Anisotropy is a petrophysical property of natural stone and other construction materials that determines their quality and resistance to decay caused by a variety of agents, such as water. A study was conducted on nine types of stone widely used in Spain's built heritage, using six previously defined anisotropy indices. This paper proposes a new index (dMm) related to the two indices, dM and dm, that best reflect anisotropy in materials. These indices can be used to determine the degree of anisotropy, which helps explain the differential decay observed in stone materials quarried in the very same bed and used to build the same structure. The conclusion reached is that anisotropy should be determined in the natural stone used both to restore the architectural heritage and in new construction, for the appropriate choice of material quality ensures greater resistance to decay and, therefore, increased durability. Materials with the lowest possible anisotropy should be selected, as this property governs their hydraulic behaviour: the lower the anisotropy in a material, the better its behaviour in relation to water and the longer its durability. 1-Introduction All kinds of natural stone used in construction have certain properties that vary according to the direction in which they are measured: in other words, they are anisotropic. A variety of causes of anisotropy in rock can be identified, including crystal and grain orientation, the accumulation of minerals, stratification and lamination, stress orientation and the number and orientation of pores and cracks. Anisotropy, then, which depends on composition, texture and structure (Takemura et al 2003, Guéguen and Schubnel 2003), is directly related to the origin of rocks and any subsequent alteration. Every type of rock (granite, limestone, slate, marble) has its own level of anisotropy. Ascertaining anisotropy in natural stone and how it develops is of utmost importance, for this information is essential to determining: a) how it should be quarried and most efficiently processed; b) the quality of the stone products and their suitability for use as ashlars or ornamental elements; and c) its placement on buildings. This is why the use of natural stone in construction is influenced by its anisotropy index. Likewise, the directions of anisotropy have a bearing on stone material decay and consequently on its quality and durability (Fort et al 2008, Fernandez-Revuelta et al 2008, Sheremeti-Kabasti and Snethlage 2000). These issues must be considered when planning restoration work on the architectural heritage, or when a certain type of natural stone is to be used for structural, aesthetic or insulation purposes in new construction, whether of buildings or civil works.
This study examines the microbial colonization of three fronts of an abandoned dolostone quarry (Redueña, Madrid, Spain) exposed to atmospheric conditions for different time periods since Roman times to the present. Through scanning electron microscopy in backscattered electron mode (SEM-BSE), endolithic colonization was predominantly detected in the most recently exposed front, while in the longer exposed quarry fronts, epilithic forms of growth were most often observed. These observations were confirmed by denaturing gradient gel electrophoresis (DGGE) analysis. Based on the distribution pattern of microbial colonization in the different quarry fronts, we then established a sequence of colonization events that took place over this long time frame. Bioalteration processes related to this sequential colonization were also identified. Characterizing these sequential processes can be useful for interpreting biodeterioration processes in historic dolostone monuments, especially those affecting constructions in the area of the Redueña stone quarry. In a second experimental stage, different biocide treatments were tested on this quarry rock to find the best way to avoid the microbial colonization effects identified. Through combined SEM-BSE/DGGE analysis, the efficacy of several biocides against the microorganisms inhabiting the dolostones was assessed after 4 and 16 months treatment. In general, all treatments were effective at reducing around 80% of the lichen cover, although effects on endolithic lithobiontic communities were dependent on how well the rock surface had been mechanically cleaned prior to treatment and gradually disappeared over time.
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