Elucidating the Evolution of Pore Structure, Microstructural Damage, and Micromechanical Response in Cement Pastes Containing Microencapsulated Phase Change Materials under Freeze-Thaw Conditions

As climate variability intensifies the frequency and severity of freeze-thaw cycles, the development of cementitious materials capable of withstanding these harsh conditions becomes increasingly crucial. This research focuses on the potential of microencapsulated phase change materials (MPCMs) to enhance the durability of hardened cement paste (HCP) in the face of such challenges. Specifically, this paper evaluates the influence of MPCMs on evolution of pore microstructure, damage, and micromechanical response in HCP subjected to extended freeze-thaw cycles, utilizing Low-Temperature Differential Scanning Calorimetry (LTDSC), X-ray tomography (XRT), and micro-indentation. LTDSC results indicate a lower ice-crystallization temperature and a significant reduction in ice formation in MPCM-integrated HCP. Micro-indentation experiments reveal that while the control HCP undergoes substantial decreases in indentation hardness (35%) and Young's modulus (37%) after 180 cycles, the MPCM samples show much lower losses (only 9% loss in hardness and 7% loss in Young's modulus for 20% MPCM inclusion). XRT image analysis reveals that MPCMs mitigate pore enlargement, preserve a stable pore size distribution, and effectively reduce the risk of increased interconnected porosity in HCP when subjected to extended freeze-thaw cycles. Crack analysis demonstrates that control HCP samples exhibit significant crack propagation with increased freeze-thaw cycles, while samples with 10% MPCM inclusion show only slight crack initiation, and those with 20% MPCM inclusion maintained their structural integrity with virtually no crack progression after 180 freeze-thaw cycles. These findings underscore the potential of MPCMs to improve the durability of HCP against freeze-thaw damage, offering key insights for designing more robust materials.