Robin Deb

Improvement of concrete pavements in cold regions is a major issue as durability is impacted by frost action and freeze-thaw cycles. In this study, thermal responsive composites were developed to improve freeze-thaw durability of concrete via incorporation of phase change materials (PCM) using two methods: (i) inclusion of PCM in porous network of lightweight aggregates, and (ii) micro-encapsulated PCM. The experimental program consisted of: (i) evaluation of fresh properties of PCM incorporated concrete mixes, (ii) mechanical and water absorption properties assessment of hardened PCM-concrete mixes, and (iii) assessment of thermal performance of PCM concrete slabs at real-time outdoor and environmental simulated conditions. It was found that the inclusion of micro-encapsulated PCM in concrete during wet mixing forms agglomerates and degrades fresh properties, requiring higher volume fraction of cement paste and superplasticizers to achieve desirable flowability and air entrainment. Incorporation methods have a significant influence on strength and durability factors. An estimation using predictive model showed concrete that has PCM stored in lightweight aggregates as storage agents will take 53.68 ~ 61.45 years until it reaches critical degree of saturation, only if. Thermal assessment results of PCM concrete slabs in outdoor conditions and simulated environmental conditions demonstrated that lightweight aggregate infusion of PCM was more suitable for freeze-thaw resilience concrete infrastructure applications. At outdoor scale, PCM-infused concrete reduced the number of freeze-thaw cycles by an average of 39.62 % in comparison to reference concrete with no PCM during two cold seasons.

This study examined the potential of using phase change material (PCM)-integrated concrete slabs for long-term thermal-responsive applications in an outdoor environment condition. The objectives were to: (i) evaluate long-term thermal response, snow melting and freeze–thaw reduction efficiency of PCM integrated concrete slabs, (ii) characterize the chemical stability of PCM in cement matrix, and (ii) assess the possibility of PCM leaching into the cement matrix and subgrade soil of the slabs. The experimental program included: (i) outdoor experimentation using large-scale field concrete slabs, (ii) guarded calorimetric (LGCC) tests of cut-bar concrete specimens, (iii) Fourier transform infrared (FTIR) spectroscopic characterization of PCM in mortar and subgrade soil specimens, and (iv) low-temperature differential scanning calorimetric (LT-DSC) tests to assess and quantify the amount of PCM contamination in subgrade soil. Results presented varying degrees of effectiveness after three years of environmental exposure: Micro-encapsulated PCM (MPCM) concrete exhibited considerable success (i.e., ~ 50%) in snow melting while PCM infused in lightweight aggregates (PCM-LWA) concrete failed to provide substantial snow-melting; moreover, both PCM-LWA and MPCM slabs showed diminished resistance to freeze–thaw (F-T) cycles compared to the first-year winter cycle data. Factors contributing to efficiency loss are found to be shell degradation of microcapsules, potential leaching of PCM into subgrade soil (i.e., between 0.2 to 0.3% wt. concentration), and effects of warm temperatures influencing the degree of evaporation, as evidenced with LGCC, FTIR and LT-DSC results. Strategies to enhance efficiency and stability include improved encapsulation techniques, and vascularization methods.

The 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 °C, in low temperature conditions (i.e., -2 °C). 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.

This study examined the potential of using PCM-integrated concrete slabs for long-term thermal-responsive applications in an outdoor environment condition. The objectives were: (i) to evaluate long-term thermal response, snow melting and freeze-thaw reduction efficiency of PCM integrated concrete slabs, (ii) to characterize the chemical stability of PCM in cement matrix, and (ii) to evaluate the possibility of PCM leaching into the cement matrix and subgrade soil of the slabs. The experimental program included: (i) outdoor experimentation using large-scale field concrete slabs, (ii) longitudinal guarded comparative calorimetric (LGCC) tests of cut-bar concrete specimens from field slabs and comparing them with lab-made samples, (iii) Fourier transform infrared (FTIR) spectroscopic characterization of PCM in mortar and subgrade soil specimens from field slabs, and (iv) low-temperature differential scanning calorimetric (LT-DSC) tests to assess heat evolution properties of small-scale PCM-integrated concrete specimens and quantify the amount of PCM contamination in subgrade soil. Results presented varying degrees of effectiveness after three years of environmental exposure: Micro-encapsulated PCM (MPCM) concrete exhibited considerable success (i.e., ~50 %) in snow melting while PCM infused in lightweight aggregates (PCM-LWA) concrete failed to provide substantial snow-melting; moreover, both PCM-LWA and MPCM slabs showed diminished resistance to freeze-thaw cycles compared to the first-year winter cycle data. Factors contributing to efficiency loss are found to be shell degradation of microcapsules, potential leaching of PCM into subgrade soil (i.e., between 2 to 3 % wt. concentration), and effects of warm temperatures influencing the degree of evaporation, as evidenced with LGCC, FTIR and LT-DSC results. Strategies to enhance efficiency and stability include improved encapsulation techniques, and vascularization methods.

This research study examines e-waste management methods and suggests sustainable solutions. Growing e-waste and its hazardous components demand robust management solutions to reduce environmental and health dangers. This report reviews the literature and analyses current processes to summarise e-waste management’s key issues. The article covers policy, regulation, collection and recycling infrastructure, technology, and public awareness. Policies and regulations shape e-waste management. EPR programs, recycling targets, and import/export laws are covered. These policies are assessed to promote responsible e-waste disposal and producer accountability. E-waste collection and recycling require effective infrastructure. Municipal collection facilities, store take-back, and recycling partnerships are compared. E-waste recycling technologies like mechanical and hydrometallurgical processes are evaluated for efficiency, environmental effect, and resource recovery. The study also evaluates how public awareness campaigns promote e-waste disposal. Effective educational, communal, and digital venues for e-waste recycling are assessed. According to the analysis, e-waste management could be improved. Policy frameworks, stakeholder participation, collecting infrastructure, sustainable recycling technologies, and public awareness are improved. This study paper helps policymakers, industry stakeholders, and researchers understand e-waste management systems and find ways to lessen their environmental and health impacts.