PSI - Issue 62

Sebastian Thöns et al. / Procedia Structural Integrity 62 (2024) 259–267 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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substructure, heat-induced damage to pavements and railways, higher wave impacts, higher thermally induced stresses and deformations, and increased risk for water-vessel collisions. Large infrastructures may be a highly valued target by terrorists due to their economic value and life safety impact at collapse (Hausken (2016)). This valuation may have been amplified due to increasing global political tensions including ongoing conflicts and wars. A higher threat level may influence the necessity of tailored analyses of these threats and related scenarios (see e.g., Thöns and Stewart (2019), Thöns and Stewart (2020)). Societally, the dynamic nature of human needs and demographic shifts also play a pivotal role. As populations grow and urbanize, the demand for more sophisticated and extensive infrastructure systems develops. This necessitates a continuous re-evaluation of existing infrastructural capacities and their ability to meet these evolving demands. Societal changes also bring about shifts in regulatory frameworks, safety standards, and public expectations; all of which can impose additional technical and economic burdens on existing infrastructure, potentially shortening their anticipated service life. 2.2 Deterioration mechanisms Deterioration mechanism may be classified into chemical, mechanical, environment as well as demand specific and material specific deterioration. Structures can be exposed to various chemicals, including acids in rainwater, alkalis, and sulfates in groundwater, or industrial pollutants. These chemicals can react with the materials in the infrastructure, leading to deterioration. For instance, sulfuric acid from industrial emissions can react with the calcium hydroxide in concrete, leading to strength loss and subsequent structural damage. Further, the ingress of chlorides (from deicing salts or seawater) or (the rising concentration of) carbon dioxide, may lead to the breakdown of the passive oxide layer protecting steel, thus initiating corrosion. Corrosion can cause significant structural damage, including cracking and spalling of reinforced concrete followed by loss of the strength during active reinforcement corrosion. Fatigue in materials is caused by repeated or cyclic loading, such as the weight of passing vehicles on bridges or the variations in pressure of wind on tall buildings. Over time, this can cause cracking and eventual fracture (failure) of structural components. Material fatigue phenomena affect a wide variety of construction materials such as steel, concrete and also fibre reinforced plastics for structural repairs. Environmental factors such as prolonged exposure to UV radiation, high temperatures, humidity can also lead to material degradation. For example, UV radiation can degrade polymers and paints used in construction, while high humidity can promote fungal and biological growth, leading to material decay. Constant wear and tear from traffic, water flow, or wind can gradually wear down directly soil and material surfaces, leading to loss of material and structural integrity. This is particularly significant in roadways, hydraulic structures, and coastal defences. In colder climates, the freeze-thaw cycle is a significant contributor to infrastructure deterioration. Water that seeps into cracks in the pavement or concrete expands when it freezes, enlarging the cracks and causing further structural weakening. Material-specific degradation includes chemical, mechanical, and biological factors that undermine structural properties of materials and potentially threaten the structural integrity. The Alkali-Aggregate Reaction (AAR) is a chemical interaction within concrete structures, where alkali hydroxides present in the concrete matrix react with reactive siliceous aggregates. This reaction culminates in the expansion and subsequent cracking of the concrete. The expansive nature of this reaction is a pivotal factor in the premature deterioration of concrete structures. This necessitates rigorous aggregate selection and chemical composition control during construction for prevention and often leads to the premature need for repair or replacements in the operation of infrastructures. Concrete is further inherently susceptible to time-dependent mechanical degradation, notably creep and shrinkage. Creep refers to the gradual long-term deformation under a constant load, a phenomenon that can significantly alter the stress distribution within the structure over extended periods. Shrinkage, primarily attributable to moisture loss, results in a reduction in volume, which can induce internal stresses leading to cracking. Timber exhibits a distinct set of degradation challenges, predominantly stemming from biological factors. The susceptibility of timber to biological deterioration, such as fungal rot and insect infestation, presents a significant risk to the longevity and structural integrity of timber-based constructions. Moreover, certain concrete types can undergo bacterial-induced deterioration (e.g., Ul-Abdin, Anwar and Khitab (2022)), especially for concrete with lower pH levels leading to enhancement of porosity and the development of cracks.