# Study About the Influence of Diatoms on the Durability of Monumental Limestone
## 2 Materials and Methods  
### Materials  
A total of 18 samples were used for the tests: 9 experimental samples and 9 control samples. All samples were made from limestone rock originating from Bonar, Spain, cut into cubes with 50 mm edges. Limestone has been widely used throughout history as a construction material, either in its natural form or crushed for use as aggregate. Manymonuments and historic buildings were constructed using limestone, and this remains an important component in the production of cement and stucco today.  
Limestone is a sedimentary rock formed by the accumulation of sediments that undergo a series of physical and chemical processes, leading to their consolidation into coherent and solid rock. This rock is primarily composed of calcium carbonate, often containing varying amounts of magnesite and other carbonates, along with small quantities of minerals such as clay and quartz. The action of water, in particular when containing carbonic acid, causes limestone dissolution through a chemical weathering process known as karstic weathering [22; 23; 24].  
The Borbar stone used in the present work is a fine-grained dolomitic limestone from the Campanian age, with cream to beige-ochre tones. This is a compact, uniform, sedimentary rock extracted in large regular blocks. The stone shows some sedimentary structures such as laminations, bioturbations, and trace fossils, indicating a lagoon-type depositional environment. Its appearance is homogeneous and finely granular, with reddish grains of varying sizes and occasional intergranular spaces filled with coarse calcite, sometimes associated with fossil remains. Its texture is crystalline and fine-grained, with an equigranular granoplastic structure and idiomorphic to subidiomorphic dolomite crystals showing a relict clastic texture. Physical and mechanical specifications are presented in detail in Table 1.  
The samples were evenly distributed across the surface of a pond to minimize potential variations among them. These specimens were submerged at a depth of 15 \(\pm\) 5 cm below the water surface, with the test face oriented parallelly to the bottom to promote the growth of diatoms. This positioning is crucial, as previous studies on concrete [14; 15] have demonstrated that orientation significantly influences the biodeposition process.  
For this reason, it is important to clearly determine the position of the faces or surfaces of the samples submerged in the pond throughout the entire experimental work. As shown in Figure 1, samples are placed with their upper face marked in red. In this manuscript, the different surfaces of these samples are referred to as:  
* Upper face: marked with a red square.
* Lateral faces: the four faces adjacent to the upper one and marked with a blue line.
* Lower face: the face opposite to the upper face.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Test** & **Standard** & **Unit** & **Value** \\ \hline True density & UNE-EN 1936 [25] & **kg/m3** & 2832 \\ \hline Apparent density & UNE-EN 1936 [25] & **kg/m3** & 2510 \\ \hline Compressive strength & UNE-EN 1926 [26] & **MPa** & 117 \\ \hline Static elastic modulus & UNE-EN 14580 [27] & **MPa** & \(34\times 10^{3}\) \\ \hline Flexural strength & UNE-EN 12372 [28] & **MPa** & 16 \\ \hline \end{tabular}
\end{table}
Table 1: Physical and mechanical properties of Borbar stone.