You will probably think of cement as a grey powder that is mixed with sand and water to make mortars that stick bricks and stones together, or with sand, water and aggregates to make concrete. More likely, even though it sticks most of the built environment together, you will never think of it at all. It must surely be one of the most 'taken for granted' man-made products around.

Once upon a time, far, far away...

In Mesopotamia, and probably many other Ancient places, the dressed stones used for buildings were sometimes stuck together with Lime mortars. Lime is very simply manufactured by heating limestone to drive out the water, grinding the stone to a powder, and then, later, adding water to the powder to form a paste that slowly hardens. Sand is added for extra strength. The practice continued with the Egyptians (yes, the pyramids are stuck together with a mortar that uses Lime as the cement) and Greeks.

In Ancient Times

The Romans later found that they could add clay to the lime mortar to make it set quicker and form a stronger material. They also used volcanic rock for the same purpose (as a source of silicates, although they wouldn't have known the chemistry). Much of the Roman practice was lost through the ages, but all round the world Lime was used as a cement to make mortars and concretes. Some, like the Romans, will surely have included clay and other materials to add strength and control the setting.

Lets blame Napoleon

Fast forward to the mid eighteenth Century. An English engineer, Smeaton was commissioned to build a lighthouse in a particularly difficult area on the south coast, and in his efforts to build a longer lasting structure, he took great care to selected his Lime from the wide variety available, and re-introduced the Roman practice of adding a silicaceous material. His lighthouse was successful, and work proceeded apace with many people experimenting with different types of Lime and adding materials to it. However, lime based cements and the mortars derived from them are not very strong, and take a long time to set. As the Napoleonic era started at the end of the 18th Century, there was a demand for quicker construction of strong buildings for the military; buildings such as Forts, Harbours and Barracks. The French, the British, and engineers in many other countries were building furiously for their Armies and Navies. Great rewards were in prospect for anyone finding a material that would enable faster building work and stronger structures.

Cement Stones

As the eighteenth century closed, a type of Limestone was discovered that had, already contained within the rocks, the right amount of clay. When these special 'Cement Stones' were fired in the same way as traditional Lime, they produced a 'cement' that was much stronger and faster setting. These 'Natural Cements' were first found as single unattached rocks or 'nodules' on the Isle of Sheppey in the UK and near Bordeaux in France. More were soon found around the coasts of England, France, Russia and Germany and the cements made from them were a great and immediate commercial success. Very soon deposits of suitable Limestones were found in many places and mines started to exploit the deposits, notably in New York State, where the suppliers were able to feed the construction of the fast growing city of New York using the purpose built Delaware and Hudson Canal.

A whole load of different cements

Deposits of suitable limestone were not always so conveniently located, and the rush was on to manufacture an artificial material to compete with these Natural Cements. Working in France for the Military, Vicat was among the first to put together a method of mixing clay and limestone in the right proportions and firing at the right temperatures. He was instrumental in setting up the first factory near Paris in 1816. Very early in the 1820,s English and German engineers and scientists developed similar methods, and it was an Englishman, Aspdin, who first used the name 'Portland' Cement because of the similarity in colour to the Portland Stone from Dorset in England, used for much construction work at the time.

Ordinary Portland Cement

From the 1820's to the 1880's there were many thousands of small factories throughout the world producing many different types of Natural Cement, Artificial Portland Cement and Limes, all with different characteristics of strength, setting time, colour etc. In the 1860's there was another change. Instead of using the traditional vertical kilns of the Lime Industry, there was a switch to a new rotating horizontal kiln, which enabled higher burning temperatures and a consistent product. The cement so produced was very much stronger and faster setting than its predecessors, and could be produced to much tighter quality standards. It also required a much greater capital investment, mitigating against the many small traditional family firms and favouring the large companies. By the 1920's this new Ordinary Portland Cement had by far the greater part of the market, and is the root of the modern family of materials that we blithely call cement, manufactured, almost exclusively, by giant multi-national corporations.

A Family of Cements

It truly is a family, there is the Ordinary Portland Cement, the common grey stuff, there are white cements, sulphate resisting cements to resist seawater, high strength cements, high alumina cements that have very high strength very quickly, dense cements for such things as Nuclear Reactors, a great many different types. There are also a few remaining Lime-cements and Natural Cements that are of interest not only for restoration work, but also for special purposes and sometimes in preference to the more highly engineered products of the fuel-hungry Cement Industry.

LINKS

If you would like to know more about cement, and who wouldn't, here are some interesting links to start you off:

• http://www.portcement.org The main site for the US Cement Industry
• http://www.widowjane.org This includes the story of Rosendale Cement from New York State, and includes many links enabling you to explore the history of the widowjane mine, the canals to New York, the town, the company and present museum and archive
• http://casamaures.free.fr Just interesting, a very early, exotic, prefabricated concrete building, now the headquarters of the local sundial preservation society. In French, with an English summary and plenty of pictures.