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Concrete was more extensively used again during the Renaissance (14th17th centuries) in structures like bridge piers.
Design Of Reinforced Concrete Structures By Krishna Raju Reader For Free Public FullDiscover the worlds research 20 million members 135 million publications 700k research projects Join for free Public Full-text 1 Content uploaded by Subramanian Narayanan Author content All content in this area was uploaded by Subramanian Narayanan on Nov 27, 2017 Content may be subject to copyright.This name was chosen perhaps due to the fact that this material grows together, due to the process of hydration, from a visco-elastic, moldable liquid into a hard, rigid, solid rock-like substance. ![]() Traditionally, concrete has been primarily composed of cement, water, and aggregates (aggre gates include both coarse and ne aggregates). Although aggregates make up the bulk of the mix, it is the hardened cement paste that binds the aggregates together and contributes to the strength of concrete, with the aggregates serving largely as low-cost llers (though their strength also is important). Concrete is not a homogeneous material, and its strength and structural properties may vary greatly depending upon its ingredients and method of manufacture. Howev er, concrete is normally treated in design as a homogeneous material. Steel reinforcements are often included to increase the tensile strength of concrete; such concrete is called reinfor ced cement concrete (RCC) or simply r einforced concrete (RC). As of 2006, about 7.5 billion cubic metres of concrete were produced each yearthis equals about one cubic metre per year for every person on the earth (see T able 1.1). The National Ready Mixed Concrete Association (NRMCA) estimates that ready-mixed concrete production in 2005 was about 349 million cubic metres in the USA alone, which is estimated to have about 6000 ready-mixed concrete plants. TABLE 1.1 Annual consumption of major structural materials in the world Material Unit Weight (kgm 3 ) Million Tonnes TonnesP erson Structural steel 7850 1244 0.18 Cement 1440 3400 0.48 Concrete 2400 18,000 2.4 (990 litres) Timber 700 277 0.04 Drinking water 1000 5132 0.73 (730 litres) Notes: The estimated world population as of August 2012 is 7.031 billion. Assumed as two litresdayperson Concrete technology has advanced considerably since its discovery by the Romans. Now, concrete is truly an engineered material, with a number of ingredients, which include a host of mineral and chemical admixtures. These ingredients should be precisely determined, properly mixed, carefully placed, vibrated (not required in self-compacting concretes), and properly cured so that the desired properties are obtained; they should also be inspected at regular intervals and maintained adequately until their intended life. Even the cement currently being used has undergone a number of changes. A variety of concretes is also being used, some tailored for their intended use and many with improved properties. Few specialized concretes ha ve compressive strength and ductility matching that of steel. Even though this is a book on RC design, it is important for the designers to know about the nature and properties of the materials they are going to specify for the structures designed by them. ![]() Hence, only a brief introduction is given about them, and interested readers should consult a book on concrete technology (many references are given at the end) for further details. Oxford University Press 2013. V olcanic ash (called pozzuolana, found near Pozzouli, by the Bay of Naples) was a key ingredient in the Roman cement used during the days of the Roman empire. Roman concrete bears little resemblance to modern Portland cement concrete. It was never put into a mould or formwork in a plastic state and made to harden, as is being done today. Instead, Roman concrete w as constructed in layers by packing mortar by hand in and around stones of various sizes. The Pantheon, constructed in AD 126, is one of the structural marvels of all times (Shaeffer 1992). During the Middle Ages, the use of concrete declined, although isolated instances of its use have been documented and some examples have survi ved.
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