Portland cement

On October 21, 1824, Joseph Aspdin, a bricklayer in Leeds, England, patented a method of making artificial cement by burning ground limestone and clay together, then grinding the result. He called it Portland cement because the hardened material resembled prized Portland stone from the Dorset coast. Mixed with water, sand and gravel, it sets into concrete, and it hardens even under water.¹

Builders had searched for such a binder since the Roman concrete of the first century BCE, whose volcanic ash recipe was lost in medieval Europe. In the 1750s the engineer John Smeaton rediscovered that limestone containing clay made a hydraulic lime when building the Eddystone Lighthouse, and in the early nineteenth century Britain's canals, docks and harbors created demand for a reliable cement. Competing inventors included Louis Vicat in France and James Parker's 'Roman cement'. Aspdin's own product was probably not the modern material, since it was fired at too low a temperature. In the mid-nineteenth century Isaac Johnson, a Kent manufacturer, fired a mix hot enough to partly fuse it into a hard clinker, producing the strong cement that the world still calls Portland.¹

Rotary kilns, introduced in the 1880s, made production continuous, and cement became a global industry. Concrete is now the most used human-made material on Earth, with more than 4 billion tonnes of cement made annually. It built the Hoover Dam, highways, sewers and skyscraper foundations. It has a cost: cement-making releases carbon dioxide from heated limestone and fuel, and the industry is responsible for roughly 7 to 8 percent of global carbon emissions, a problem that engineers now work to reduce.¹²³