Magnitude of the stage I drying rate of porous building materials with different porosity

Abstract

In building conservation, many problems are related to the presence of water in porous materials such as stone, mortars and ceramics. Indeed, moisture can be seen as the catalyst for many deterioration mechanisms. It gives rise to harmful chemical reactions, such as sulphate attack, enables biodeterioration and prompts salt decay, one of the most harmful deterioration mechanisms of porous building materials. A better understanding of drying processes can provide an important basis to find efficient ways of controlling the presence and, therefore, mitigating the damaging effects of moisture. In this study we analyze the drying rate of eight porous building materials during the so-called Constant Drying Rate Period (CDRP). Both natural stones and artificial materials were tested: the Bentheimer sandstone, four limestone varieties (Ançã, Lecce, Malta’s Globigerina, and a Portuguese low porosity limestone), red ceramic brick, slaked lime/sand mortar (1:3 in volume) and three kinds of calcium silicate material. The capillary porosity of the stones, mortar and bricks is in the interval 9-27%, whereas two of the calcium silicate materials (with 82% and 83% porosity, respectively) cover the higher range of values.