Brick of the Historical Heritage: Comparative Analysis of The Thermal Conductivity, Density and Moisture

Abstract

In the renovation of historic buildings, the facades deserve special attention because, in general, it is where the property’s value and heritage lies. Additionally, they have a fundamental impact in the energetic efficiency of buildings. When you want to achieve an efficient building, the facades must comply with certain construction standards, generally difficult to achieve in renovations, especially in facades built with exposed brick, not altering their external appearance is a sine qua non condition. Against this background, in order to carry out optimal interventions in the thermal behavior of a brick wall, it is essential to have an exhaustive knowledge of the characteristics and values that influence thermal conductivity. To do so, calculations and simulations are carried out using the density and porosity parameters that are published in the different documents and regulations. However, these values are not reliable because they refer to the materials currently manufactured, and therefore, they are not valid when working with centenary materials that have been produced without quality control or precise technical specifications. On the other hand, the values provided by the regulations refer to the material in the dry state. It has not been considered that bricks, and especially those manufactured manually, due to their intrinsic conditions, are capable of absorbing large amounts of water, and therefore, of significantly varying its thermal conductivity. This feature is extrapolated to brickwork facades, where water can rise from the ground and penetrate from the rain. Thus, it is necessary that in the thermal conductivity study its hygrothermal behavior is taken into consideration. Against this background, this article presents the results of the tests carried out on specimens of various bricks from different traditional bricks factories and manufacturing processes and with an approximate age of about 100 years, to show that the old bricks have very different density, porosity and thermal conductivity values from the current ones. In addition, these values vary greatly depending on the moisture they contain, and also, the manufacturing system they had. Likewise, it is clear that the bricks of the facades of historic buildings, even if they are contemporaries, have different characteristics among them, showing different thermal behavior.