Date of Award

1-1-2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Civil and Environmental Engineering

Department

Civil and Environmental Engineering

First Advisor

Sumanta Das

Abstract

As climate variability continues to intensify, the durability of cementitious materials under repeated freeze-thaw (FT) cycles becomes a critical concern for infrastructure longevity in cold regions. This dissertation systematically investigates advanced material strategies - specifically the integration of microencapsulated Phase Change Materials (MPCMs) and synthetic Antifreeze Biomimetic Polymers (ABPs) to enhance the freeze-thaw resistance of cementitious composites. Through a combination of experimental evaluation, microstructural characterization, numerical modeling, and critical literature synthesis, this research provides a comprehensive framework for designing resilient and sustainable cement-based systems.

Chapter 1 initiates the investigation at the hardened cement paste (HCP) level, evaluating the influence of MPCMs on microstructural evolution, mechanical degradation, and damage mechanisms under extended FT cycling. Using Low-Temperature Differential Scanning Calorimetry (LTDSC), X-ray Tomography (XRT), and micro-indentation, the study demonstrates that MPCM integration substantially lowers ice-crystallization onset, mitigates pore enlargement, and preserves mechanical properties. Notably, samples with 20% MPCM exhibit only 9% reduction in indentation hardness and 7% reduction in Young’s modulus after 180 FT cycles, compared to 35% and 37% losses in control samples, respectively. XRT analysis confirmed that MPCMs effectively limit pore coarsening and crack propagation, preserving a stable pore size distribution and mechanical integrity even under severe cyclic loading.

Building upon these findings, Chapter 2 explores the influence of MPCM addition in mortar composites, examining the meso-structural behavior under prolonged FT exposure. Differential Scanning Calorimetry (DSC) confirmed the thermoregulatory capacity of MPCMs by buffering internal temperature fluctuations, thereby reducing thermal stresses during phase transitions. Mechanical testing revealed a characteristic trade-off: while initial compressive strength decreased by approximately 10-15% with MPCM incorporation, mortars with higher MPCM dosages exhibited significantly lower degradation rates, retaining over 80% of their initial mechanical strength after 300 FT cycles compared to only 60% retention in control samples. High-resolution XRT images further demonstrated that MPCM integration mitigates internal meso-crack formation and pore connectivity enhancement over extended cycling.

Recognizing the compounded effects of freeze-thaw damage and chloride ingress, Chapter 3 investigates the evolution of pore structure and ion transport resistance in HCP, mortar, and concrete systems modified with MPCMs. Utilizing 3D X-ray microtomography, Rapid Chloride Penetration (RCP), and Non-Steady-State Migration (NSSM) tests, the study reveals that MPCMs increase isolated pore formation and decrease pore interconnectivity, thereby impeding ion migration pathways. Despite an initial 5-8% increase in total porosity, the MPCM-integrated systems displayed 30-40% reductions in RCP charge passed and NSSM diffusion coefficients compared to controls after 300 FT cycles. Notably, the 20% MPCM mixture provided optimal resistance against combined thermal and chemical degradation, indicating the effectiveness of thermal regulation and pore disruption strategies in enhancing long-term durability.

Scaling from material-level to structural applications, Chapter 4 employs numerical simulations to evaluate the thermal performance of PCM-enhanced bridge decks under realistic diurnal and seasonal temperature variations. Three configurations: single-layer, two-layer, and three-layer PCM systems - were analyzed with transition temperatures of 0°C, -5°C, and -10°C. Simulations demonstrated that multilayer PCM arrangements, particularly the three-layer system with sequential phase transitions, achieved up to a 29% reduction in freeze-thaw cycle occurrences by smoothing thermal gradients and prolonging subzero phase buffering. The 10% PCM volume fraction design offered superior latent heat storage capacity, significantly minimizing the occurrence of critical thermal stress thresholds and extending bridge deck service life predictions by over 20% relative to conventional designs.

Finally, Chapter 5 explores a biomimetic paradigm by reviewing synthetic Antifreeze Biomimetic Polymers (ABPs) inspired by natural antifreeze proteins. Through critical analysis of Polyvinyl Alcohol (PVA) and Polyethylene Glycol-Polyvinyl Alcohol (PEG-PVA), and peptoid-based structures, the chapter elucidates their ice-binding mechanisms, chemical integration pathways, and mechanical trade-offs in cementitious matrices. ABPs offer a complementary mechanism to MPCMs, regulating ice crystallization at the molecular level without solely relying on bulk thermal buffering. Despite promising laboratory outcomes, field-scale challenges such as chemical compatibility, mechanical durability, and environmental impacts are identified, guiding future directions for material innovation.

Collectively, this dissertation advances a multi-scale, multi-strategy framework for enhancing the freeze-thaw and chloride resistance of cementitious materials. By integrating passive thermal regulation via MPCMs and active ice-growth control via ABPs, the research establishes a scientifically robust foundation for the design of next-generation resilient infrastructure capable of withstanding the escalating impacts of climate-induced stressors in cold environments.

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