Long-term Performance of Self-heating Concrete Composites using Low-Temperature Phase Change Materials for Snow-melting and Freeze-thaw Resilience Applications
Authors:   , Deb Robin , Farnam Yaghoob 
Published: September 2024

This goal of this thesis was to investigate the potential of utilizing low-temperature phase change materials (PCM) integrated concrete composites in cold regions for snow melting and freeze-thaw resilient applications. First and foremost, incorporating PCM into cementitious matrix had its' own challenges; PCM needed to be incorporated by two viable methods: (i) PCM infused in porous network of lightweight aggregates (PCM-LWA), and (ii) micro-encapsulated PCM (MPCM). Incorporation techniques affect the thermal properties; these factors included ambient temperature change rate and pore confinement effect in LWA. Thermal and pore size analyses revealed that supercooling phenomena of PCM increases with higher ramp rates, affecting nucleation and crystallization process during phase transition. PCM incorporated within LWA pores experienced varying degrees of supercooling, influenced by pore structure, diameter, and tortuosity. Second, the snow melting and freeze-thaw performance of self-heating concrete in controlled laboratory and real-time outdoor conditions during fall and winter seasons were evaluated; both PCM-LWA and MPCM concrete demonstrated promising snow-melting efficiency and curbed the number of freeze-thaw cycles. PCM-LWA concrete outperformed MPCM concrete in decreasing the number of freeze-thaw cycles due to the undercooling phenomenon created by the LWA pore network confinement pressure, allowing gradual latent heat release and effective snow melting across a wider temperature range. Third, incorporating PCM in concrete mixtures affected the fresh, mechanical, and water absorption properties; results showed that inclusion of PCM, especially MPCM, in concrete during wet mixing led to formation of agglomerates and decreased slump values due to hydrophobic property of shell material, necessitating higher requirements of cement paste and admixtures to achieve desired flowability and air entrainment. Predictive modeling estimated that PCM-LWA concrete would take between 53.68 to 61.45 years to reach critical degree of saturation levels, while achieving sufficient strength values for structural applications. Furthermore, PCM-LWA concrete was more suitable for freeze-thaw resilient applications, reducing the number of freeze-thaw cycles by approximately ~39.62 % over two winter seasons. Thermal contour mapping under controlled simulated conditions revealed that PCM-LWA concrete, specifically sections 50 mm below the top surface of the slab were able to maintain temperatures between +2 to +4 oC, in low temperature conditions (i.e., -2 oC). Finally, to evaluate the long-term performance and chemical stability of PCM in concrete slabs and potential of PCM leaching into the subgrade soil, outdoor scale testing after three years of construction revealed variable degree of effectiveness. MPCM concrete slab exhibited partial success in snow melting (i.e., 50 %), while PCM-LWA concrete slab failed to demonstrate any evidence over long-term. Both slabs showed diminishing resilience against freezing and thawing cycles compared to previous years. Factors contributing to efficiency loss included shell degradation of microcapsules, potential leaching of PCM, and effects of warm temperatures influencing degree of evaporation from the surfaces of the slabs. Strategies to enhance efficiency and stability include improved encapsulation techniques, better interfacial transition zone formations, and vascularization methods to incorporate and recharge concrete elements with PCM over time.