Optimal integration of phase-change microcapsules and nano-silica for improving the strength of phase-change concrete

Phase-change microcapsules, consisting of urea-melamine-formaldehyde as the shell material and n-tetradecane as the core material, offer effective temperature regulation within concrete under low-temperature conditions, mitigating the impact of freeze–thaw cycles. However, their incorporation can exert a notable influence on concrete strength. In this study, microcapsules were utilized as an admixture, and nano-silicon dioxide replaced an equivalent amount of cement to prepare modified phase-change concrete, focusing on investigating mechanical properties. Results indicate that under consistent parameters—emulsifier concentration of 10% and an oil–water ratio of 1:6—the produced microcapsules exhibit uniform dispersion, with particle sizes ranging from 10 to 20 μm and latent heat of phase change reaching 117 J g⁻¹. Incorporating microcapsules reduced concrete strength, with a decrease in compressive strength within the range of 15% when microcapsule dosage was set at 10%. On the other hand, nano-silica demonstrated the capability to significantly enhance the strength of phase-change concrete by 15%–30% at dosages ranging from 5% to 10%. Optimal enhancement in concrete strength was achieved when phase-change microcapsules were dosed at 10% and nano-silica replaced 10% of the cement mass, resulting in compressive strength reaching 90% of normal concrete.