mesh of iron rods to strengthen it. The modern types of concrete include cellular or aerated concrete. It is light weight and durable, making it easy to be handled. Aerated concrete is widely used for modern construction as it is mortar-less and can be produced with different densities. (Jezek)
Manufacture concrete is relatively simple. First, the cement is prepared. Next, the other ingredient which are aggregates (such as sand or gravel), admixtures (chemical additives), any necessary fibers, and water are then mixed together with the cement to form concrete. The concrete is then shipped to the work site and placed, compacted, and cured. (Advameg)
Works Cited
Advameg, Inc. "Concrete." 30 May 2014. How Products are Made. 1 July 2014 <http://www.madehow.com/Volume-1/Concrete.html>.
Bye, G. C. Portland Cement: Composition, Production and Properties. Thomas Telford, 1999.
Civil Engineering Forum. "Concrete | Advantages and Disadvantages of Concrete." 29 May 2014. Civil Engineering Forum. 2 July 2014 <http://civilengineersforum.com/concrete-advantages-disadvantages/>.
Constructor, The. "TYPES OF CONCRETE WITH APPLICATIONS." 30 June 2014. Civil Engineering Home. 2 July 2014 <http://theconstructor.org/concrete/types-of-concrete/966/>.
Jacobs, J.P. "The Benefits of Concrete Construction." CCANZ Briefing Note 01–2011 (2011): 4.
Jezek, Geno. "Types of Concrete!" 30 May 2014. How Conrete Works. 1 July 2014 <www.howconcreteworks.com/types_of_concrete.html>.
PCA. How Concrete is Made. 1 July 2014. 2 July 2014 <http://www.cement.org/cement-concrete-basics/how-concrete-is-made>.
Taylor, H. F. W. Cement Chemistry. Thomas Telford, 1997, 1997.