The investigation of the effect of pore size distribution on salt damage in different types of building stones in the Afyonkarahisar (Turkey) region

This thesis examines the effect of pore size distribution on the salt crystallization and weathering characteristics of natural building stones produced in the Afyonkarahisar region. Sample stones of different origins, such as İscehisar andesite (İA), Döğer tuff (DT), Emirdağ silver travertine (EGT), Şuhut limestone (SK), and Afyon gray marble (AGM), were selected. Salt crystallization experiments were conducted to determine the resistance of these stones to salt crystallization, and their strength properties were evaluated in different saline solutions. Additionally, the effect of the pore size distribution on the salt crystallization resistance was investigated for the examined building stones. This study was conducted in three stages. In the first stage, characterization studies were performed on the test samples, including mineralogical-petrographic (optical microscopy, SEM), chemical (XRF), mercury porosimetry, and mechanical-physical tests and analyses. In the second stage, weathering experiments were conducted in the laboratory, including tests to determine resistance to salt crystallization. Pure water, sodium chloride (NaCl), sodium sulfate decahydrate (Na2SO4·10H2O), and magnesium sulfate (MgSO4·7H20) solutions with a concentration of 14% were used in the salt crystallization experiments. In the third stage, weight loss, ultrasonic wave velocity, and uniaxial compressive strength were determined as the physical and mechanical properties of the samples after weathering experiments. After salt crystallization experiments in four different liquid environments (pure water, sodium chloride, sodium sulfate, and magnesium sulfate), the pore size distribution was re-evaluated for five different natural building stones (İA, DT, EGT, ŞK, and AGM). The pore size distribution data were compared with those of fresh (unweathered) samples. Furthermore, weathering of the samples and the effect of salt crystals were examined using SEM-EDX analysis. The pore size distribution data obtained from the mercury porosimetry analysis revealed significant changes in the pore characteristics of the examined natural building stones. It was determined that the Döğer tuff, with a porosity of 47.5%, suffered the most damage, with weight losses of 0.29% in pure water, 3.74% in NaCl solution, complete dissolution in sodium sulfate solution, and 83.30% in magnesium sulfate solution. In the andesite samples, it was observed that most of the pores in the 0.01-1 µm range were filled with salt crystals after the salt crystallization tests. For Döğer tuff, the percentage of pores smaller than 0.1 µm was 15.56% in fresh samples, which decreased to 15.05%, 8.75%, and 6.90% in sodium chloride, sodium sulfate, and magnesium sulfate solutions, respectively. This decrease was attributed to the accumulation of salt crystals in pores smaller than 0.1 µm. For Emirdağ silver travertine, the percentage of pores larger than 1 µm was 69.89% in the fresh samples, which decreased to 51.77% in a magnesium sulfate solution. This percentage increased to 89.52% in the sodium sulfate solution owing to the formation of new microcracks. The micro-porosity of Şuhut limestone before the weathering experiments was zero, while it increased to 1.63% after the experiment with magnesium sulfate solution owing to the formation of new pores. For the Afyon gray marble, 88.39% of the fresh samples had pores larger than 0.1 µm, which decreased to 75.49%, 85.39%, and 70.29% in the NaCl, Na2SO4, and MgSO4 solutions, respectively. The experimental results demonstrate that salt crystallization is crucial for altering the pore size distribution. This confirms the theoretical assumption that micropores with diameters smaller than 1 µm critically impact the salt crystallization damage. Moreover, the pore size distribution of the natural building stones' pre- and post-experiment samples verifies the importance of pore diameters between 1 and 4 µm in salt crystallization experiment-induced damage.