Development Of Demountable Structural Elements For A Sustainable Construction Approach Based On Green Concrete Utilizing Recycled Construction Demolition Waste

Abstract

The urgent demand for sustainable solutions in the construction industry, driven by environmental concerns and seismic safety requirements, has led to increasing interest in alternative materials and structural systems. This thesis presents a comprehensive experimental investigation into the structural performance, seismic behavior, and reusability potential of precast reinforced concrete elements incorporating geopolymer concrete made from construction and demolition waste (CDW). The research comprises four integrated studies. The first study evaluates four different demountable column base connections design by investigating the seismic performance and damage characteristics of moment-resisting bolted joints under different axial compression ratios. Its primary aim is to identify the optimal connection design that balances strength, ductility, and energy dissipation for seismic applications. The second study experimentally assesses seismic performance of fully demountable column base connection systems for CDW-based geopolymer concrete columns. Six half-scale specimens, three demountable and three monolithic, were tested under reversed cyclic lateral displacements and three levels of constant axial load. The study compares failure modes, load–displacement behavior, ductility, energy dissipation, stiffness degradation, and curvature distributions between the two connection types. The third study evaluates the seismic behavior of an innovative demountable connection system for reinforced concrete columns featuring bolted dry joints, subjected to combined axial and cyclic lateral loading. Its performance is compared to that of conventional monolithic connections. Six half-scale specimens, half with bolted connections, half monolithic, were tested under axial compression ratios of 0.10, 0.20, and 0.30. The investigation focused mainly on evaluating failure mechanisms, damage characteristics, and seismic response. The results emphasize the influence of axial load intensity and reinforcement detailing on plastic hinge formation and damage progression. The fourth study explores the feasibility of constructing demountable precast buildings using CDW-based geopolymer concrete under real-life field conditions, highlighting both technical challenges and sustainability benefits. Experimental results demonstrate that CDW-based geopolymer concrete provides structural performance comparable to that of conventional concrete. Furthermore, the dry type demountable connections exhibited adequate ductility and strength under seismic loading while enabling disassembly and reuse. These findings confirm the potential of geopolymer concrete as a low-carbon, high-performance alternative to Portland cement and emphasize the role of connection design in supporting circular construction strategies. This research contributes to the growing body of knowledge on sustainable prefabricated construction by integrating innovative materials with advanced structural detailing, offering new pathways for resilient, reusable, and environmentally responsible building systems.