ConcreteConcrete is a hardened building material created by combining a chemically inert mineral aggregate (usually sand, gravel, or crushed stone), a binder (natural or synthetic cement), chemical additives, and water. Although people commonly use the word cement as a synonym for concrete, the terms in fact denote different substances: cement, which encompasses a wide variety of fine-ground powders that harden when mixed with water, represents only one of several components in modern concrete. As concrete dries, it acquires a stone-like consistency that renders it ideal for constructing roads, bridges, water supply and sewage systems, factories, airports, railroads, waterways, mass transit systems, and other structures that comprise a substantial portion of the U.S. wealth. According to the National Institute of Standards and Technology (NIST), building such facilities is in itself one of the nations largest industries and represents about 10 percent of the gross national product. Over $4 billion worth of hydraulic cement, a variety which hardens under water, is produced annually in the United States for use in $20 billion worth of concrete construction. The value of all cement-based structures in the United States is in the trillions of dollarsroughly commensurate with the anticipated cost of repairing those structures over the next twenty years.The words cement and concrete are both of Latin origin, reflecting the likelihood that the ancient Romans were the first to use the substances. Many examples of Roman concrete construction remain in the countries that encircle the Mediterranean, where Roman builders had access to numerous natural cement deposits. Natural cement consists mainly of lime, derived from limestone and often combined with volcanic ash. It formed the basis of most civil engineering until the eighteenth century, when the first synthetic cements were developed.The earliest manmade cement, called hydraulic lime, was developed in 1756, when an English engineer named John Smeaton needed a strong material to rebuild the Eddystone lighthouse off the coast of Devon. Although the Romans had used hydraulic cement, the formula was lost from the collapse of their empire in the fifth century A.D. until Smeaton reinvented it. During the early nineteenth century several other Englishmen contributed to the refinement of synthetic cement, most notably Joseph Aspdin and Isaac Charles Johnson. In 1824 Aspdin took out a patent on a synthetic blend of limestone and clay which he called Portland cement because it resembled limestone quarried on the English Isle of Portland. However, Aspdins product was not as strong as that produced in 1850 by Johnson, whose formula served as the basis of the Portland cement that is still widely used today. Concrete made with Portland cement is considered superior to that made with natural cement because it is stronger, more durable, and of more consistent quality. According to the American Society of Testing of Materials (ASTM), Portland cement is made by mixing calcareous (consisting mostly of calcium carbonate) material such as limestone with silica-, alumina-, and iron oxide-containing materials. These substances are then burned until they fuse together, and the resulting admixture, or clinker, is ground to form Portland cement.
What made the difference was aloof frontwoman Victoria Bergsman, who last year dramatically left the band hours before an appearance on the Jonathan Ross show. This in the wake of a traumatic trip to the States, where she collapsed on a New York stage and the band had their equipment nicked in Boston. The Concretes have recruited a new singer from within their own ranks- drummer Lisa Millberg. Taking just the bands nervy start, Millberg seems to be a mistake. The gangly blondes awful melodic aim makes you fear for the lights. You only snatch at rare moments where she finds a delicate sigh that matches the tenderness of certain songs. Uncomfortable at the front of the stage, Millberg continually seeks reassurance from colleagues, especially guitarist Maria Eriksson, with whom she shares some wayward call and responses. Yet Millberg connects with the crowd, not only through vulnerability, but also with a playful banter unknown in previous shows. She points out that this is the 11th time the outfit have performed in London and adds that “the venues keep getting smaller”. Such is The Concretes plight that the vocalist introduces “Oh Boy” with an urge to vote for their forthcoming single on digital station BBC6. This is one of the few numbers close to matching the band in their pomp.
Prepared by a Working Party of The Concrete Societys Materials Group
vertical stamping fort worth
No comments »