Surface Ageing and Visual Changes of Architectural Concrete under Accelerated Exposure

Architectural concrete is expected to provide not only structural performance but also long-term aesthetic quality. While concrete durability has been widely investigated, the visual ageing of exposed concrete surfaces has received considerably less attention. This study evaluates the visual durability of four concrete mixtures: a reference concrete (REF), two recycled aggregate concretes containing crushed concrete aggregate (RACC) and crushed clay brick aggregate (RACB), and a high-performance concrete (HPC). Ground surfaces, untreated or protected with transparent polyurethane or silane-based coatings, were subjected to accelerated freeze–thaw cycling, carbonation and repeated urea exposure. Surface changes were systematically documented under visible and ultraviolet (UV) light and evaluated together with conventional durability measurements.All investigated mixtures exhibited high resistance to accelerated ageing. Freeze–thaw cycling caused only limited permanent visual deterioration, while carbonation and urea exposure resulted mainly in subtle colour changes without significant surface damage. The recycled aggregate concretes showed freeze–thaw performance comparable to the reference concrete despite greater carbonation depths, whereas HPC demonstrated the highest overall stability. UV illumination revealed minor surface changes that were not detectable under visible light.The results show that conventional durability indicators alone do not fully describe the long-term performance of architectural concrete. Combining accelerated durability testing with systematic visual assessment provides a comprehensive approach for evaluating both structural durability and long-term aesthetic performance. Received: 20.07.2026 Received in revised form: 08.09.2026 Accepted: 29.09.2026