Development of Portland Cement – Landmarks
From ancient times, human civilizations have searched for ways and mixtures to join stones and other raw materials into a solid form useful for constructing purposes. And, with many trials the Assyrians and Babylonians were the first to pick up the concept by using clay as a natural binder. During the same time, the Egyptians discovered lime and gypsum, which highly contributed to the building of the famous pyramids.
The Greeks also went on to make further contributions toward the construction realm. Yet with advanced cements from the Romans, who developed a highly durable cement, building became much more sturdy. With such a discovery, renowned Roman structures were built, such as the famous Roman Baths, constructed around 27 B.C. The Coliseum and Constantine’s vast basilica are other examples of ancient Roman architecture which made use of cement binders.
The secret of success of the Roman’s caementum came from a combination of lime with “pozolana”, a volcanic ash from Mount Vesuvius in the area around Pozzuoli. This process yielded cement, which was more resistant to salt and freshwater. The craft was lost during the Middle Ages and was only revived by the enterprising scientists of the eighteenth century who rediscovered the concept of hydraulic cement which hardens even when submersed in water.
John Smeaton, an English engineer, was faced with the challenge of building a solid structure for Eddystone lighthouse on the Cornish Coast. He undertook a series of experiments with binders in fresh water as well as salt water and discovered cement based on limestone. Limestone mixed with the right proportion of clay hardened under water, for that reason it was used in building the lighthouse in 1759. The original cement lasted 126 years without needing any reinforcement!
Prior to the discovery of Portland cement, large amounts of natural cement were used, which were obtained from burning a natural mixture of lime and clay. As this mixture existed in nature without any human intervention, the properties of this cement varied widely.
In 1830, Joseph Aspdin patented the process for manufacturing a hydraulic binder by combining precise proportions of lime and clay. This would reduce the combined to dust and fire them in a kiln, thereby producing clinker, which was then grinded until it turned into cement.
The resulting product, once milled, has colour and characteristics similar to those of the stones on the island of Portland. That is how the product got the name Portland cement.
Later, in 1844, I. C. Johnson defined the first precise rules for calculating the blend of raw materials, paving the way for scientific control of the whole production process.
Portland cement today, as in Aspdin’s time, is a pre-determined and carefully measured chemical combination of calcium, silica, iron and aluminum. It is yielded by a complex manufacturing process which is subject to rigorous control and involves a wide range of operations.