Cement
Cement is a fine ground powder which when mixed with water forms a paste which quickly dries and hardens. Cement is an excellent binding agent and is often used in construction applications to create a bond between the surfaces of two or more objects. Cement is also used heavily in the manufacturing of both concrete and mortar, where its binding properties are used in conjunction with various aggregates to form strong and durable building materials. The most commonly used type of cement today is Portland cement, patented in 1824, and so named by its inventor, Joseph Aspdin, because he thought that the color of the cement was very similar to the limestone which was mined at the time from the Isle of Portland in the English Channel.
Cement Ingredients
Long story short, cement is made by transforming quarry rock into a powder so incredibly fine that it will even pass through a sieve capable of holding water. The most commonly used type of modern cement, Portland cement, is made by blending iron, aluminum, silicone, and calcium. These are extracted from one or more of the following sources: limestone, chalk, silica sand, iron ore, shale, shells, clay and blast furnace slag.
Though cement appears to be a fairly dull and simple substance, a great deal of effort must be expended in the manufacturing process to ensure that the raw material mix contains the correct amounts of each element, and that production conditions such as temperature and pressure remain within acceptable predetermined limits throughout the process. Deviations in any of these elements could jeopardize the quality of the entire batch.
A major part of the cement producing process is microscopy, a science which involves analyzing the structure of materials on a microscopic level, and which allows producers to know the precise amounts of each of the elements present in a sample, and how these elements are bound together. Without the ability to tell exactly what elements are present in a sample, and in what quantites they are present, it would be almost impossible to create a homogeneous cement product that could be relied upon to behave in the same fashion, and possess the same chemical and physical properties as other cement batches when mixed and poured. This could be potentially disastrous in construction applications where strength tolerance, chemical resistance, and other factors must be consistent and predictable from batch to batch.
Making Cement
The actual production of cement involves crushing large amounts of rock, reducing it little by little until no piece exceeds roughly three inches in diameter. Usually this takes place in two stages, with large rocks being crushed and broken up, and then the smaller pieces being hammered until they reach the desired size. In some operations, this crushing is undertaken in a one step operation which reduces large chunks of rock into small fragments relatively quickly.
Once the rocks are crushed there are two possible means of processing the raw materials further. The first process, the ‘dry’ process, involves grinding the rock up into a very fine powder and sending it into a kiln in a dry state. In the second type of process, the ‘wet’ process, the raw rock and other materials are mixed with care to predetermined specifications, and mixed with water before being ground up and fed into the kiln wet.
Of course, it is not so simple as merely grinding up rock and then heating it in a kiln. The ground rock must first be analyzed to determine its content, and then blended in correct proportions before it is sent on to the kiln. In order to get to the kiln, the ground rock is sent through a preheated tower, where the raw material is preheated by the gases exiting the kiln, speeding the process up and saving the plant a great deal of energy and expense.
Once inside the kiln, which is a very large structure, sometimes over three meters in diameter and over sixty meters tall, the materials are heated to tremendous temperatures of 2,700 degrees Fahrenheit or more. The firing process melts the materials and causes waste gases to be released, (the same gases which are then used to preheat the raw material entering the kiln), and as the gases are released, the various elements form entirely new compounds, and emerge from the kiln in the form of pebble type structures called ‘Clinker’. To the clinker is added gypsum, a chemical which helps control the way that cement sets. The clinker is then ground down in a rotating chamber into the very fine power that comprises cement, packed into bags, and sent off for mixing and use in construction applications.