Enhancing evaporative cooling and surface methylene blue decolouration of cement pastes through combined incorporation of HPMC, nano-TiO2 and nano-SiO2

Improving evaporative cooling and surface methylene blue (MB) decolouration while maintaining mechanical strength is an important objective in the development of multifunctional cementitious materials. However, such an integrated design remains challenging because these functionalities rely on distinct mechanisms associated with internal water transport, pore structure, and interfacial microenvironments. In this study, a hydroxypropyl methylcellulose (HPMC)–nano-SiO 2 –nano-TiO 2 (HST) cementitious composite was developed, and its thermal regulation behaviour, surface functional response, and structural evolution were systematically characterised. The results showed that, although HST did not exhibit the highest average evaporation flux, it achieved the highest apparent cooling efficiency and the lowest surface temperature rise. The improved cooling response was therefore not accompanied by a higher average evaporation flux. The pore-structure and capillary water absorption results suggested a possible contribution from differences in internal water supply. Multiscale pore-structure analysis revealed changes in the pore-size distribution of HST, accompanied by higher capillary water uptake through lightly ground specimen faces. Meanwhile, HST exhibited the highest apparent surface methylene blue decolouration under the tested irradiation conditions, along with less pronounced coarse surface deposition after LiCl exposure. In addition, HST demonstrated the highest compressive strength. Combined microstructural and hydration analyses revealed differences in the spatial distribution of the mapped Ti signal, smaller maximum segmented dark-region areas, and changes in hydration-related structural indicators in the HST system, providing a basis for interpreting its overall performance. These findings helped relate the performance of the combined formulation to its microstructural characteristics and provided guidance for the design of multifunctional cementitious materials.