Geopolymer is a promising porous material that can be used for evaporative cooling applications. Developing a greener geopolymer using agricultural and industrial wastes is a promising research area. In this study, we utilize rice husk (RH), rice husk ash (RHA), metakaolin (MK), ground granulated blast furnace slag (GGBS), and palm oil fuel ash (POFA) to prepare geopolymer pastes, with alkali liquid as an activator. Many geopolymer samples have been prepared as per the Design of Experimental software (DOE), and its corresponding response surface mode and central composite design and later they were characterized. The samples were cured in an oven for 2 h at 80 °C, and thereafter stored at room temperature (~25–30 °C) prior to being tested for its water absorption and compressive strength. The effect of the different composition of precursors on water absorption, density, porosity, and the compressive strength of the prepared geopolymers have been investigated. The results showed that the compressive strength of geopolymers is directly proportional to the ratio of the alkali liquid. Post-optimization, the best geopolymer paste mixture was confirmed to contain 10% of RH, 15% RHA, 35% MK, 10% POFA and 30% of GGBS, with 72% desirability for maximum water absorption (~38%) and compressive strength (4.9 MPa). The results confirmed its applicability for evaporative cooling.

The use of rice husks (RHs), treated RHs, and blends thereof as desiccants was studied. Bare RHs, treated RHs, and blends were characterized, and their water absorbances compared. Acid‐treated RHs showed better moisture absorbance than alkali‐treated RHs and hence were used to prepare blends. Moisture absorption of RH materials and silica gel were compared. Blends with a higher content of acid‐treated RHs showed higher water and moisture absorbency. The moisture absorbency of the blends was enhanced, and they exceeded the silica‐gel limit at 48 h of exposure time. The higher absorbency in blends with higher contents of acid‐treated RHs is likely due to higher porosity and improved adhesion properties owing to surface OH groups. Moreover, RH blends require shorter regeneration times than silica gel.

Building energy consumption will likely increase in the future due to enhanced living standards and greater use of air-conditioning. This article reviews the technologies associated with evaporative passive cooling including roof surface evaporative cooling, evaporative cooling walls, and downdraft evaporative cooling in buildings. Our intent is to attract architects and building engineers to the energy-saving benefits of incorporating passive evaporative cooling in building designs.

Evaporative passive cooling systems are considered as interesting technique to address the environmental and energy crises. Within this context, the development of new porous materials has attracted a lot of attention recently. The utilization of industrial and agricultural waste byproduct will also make this technology more environmentally friendly. This article reviews the application of byproduct, industrial wastes materials, and other agricultural residuals as raw materials for the preparation of geopolymers. It must also be taken into due consideration that many potential waste and residuals have not been extensively studied, and requires extensive investigations