Study of the impact of aggressive environment on the color discoloration of stone surfaces

Abstract

In this study, the impact of aggressive environments on the color characteristics of natural stone was thoroughly investigated. The research focused on samples of facing stones, namely: Kamyanobridsky labradorite, Bukynske gabbro, Pokostivsky granodiorite, and Kapustinsky granite. Experiments to determine the color changes of natural stone were conducted at a temperature of 20 °C in aggressive environments such as sodium hydroxide (NaOH) with a concentration of 40 g/L, sulfuric acid (H2SO4) – 40 g/L, and ammonium chloride (NaCl) – 40 g/L. The overall exposure duration was 50 days. Before placing the natural stone samples in an aggressive environment, their polished surface was scanned using a digital scanner. The average gloss value of the polished surface was also measured using a gloss meter BF-3. The natural stone samples were exposed to aggressive solutions, and measurements of gloss and color were taken every 240 hours. Prior to each new measurement of color characteristics and gloss of natural stone, they were thoroughly rinsed with distilled water and dried. In case of the appearance of white spots on the stone surface after drying, they were carefully wiped with a damp cloth. Scanned digital images were processed in specialized graphic programs to obtain color coordinates of the natural stone surface. The average value of color difference in the CIELab system was evaluated. As a result of the conducted research, it was determined that key changes in the color of stone facing surfaces occur within the first 30 days (720 hours) for rocks of the primary composition. This indicates the necessity of considering this period in project planning. Under the influence of aggressive solutions on rocks of the primary composition, during 720 hours, the most significant reduction in gloss indicators was observed when interacting with an acidic solution, specifically by 26 units, while the least impact was from the saline solution, reducing gloss by only 3.7 units. In rocks of acidic composition, the saline solution increased gloss by 3.3 units.

Keywords

• aggressive environment
• color
• natural stone
• rock-forming minerals