Coastal Construction: Sustainability through Preventive Maintenance

By Nidhi DhullReviewed by Susha Cheriyedath, M.Sc.Jul 17 2024

An article published in the Journal of Building Engineering has assessed the life cycle impact of preventive maintenance on modern methods of construction (MMC)-based concrete structures in a chloride-rich, aggressive corrosion environment.

Background

The global resource-intensive construction industry consumes around 50 % of non-renewable resources, posing a significant sustainability challenge. Among various solutions for efficient building design and construction, MMC utilizes conventional materials with unconventional techniques. These efficient construction methods promote material waste reduction and mitigate potential cost increases through industrialization.

The importance of sustainability assessment in the construction sector is well established. However, considering the impacts of the long-term maintenance phase covering the entire infrastructure and building cycle is more important than conventional short-term assessments focused on the construction phase, especially for constructions subjected to harsh environmental conditions.

Structures in coastal areas are repeatedly subjected to intense chloride attacks. Despite this, a multi-criteria decision-making (MCDM) model has not yet been used to assess the sustainability of MMC-based residential building structures in such environments. Therefore, this study evaluated the sustainability of different maintenance designs implemented over the lifespan of structures exposed to chloride-induced corrosion.

Methods

Here, the researchers evaluated the sustainability performance of different alternatives compared to the baseline design of a public residential building on the coast of Sancti Petri, Spain. The chosen standard structure, REF, had three ‘unidome’ slab levels constructed using an in-situ MMC. Subsequently, the life cycle impacts of ten construction options for designing a 1 m² slab were evaluated.

The durability of concrete is significantly affected by chloride penetration from seawater, which can cause corrosion. Therefore, the alternative designs aimed to enhance the durability of the concrete structure by improving corrosion resistance, increasing slab thickness, applying inhibitory protection, or utilizing different types of steel.

The sustainability assessment incorporated economic, environmental, and social factors, addressing both construction and maintenance activities to ensure a 50-year service life of the structure in accordance with national standards. Economic impacts were analyzed in terms of initial construction and long-term maintenance costs.

The ReCiPe environmental assessment method was employed to evaluate impacts on human health, ecosystems, and resource availability. Social impacts were assessed using the SOCA (Social LCA) database, considering the perspectives of four stakeholder groups: workers, local communities, society, and value chain actors.

Overall, nine different impact categories were used as decision criteria in this Multi-Criteria Decision Making (MCDM) assessment. The best-worst method (BWM) facilitated pairwise comparisons, while the classical VIKOR method helped derive a comprehensive sustainability indicator. Furthermore, the material costs included in this analysis were drawn from Spanish construction databases and supplemented with detailed data from specific suppliers.

Results and Discussion

Enhancing the strength of structures in harsh environments not only increases their longevity but also contributes to the environmental sustainability of maintenance activities. For instance, modifying standard concrete mixes by incorporating pozzolans, fly ash, silica fume, and other additives has been shown to significantly reduce CO₂ emissions.

A comprehensive Life Cycle Assessment (LCA) utilizing the Multi-Criteria Decision Making (MCDM) method identified 5 % silica fume concrete as the most cost-effective and environmentally friendly option for improving the durability of coastal structures. Additionally, hydrophobic impregnation emerged as the most effective method for minimizing social impacts.

By simultaneously considering economic, environmental, and social impacts—rather than limiting the evaluation to one or two dimensions—a more holistic approach to sustainability in maintenance was achieved. A specific design that used sulforesistant cement in the concrete mix received an 86 % higher sustainability rating compared to the baseline.

While alternative durable designs, such as unconventional steel types, oversized structural elements, or cathodic corrosion protection, enhanced sustainability in certain scenarios, others, like periodic hydrophobic surface treatments, proved more effective when requiring extensive maintenance. Notably, adopting multiple preventive maintenance cycles throughout a structure’s life is more sustainable than opting for reactive maintenance.

Expert consultations indicated that environmental factors were deemed most crucial, accounting for 38.6 % of the sustainability evaluation, followed by social (34.6 %) and economic (26.8 %) aspects. Among these, the most highly valued criteria were the impacts on value chain actors and maintenance costs, with significant consideration also given to human health and resource management.

Conclusion and Future Prospects

In this study, researchers utilized a comprehensive gate-to-grave approach to evaluate the life cycle impacts of ten design alternatives for 'unidome' slabs in a coastal hotel structure. Employing both the BWM and the VIKOR technique, they systematically assessed the economic, environmental, and social impacts based on the required maintenance cycles throughout the structure's lifetime.

However, the Ecoinvent and SOCA databases used in this study were limited in terms of the specific building materials (required for the preparation and repair of slabs and reinforcements during maintenance) involved in the assessment. Consequently, the LCA of these materials was conducted using concepts similar to those in Ecoinvent.

Looking ahead, the researchers propose the exploration of additional MCDM methods to more accurately determine subjective weights and sustainability scores tailored to different maintenance activities. There is also a recommendation to expand the range of design options for reactive maintenance strategies. This expansion would allow for an optimization of repair intervals, leveraging the findings from preventive maintenance analyses. Moreover, the study suggests that the integration and evaluation of various preventive measures could provide insights into their compatibility and collective sustainability impact over the long term, paving the way for more resilient and sustainable building practices in coastal environments.

Journal Reference

Sánchez-Garrido, A. J., Navarro, I. J., & Yepes, V. (2024). Sustainable preventive maintenance of MMC-based concrete building structures in a harsh environment. Journal of Building Engineering, 110155. DOI: 10.1016/j.jobe.2024.110155, https://www.sciencedirect.com/science/article/pii/S2352710224017236

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