###### Abstract
This variety of pollutants and techniques results in heterogeneous data, making direct comparisons among studies difficult. Figure 1: Photocatalysis schematic process. Test methods for assessing photocatalytic efficiency (PE) must take into account the type of pollutant (e.g., NOx and organic compounds) and the type of substrate material (e.g., composition and physical and chemical properties). In the specific case of cementitious materials, the efficiency of photocatalysts is strongly influenced by factors such as the interaction with the substrate, the application method, curing age, and surface properties such as roughness and porosity, which affect exposure to light and consequently the photocatalytic performance [12; 13; 14; 15]. This complexity underscores the importance of selecting appropriate evaluation techniques, as different methods may provide different levels of sensitivity to these factors. Despite the advancements in photocatalytic materials, standardized testing methods specifically for cementitious surfaces remain underdeveloped. Current standards, such as ISO 10678 [16], primarily target ceramics, requiring adaptations for cement-based applications due to their unique porosity and adsorption characteristics. Thus, standardized tests for quantifying self-cleaning properties on cementitious or opaque substrates remain limited in both the scientific literature and regulatory guidelines [17; 18]. This gap highlights the need for specialized methodologies to accurately evaluate the photocatalytic efficiency of TiO\({}_{2}\)-based coatings on cementitious materials, ensuring reliable performance assessments in real-world conditions. Among the available techniques, spectrophotometric colorimetry (SPC) stands out for its speed and reliability in assessing photocatalytic activity. This method involves measuring the degradation of dry dyes, such as Rhodamine B (RhB) or Methylene Blue (MB), on photocatalytic surfaces [19; 20; 21; 22; 23]. Another widely recognized technique is UV-Vis spectrophotometry (UV-Vis), which quantifies changes in pollutant concentration by analyzing light absorbance, following the Beer-Lambert law [24; 25]. However, these methods of evaluation use expensive and time-consuming laboratory equipment. In recent years, the use of technology and artificial intelligence has proven to be an affordable and reliable alternative to traditional techniques [26]. Digital image techniques are powerful tools for optical analysis and have been widely applied across various scientific fields due to their matrix-based format, which simplifies computational processing compared to analog images [27]. The application of digital image processing combined with colorimetric analysis is widely used, as long as standard image capture conditions are guaranteed [28; 29]. Experimental work remains essential to refine and validate the best practices for cementitious materials. Thus, this study aimed to evaluate and compare three techniques for assessing the photocatalytic efficiency (PE) of cementitious materials of two colors (gray and white) coated with TiO\({}_{2}\). The methods analyzed include the following: (i) spectrophotometric colorimetry (SPC), widely used for tracking visible color changes in pollutant degradation; (ii) digital image processing-based colorimetry (DIP), an emerging, cost-effective technique offering detailed color analysis; and (iii) UV-Vis spectrophotometry (UV-Vis), recognized for its precision and versatility in detecting pollutant concentration changes. The gray and white cementitious substrates were chosen for their practical relevance in urban facades, where esthetic conditions are a key consideration. This choice allowed us to evaluate how the photocatalytic properties varied depending on the color contrast with RhB, applied as a model pollutant, and the photocatalytic activity was monitored under UV-Vis light to assess the degradation over time. The comparison focused on evaluating the sensitivity and practicality of each test method (SPC, DIP, and UV-Vis).