Ethyl cellulose–coated phase change cenospheres: Coupled hydration heat regulation and interfacial strengthening in cementitious materials

A novel EC-coated phase change microcapsule (EC-CenoPCM) was developed to prevent PCM leakage in cementitious materials. • EC coating (2 wt%) completely sealed perforated cenospheres while retaining a high melting enthalpy of 97.15 J/g. • EC-CenoPCM effectively regulated hydration heat via physical thermal buffering, delaying and attenuating exothermic peaks. • The EC shell enhanced capsule–matrix bonding, reduced harmful pores, and improved 28-day compressive strength. To enhance the thermal energy storage capacity of cementitious materials while overcoming phase change material (PCM) leakage and interfacial incompatibility, an effective microencapsulated PCM (MPCM) was developed using ethyl cellulose (EC)–coated paraffin-loaded perforated cenospheres (CenoPCM). Paraffin wax was first vacuum-impregnated into acid-etched cenospheres and subsequently sealed by an EC shell via a solvent evaporation process. Morphological and chemical characterizations confirmed that a continuous and compact EC coating was formed, with 2 wt% EC identified as the optimal concentration, completely preventing PCM leakage at 60 °C while retaining a melting enthalpy of 97.15 J/g. When incorporated into cement mortar as a partial sand replacement, EC-CenoPCM effectively regulated hydration heat through a physical heat-buffering mechanism associated with the solid–liquid phase transition of paraffin wax. Isothermal calorimetry and semi-adiabatic temperature rise tests revealed delayed and attenuated exothermic peaks without altering the cumulative hydration heat, indicating that hydration regulation primarily through the solid-liquid transition of PCM. Microstructural observations and pore structure analysis demonstrated that the EC coating significantly enhanced capsule–matrix interfacial bonding and reduced the proportion of harmful pores by suppressing leakage-induced defects. As a result, mortar containing 3 vol% EC-CenoPCM achieved a higher 28-day compressive strength (57.8 MPa) and a moderated reduction in thermal conductivity compared with mortars incorporating uncoated CenoPCM. These findings demonstrate that ethyl cellulose–coated cenospheres provide an effective and promising strategy for integrating latent heat storage into cementitious materials, enabling hydration heat regulation while preserving mechanical and thermal performance. This approach offers promising potential for hydration-temperature control in mass concrete and the development of thermally functional cementitious components.