Interfacial strengthening and UV weathering resistance of mortar with thermal storage aggregate impregnated with PCM using epoxy-xGnP coating

초록

PCM-based thermal storage aggregates are incorporated into exterior mortar to mitigate temperature-sensitive responses under outdoor conditions. Although PCM-impregnated porous loess ball (PLB) aggregates were expected to reduce thermal sensitivity, PLB mortar developed spatially nonuniform thermal response under repeated thermal loading, potentially degrading long-term performance compared with conventional mortar. To address this limitation, an epoxy and expanded graphite nanoplatelets (xGnP) composite coating was applied to the PCM-impregnated aggregates to reinforce the interfacial transition zone (ITZ) and stabilize thermal behavior using a viscosity-guided coating procedure. Mortar with PLB yielded heating and cooling delays of 19 and 100 min, respectively, relative to neat mortar, but exhibited increasing spatial non-uniformity during cyclic thermal loading. With the coated PLB, the thermal delay effect was maintained while surface temperature distribution became more uniform, and the internally fixed coating configuration increased the compressive strength by up to 8 MPa while reducing epoxy agglomeration. Long-term durability was assessed by comparing the optimized aggregate coating with an epoxy surface coating under UV-accelerated weathering. The surface-coated mortar exhibited rapid loss of reflectance and contact angle, whereas the aggregate-coated mortar showed modest albedo reduction and maintained a color difference Delta E00 below 1 with high contact-angle retention over 200 cycles. Results indicate that epoxy-xGnP aggregate coating enhances the thermal stability, interfacial integrity, and UV weathering resistance of PCM-based exterior mortars. This composite mortar is intended for exterior wall finishes exposed to large thermal fluctuations and strong UV irradiation, where mitigation of temperature-induced degradation and reduced maintenance demand are prioritized.

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