The solar reflectance (SR) of surfaces in the built environment influences the urban heat island phenomenon, while surface lightness (L* in color measurement) serves as an indicator of surface appearance. Both parameters are closely related to the surface temperature (Ts), which affects thermal comfort and building energy performance. Ground granulated blast-furnace slag (GGBS) is a whitish supplementary cementitious material. High-volume replacement of cement with GGBS can significantly lower the carbon footprint of cement-based materials. This study systematically examines the comprehensive effects of GGBS on gray (OPC) and white Portland cement (WPC) pastes on their SR, appearance (through L* value), and Ts performance. The SR and L* values of the pastes were determined using spectrophotometers at different wavelength ranges, and their Ts were measured using a thermocouple under direct solar exposure. Results show that replacement of GGBS at 0%, 30%, 50%, and 70% in the OPC and WPC pastes had a linear relationship, with strong correlation between Ts and L* and between Ts and SR. When red iron oxide pigment was added to the mixture, the pigmented pastes exhibited close values for L* regardless of the binder type. GGBS replacement in the WPC mixture lowers the SR and L* values, which is advantageous for producing off-white surfaces in areas with thermal comfort and glare concerns. The SR and L* values that affect the Ts of a cementitious surface can be adjusted by altering the GGBS content in the cement paste.
Shafigh et al. (Mon,) studied this question.