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• Simplex-centroid method was applied to geopolymer (GP) foam adsorbent. • Effects of precursor fractions on the GP absorbents properties were evaluated. • Chemical foaming applied to the optimal component to prepare an excellent GP foam. • The optimal absorbent out-performs state-of-the-art materials from the literature. Geopolymer foams (GPFs) are promising materials for heavy-metal-containing wastewater treatment. However, because of the diversity of precursors and the complex application environments, it is challenging to balance the processing and application performances. Herein, a "simplex-centroid" mixture design method was explored to optimize the performances and establish relationships between the precursors, microstructure, and molecular structure. Further, according to the design performance and rheological limitations of the foaming system, an optimal component was selected to fabricate a GPF using chemical foaming. The fabricated GPF exhibited a high compressive strength (0.86 MPa) and high open porosity (∼86%) with uniform pores with diameters of 0.1–1.2 mm. Pb2+, Cu2+, and Ni2+ static adsorption capacities of 112.8, 64.9, and 40.2 mg/g, respectively, were achieved. The combination of simplex-centroid method and chemical foaming is effective for optimizing the processing and application performances of GPF, and could be beneficial for future large-scale manufacturing of GPFs for water-treatment applications. [ABSTRACT FROM AUTHOR]

• The rheology of geopolymer slurry varies with metakaolin/fly ash ratio (MFR). • The foaming properties were dependent on the slurry rheology. • Geopolymer foams pore structure vary with their rheological and foaming property. • A mechanistic model was proposed to describe the bubble deformation process. • Bubble deformation during foaming was classified into four phases. Interstitial slurry rheology significantly influences the pore structure of chemically foamed geopolymer foams (GPFs). However, the relationship between these two factors has not been elucidated completely. To achieve a range of slurry rheological properties, different metakaolin/fly ash ratios were used, and a high-foam-content system was realized using a H 2 O 2 solution. The slurry rheological properties, foaming properties, and pore structures of the GPFs were tested to establish the influence mechanism of rheology on bubble behavior and pore structures from the perspective of foaming systems. Moreover, equations describing the relationship between the internal and external bubble pressure, extrusion pressure, and slurry yield stress are discussed from the perspective of a single bubble. Four sequential phases of bubble deformation were identified during the foaming process, namely, bubble nucleation, extrusion, expansion, and solidification. The intrinsic relationship between the interstitial slurry rheology and final pore structure of the GPF established herein will provide essential guidance for designing and synthesizing porous cementitious materials. [ABSTRACT FROM AUTHOR]

• A novel bio-based material with good hygrothermal and mechanical properties is developed. • The novel material shows better hygrothermal performance in multilayer wall, especially in wintertime. • Investigation of hysteresis effect on the multilayer wall and indoor environment is performed. • Considering the effect of temperature on hygrothermal behavior of multilayer wall. In this work, the hygrothermal properties of a novel bio-insulation material made of magnesium phosphate cement (MPC) and corn stalk (CS) were measured and compared with three excellent materials (date palm concrete, hemp-lime concrete and rape straw concrete) from previous study. To analyze the hygrothermal behavior of MPC-CS as the exterior insulation layer of multi-layer wall. The numerical model for multilayer walls with different bio-insulation layers was established to study the coupled heat and moisture transfer under real summer and winter climatic conditions. Furthermore, the effect of hysteresis on the hygrothermal behavior of external insulation multilayer walls was investigated. The results showed that multilayer wall containing MPC-CS insulation layer can better regulate temperature (T) and relative humidity (RH) variations, especially during the wintertime. When the hysteresis effect is taken into account, the accuracy of calculation will be improved. For highly dependent materials, it is necessary to calibrate the sorption isotherms to obtain more accurate results. However, as the depth of multilayer wall increased, the influence of hysteresis gradually decreased. [ABSTRACT FROM AUTHOR]

• The proposed multi-phase model can illustrate the heat and moisture transfer features of plant aggregates concrete. • The relative humidity distribution profiles show the aggregates shapes influence the heat and moisture transfer. • Effect of aggregate volume fractions is greater than that of aggregate shapes. • Temperature significantly affects the time to reach equilibrium state and moisture transfer. This study includes the experimental and numerical investigation of the hygrothermal properties of magnesium phosphate cement (MPC) and corn stalk (CS) based bio-composites. Bio-composites were formulated using large size and small size corn stalk aggregates. Corresponding numerical models were established to investigate the effect of corn stalk aggregate on the hygrothermal properties of bio-composites. The validity of the numerical models was confirmed by comparing the experimental and numerical results. Hygrothermal properties of bio-composites were predicted through the heat and moisture transfer models. It was observed that numerical results showed satisfactory and close results with the experimental values. Finally, by using the proposed model, the effects of aggregates with different shapes and different volume fractions on heat and moisture transfer were studied. Results showed that the presented model is promising, and it can well evaluate the aggregates effect. The numerical results also showed that the aggregates effect can significantly affect the heat and moisture transfer. At the same time, the temperature effect cannot be ignored when predicting the heat and moisture transfer of the material. With increasing temperature, the aggregate effect will be relatively weakened. Meanwhile, based on this numerical model, the effect of temperature on sorption isotherm and relative humidity distributions in the bio-composites can be well predicted. [ABSTRACT FROM AUTHOR]