Sustainable Lightweight High-Performance Concrete for Seismic Retrofits

Thesis Abstract

This study addresses the critical challenge of enhancing seismic resilience in existing concrete structures through the use of sustainable lightweight high-performance concrete (SLHPC), which combines reduced dead load with improved strength, ductility, and environmental performance. The problem stems from the limited availability of materials that simultaneously meet stringent seismic performance criteria, weight reduction targets, and lower life-cycle emissions. The aim is to design, fabricate, and evaluate SLHPC mixes tailored for retrofitting seismic-critical members, and to develop an evidence-based framework for performance-based rehabilitation. Specific objectives include (1) optimizing mix proportions to achieve compressive strengths of 40–60 MPa at 28 days while maintaining density below 1900 kg/m3, (2) assessing dynamic seismic performance through shake-table and pseudo-dynamic tests on full-scale or near-full-scale reinforced concrete frames retrofitted with SLHPC, (3) evaluating fire resistance, long-term durability, and corrosion mitigation under accelerated aging and cyclic loading, (4) conducting life-cycle assessment (LCA) and techno-economic analysis (TEA) to quantify environmental benefits and cost implications, and (5) developing design guidelines and a decision-support tool for practitioners. The population comprises concrete materials, reinforced concrete elements, and structural assemblies representative of mid-rise buildings in seismically active regions. A multifactorial sampling regime will be employed, including 12 SLHPC mixes with varying aggregate porosity, lightweight aggregates, and supplementary cementitious materials (SCMs), tested on 150 mm and 300 mm cylindrical specimens, as well as scaled frame subassemblies. Data collection will integrate material characterization (compressive and tensile strength, modulus of elasticity, shear strength, density, porosity, thermal conductivity), durability indicators (water absorption, ASR resistance, freeze–thaw performance), and seismic response metrics (peak accelerations, inter-story drifts, hysteretic energy dissipation) obtained from shake-table tests, cyclic loading, and finite element analyses. The study will deploy a mixed-methods approach quantitative analyses using regression modeling, ANOVA, and nonlinear time-history analysis to correlate SLHPC mix design with structural performance, and qualitative assessment through expert interviews with practicing engineers to contextualize design guidelines. Validity will be reinforced through triangulation across material tests, experimental frame tests, and numerical simulations, with reliability checked via repeat tests (n=3) and sensitivity analyses. The theoretical framework will draw on Performance-Based Seismic Design and Composite Material Theory, with empirical calibration against established standards. The expected findings indicate that SLHPC can reduce structural dead load by up to 22% without compromising strength, while improving energy dissipation and damage confinement under modal and irregular seismic demands. It is anticipated that frames retrofitted with SLHPC will exhibit reduced inter-story drifts, enhanced post-yield stiffness, and improved residual strength, compared with conventional high-strength concrete retrofits. Durability and fire resistance are expected to meet or exceed standard performance thresholds due to refined pore structure and SCM synergy. The LCA is projected to show 15–25% lower global warming potential per structure, and TEA to demonstrate competitive lifecycle costs relative to traditional retrofit materials. The study contributes to knowledge by delivering validated mix-design procedures for SLHPC, performance benchmarks for seismic retrofits, and a decision-support framework that integrates structural performance, durability, and sustainability considerations. The main conclusion is that sustainably engineered SLHPC provides a viable, performance-based retrofit solution that achieves seismic resilience with reduced environmental impact. Practical recommendations will include specific mix-design recipes, construction practices for field implementation, and an annotated design guideline outlining when and how to apply SLHPC retrofits in different seismicity scenarios. Suggestions for further research include long-term field monitoring of retrofitted structures, exploration of recycled aggregate variants, and refinement of optimization algorithms for real-time retrofit decision-making.