Predicting the initial rate of water absorption in clay bricks

In this work the capillary suction behaviour of fifteen clay bricks was investigated (UNI 10859) in order to assess the effect of product characteristics and processing conditions and to verify the reliability of the available models. The suction behaviour of bricks, in terms of both total amount of liquid absorbed and kinetics of the process, can basically be brought back to the models of Gummerson et co-workers and Hoffman and Niesel; these latter, however, do not make provision for the effect of product microstructure and water physical properties on the liquid-porous solid interactions. Even if experimentally the liquid suction presents a first dependence on the amount of porosity - a less dense ceramic body is undoubtedly able to absorb a larger liquid amount - other characteristics of the porous structure (size, tortuosity and internal specific surface of the capillary system, as well as the presence of mineralogical phases) request to be more deeply investigated since they could affect the process kinetics. According with the Beltran's model, which revealed to be sufficiently reliable, the values of capillary coefficient Ks were calculated and their correlation with the experimental ones has been provided. The results obtained indicate that, for a given liquid and in the same experimental conditions, varying in a controlled way the product microstructure (i.e. decreasing the pore size, increasing the pore tortuosity and/or controlling the amorphous/new formed phases ratio) should allow to design materials having a more suitable behaviour.