The Story of Cement
Created | Updated Apr 27, 2005
It's more than likely that you don't think about cement very much at all, even though it sticks most of the urban environment together. It must surely be one of the most taken for granted man-made products around. It's a grey powder that is mixed with sand and water to make a mortar that's perfect for bonding bricks and stones together. It's also mixed with sand, water and aggregates to make concrete.
Once Upon a Time, Far, Far Away...
... In Mesopotamia, the dressed stones used for buildings were sometimes stuck together with lime mortars. Lime is simply made by heating up limestone to drive out the water, then the stone is ground to a powder. Later sand is added for extra strength and is mixed with water to form a paste that slowly hardens. The ancient Greeks and Egyptians continued this practice (yes, The Pyramids are stuck together with a mortar that uses lime as a cement).
More Recent Ancient Times
The Romans later found that adding clay to the lime mortar made it set quicker and it formed a strong material. They also found that adding volcanic ash (a silicate material) had the same effect. However, many of the Roman methods were lost through the ages, but all round the world lime continued to be used as a cement. Some of these small-scale producers will surely have included clay and other materials to add strength and to control the setting, much as the Romans had done.
Let's Blame Napoleon
In the mid-18th Century, an English engineer, Smeaton, was commissioned to build a lighthouse on the partially-submerged rocks 14 miles off the coast of Plymouth, England. In his effort to build a longer-lasting structure, he took great care in selecting his lime from the many varieties available and he re-introduced the Roman practise of adding a silicaceous material. His Eddystone Lighthouse was so successful that the progress of cement went ahead apace with many people experimenting by adding different materials and types of lime.
However, these lime-based silicate cements and the mortars that were used were not very strong and took a long time to set. As the Napoleonic era began, at the end of the 18th Century, there was a demand for the quick construction of strong buildings for the military, such as forts, harbours and barracks. The French, the British and engineers in many other countries were building furiously for their armies and navies and great rewards were in prospect for anyone finding a material that would enable faster building work and stronger structures.
As the 18th Century came to a close, a type of limestone was discovered that contained naturally 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 strong and fast-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. Similar rocks were soon found elsewhere around the coasts of England, France, Russia and Germany and cements made from them were a great and immediate commercial success. Very soon other deposits of suitable limestones were found, and mines opened up to exploit the deposits, notably in New York State, where the mine owners were able to supply the construction of the fast-growing city of New York using the purpose-built Hudson and Delaware Canal system.
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 natural cements. Working in France for the military, Vicat was among the first to come up with a method of mixing clay and limestone to the right proportions and he also discovered the correct firing temperature for the mixture. He was instrumental in setting up the first cement factory near Paris in 1816. Very early in the 1820s 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 of this latest version of cement to the Portland stone of Dorset in England, used for a lot of construction work at the time.
Ordinary Portland Cement
From the 1820s to the 1880s there existed thousands of small factories producing different types of natural cement, artificial portland cement and limes, each with its own characteristics of strength, setting time and colour.
In the 1860s there was another landmark change in the history of cement. Instead of using the traditional vertical kilns of the lime industry, manufacturers began using a new rotating horizontal kiln, which enabled higher burning temperatures and a consistent product. The cement produced using this method was 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, a circumstance which mitigated against many small traditional family firms in favour of larger companies. By the 1920s 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 made to resist seawater; high strength cements; high alumina cements, that become very strong very quickly; and dense cements suitable for constructions such as nuclear reactors. Also, a few lime and natural cements are available, that are used for restoration work and are sometimes favoured in place of more highly engineered products of the fuel-hungry cement industry.