The Search for Affordable Cement and Concrete in the 18th and 19th Century

At the turn of the 19th century, the production and use of concrete were limited by the unavailability of raw materials to produce good cement in several places. From that time onwards, the progress of chemistry and a number of empirical discoveries opened new possibilities. Lime, natural cements and volcanic additives - like pozzolana and trass - were analysed on scientific bases, their compositions were ascertained and it became possible to reproduce these substances artificially from raw materials that were affordable and easy to find. This was a fundamental step to reduce the cost of concrete and allow a better spread of it. A second step was the search for affordable mixtures. The key factors were: a reduced use of cement and the provision of aggregates from local and recycled materials. A number of different mixtures were developed and tested. The main components were hydraulic lime, aerial lime - with or without pozzolana or trass - Roman cement, Portland cement and several kinds of aggregates. The paper will analyse the development of modern cement and the evolution of concrete mixtures during the first three quarter of the 19th century, from the rudimental and less-known experiments by Carl August Rydin in Sweden to the compounds by François Coignet in France and the early use of slags in concrete, going through the attempts at using lean conglomerate instead of concrete in several German countries around 1850. The search for affordability will be the interpretation key, based on the hypothesis that the need for affordable concrete mixtures is increasing nowadays - especially in developing countries where economic constraints are significant - and the interest of scientists and entrepreneurs in historic concrete is growing.