Doctor of Philosophy
Civil and Environmental Engineering
Nehdi, Moncef L.
The research conducted in this thesis investigates the effects of phase change materials (PCMs) on the hydration kinetics and strength development of cement-based composites using extensive experimental and numerical analyses. Purposefully, the effect of microencapsulated PCMs (MPCMs) on the strength development of cement-based mortars and concretes was evaluated using powerful machine learning models trained with the largest available experimental data. Furthermore, a novel ternary machine learning approach was proposed to optimize the mixture design of mortars and concretes based on the thermos-physical properties of the MPCMs. The results obtained from machine learning simulations suggest the assessment of the effects of MPCMs on the maturity-strength relationship. Multitudinous laboratory experiments were therefore performed to collect data for the calculation of the apparent activation energy. The analysis of isothermal calorimetry and compressive strength measurements at various curing temperatures revealed the reduction of apparent activation energy after the addition of MPCMs, indicating less sensitivity of such composites to curing temperatures. Deep learning proved capable of predicting the hydration kinetics of MPCM-integrated cementitious systems, and thus calculating the apparent activation energy of diverse systems. Furthermore, eco-friendly shape-stabilized PCMs (SSPCMs) were fabricated using bio-based PCMs and recycled supporting agent to promote the sustainability of the built environment. Finally yet importantly, a low-carbon latent heat thermal energy storage (LHTES) system was developed based on bio-based MPCMs and limestone calcined clay cement (LC3) binder with lower clinker content. It was shown that utilizing such environmentally friendly construction materials could contribute to lowering the operational and embodied energy and emissions of major infrastructures.
Summary for Lay Audience
Reducing the energy consumption of buildings is an important step toward mitigating climate change and attaining a sustainable and resilient built environment. Researchers have coined brilliant solutions to increase the energy efficiency in the heating and cooling of buildings, very similar to the idea of manufacturing energy-star appliances. One emerging idea is to integrate phase change materials (PCMs) in buildings. PCMs, perform similarly to a battery that can store thermal energy. Using this technology, the change in the indoor temperature of buildings can be narrowed down and major energy savings for heating, ventilation and air conditioning (HVAC) systems are achieved. PCMs can be added to construction materials, such as concrete, and used for building various elements such as walls, roofs, and envelopes. However, they can cause negative impacts on the mechanical strength of the materials. In this research, advanced experimental and computational tools were employed to evaluate the effects of PCMs on the mechanical performance of concrete and predict its strength after the addition of PCMs. Recommendations are given for proper mixture proportioning of concrete with PCM considering different levels of strength. Furthermore, novel and environmentally friendly materials are developed with PCM inclusion to benefit the sustainability of buildings. The results obtained from this research can better help engineers and policy-makers develop sustainable and resilient frameworks for the construction industry and reduce the impact of the built environment on exacerbating climate change.
Marani, Afshin, "Hydration Kinetics, Microstructure, and Mechanical Strength Development of Cement-based Composites Incorporating Phase Change Materials" (2022). Electronic Thesis and Dissertation Repository. 8617.
Available for download on Sunday, April 30, 2023