Traditional brick productions in Madagascar: From raw material processing to firing technology

Bricks are the most common building materials of Madagascar due to the large availability of clayey raw material, the simple technology of production and the ease of use. The brick production is mainly organised in local workshops close to supplying site of clayey deposit where sediments are extracted, moulded in bricks, dried and then fired in open-air furnaces. Fuel varies from peat soils to wood depending on the local availability. Correspondingly, firing time varies from few days in wood furnaces to some weeks in peat fired furnaces. Samples of bricks and raw materials as well as peat fuel, from four workshops located in central and southwestern Madagascar were collected and analysed to infer the technological skills of the Malagasy traditional brick manufacture. Central Highlands Madagascar workshops use clayey lateritic soils formed from in situ weathering of basement rocks. The main plastic component of these deposits is kaolinite. Also the clayey sediments from southwestern Madagascar have kaolinite along with low-ordered clay minerals and carbonates such as calcite and minor Sr-rich dolomite. As far as fired bricks are concerned, experimental data evidenced quite low firing temperatures (below 600 °C) in the two different furnaces, regardless the type of fuel. As far as peat fuel is concerned, its low calorific value along with a large amount of furnace energy dispersion does not allow to achieve the temperatures required to produce good quality bricks, notwithstanding long firing time (some weeks). On the other hand, firewood powdered furnaces, although providing much higher energy and a consequent much shorter firing process (few days), also suffer of diffuse heat dispersions which concur to the bad quality of the final product. The specific energy input calculated for type 1 furnace (peat fuel) ranges between 0.09 MJ/kg and 0.18 MJ/kg of clayey material thus confirming a rather inadequate firing process for the production of good quality bricks, and a rough estimate indicates that volume ratios between peat and clayey material as low as 1:1 should be used in order to reach “modern” specific energy inputs