THE TRANSFORMATION OF ADDED VEGETAL WASTE MATERIALS DURING CLAY BRICK FIRING

Since ancient times, the enhancement of properties of fired clay products was solved by adding different materials to the clay mixtures. The role of added materials, such as sand or vegetal materials (mainly straw) was to reduce the plasticity of mixtures — slenderizing — for shaping. But the non-plastic components introduced also inhibited the shrinkage of products, by two mechanisms. Frequently, excessive plasticity of raw clays was treated by the addition of vegetal materials, usually straw. The same technique was applied when an increase in the dry mechanical resistance was desired. By the increasing energy demand of heating of buildings for human living, the attention of brick producers was directed towards the thermal insulation capacity of building materials. In the case of traditional clay brick, the solution for increasing the thermal insulation capacity is the artificial increase of porosity. Beyond the primary porosity of fired clay material, caused by the decomposition of carbonates, contraction of clay minerals and organic matter combustion, the introduction of pore-forming additives contributes to the increase of porosity of bricks