Development of Mathematical Models for Predicting The Capacity of Waste-Based Sustainable Green Structural Elements for New-Generation Rapid Construction Techniques

Abstract

The escalation of natural disasters globally is evidenced by a significant increase in frequency and severity over recent years. Earthquakes worldwide, spanning 20 years from 1998 to 2017, resulted in approximately 750,000 fatalities and impacted over 125 million people. Turkey is located in a critical seismic belt with over 500 active faults; 92% of the population resides close to active faults. Unfortunately, due to this critical location, the 7.8 magnitude earthquake in Kahramanmaraş, Turkey, in 2023 caused significant damage to thousands of buildings and spurred urgent demolition and reconstruction efforts by government authorities. These catastrophes leave millions displaced, lacking necessities, and suffering significant economic setbacks. Alongside disasters, political instability in many regions further exacerbates housing challenges, necessitating rapid, safe, and sustainable urbanization efforts to accommodate the growing population. To overcome these challenges, it is necessary to develop structural systems that are adaptable, cost-effective, and can be quickly transported to desired locations. Circular economy principles, essential for waste reduction, extend beyond material usage to encompass production practices. Sustainable construction necessitates reducing environmental impacts across the building's lifecycle and value chain, aligning with circular economy principles. At this point, Design for Manufacture and Assembly (DfMA) and Design for Deconstruction (DfD) play a crucial role in simplifying processes to minimize disadvantages while maximizing the benefits of modular construction. Addressing these challenges motivates the present thesis, which focuses on designing a building system that integrates circular economy principles, maximizes waste recycling, and allows for the reuse of elements. It includes an in-depth analysis of Construction and Demolition Waste (CDW) based geopolymers to develop mathematical models for predicting the capacity of building elements. By encompassing a broad parameter range, the study seeks to develop a new stress-strain model applicable to various types of geopolymers, facilitating sustainable construction practices. To this end, a stress-strain model was initially developed on compressive behavior, followed by the formulation of geopolymer’s flexural behavior based on experimental findings. In estimating the ultimate moment capacities, the proposed stress-strain model was validated by 36 bending tests from the literature, demonstrating minor deviations and enhanced accuracy compared to ACI318. A soft database of 50 beam specimens with varying mechanical properties and reinforcement patterns was also established, generating numerical models for all possible parameter combinations to determine load capacities. The performance of the proposed method, stress-strain models from the literature and the ACI318 procedure were investigated and provided promising results with an absolute mean percentage error of 5.13% regardless of the failure mode.

Continuing the mathematical modeling of geopolymer concrete, a comprehensive material model was developed to predict the flexural capacities of geopolymer columns, inspired by Kent and Park's confinement model. The proposed stress-strain model, validated with 41 test results, accurately estimated moment capacity. Comparison with moment-curvature curves from six recent experiments confirmed the model's accuracy for performance-based design calculations. Additionally, comparisons with four international codes (ACI318, BS8110-97, TS500, and AASHTO) revealed significant deviations in flexural capacity calculations; however, highlighting the proposed model's strong correlation with the experimental data, ensuring accurate predictions for geopolymer columns.