Cement
June 3, 2009 by blogtopia
Filed under Definitions
In the most general sense of the word, a cement is a binder, a substance which sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term "opus caementicium" to describe masonry which resembled concrete and was made from crushed rock with burnt lime as binder. The volcanic ash and pulverized brick additives which were added to the burnt lime to obtain a hydraulic binder were later referred to as cementum, cimentum, cäment and cement. Cements used in construction are characterized as hydraulic or non-hydraulic.
The most important use of cement is the production of mortar and concrete – the bonding of natural or artificial aggregates to form a strong building material which is durable in the face of normal environmental effects.
Portland cement
June 3, 2009 by blogtopia
Filed under Definitions
Portland cement is the most common type of cement in general use around the world, because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout. It is a fine powder produced by grinding Portland cement clinker (more than 90%), a limited amount of calcium sulfate which controls the set time, and up to 5% minor constituents (as allowed by various standards).
As defined by the European Standard EN197.1, "Portland cement clinker is a hydraulic material which shall consist of at least two-thirds by mass of calcium silicates (3CaO.SiO2 and 2CaO.SiO2), the remainder consisting of aluminium- and iron-containing clinker phases and other compounds. The ratio of CaO to SiO2 shall not be less than 2.0. The magnesium content (MgO) shall not exceed 5.0% by mass." (The last two requirements were already set out in the German Standard, issued in 1909).
Rosendale cement
June 3, 2009 by blogtopia
Filed under Definitions
Rosendale cement refers to a type of natural cement produced in and around Rosendale, New York. Because of its reputation, "Rosendale Cement" has also been used as a generic term to refer to natural hydraulic cement produced elsewhere. It was used in the construction of many of the United States most important landmarks, including the Brooklyn Bridge, the pedestal of the Statue of Liberty, Federal Hall, and one of the wings of the United States Capitol building.
Natural cement is produced in a simple process that begins with the calcination of crushed carbonate sedimentary rocks in kilns. The resulting clinker is ground into a fine powder before being shipped to market. Historically, this natural cement product was packaged in paper-lined wooden barrels or heavy canvas bags.
Cement kiln
June 3, 2009 by blogtopia
Filed under Definitions
Cement kilns are used for the pyroprocessing stage of manufacture of Portland and other types of hydraulic cement, in which calcium carbonate reacts with silica-bearing minerals to form a mixture of calcium silicates. Over a billion tonnes of cement are made per year, and cement kilns are the heart of this production process: their capacity usually define the capacity of the cement plant. As the main energy-consuming and greenhouse-gas–emitting stage of cement manufacture, improvement of their efficiency has been the central concern of cement manufacturing technology.
The objective of kiln operation is to make clinker with the required chemical and physical properties, at the maximum rate that the size of kiln will allow, while meeting environmental standards, at the lowest possible operating cost. The kiln is very sensitive to control strategies, and a poorly run kiln can easily double cement plant operating costs.
Calcium aluminate cements
June 3, 2009 by blogtopia
Filed under Definitions
Calcium aluminate cements are cements consisting predominantly of hydraulic calcium aluminates. Alternative names are "aluminous cement", "high-alumina cement" and "ciment fondu". They are used in a number of small-scale, specialist applications.
The method of making cement from limestone and low-silica bauxite was patented in France in 1908 by Bied of the Pavin de Lafarge Company. The initial development was as a result of the search for a cement offering sulfate resistance. The cement was called "Ciment Fondu". Subsequently, its other special properties were discovered, and these guaranteed its future in niche applications.