Comparative Life-Cycle Assessment of Concrete Alternatives in Bridges

Thesis Abstract

The increasing demand for durable, sustainable, and cost-effective bridge infrastructure has intensified interest in replacing conventional Portland cement concrete with alternative concrete materials and mixtures, necessitating a rigorous evaluation of life-cycle environmental, economic, and performance implications. This study addresses the problem of uncertainty and regional variability in the environmental performance and structural reliability of concrete alternatives used in bridge superstructures and substructures, with particular emphasis on balancing embodied energy, material durability, and constructability. The aim is to compare Life-Cycle Assessment (LCA) outcomes, structural performance indicators, and cost implications of at least three concrete alternatives—high-performance reinforced concrete (HPRC), geopolymer concrete (GPC), and ultra-high-performance fiber-reinforced concrete (UHPFRC)—against conventional Portland cement concrete (PCC) across multiple bridge typologies. Specific objectives are to (i) quantify cradle-to-grave environmental burdens (global warming potential, abiotic depletion, and freshwater eutrophication) for each concrete type using ISO 14040/44-compliant LCA, (ii) evaluate long-term durability, maintenance requirements, and life-cycle costs (LCC) through accelerated aging tests, field monitoring data, and reliability analysis, (iii) develop a comparative decision framework incorporating qualitative stakeholder preferences and quantitative performance metrics, (iv) assess regional material supply constraints and transportation impacts on overall sustainability, and (v) propose practical design guidance and policy-relevant recommendations to optimize the selection of concrete types for bridge projects. The research adopts a mixed-methods design in which a cross-sectional sample of ten representative bridge projects (five highways and five railway bridges) across three climatic zones is analyzed. The population includes bridge components such as decks, piers, and abutments constructed with PCC, HP-SCC (self-compacting HPC), GPC, and UHPFRC. Data collection instruments comprise (a) material composition records, batch data, and supplier environmental product declarations (EPDs); (b) field performance data from sensor-equipped bridge sections (crack width, chloride penetration, and dynamic modulus measurements) monitored over a three-year period; (c) laboratory test results from standardized accelerated aging protocols (ASTM C1303 for sulfate exposure, ASTM C666 for freeze–thaw, and ASTM C1583 for surface deterioration); and (d) semi-structured interviews with engineers and procurement officers to capture decision criteria. Validity and reliability are upheld through triangulation of LCA results with multiple attributional modeling approaches (modular LCA and input-output LCA cross-checks), calibration against field performance, and inter-laboratory comparisons of material tests. Data analysis employs regression analysis to relate environmental indicators to material proportions, ANOVA to compare performance metrics across concrete types, and survival analysis to model time-to-require maintenance interventions. A life-cycle cost model integrates material, construction, and maintenance costs over a 50-year horizon, incorporating discounting and probabilistic failure distributions. The study also employs a Bayesian network to synthesize uncertainties in material performance and environmental impacts, and a multi-criteria decision analysis (MCDA) framework to support stakeholders’ choices under varied weightings. Anticipated findings indicate that GPC offers substantially reduced embodied energy and global warming potential relative to PCC, while UHPFRC may incur higher initial costs but exhibit lower maintenance demands and extended service life; HPRC is expected to provide a balanced performance with moderate environmental benefits. The research is expected to reveal context-dependent trade-offs among environmental, economic, and durability outcomes, with regional climate and transport distance influencing overall advantage. The study contributes to knowledge by providing a robust, comparative, and transferable framework for evaluating concrete alternatives in bridges through integrated LCA, durability assessment, and lifecycle cost analysis, complemented by a practical decision-support tool for engineers and policymakers. It is anticipated that the findings will inform design codes, procurement strategies, and sustainability guidelines, recommending preferential use of low-embodied-energy concretes in climate-sensitive regions while recognizing scenarios where high-performance concretes yield superior long-term value due to reduced maintenance and longer service life. The main conclusion emphasizes the necessity of context-aware material selection and the integration of LCA with durability and cost metrics in bridge engineering practice, with policy recommendations to standardize EPD usage, incentivize material innovation, and incorporate lifecycle thinking into bridge project planning and governance.