higher concentration 128on the first millimetres of the material surface, while lower concentrations correspond to deeper sampling. In our case sampling depth has been 5 mm from the surface. Nevertheless, sampling depth in literature works usually it is not adequately reported (Ahmad & Haris Fadzilah 2010; C, Lopez-Arce et al. 2016). Hence, a comparison is risky and not appropriate (Figure 3).
Table 2: Stone Physical-mechanical Characteristics.
| Characteristic | Quarry Stone |
| VR (mm3 × 105) | 1.55±0.11 |
| Ms (g × 102) | 2.75±0.12 |
| Mh (g × 102) | 1.03±0.09 |
| Md (g × 102) | 1.55±0.12 |
| P0 (%) | 42.78±1.88 |
| ρb (kg m–3) | 1411±47 |
| SUCS (MPa) | 1.86±0.36 |
VR is Real Volume Po Open Porosity, ρb Apparent Density, md is the Dry mass, ms Saturated mass, mh water immersion mass, SUCS is Stone Uniaxial Compressive strength
Figure 3: Structure samples Ion Chromatography results elaborated with Runsalt®.
Salt crystallization process is not directly observed in the structure surface of the area of study, nevertheless, a careful revision of the whole structure should be done to eventually detect this type of deterioration and compare salt concentrations with generic sections of the structure and define if ion chromatograph results are effectively reliable to correctly detect the deterioration process in this case of study.
Results were further analysed with Runsalt software (V. 1.9), (Bionda 2005). It is the graphical user interface to the ECOS thermodynamic model (Price 2000). It allows to define which salts are crystallizing from a mixture depending on temperature and RH conditions. The ion contents, as determined by IC, are input for the model. As an example, sample 5 ion and cation values were introduced as a input, as well as the average temperature in Cartagena, 27.7 °C according to DIMAR (2018).
Table 3: Ion Chromatography results (%), input data of Runsalt. N.= Number of Sample.
| N | Cl– | SO4– | NO3– | Na+ | Mg+ | K+ |
| 1 | 0.044 | 0.171 | 0.048 | 0.074 | 0.025 | 0.042 |
| 2 | 0.196 | 0.15 | 0.005 | 0.25 | 0.036 | 0.003 |
| 3 | 0.861 | 0.587 | 0.016 | 0.814 | 0.11 | 0.077 |
| 4 | 0.481 | 0.162 | 0.035 | 0.431 | 0.037 | 0.064 |
| 5 | 0.115 | 0.134 | 0.008 | 0.207 | 0.04 | 0.007 |
Results are reported in Figure 3 and are similar for the whole structure samples. The mix of salts on the samples is identified and Relative Humidity of equilibrium (RHeq) is reported for each salt in the solution. It is worth to mention that Cartagena stands in a tropical area, with a Relative Humidity range between 72 % to 90 % during the year, considering minimum and maximum values of daily and seasonal variations. From these preliminary studies, Thenardite and Bloedite could crystalize having a RHeq of 75 %, although their role on the material deterioration should be further studied, for example pondering whether the number of crystallization cycles per year is relevant.
Regarding mechanical properties, SUCS varies between 1.5 MPa to 2.2 MPa which is typical of a soft pure limestone (Table 3).
Conclusions
In the present research structure sample were analysed and the problem of salt crystallization in the structure deterioration was approached.
It was found that salts on the structure surface rarely crystalize due to high environmental RH in the area of study. Therefore, it can be inferred that probably salt plays a minor role in the stone deterioration, while the main causes of deterioration should be further studied.
129Quarry and structure stone were physical-chemical compared through X-ray and petrographical analysis. Quarry stones were found compatible for replacement of deteriorated block, although further research is needed to include more relevant physical and aesthetic variables in the analysis of stone replacement such as colour, texture and moisture transport properties.
Acknowledgements
This Project has been funded by the Universidad de Cartagena, Colombia, through the resolution number 00473 of 2016 “Octava convocatoria a proyectos de investigación, para grupos de investigación visibles (categorizados o reconocidos) en la plataforma Scienti del departamento de Ciencia, Tecnología e Innovación-Colciencias y avalados por la Universidad de Cartagena”. Furthermore, this project has been funded with the support of the European Commission (Grant agreement no. 2014-0873/001-001). This publication only reflects the view of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein - Elarch Program (project reference number: 552129-em-1-2014-1-it-era mundus-ema21). Finally, Authors would like to acknowledge the development of this work to Universidad Nacional de Colombia by funding DIB 34835.
References
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