It’s in buildings all around us. It’s in the roads we walk on. In fact, it’s the most widely used man made material on the planet. We consume around 30 billion tonnes of it a year. So what is it?
The simple answer is cement. But what is it really? One definition of cement is that it is a binder, a substance that sets and hardens independently, and that binds other materials together.
Cement is made by grinding calcified limestone, the stuff in caves that makes stalagmites and stalactites, and clay (i.e. pottery) into a fine powder, which can be mixed with water. It is then poured to set as a solid mass or used as an ingredient in making mortar or concrete.
The most important use of cement is the production of mortar and concrete. Here, cement is added to natural or artificial aggregates -- gravel and sand are examples -- to form a strong and durable building material.
Both concrete and cement have been used for thousands of years, the ancient Romans (see photo right) are one of the first known users but this doesn’t stop common misconceptions about the two substances to remain.
One common one is to confuse concrete with cement when the latter is actually an ingredient of the former. As has been said, the term cement refers to the material used to bind the aggregate materials of concrete. Concrete is a combination of a cement and aggregate.
Here is a technical explanation of cement production from Wikipedia: “Cement is made by heating limestone (calcium carbonate) with small quantities of other materials (such as clay) to 1450 °C in a kiln, in a process known as calcination, whereby a molecule of carbon dioxide is liberated from the calcium carbonate to form calcium oxide, or quicklime, which is then blended with the other materials that have been included in the mix. The resulting hard substance, called 'clinker', is then ground with a small amount of gypsum into a powder. This sets when added to aggregates and water via a number of complicated chemical reactions.”
Interestingly, although the process for making concrete has been around with some modifications for thousands of years the molecular structure of cement was only worked out by scientists a few years ago. A good video showing the structure of concrete under an electron microscope can be found here.
Making cement commercially is a resource and energy-intensive process, and cement factories are usually large operations that produce many million tons of cement a year. One company making cement in Indonesia is Holcim Indonesia.
Currently Holcim produces cement at two factories in Indonesia: in Narogong, West Java, Cilacap in Central Java; and soon in a third factory in Tuban, East Java. The cement that Holcim produces is used by large customers, like developers for high rise building, and also by many retail customers to build houses.
Holcim cement is produced as sustainably as possible. By mixing Indonesia’s natural limestone resource with mineral components and selected alternative materials such as pozzolana and fly ash in the production of our cement, Holcim cement consumes less energy to produce, and conserves coal and lowers the level of CO2 produced per ton of cement. For more information, see Holcim’s corporate website, their retail website for home owners and builders, Membangun Bersama and Holcim’s co-processing business Geocycle.