Self-cleaning capacity of photocatalytic building plasters under frost attack

Introduction. The durability of the self-cleaning capacity of photocatalytic building materials under real operating conditions is a crucial issue, as their efficiency decreases over time due to surface degradation and carbonation. The purpose of the research is to evaluate the stability of the photocatalytic activity in two types of plasters – gypsum-cement-pozzolan plaster (based on red gypsum) and cement plaster (with anatase photocatalyst) – to cyclic freezing and thawing, as well as to investigate the effect of water-reducing and pozzolan additives on maintaining their self-cleaning ability. Materials and Methods. Series of plaster samples were prepared with and without different combinations of additives. Photocatalytic activity was assessed using the rhodamine test. Changes in the materials were analyzed using compressive strength, density, and water absorption test methods. Scanning electron microscopy with energy-dispersive spectrometry was used to measure the titanium (photocatalyst marker) and calcium (carbonation marker) content on the surface. Destructive frost effects were simulated by the cyclic freezing and thawing of samples in a water-saturated state. Results. It was found that the primary mechanism causing the loss of the self-cleaning capacity was photocatalyst washout due to surface degradation. Shielding of the photocatalyst by carbonation products is also crucial for cement plasters. Water-reducing additives increased the initial self-cleaning efficiency by 45% due to structure compaction, which slowed surface degradation. Pozzolan additives reduced surface calcium content by 6–8%, suppressing carbonation and almost doubled the initial efficiency. The combined use of these additives demonstrated the best results in maintaining photocatalytic activity after freezing and thawing. Discussion and Conclusion. The durability of the self-cleaning capacity directly depends on the resistance of the carrier material to climatic impacts. Combined modification with water-reducing and pozzolan additives is the most effective strategy for improving the durability of self-cleaning plasters, as it simultaneously counteracts two key degradation mechanisms: physical washout of the photocatalyst and its chemical shielding by carbonates. This study provides a practical approach to developing more sustainable photocatalytic building materials.