Testing a 2000-year-old technique 

Natural pozzolana mixed with cement is one of the methods that will be tested in Uganda. The technique of using natural pozzolana was known 2000 years ago, when the ancient Greeks and Romans used the molten lava from erupting volcanoes to build monuments like the Pantheon. On encountering cold air, molten lava forms a material known as pozzolana, which when mixed with lime takes on cement-like qualities.

In recent years, too, tests have been carried out with pozzolana. Three years ago, COWI used artificial pozzolana in the form of shock-cooled blast-furnace slag and local sand to reconstruct the 56 km long main road between Dar es Salaam and Mlandizi in Tanzania. As with natural pozzolana, the metal-free, sand-like product known as slag takes on cement-like qualities when mixed with lime. Dansk Beton Teknik has also previously worked with natural pozzolana in Uganda.

Another method is to mechanically stabilise the road base with local sand, while a chemical method will test the possibility of stabilisation using a liquid by-product from the production of bitumen as a binder. The liquid forms a film around the argillaceous minerals, causing them to compress and solidify. This results in the cessation of chemical processes and reduces the plastic deformation caused by dislocation movement. More traditional methods, such as stabilisation using hydrated lime and cement, are also being tested.


Published: 28.06.2004
By: Christina Tækker, cht@cowi.dk