Joseph Aspdin patented an artificial cement in 1824, made by burning ground limestone with clay and grinding the product; Isaac Johnson's higher, clinkering kiln temperatures from about 1845 produced true Portland cement with reliable strength. Unlike lime mortar it sets hydraulically — under water — and gains strength predictably, so it could be specified by test rather than by craft judgement. Rotary kilns from the 1890s turned it into a bulk commodity, and it became the binder for mass concrete, mortar, precast units and eventually reinforced concrete. By the 20th century it was the most-used manufactured material on earth.
Portland cement is what made 19th-century sanitary and harbour engineering possible: sewer eggs, aqueduct siphons, dock walls, dams and foundations that hold in water. As a cheap, standardised, testable material it also decoupled construction from local stone and skilled masonry, enabling mass housing, road and bridge programmes anywhere with a kiln. Its carbon intensity — roughly 7 to 8 per cent of global CO2 emissions — is now a central constraint on how cities can be built.
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